184 results on '"Stammes, Piet"'
Search Results
2. Extended aerosol and surface characterization from S5P/TROPOMI with GRASP algorithm. Part II: Global validation and Intercomparison
- Author
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Chen, Cheng, Litvinov, Pavel, Dubovik, Oleg, Bindreiter, Lukas, Matar, Christian, Fuertes, David, Lopatin, Anton, Lapyonok, Tatyana, Lanzinger, Verena, Hangler, Andreas, Aspetsberger, Michael, de Graaf, Martin, Tilstra, Lieuwe Gijsbert, Stammes, Piet, Dandocsi, Alexandru, Gasbarra, Daniele, Fluck, Elody, Zehner, Claus, and Retscher, Christian
- Published
- 2024
- Full Text
- View/download PDF
3. Extended aerosol and surface characterization from S5P/TROPOMI with GRASP algorithm. Part I: Conditions, approaches, performance and new possibilities
- Author
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Litvinov, Pavel, Chen, Cheng, Dubovik, Oleg, Bindreiter, Lukas, Matar, Christian, Fuertes, David, Lopatin, Anton, Lapyonok, Tatyana, Lanzinger, Verena, Hangler, Andreas, Aspetsberger, Michael, de Graaf, Martin, Tilstra, Lieuwe Gijsbert, Stammes, Piet, Dandocsi, Alexandru, Gasbarra, Daniele, Fluck, Elody, Zehner, Claus, and Retscher, Christian
- Published
- 2024
- Full Text
- View/download PDF
4. Retrieval of Aerosol and Surface Properties at High Spatial Resolution: Hybrid Approach and Demonstration Using Sentinel‐5p/TROPOMI and PRISMA.
- Author
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Chen, Cheng, Litvinov, Pavel, Dubovik, Oleg, Fuertes, David, Matar, Christian, Miglietta, Franco, Pepe, Monica, Genesio, Lorenzo, Busetto, Lorenzo, Bindreiter, Lukas, Lanzinger, Verena, de Graaf, Martin, Tilstra, Gijsbert, Stammes, Piet, and Retscher, Christian
- Subjects
SPATIAL resolution ,AIR quality ,SURFACE properties ,SURFACE analysis ,AEROSOLS - Abstract
Satellite remote sensing of aerosol is largely conducted at moderate or coarse spatial resolution around 1–10 km. Nevertheless, at urban areas with high human activity, aerosol can originate from complex emission sources and may also vary strongly in space. Therefore, aerosol characterization at fine spatial resolution is essential for air quality study and assessment of anthropogenic pollution as well as climate effects. However, space‐borne instruments with high spatial resolution are usually limited in swath width or spectral coverage which result in lowering information content required for aerosol and surface retrieval. Based on the Generalized Retrieval of Atmosphere and Surface Properties (GRASP) algorithm, we propose a hybrid approach by combining fine and coarse spatial resolution measurements to retrieve aerosol and surface properties simulataneously at fine spatial resolution. The instruments with coarse spatial resolution and high revisting time can provide advanced aerosol characterization. At the same time, the instruments with fine spatial resolution are sensitive to spatial variability of aerosol nearby sources. In this study, the GRASP/Hybrid approach is demonstrated and tested based on the European Space Agency Sentinel‐5p/TROPOMI together with the Italian Space Agency PRISMA satellite data. Specifically, the detailed aerosol microphysical properties from Sentinel‐5p/TROPOMI 10 km retrievals are used as a priori information for PRISMA to derive aerosol loading and surface properties at 100 meter (m) spatial resolution. The PRISMA 100 m aerosol and surface retrieval based on the developed GRASP/Hybrid approach are evaluated using available ground‐based and satellite measurements, including AERONET, VIIRS/DB aerosol and PRISMA Level 2 surface reflectance products. Plain Language Summary: Both aerosol and surface characterization at high spatial resolution are always highly demanded especially over densely populated urban areas. However, the high spatial resolution space‐borne instruments typically have small swaths that, in general, reduce the possibility of aerosol and surface decoupling. In this paper, we develop a hybrid approach based on GRASP algorithm (GRASP/Hybrid) to retrieve aerosol and surface properties at fine spatial granularity by combining fine and coarse spatial resolution satellite data. The GRASP/Hybrid approach is demonstrated using European Space Agency (ESA) Sentinel‐5p/TROPOMI and Italian Space Agency (ASI) PRISMA (Hyperspectral Precursor of the Application Mission) measurements. Specifically, the detailed aerosol microphysical properties from Sentinel‐5p/TROPOMI 10 km retrievals are used as a priori information to derive aerosol loading and surface properties exploiting PRISMA at 100 m spatial resolution. Overall, the results obtained in this study demonstrate the big potential of the approach based on the combination of instruments for a number of climate and environment monitoring studies. Key Points: Generalized Retrieval of Atmosphere and Surface Properties (GRASP)/Hybrid approach is developed and demonstrated using Sentinel‐5p/TROPOMI and PRISMA measurementsPRISMA 100 m aerosol and surface properties are retrieved based on GRASP/Hybrid approach and evaluated using reference data setsWe demonstrate the big potential of hybrid approach based on the combination of instruments for climate and environment studies [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
5. Calm ocean, stormy sea: Atmospheric and oceanographic observations of the Atlantic during the ARC ship campaign.
- Author
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Köhler, Laura, Windmiller, Julia, Baranowski, Dariusz, Brennek, Michał, Ciuryło, Michał, Hayo, Lennéa, Kepski, Daniel, Kinne, Stefan, Latos, Beata, Lobo, Bertrand, Marke, Tobias, Nischik, Timo, Paul, Daria, Stammes, Piet, Szkop, Artur, and Tuinder, Olaf
- Subjects
INTERTROPICAL convergence zone ,OCEANOGRAPHIC observations ,CEILOMETER ,RADIOSONDES ,AEROSOLS - Abstract
During the Atlantic References and Convection (ARC) ship campaign with the reference MSM114/2, which took place in early 2023, the German research vessel Maria S. Merian travelled from Mindelo, Cape Verde, to Punta Arenas, Chile. One of the main objectives of ARC was to obtain vertically resolved cross sections of the Intertropical Convergence Zone (ITCZ). To this end, we crossed the ITCZ three times in the meridional direction. We present the atmospheric and oceanographic measurements collected during ARC in a standardized way to facilitate working with data from different instruments and to make the data easily accessible. This approach is not limited to ARC but could serve as a prototype for future (and past) ship campaigns. We present data from the integrated ship sensors (DShip), a Humidity and Temperature Profiler (HATPRO), a Ceilometer, aerosol instruments (DustTrak, Microtops, and Calitoo), radiosondes, Uncrewed Aircaft Vehicles (UAV), and Conductivity, Temperature, and Depth (CTD) profiles of the upper ocean. We distinguish temporal continuous data (DShip, HATPRO, Ceilometer, DustTrak) from point measurements (radiosondes, UAVs, CTDs, Calitoo, Microtops). To illustrate the data sets provided, we present examples of measurements taken during the three crossings of the ITCZ and during a storm in the Roaring Forties in the South Atlantic at the end of the campaign. All data sets can be downloaded from Köhler et al. (2024a). An overview of all available data sets, including dois, can be found here: https://doi.pangaea.de/10.1594/PANGAEA.966616. For references to the individual data sets, please refer to the data availability section. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
6. Monitoring the impact of forest changes on carbon uptake with solar-induced fluorescence measurements from GOME-2A and TROPOMI for an Australian and Chinese case study.
- Author
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Anema, Juliëtte C. S., Boersma, Klaas Folkert, Stammes, Piet, Koren, Gerbrand, Woodgate, William, Köhler, Philipp, Frankenberg, Christian, and Stol, Jacqui
- Subjects
FOREST monitoring ,FLUORESCENCE ,WATER supply ,FOREST soils - Abstract
Reliable and robust monitoring tools are crucial to assess the effectiveness of land mitigation techniques (LMTs) in enhancing carbon uptake, enabling informed decision making by policymakers. This study, addressing one of the scientific goals of the EU Horizon 2020 Land Use Based Mitigation for Resilient Climate Pathways (LANDMARC) project, examines the feasibility of using satellite solar-induced fluorescence (SIF) in combination with other satellite data as a monitoring proxy to evaluate the effects of LMTs on carbon uptake. Two distinct cases are explored: (1) instantaneous vegetation destruction caused by a 2019 eucalyptus wildfire in southeast Australia and (2) gradual forest gain resulting from reforestation efforts in northern China in 2007–2012. The cases are monitored using SIF from the TROPOspheric Monitoring Instrument (TROPOMI) and Global Ozone Monitoring Experiment-2A (GOME-2A), respectively. Comparing the temporal variability in SIF across the affected areas and nearby reference areas reveals that vegetation dynamics changed as a consequence of the land-use changes in both cases. Specifically, in the Australia case, TROPOMI demonstrated an immediate reduction in the SIF signal of 0.6 mW m -2 sr -1 nm -1 (- 72 %) over the eucalypt forest right after the fire. Exploiting the strong correspondence between TROPOMI SIF and gross primary productivity (GPP) at the nearby representative eddy covariance Tumbarumba site and through the FluxSat product, we estimate that the Australian fire led to a loss in GPP of 130–200 GgC in the first 8 months after the fire. Over the northern Chinese provinces of Gansu, Shaanxi, Sichuan, Chongqing, and Shanxi, we report an increase in GOME-2A summertime SIF of 0.1–0.2 mW m -2 sr -1 nm -1 , coinciding with reforestation efforts between 2007 and 2012. This increase in the SIF signal is likely driven by a combination of increasingly favourable natural conditions and by the reforestation effort itself. A multivariate model that takes into account growth factors such as water availability and maximum temperature as well as satellite-derived forest-cover data explains the observed variability in GOME-2A SIF in the Chinese case reasonably well (R2=0.72). The model suggests that increases in both forest cover and soil moisture have led, in step, to the observed increase in vegetation activity over northern China. In that region, for every 100 km 2 of additional forest cover, SIF increases by 0.1 mW m -2 sr -1 nm -1 between 2007 and 2012. Our study highlights that the use of satellite-based SIF, together with supporting in situ, modelled, and satellite data, allows us to monitor the impact of LMT implementation on regional carbon uptake as long as the scale of the LMT is of sufficient spatial extent. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
7. Cancellation of cloud shadow effects in the absorbing aerosol index retrieval algorithm of TROPOMI.
- Author
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Trees, Victor J. H., Wang, Ping, Stammes, Piet, Tilstra, Lieuwe G., Donovan, David P., and Siebesma, A. Pier
- Subjects
BIG data ,AEROSOLS ,ALGORITHMS ,ALBEDO ,RADIATIVE transfer ,AIR quality ,PHASE-shifting interferometry - Abstract
Cloud shadows can be detected in the radiance measurements of the TROPOMI instrument on board the Sentinel-5P satellite due to its high spatial resolution, and could possibly affect its air quality products. The cloud shadow induced signatures are, however, not always apparent and may depend on various cloud and scene parameters. Hence, the quantification of the cloud shadow impact requires the analysis of large data sets. Here we use the cloud shadow detection algorithm DARCLOS to detect cloud shadow pixels in the TROPOMI absorbing aerosol index (AAI) product over Europe during 8 months. For every shadow pixel, we automatically select cloud- and shadow-free neighbour pixels, in order to estimate the cloud shadow induced signature. In addition, we simulate the measured cloud shadow impact on the AAI with our newly developed 3D radiative transfer algorithm MONKI. Both the measurements and simulations show that the average cloud shadow impact on the AAI is close to zero (0.06 and 0.16, respectively). However, the top-of-atmosphere reflectance ratio between 340 and 380 nm, which is used to compute the AAI, is significantly increased in 95 % of the shadow pixels. So, cloud shadows are bluer than surrounding non-shadow pixels. Our simulations explain that the traditional AAI formula intrinsically already corrects for this cloud shadow effect, via the lower retrieved scene albedo. This cancellation of cloud shadow signatures is not always perfect, sometimes yielding second order low and high biases in the AAI which we also successfully reproduce with our simulations. We show that the magnitude of those second order cloud shadow effects depends on various cloud parameters which are difficult to determine for the shadows measured with TROPOMI. We conclude that a potential cloud shadow correction strategy for the TROPOMI AAI would therefore be complicated if not unnecessary. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
8. Assessment of the spectral misalignment effect (SMILE) on EarthCARE's Multi-Spectral Imager aerosol and cloud property retrievals.
- Author
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Docter, Nicole, Hünerbein, Anja, Donovan, David P., Preusker, Rene, Fischer, Jürgen, Meirink, Jan Fokke, Stammes, Piet, and Eisinger, Michael
- Subjects
AEROSOLS ,GAS absorption & adsorption ,SMILING ,ICE clouds ,WATER vapor ,WEATHER - Abstract
The Multi-Spectral Imager (MSI) on board the Earth Cloud, Aerosol and Radiation Explorer (EarthCARE) will provide horizontal information about aerosols and clouds. These measurements are needed to extend vertical cloud and aerosol property information, which is obtained from EarthCARE's active sensors, in order to obtain a full three-dimensional view of cloud and aerosol conditions. Mesoscale weather systems, in particular, will be characterized. The discovery of a non-compliance of the MSI visible–near-infrared–shortwave infrared (VNS) camera's visible (VIS) and shortwave infrared (SWIR1) channels regarding a spectral central wavelength (CWVL) shift across-track of up to 14 nm (VIS) and 20 nm (SWIR1) led to the need for an analysis regarding its impact on MSI Level-2A aerosol and cloud products. A significant influence of the spectral misalignment effect (SMILE) on MSI retrievals is identified due to the spectral variation in gas absorption, surface reflectance, and aerosol and cloud properties within the spectral ranges of these MSI bands. For example, the VIS channel is positioned in close proximity to the red edge of green vegetation and is impacted by residual absorption of water vapor and ozone. Small central wavelength variations introduce uncertainties due to the rapid change in surface reflectance for conditions with low optical thickness. The present central wavelength shift in the VIS towards shorter wavelengths than at nadir introduces a relative error in transmission of up to 3.3 % due to the increasing influence of water vapor and ozone absorption. We found relative errors in the top-of-atmosphere (TOA) signal due to the SMILE of up to 30 % for low optical thickness over a land surface in that band. Since the magnitude of the impact strongly depends on the underlying surface and atmospheric conditions, we conclude that accounting for the SMILE in Level-2 retrievals or correcting the Level-1 signal will improve MSI aerosol and cloud product quality. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
9. A directional surface reflectance climatology determined from TROPOMI observations.
- Author
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Tilstra, Lieuwe G., de Graaf, Martin, Trees, Victor J. H., Litvinov, Pavel, Dubovik, Oleg, and Stammes, Piet
- Subjects
CLIMATOLOGY observations ,SURFACE of the earth ,DATABASES ,CLIMATOLOGY ,REFLECTANCE - Abstract
In this paper, we introduce a spectral surface reflectivity climatology based on observations made by TROPOMI on board the Sentinel-5P satellite. The database contains the directionally dependent Lambertian-equivalent reflectivity (DLER) of the Earth's surface for 21 wavelength bands ranging from 328 to 2314 nm and for each calendar month. The spatial resolution of the database grid is 0.125° × 0.125°. A recently developed cloud shadow detection technique is implemented to avoid dark scenes due to cloud shadow. In the database, the anisotropy of the surface reflection is described using a third-order parameterisation of the viewing angle dependence. The viewing angle dependence of the DLER is analysed globally and for a selection of surface type regions. The dependence is found to agree with the viewing angle dependence found in the GOME-2 surface DLER database. Differences exist, related to the actual solar position. On average, the viewing angle dependence in TROPOMI DLER is weaker than for GOME-2 DLER, but still important. Validation of the new database was first performed by comparison of the non-directional TROPOMI surface LER with heritage LER databases based on GOME-1 , OMI, SCIAMACHY, and GOME-2 data. Agreement was found within 0.002–0.02 in the UV-VIS (below 500 nm), up to 0.003 in the NIR (670–772 nm), and below 0.001 in the short-wave infrared (SWIR) (2314 nm). These performance numbers are dominated by the performance over ocean, but they are in most cases also representative for land surfaces. For the validation of the directional TROPOMI surface DLER, we made use of comparison with the MODIS surface bi-directional reflectance distribution function (BRDF) for a selection of surface type regions. In all cases the DLER performed significantly better than the traditional LER, and we found good agreement with the MODIS surface BRDF. The TROPOMI surface DLER database is a clear improvement on previous surface albedo databases and can be used as input not only for satellite retrievals from TROPOMI observations, but also for retrievals from observations from other polar-orbiting satellite instruments provided that their equator crossing time is close to that of TROPOMI. The algorithm that is introduced in this paper can be used for the retrieval of surface reflectivity climatologies from other polar satellite missions as well, including Ocean and Land Colour Instrument (OLCI) on the Sentinel-3 satellites, Sentinel-5, and Multi-viewing Multi-channel Multi-polarisation imager (3MI) on the MetOp-SG-A1 satellite to be launched in 2025, as well as the future CO2M mission. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
10. The Antarctic stratospheric nitrogen hole: Southern Hemisphere and Antarctic springtime total nitrogen dioxide and total ozone variability as observed by Sentinel-5p TROPOMI.
- Author
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de Laat, Adrianus, van Geffen, Jos, Stammes, Piet, van der A, Ronald, Eskes, Henk, and Veefkind, J. Pepijn
- Subjects
OZONE layer ,NITROGEN dioxide ,OZONE ,POLAR vortex ,OZONE layer depletion ,NITROGEN oxides ,PHASE space - Abstract
Denitrification within the stratospheric vortex is a crucial process for Antarctic ozone hole formation, resulting in an analogous stratospheric "nitrogen hole". Sedimentation of large nitric acid trihydrate polar stratospheric cloud particles within the Antarctic polar stratospheric vortex that form during winter depletes the inner vortex of nitrogen oxides. Here, 2018–2021 daily TROPOspheric Monitoring Instrument (TROPOMI) measurements are used for the first time for a detailed characterization of this nitrogen hole. Nitrogen dioxide total columns exhibit strong spatiotemporal and seasonal variations associated with photochemistry as well as transport and mixing processes. Combined with total ozone column data two main regimes are identified: inner-vortex ozone- and nitrogen-dioxide-depleted air and outer-vortex air enhanced in ozone and nitrogen dioxide. Within the vortex total ozone and total stratospheric nitrogen dioxide are strongly correlated, which is much less evident outside of the vortex. Connecting the two main regimes is a third regime of coherent patterns in the total nitrogen dioxide column–total ozone column phase space – defined here as "mixing lines". These mixing lines exist because of differences in three-dimensional variations of nitrogen dioxide and ozone, thereby providing information about vortex dynamics and cross-vortex edge mixing. On the other hand, interannual variability of nitrogen dioxide–total ozone characteristics is rather small except in 2019 when the vortex was unusually unstable. Overall, the results show that daily stratospheric nitrogen dioxide column satellite measurements provide an innovative means for characterizing polar stratospheric denitrification processes, vortex dynamics, and long-term monitoring of Antarctic ozone hole conditions. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
11. Polarimetric remote sensing of atmospheric aerosols: Instruments, methodologies, results, and perspectives
- Author
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Dubovik, Oleg, Li, Zhengqiang, Mishchenko, Michael I., Tanré, Didier, Karol, Yana, Bojkov, Bojan, Cairns, Brian, Diner, David J., Espinosa, W. Reed, Goloub, Philippe, Gu, Xingfa, Hasekamp, Otto, Hong, Jin, Hou, Weizhen, Knobelspiesse, Kirk D., Landgraf, Jochen, Li, Li, Litvinov, Pavel, Liu, Yi, Lopatin, Anton, Marbach, Thierry, Maring, Hal, Martins, Vanderlei, Meijer, Yasjka, Milinevsky, Gennadi, Mukai, Sonoyo, Parol, Frederic, Qiao, Yanli, Remer, Lorraine, Rietjens, Jeroen, Sano, Itaru, Stammes, Piet, Stamnes, Snorre, Sun, Xiaobing, Tabary, Pierre, Travis, Larry D., Waquet, Fabien, Xu, Feng, Yan, Changxiang, and Yin, Dekui
- Published
- 2019
- Full Text
- View/download PDF
12. Aerosol Shortwave Radiative Heating and Cooling by the 2017 and 2023 Chilean Wildfire Smoke Plumes.
- Author
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de Graaf, Martin, Tilstra, L. Gijsbert, and Stammes, Piet
- Subjects
SMOKE plumes ,SMOKE ,AEROSOLS ,WILDFIRES ,MINERAL dusts ,SOLAR atmosphere ,WILDFIRE prevention ,RADIATIVE transfer - Abstract
The aerosol shortwave, direct radiative effects of smoke plumes from Chilean wildfires in 2017 and 2023 were derived from satellite observations in both cloud‐free and cloud scenes. At the top of the atmosphere, the aerosol DRE changes sign when aerosol overly clouds or open ocean, confirmed by both measurements and a simulation study. The cloud‐free daily‐mean DRE, computed using an offline radiative transfer model (RTM), was 66 W m−2 in 2023 and 42 W m−2 in 2017, due to absorption by smoke. However, the total radiative effects were larger in 2017 due to a larger plume size compared to 2023. The method presented here provides a new conceptual model to quickly assess the radiative effects of wildfire smoke plumes using satellite measurements and pre‐computed RTM results. The presented estimates are strongly affected by the uncertainty of aerosol optical thickness retrievals from satellite, which can be large in the presence of clouds. Plain Language Summary: From 30 January to the end of February 2023, central Chile experienced over 400 individual wildfires, consuming over 430,000 ha of native sclerophyllous forests, with 25 fatalities as of 14 February. Wildfires are common in central Chile during dry periods, but seem intensified due to the mega‐drought since 2010. Next to health effects, the smoke from these wildfires has important climatic impacts through the change of solar insolation in the atmosphere: smoke strongly absorbs solar radiation and heats the atmosphere, changing the vertical stability. In this paper, the horizontal and vertical smoke distribution in the atmosphere is presented using satellite observations, and the radiative effects in the atmosphere and at the surface are quantified for the recent fires and as well as for the record‐breaking wildfires in 2017, which were the most devastating in the modern history of central‐Chile. Our results show that the radiative effects of the smoke from the recent wildfires were stronger in magnitude during the first few days, but confined to a smaller area, reducing their overall effect. Key Points: The radiative effects of the recent 2023 Chilean wildfire smoke plumes are assessed and compared to the 2017 Chilean wildfires smoke plumesPre‐computed radiative transfer model results can provide readily available aerosol direct radiative effects in clear‐sky for smokeSatellite measurements can further improve the aerosol direct effect and direct forcing estimates for both clear sky and cloud scenes [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
13. Assessment of the Spectral MIsaLignment Effect (SMILE) on EarthCARE's Multi-Spectral Imager aerosol and cloud property retrievals.
- Author
-
Docter, Nicole, Hünerbein, Anja, Donovan, David Patrick, Preusker, Rene, Fischer, Jürgen, Meirink, Jan Fokke, Stammes, Piet, and Eisinger, Michael
- Subjects
AEROSOLS ,GAS absorption & adsorption ,SMILING ,WATER vapor ,ICE clouds ,WEATHER - Abstract
The Multi-spectral Imager (MSI) on board the Earth Cloud, Aerosol and Radiation Explorer (EarthCARE) will provide horizontal information about aerosols and clouds. These measurements are needed to extend vertical cloud and aerosol property information, which are obtained from EarthCARE's active sensors, in order to obtain a full three dimensional view on cloud and aerosol conditions. Especially, meso-scale weather systems will be characterized. The discovery of a non-compliance of the MSI VNS camera's visible (VIS) and shortwave-infrared (SWIR1) channels regarding a spectral central wavelength (CWVL) shift across track of up to 14 nm (VIS) and 20 nm (SWIR1), led to the need for an analysis regarding its impact on MSI Level 2A aerosol and cloud products. A significant influence of the Spectral MIsaLignment Effect (SMILE) on MSI retrievals is identified due to the spectral variation of gas absorption, surface reflectance as well as aerosol and cloud properties within the spectral ranges of these MSI bands. For example, the VIS channel is positioned in close proximity to the red edge of green vegetation and is impacted by residual absorption of water vapour and ozone. Small central wavelength variations introduce uncertainties due to the rapid change in surface reflectance for conditions with low optical thickness. The present central wavelength shift in the VIS towards shorter wavelengths than at nadir introduces a relative error in transmission of up to 3.3 % due to the increasing influence of water vapour and ozone absorption. We found relative errors in the TOA signal due to the SMILE of up to 30 % for low optical thickness over a land surface in that band. Since the magnitude of the impact strongly depends on the underlying surface and atmospheric conditions, we conclude that accounting for the SMILE in Level 2 retrievals or correcting the Level 1 signal will improve MSI aerosol and cloud product quality. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
14. A directional surface reflectance climatology determined from TROPOMI observations.
- Author
-
Tilstra, Lieuwe G., de Graaf, Martin, Trees, Victor J. H., Litvinov, Pavel, Dubovik, Oleg, and Stammes, Piet
- Subjects
CLIMATOLOGY observations ,SURFACE of the earth ,CLIMATOLOGY ,DATABASES ,REFLECTANCE - Abstract
In this paper we introduce a spectral surface reflectivity climatology based on observations made by the TROPOMI instrument on board the Sentinel-5P satellite. The database contains the directionally dependent Lambertian-equivalent reflectivity (DLER) of the Earth's surface for 21 wavelength bands ranging from 328nm to 2314nm and for each calendar month. The spatial resolution of the database grid is 0.125° × 0.125°. A recently developed cloud shadow detection technique is implemented to avoid dark scenes due to cloud shadow. In the database, the anisotropy of the surface reflection is described using a third-order parameterisation of the viewing angle dependence. The viewing angle dependence of the DLER is analysed globally and for a selection of surface type regions. The dependence is found to agree with the viewing angle dependence found in the GOME-2 surface DLER database. Differences exist, related to the actual solar position. On average, the viewing angle dependence in TROPOMI DLER is weaker than for GOME-2 DLER, but still important. Validation of the new database was first performed by comparison of the non-directional TROPOMI surface LER with heritage LER databases based on GOME-1, OMI, SCIAMACHY, and GOME-2 data. Agreement was found within 0.002-0.02 in the UV-VIS (below 500nm), up to 0.003 in the NIR (670-772nm), and below 0.001 in the SWIR (2314nm). These performance numbers are dominated by the performance over ocean, but they are in most cases also representative for land surfaces. For the validation of the directional TROPOMI surface DLER we made use of comparison with MODIS surface BRDF for a selection of surface type regions. In all cases the DLER performed significantly better than the traditional LER and we found good agreement with MODIS surface BRDF. The TROPOMI surface DLER database is a clear improvement on previous surface albedo databases and can be used as input not only for satellite retrievals from TROPOMI observations, but also for retrievals from observations from other polarorbiting satellite instruments provided that their equator crossing time is close to that of TROPOMI. The algorithm that is introduced in this paper can be used for the retrieval of surface reflectivity climatologies from other polar satellite missions as well, including OLCI on the Sentinel-3 satellites, Sentinel-5 and 3MI on the MetOp-SG-A1 satellite to be launched in 2025, and the future CO2M mission. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
15. The Antarctic stratospheric Nitrogen Hole: Southern Hemisphere and Antarctic springtime total nitrogen dioxide and total ozone variability as observed in Sentinel-5p TROPOMI data.
- Author
-
Laat, Adrianus de, Geffen, Jos van, Stammes, Piet, A, Ronald van der, Eskes, Henk, and Veefkind, Pepijn
- Subjects
OZONE layer ,NITROGEN dioxide ,OZONE ,OZONE layer depletion ,PHASE space ,NITROGEN - Abstract
Denitrification of the stratospheric vortex is a crucial process for the Antarctic Ozone Hole formation resulting in an analogous stratospheric "Nitrogen Hole". Here, 2018–2021 daily TROPOMI measurements are used for the first time for a detailed characterization of this Nitrogen Hole. Nitrogen dioxide total columns exhibit strong spatiotemporal and seasonal variations associated with both photochemistry as well as transport and mixing processes. Combined with total ozone column data two main regimes are identified: inner-vortex ozone and nitrogen dioxide depleted air and outer-vortex air enhanced in ozone and nitrogen dioxide. Within the vortex total ozone and total stratospheric nitrogen dioxide are strongly correlated which is much less evident outside of the vortex. Connecting both main regimes are what is defined here as "mixing lines", a third regime of coherent patterns in the total nitrogen dioxide column – total ozone column phase space. These mixing lines exist because of differences in three dimensional variations of nitrogen dioxide and ozone thereby providing information about vortex dynamics and cross-vortex edge mixing. On the other hand, interannual variability of nitrogen dioxide – total ozone characteristics are rather small except in 2019 when the vortex was unusually unstable. Overall, the results show that daily stratospheric nitrogen dioxide column satellite measurements provide an innovative means for characterizing and Polar stratospheric denitrification processes and vortex dynamics and potentially long term monitoring if the total nitrogen column data record is extended with past satellite observations. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
16. The Antarctic stratospheric Nitrogen Hole: Southern Hemisphere and Antarctic springtime total nitrogen dioxide and total ozone variability as observed in Sentinel-5p TROPOMI data.
- Author
-
de Laat, Adrianus, van Geffen, Jos, Stammes, Piet, van der A., Ronald, Eskes, Henk, and Veefkind, J. Pepijn
- Abstract
Denitrification of the stratospheric vortex is a crucial process for the Antarctic Ozone Hole formation resulting in an analogous stratospheric “Nitrogen Hole”. Here, 2018-2021 daily TROPOMI measurements are used for the first time for a detailed characterization of this Nitrogen Hole. Nitrogen dioxide total columns exhibit strong spatiotemporal and seasonal variations associated with both photochemistry as well as transport and mixing processes. Combined with total ozone column data two main regimes are identified: inner-vortex ozone and nitrogen dioxide depleted air and outer-vortex air enhanced in ozone and nitrogen dioxide. Within the vortex total ozone and total stratospheric nitrogen dioxide are strongly correlated which is much less evident outside of the vortex. Connecting both main regimes are what is defined here as “mixing lines”, a third regime of coherent patterns in the total nitrogen dioxide column - total ozone column phase space. These mixing lines exist because of differences in three dimensional variations of nitrogen dioxide and ozone thereby providing information about vortex dynamics and cross-vortex edge mixing. On the other hand, interannual variability of nitrogen dioxide – total ozone characteristics are rather small except in 2019 when the vortex was unusually unstable. Overall, the results show that daily stratospheric nitrogen dioxide column satellite measurements provide an innovative means for characterizing polar stratospheric denitrification processes, vortex dynamics and potentially long term monitoring if the total nitrogen column data record is extended with past satellite observations. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
17. Monitoring the regional impact of forest loss and gain on carbon uptake with solar-induced fluorescence measurements from the GOME-2A and TROPOMI sensors.
- Author
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Anema, Juliëtte C. S., Boersma, Klaas Folkert, Stammes, Piet, Koren, Gerbrand, Woodgate, William, Köhler, Philipp, Frankenberg, Christian, and Stol, Jacqui
- Subjects
FLUORESCENCE ,WATER supply ,VEGETATION dynamics ,REFORESTATION ,CARBON - Abstract
Reliable and robust monitoring tools are crucial to assess the effectiveness of land mitigation techniques (LMTs) in enhancing carbon uptake, enabling informed decision-making by policymakers. This study, addressing one of the scientific goals of the EU H2020 LANDMARC project, examines the feasibility of using satellite solar-induced fluorescence (SIF), in combination with other satellite data, as a monitoring proxy to evaluate the effects of LMTs on carbon uptake. Two distinct cases are explored: (1) instantaneous vegetation destruction caused by a 2019 Eucalyptus wildfire in south-east Australia, and, (2) gradual forest gain resulting from reforestation efforts in northern China over 2007–2012. The cases are monitored using TROPOMI and GOME-2A SIF, respectively. Comparing the temporal variability in SIF across the affected and nearby reference areas reveals that vegetation dynamics changed as a consequence of the land use changes in both cases. Specifically, in the Australia case, TROPOMI demonstrated an immediate reduction in SIF signal of 0.6 mW m
−2 sr−1 nm−1 (−72 %) over the Eucalypt Forest right after the fire. Exploiting the strong correspondence between TROPOMI SIF and gross primary productivity (GPP) at the nearby eddy-covariance Tumbarumba site and through the FluxSat product, we estimate that the fire led to a loss in GPP of 130–200 GgC in the first eight months after the fire. Over the northern Chinese provinces of Gansu, Shaanxi, Sichuan, Chongqing and Shanxi, we report an increase in GOME-2A summertime SIF of 0.1–0.2 mW m−2 sr−1 nm−1 coinciding with reforestation efforts between 2007 and 2012. This increase in SIF signal is likely driven by a combination of increasingly favourable natural conditions and the reforestation effort itself. A multivariate model that takes into account growth factors such as water availability and maximum temperature as well as satellite-derived forest cover data explains the observed variability in GOME-2A SIF in the Chinese case reasonably well (R2 =0.72). The model suggests that both increases in forest cover as well as in soil moisture have led, in step, to the observed increase in vegetation activity over northern China. In that region, for every 100 km2 of additional forest cover, SIF increases by 0.1 mW m−2 sr−1 nm−1 between 2007 and 2012. Our study highlights that the combined use of satellite-based SIF, together with supporting in situ, modelled and satellite-data, allows to monitor the impact of LMT implementation on regional carbon uptake as long as the scale of the LMT is of sufficient spatial extent. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
18. Advances in Lidar Observations for Airborne Hazards for Aviation in the Framework of the EUNADICS-AV Project
- Author
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Apituley Arnoud, Mona Lucia, Papagiannopoulos Nikolas, Rufenacht Rolf, Wagenaar Saskia, Stammes Piet, de Laat Jos, de Cerff Wim Som, de Haij Marijn, Marchese Francesco, Falconieri Alfredo, Haefele Alexander, and Hervo Maxime
- Subjects
Physics ,QC1-999 - Abstract
The vulnerability of the (European) aviation system to the airborne hazards was evident during the Eyjafjallajökull volcanic eruption in 2010. For support of Air Traffic Control (ATC) many observations of the event were available from satellites, ground based instruments and airborne platforms, at pan-European scale. However, efficient use of the data for ATC proved difficult mainly due to sub-optimal aggregation and integrated assessment of the available information in near-real-time. The project EUNADICS-AV (European Natural Disaster Coordination and Information System for Aviation) aims to close this gap. The observational component of the project will make existing data products for airborne hazards more accessible, visible and used, and to foster tailored product development. Once assimilated into models and integrated in the EUNADICS-AV Data Portal these data can be the base to efficiently improve European airspace resilience to airborne hazards. Since 2010 new data products have become available specifically for for airborne hazard alerting and monitoring together with specific tailored products designed for replying to user needs and recommendations. This paper describes the EUNADICS-AV approach and will focus on the role of operational and research grade ground based lidars.
- Published
- 2020
- Full Text
- View/download PDF
19. Polarimetric Remote Sensing of Atmospheric Aerosols: Instruments, Methodologies, Results, and Perspectives
- Author
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Dubovik, Oleg, Li, Zhengqiang, Mishchenko, Michael I, Tanre, Didier, Karol, Yana, Bojkov, Bojan, Cairns, Brian, Diner, David J, Espinosa, W. Reed, Goloub, Philippe, Gu, Xingfa, Hasekamp, Otto, Hong, Jin, Hou, Weizhen, Knobelspiesse, Kirk D, Landgraf, Jochen, Litvinov, Pavel, Liu, Yi, Lopatin, Anton, Marbach, Thierry, Maring, Hal, Martins, Vanderlei, Meijer, Yasjka, Milinevsky, Gennadi, Mukai, Sonoyo, Parol, Frederic, Qiao, Yanli, Remer, Lorraine, Rietjens, Jeroen, Sano, Itaru, Stammes, Piet, Stamnes, Snorre A, Sun, Xiaobing, Tabary, Pierre, Travis, Larry D, Waquet, Fabien, Xu, Feng, Yan, Changxiang, and Yin, Dekui
- Subjects
Earth Resources And Remote Sensing ,Instrumentation And Photography - Abstract
Polarimetry is one of the most promising types of remote sensing for improved characterization of atmospheric aerosol. Indeed, aerosol particles constitute a highly variable atmospheric component characterized by a large number of parameters describing particle sizes, morphologies (including shape and internal structure), absorption and scattering properties, amounts, horizontal and vertical distribution, etc. Reliable monitoring of all these parameters is very challenging, and therefore the aerosol effects on climate and environment are considered to be among the most uncertain factors in climate and environmental research. In this regard, observations that provide both the angular distribution of the scattered atmospheric radiation as well as its polarization state at multiple wavelengths covering the UV–SWIR spectral range carry substantial implicit information on the atmospheric composition. Therefore, high expectations in improving aerosol characterization are associated with detailed passive photopolarimetric observations. The critical need to use space-borne polarimetry for global accurate monitoring of detailed aerosol properties was first articulated in the late 1980s and early 1990s. By now, several orbital instruments have already provided polarization observations from space, and a number of advanced missions are scheduled for launch in the coming years by international and national space agencies. The first and most extensive record of polarimetric imagery was provided by POLDER-I, POLDER-II, and POLDER/PARASOL multi-angle multi-spectral polarization sensors. Polarimetric observations with the POLDER-like design intended for collecting extensive multi-angular multi-spectral measurements will be provided by several instruments, such as the MAI/TG-2, CAPI/TanSat, and DPC/GF-5 sensors recently launched by the Chinese Space Agency. Instruments such as the 3MI/MetOp-SG, MAIA, SpexOne and HARP2 on PACE, POSP, SMAC, PCF, DPC–Lidar, ScanPol and MSIP/Aerosol-UA, MAP/Copernicus CO2 Monitoring, etc. are planned to be launched by different space agencies in the coming decade. The concepts of these future instruments, their technical designs, and the accompanying algorithm development have been tested intensively and analyzed using diverse airborne prototypes. Certain polarimetric capabilities have also been implemented in such satellite sensors as GOME-2/MetOp and SGLI/GCOM-C.
- Published
- 2018
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20. Comparison of Cloud Parameters from GOME-2 and Assessment of Cloud Impact on Tropospheric NO2 and HCHO Retrievals.
- Author
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Argyrouli, Athina, Lutz, Ronny, Romahn, Fabian, García, Víctor Molina, Loyola, Diego, Seo, Sora, Valks, Pieter, De Smedt, Isabelle, Boersma, Folkert, Tilstra, Lieuwe Gijsbert, Stammes, Piet, and Compernolle, Steven
- Subjects
CLOUDS ,OXYGEN ,TRACE gases ,AIR quality ,CLIMATE change - Abstract
In recent decades, there has been an increasing interest in making use of satellite measurements for identifying trends in atmospheric composition and climate. Instruments like GOME-2 and TROPOMI are dedicated to air-quality and global trace gas monitoring. For the accurate retrieval of columnar information of the trace gases, cloud correction is necessary. This work is meant to examine the quality of the GOME-2 operational cloud product from AC SAF and to propose enhancements of the current dataset to improve the retrieval of the NO
2 and HCHO tropospheric gases. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
21. DARCLOS: a cloud shadow detection algorithm for TROPOMI
- Author
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Trees, V.J.H., Wang, Ping, Stammes, Piet, Tilstra, Lieuwe G., Donovan, D.P., and Siebesma, A.P.
- Abstract
Cloud shadows are observed by the TROPOMI satellite instrument as a result of its high spatial resolution compared to its predecessor instruments. These shadows contaminate TROPOMI's air quality measurements, because shadows are generally not taken into account in the models that are used for aerosol and trace gas retrievals. If the shadows are to be removed from the data, or if shadows are to be studied, an automatic detection of the shadow pixels is needed. We present the Detection AlgoRithm for CLOud Shadows (DARCLOS) for TROPOMI, which is the first cloud shadow detection algorithm for a spaceborne spectrometer. DARCLOS raises potential cloud shadow flags (PCSFs), actual cloud shadow flags (ACSFs), and spectral cloud shadow flags (SCSFs). The PCSFs indicate the TROPOMI ground pixels that are potentially affected by cloud shadows based on a geometric consideration with safety margins. The ACSFs are a refinement of the PCSFs using spectral reflectance information of the PCSF pixels and identify the TROPOMI ground pixels that are confidently affected by cloud shadows. Because we find indications of the wavelength dependence of cloud shadow extents in the UV, the SCSF is a wavelength-dependent alternative for the ACSF at the wavelengths of TROPOMI's air quality retrievals. We validate the PCSF and ACSF with true-colour images made by the VIIRS instrument on board Suomi NPP orbiting in close proximity to TROPOMI on board Sentinel-5P. We find that the cloud evolution during the overpass time difference between TROPOMI and VIIRS complicates this validation strategy, implicating that an alternative cloud shadow detection approach using co-located VIIRS observations could be problematic. We conclude that the PCSF can be used to exclude cloud shadow contamination from TROPOMI data, while the ACSF and SCSF can be used to select pixels for the scientific analysis of cloud shadow effects.
- Published
- 2022
22. Introduction of the DISAMAR radiative transfer model: determining instrument specifications and analysing methods for atmospheric retrieval (version 4.1.5).
- Author
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de Haan, Johan F., Wang, Ping, Sneep, Maarten, Veefkind, J. Pepijn, and Stammes, Piet
- Subjects
RADIATIVE transfer ,OZONESONDES ,MICROWAVE remote sensing ,OZONE layer ,ATMOSPHERIC layers ,TRACE gases ,LIGHT absorption ,TECHNICAL specifications - Abstract
DISAMAR (determining instrument specifications and analysing methods for atmospheric retrieval) is a computer model developed to simulate retrievals of properties of atmospheric trace gases, aerosols, clouds, and the ground surface from passive remote sensing observations in a wavelength range from 270 to 2400 nm. It is being used for the TROPOMI/Sentinel-5P and Sentinel-4/5 missions to derive Level-1b product specifications. DISAMAR uses the doubling–adding method and the layer-based orders of scattering method for radiative transfer calculations. It can perform retrievals using three different approaches: optimal estimation (OE), differential optical absorption spectroscopy (DOAS), and the combination of DOAS and OE, called DISMAS (differential and smooth absorption separated). The derivatives, which are needed in the OE and DISMAS retrievals, are derived in a semi-analytical way from the adding formulae. DISAMAR uses plane-parallel homogeneous atmospheric layers with a pseudo-spherical correction for large solar zenith angles. DISAMAR has various novel features and diverse retrieval possibilities, such as retrieving aerosol layer heights and ozone vertical profiles. This paper provides an overview of the DISAMAR model version 4.1.5 without treating all the details. We focus on the principle of the layer-based orders of scattering method, the calculation of the semi-analytical derivatives, and the DISMAS retrieval method, and it is to our knowledge the first time that these methods are described. We demonstrate some applications of DISMAS and the derivatives. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
23. Aerosol influence on polarization and intensity in near-infrared O 2 and CO 2 absorption bands observed from space
- Author
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Boesche, Eyk, Stammes, Piet, and Bennartz, Ralf
- Published
- 2009
- Full Text
- View/download PDF
24. Validation of the Sentinel-5 Precursor TROPOMI cloud data with Cloudnet, Aura OMI O2-O2, MODIS, and Suomi-NPP VIIRS
- Author
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Compernolle, Steven, Argyrouli, Athina, Lutz, Ronny, Sneep, Maarten, Lambert, Jean-Christopher, Fjæraa, Ann Mari, Hubert, Daan, Keppens, Arno, Loyola, Diego, O'Connor, Ewan, Romahn, Fabian, Stammes, Piet, Verhoelst, Tijl, and Wang, Ping
- Subjects
Remote Sensing ,Clouds ,Validation ,TROPOMI ,Atmosphärenprozessoren - Abstract
Accurate knowledge of cloud properties is essential to the measurement of atmospheric composition from space. In this work we assess the quality of the cloud data from three Copernicus Sentinel-5 Precursor (S5P) TROPOMI cloud products: (i) S5P OCRA/ROCINN_CAL (Optical Cloud Recognition Algorithm/Retrieval of Cloud Information using Neural Networks;Clouds-As-Layers), (ii) S5P OCRA/ROCINN_CRB (Clouds-as-Reflecting Boundaries), and (iii) S5P FRESCO-S (Fast Retrieval Scheme for Clouds from Oxygen absorption bands – Sentinel). Target properties of this work are cloud-top height and cloud optical thickness (OCRA/ROCINN_CAL), cloud height (OCRA/ROCINN_CRB and FRESCO-S), and radiometric cloud fraction (all three algorithms). The analysis combines (i) the examination of cloud maps for artificial geographical patterns, (ii) the comparison to other satellite cloud data (MODIS, NPP-VIIRS, and OMI O2–O2), and (iii) ground-based validation with respect to correlative observations (30 April 2018 to 27 February 2020) from the Cloudnet network of ceilometers, lidars, and radars. Zonal mean latitudinal variation of S5P cloud properties is similar to that of other satellite data. S5P OCRA/ROCINN_CAL agrees well with NPP VIIRS cloud-top height and cloud optical thickness and with Cloudnet cloud-top height, especially for the low (mostly liquid) clouds. For the high clouds, S5P OCRA/ROCINN_CAL cloud-top height is below the cloud-top height of VIIRS and of Cloudnet, while its cloud optical thickness is higher than that of VIIRS. S5P OCRA/ROCINN_CRB and S5P FRESCO cloud height are well below the Cloudnet cloud mean height for the low clouds but match on average better with the Cloudnet cloud mean height for the higher clouds. As opposed to S5P OCRA/ROCINN_CRB and S5P FRESCO, S5P OCRA/ROCINN_CAL is well able to match the lowest CTH mode of the Cloudnet observations. Peculiar geographical patterns are identified in the cloud products and will be mitigated in future releases of the cloud data products.
- Published
- 2021
25. Validation of the Sentinel-5 Precursor TROPOMI cloud data withCloudnet, Aura OMI O2–O2, MODIS, and Suomi-NPP VIIR
- Author
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Compernolle, Steven, Argyrouli, Athina, Lutz, Ronny, Sneep, Maarten, Lambert, Jean-Christopher, Fjæraa, Ann Mari, Hubert, Daan, Keppens, Arno, Loyola, Diego, O'Connor, Ewan, Romahn, Fabian, Stammes, Piet, Verhoelst, Tijl, and Wang, Ping
- Abstract
Accurate knowledge of cloud properties is essential to the measurement of atmospheric composition from space. In this work we assess the quality of the cloud data from three Copernicus Sentinel-5 Precursor (S5P) TROPOMI cloud products: (i) S5P OCRA/ROCINN_CAL (Optical Cloud Recognition Algorithm/Retrieval of Cloud Information using Neural Networks;Clouds-As-Layers), (ii) S5P OCRA/ROCINN_CRB (Clouds-as-Reflecting Boundaries), and (iii) S5P FRESCO-S (Fast Retrieval Scheme for Clouds from Oxygen absorption bands – Sentinel). Target properties of this work are cloud-top height and cloud optical thickness (OCRA/ROCINN_CAL), cloud height (OCRA/ROCINN_CRB and FRESCO-S), and radiometric cloud fraction (all three algorithms). The analysis combines (i) the examination of cloud maps for artificial geographical patterns, (ii) the comparison to other satellite cloud data (MODIS, NPP-VIIRS, and OMI O2–O2), and (iii) ground-based validation with respect to correlative observations (30 April 2018 to 27 February 2020) from the Cloudnet network of ceilometers, lidars, and radars. Zonal mean latitudinal variation of S5P cloud properties is similar to that of other satellite data. S5P OCRA/ROCINN_CAL agrees well with NPP VIIRS cloud-top height and cloud optical thickness and with Cloudnet cloud-top height, especially for the low (mostly liquid) clouds. For the high clouds, S5P OCRA/ROCINN_CAL cloud-top height is below the cloud-top height of VIIRS and of Cloudnet, while its cloud optical thickness is higher than that of VIIRS. S5P OCRA/ROCINN_CRB and S5P FRESCO cloud height are well below the Cloudnet cloud mean height for the low clouds but match on average better with the Cloudnet cloud mean height for the higher clouds. As opposed to S5P OCRA/ROCINN_CRB and S5P FRESCO, S5P OCRA/ROCINN_CAL is well able to match the lowest CTH mode of the Cloudnet observations. Peculiar geographical patterns are identified in the cloud products and will be mitigated in future releases of the cloud data products.
- Published
- 2021
26. Polarization of skylight in the [0.sub.2]A band: effects of aerosol properties
- Author
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Boesche, Eyk, Stammes, Piet, Preusker, Rene, Bennartz, Ralf, Knap, Wouter, and Fischer, Juergen
- Subjects
Skylights -- Optical properties ,Polarization (Light) -- Research ,Aerosols -- Optical properties ,Aerosols -- Influence ,Astronomy ,Physics - Abstract
Motivated by several observations of the degree of linear polarization of skylight in the oxygen A ([O.sub.2]A) band that do not yet have a quantitative explanation, we analyze the influence of aerosol altitude, microphysics, and optical thickness on the degree of linear polarization of the zenith skylight in the spectral region of the [O.sub.2]A band, between 755 to 775 nm. It is shown that the degree of linear polarization inside the [O.sub.2]A band is particularly sensitive to aerosol altitude. The sensitivity is strongest for aerosols within the troposphere and depends also on their microphysical properties and optical thickness. The polarization of the [O.sub.2]A band can be larger than the polarization of the continuum, which typically occurs for strongly polarizing aerosols in an elevated layer, or smaller, which typically occurs for depolarizing aerosols or cirrus clouds in an elevated layer. We show that in the case of a single aerosol layer in the atmosphere a determination of the aerosol layer altitude may be obtained. Furthermore, we show limitations of the aerosol layer altitude determination in case of multiple aerosol layers. To perform these simulations we developed a fast method for multiple scattering radiative transfer calculations in gaseous absorption bands including polarization. The method is a combination of doubling-adding and k-binning methods. We present an error estimation of this method by comparing with accurate line-by-line radiative transfer simulations. For the [O.sub.2]A band, the errors in the degree of linear polarization are less than 0.11% for transmitted light, and less than 0.31% for reflected light. OCIS codes: 010.1110, 260.5430, 280.1310, 101.320, 300.1030.
- Published
- 2008
27. Effect of aerosol microphysical properties on polarization of skylight: sensitivity study and measurements
- Author
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Boesche, Eyk, Stammes, Piet, Ruhtz, Thomas, Preusker, Rene, and Fischer, Juergen
- Subjects
Polarization (Light) -- Research ,Aerosols -- Optical properties ,Refractive index -- Measurement ,Astronomy ,Physics - Abstract
We analyze the sensitivity of the degree of linear polarization in the Sun's principal plane as a function of aerosol microphysical parameters: the real and imaginary parts of the refractive index, the median radius and geometric standard deviation of the bimodal size distribution (both fine and coarse modes), and the relative number weight of the fine mode at a wavelength of 675 nm. We use Mie theory for single-scattering simulations and the doubling--adding method with the inclusion of polarization for multiple scattering. It is shown that the behavior of the degree of linear polarization is highly sensitive to both the small mode of the bimodal size distribution and the real part of the refractive index of aerosols, as well as to the aerosol optical thickness; whereas not all parameters influence the polarization equally. A classification of the importance of the input parameters is given. This sensitivity study is applied to an analysis of ground-based polarization measurements. For the passive remote sensing of microphysical and optical properties of aerosols, a ground-based spectral polarization measuring system was built, which aims to measure the Stokes parameters I, Q, and U in the visible (from 410 to 789 nm) and near-infrared (from 674 to 995 nm) spectral range with a spectral resolution of 7 nm in the visible and 2.4 nm in the near infrared. We compare polarization measurements taken with radiative transfer simulations under both clear- and hazy-sky conditions in an urban area (Cabauw, The Netherlands, 51.58[degrees] N, 4.56[degrees] E). Conclusions about the microphysical properties of aerosol are drawn from the comparison. OCIS codes: 010.1110, 260.5430, 280.1310.
- Published
- 2006
28. Intercomparison of reflectances observed by GOME and SCIAMACHY in the visible wavelength range
- Author
-
Tilstra, Lieuwe G. and Stammes, Piet
- Subjects
Reflectance -- Measurement ,Spectrometer -- Design and construction ,Radiation -- Measurement ,Radiation -- Analysis ,Astronomy ,Physics - Abstract
We compare the Earth reflectances of the spectrometers Global Ozone Monitoring Experiment (GOME) and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) over their overlapping wavelength range (240-800 nm). The goal is to investigate the quality of the radiometric calibration of SCIAMACHY using calibrated GOME data as a reference. However, severe degradation of the GOME instrument in the UV since 2001 prevents it from being a reliable reference below 500 nm. Above 500 nm, GOME is reliable and we find substantial disagreement between GOME and SCIAMACHY, of the order of 15%-20%, which we can attribute completely to the current calibration problems of SCIAMACHY. These numbers are supported by a previous study in which SCIAMACHY was compared with the imager Medium Resolution Imaging Spectrometer (MERIS) onboard the Envisat satellite. OCIS codes: 280.0280, 010.0010.
- Published
- 2006
29. The Ozone Monitoring Instrument
- Author
-
Levelt, Pieternel F., van den Oord, Gijsbertus H.J., Dobber, Marcel R., Malkki, Anssi, Visser, Huib, de Vries, Johan, Stammes, Piet, Lundell, Jens O.V., and Saari, Heikki
- Subjects
Air quality -- Measurement ,Air quality -- Analysis ,Atmospheric research -- Forecasts and trends ,Ozone layer -- Environmental aspects ,Ozone layer -- Research ,Market trend/market analysis ,Business ,Earth sciences ,Electronics and electrical industries - Abstract
The Ozone Monitoring Instrument (OMI) flies on the National Aeronautics and Space Adminsitration's Earth Observing System Aura satellite launched in July 2004. OMI is a ultraviolet/visible (UV/VIS) nadir solar backscatter spectrometer, which provides nearly global coverage in one day with a spatial resolution of 13 km x 24 km. Trace gases measured include [O.sub.3], N[O.sub.2], S[O.sub.2], HCHO, BrO, and OCIO. In addition, OMI will measure aerosol characteristics, cloud top heights, and UV irradiance at the surface. OMI's unique capabilities for measuring important trace gases with a small footprint and dally global coverage will be a major contribution to our understanding of stratospheric and tropospheric chemistry and climate change. OMI's high spatial resolution is unprecedented and will enable detection of air pollution on urban scale resolution. In this paper, the instrument and its performance will be discussed. Index Terms--Air quality, atmospheric research, ozone layer, ultraviolet/visible (UVMS) satellite instruments.
- Published
- 2006
30. Modeling total and polarized reflectances of ice clouds: evaluation by means of POLDER and ATSR-2 measurements
- Author
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Knap, Wouter H., C.-Labonnote, Laurent, Brogniez, Gerard, and Stammes, Piet
- Subjects
Remote sensing -- Research ,Ice crystals -- Research ,Optics -- Research ,Radiation -- Measurement ,Radiation -- Research ,Astronomy ,Physics - Abstract
Four ice-crystal models are tested by use of ice-cloud reflectances derived from Along Track Scanning Radiometer-2 (ATSR-2) and Polarization and Directionality of Earth's Reflectances (POLDER) radiance measurements. The analysis is based on dual-view ATSR-2 total reflectances of tropical cirrus and POLDER global-scale total and polarized reflectances of ice clouds at as many as 14 viewing directions. Adequate simulations of ATSR-2 total reflectances at 0.865 [micro]m are obtained with model clouds consisting of moderately distorted imperfect hexagonal monocrystals (IMPs). The optically thickest clouds ([tau] > ~16) in the selected case tend to be better simulated by use of pure hexagonal monocrystals (PHMs). POLDER total reflectances at 0.670 [micro]m are best simulated with columnar or platelike IMPs or columnar inhomogeneous hexagonal monocrystals (IHMs). Less-favorable simulations are obtained for platelike IHMs and polycrystals (POLYs). Inadequate simulations of POLDER total and polarized reflectances are obtained for model clouds consisting of PHMs. Better simulations of the POLDER polarized reflectances at 0.865 [micro]m are obtained with IMPs, IHMs, or POLYs, although POLYs produce polarized reflectances that are systematically lower than most of the measurements. The best simulations of the polarized reflectance for the ice-crystal models assumed in this study are obtained for model clouds consisting of columnar IMPs or IHMs. OCIS codes: 010.2940, 280.1310, 290.1090.
- Published
- 2005
31. Validation of space-based polarization measurements by use of a single-scattering approximation, with application to the Global Ozone Monitoring Experiment
- Author
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Aben, Ilse, Tanzi, Cristina P., Hartmann, Wouter, Stam, Daphne M., and Stammes, Piet
- Subjects
Light scattering -- Research ,Optical communications -- Research ,Astronomy ,Physics - Abstract
A method is presented for in-flight validation of space-based polarization measurements based on approximation of the direction of polarization of scattered sunlight by the Rayleigh single-scattering value. This approximation is verified by simulations of radiative transfer calculations for various atmospheric conditions. The simulations show locations along an orbit where the scattering geometries are such that the intensities of the parallel and orthogonal polarization components of the light are equal, regardless of the observed atmosphere and surface. The method can be applied to any space-based instrument that measures the polarization of reflected solar light. We successfully applied the method to validate the Global Ozone Monitoring Experiment (GOME) polarization measurements. The error in the GOME's three broadband polarization measurements appears to be ~1%. OCIS codes: 010.0010, 010.1280, 280.0280.
- Published
- 2003
32. DARCLOS: a cloud shadow detection algorithm for TROPOMI.
- Author
-
Trees, Victor, Wang, Ping, Stammes, Piet, Tilstra, Lieuwe G., Donovan, David P., and Siebesma, A. Pier
- Subjects
SPECTRAL reflectance ,SPACE-based radar ,TRACE gases ,AIR quality ,SPATIAL resolution ,ALGORITHMS - Abstract
Cloud shadows are observed by the TROPOMI satellite instrument as a result of its high spatial resolution as compared to its predecessor instruments. These shadows contaminate TROPOMI's air quality measurements, because shadows are generally not taken into account in the models that are used for aerosol and trace gas retrievals. If the shadows are to be removed from the data, or if shadows are to be studied, an automatic detection of the shadow pixels is needed. We present the Detection AlgoRithm for CLOud Shadows (DARCLOS) for TROPOMI, which is the first cloud shadow detection algorithm for a spaceborne spectrometer. DARCLOS raises potential cloud shadow flags (PCSFs), and actual cloud shadow flags (ACSFs). The PCSFs indicate the TROPOMI ground pixels that are potentially affected by cloud shadows based on a geometric consideration with safety margins. The ACSFs are a refinement of the PCSFs using spectral reflectance information of the PCSF pixels, and identify the TROPOMI ground pixels that are confidently affected by cloud shadows. We validate DARCLOS with true color images made by the VIIRS instrument on board of Suomi NPP orbiting in close constellation with TROPOMI on board of Sentinel 5-P. We conclude that the PCSF can be used to exclude cloud shadow contamination from TROPOMI data, while the ACSF can be used to select pixels for the scientific analysis of cloud shadow effects. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
33. Trends and trend reversal detection in 2 decades of tropospheric NO2 satellite observations
- Author
-
Georgoulias, Aristeidis K., A, Ronald J., Stammes, Piet, Boersma, K. Folkert, and Eskes, Henk J.
- Abstract
In this work, a ∼21-year global dataset from four different satellite sensors with a mid-morning overpass (GOME/ERS-2, SCIAMACHY/ENVISAT, GOME-2/Metop-A, and GOME-2/Metop-B) is compiled to study the long-term tropospheric NO2 patterns and trends. The Global Ozone Monitoring Experiment (GOME) and GOME-2 data are “corrected” relative to the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) data to produce a self-consistent dataset that covers the period April 1996–September 2017. The highest tropospheric NO2 concentrations are seen over urban, industrialized, and highly populated areas and over ship tracks in the oceans. Tropospheric NO2 has generally decreased during the last 2 decades over the industrialized and highly populated regions of the western world (a total decrease of the order of ∼49 % over the US, the Netherlands, and the UK; ∼36 % over Italy and Japan; and ∼32 % over Germany and France) and increased over developing regions (a total increase of ∼160 % over China and ∼33 % over India). It is suggested here that linear trends cannot be used efficiently worldwide for such long periods. Tropospheric NO2 is very sensitive to socioeconomic changes (e.g., environmental protection policies, economic recession, warfare, etc.) which may cause either short-term changes or even a reversal of the trends. The application of a method capable of detecting the year when a reversal of trends happened shows that tropospheric NO2 concentrations switched from positive to negative trends and vice versa over several regions around the globe. A country-level analysis revealed clusters of countries that exhibit similar positive-to-negative or negative-to-positive trend reversals, while 29 out of a total of 64 examined megacities and large urban agglomerations experienced a trend reversal at some point within the last 2 decades.
- Published
- 2019
34. Polarimetric remote sensing of atmospheric aerosols: Instruments, methodologies, results, and perspectives
- Author
-
Doubovik, Oleg, Dubovik, Oleg, Li, Zhengqiang, Mishchenko, Michael, Tanré, Didier, Karol, Yana, Bojkov, Bojan, Cairns, Brian, Diner, David, Espinosa, W. Reed, Goloub, Philippe, Gu, Xingfa, Hasekamp, Otto, Hong, Jin, Hou, Weizhen, Knobelspiesse, Kirk, Landgraf, Jochen, Li, Li, Litvinov, Pavel, Liu, Yi, Lopatin, Anton, Marbach, Thierry, Maring, Hal, Martins, Vanderlei, Meijer, Yasjka, Milinevsky, Gennadi, Mukai, Sonoyo, Parol, Frederic, Qiao, Yanli, Remer, Lorraine, Rietjens, Jeroen, Sano, Itaru, Stammes, Piet, Stamnes, Snorre, Sun, Xiaobing, Tabary, Pierre, Travis, Larry, Waquet, Fabien, Xu, Feng, Yan, Changxiang, Yin, Dekui, Laboratoire d’Optique Atmosphérique - UMR 8518 (LOA), and Institut national des sciences de l'Univers (INSU - CNRS)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)
- Subjects
[SDE]Environmental Sciences ,ComputingMilieux_MISCELLANEOUS - Abstract
International audience
- Published
- 2019
35. Minimizing aerosol effects on the OMI tropospheric NO2 retrieval – An improved use of the 477 nm O2 − O2 band and an estimation of the aerosol correction uncertainty
- Author
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Chimot, Julien, Veefkind, J. Pepijn, Haan, Johan F., Stammes, Piet, and Levelt, Pieternel F.
- Abstract
Global mapping of satellite tropospheric NO2 vertical column density (VCD), a key gas in air quality monitoring, requires accurate retrievals over complex urban and industrialized areas and under any atmospheric conditions. The high abundance of aerosol particles in regions dominated by anthropogenic fossil fuel combustion, e.g. megacities, and/or biomass-burning episodes, affects the space-borne spectral measurement. Minimizing the tropospheric NO2 VCD biases caused by aerosol scattering and absorption effects is one of the main retrieval challenges from air quality satellite instruments. In this study, the reference Ozone Monitoring Instrument (OMI) DOMINO-v2 product was reprocessed over cloud-free scenes, by applying new aerosol correction parameters retrieved from the 477 nm O2−O2 band, over eastern China and South America for 2 years (2006–2007). These new parameters are based on two different and separate algorithms developed during the last 2 years in view of an improved use of the OMI 477 nm O2−O2 band: the updated OMCLDO2 algorithm, which derives improved effective cloud parameters, the aerosol neural network (NN), which retrieves explicit aerosol parameters by assuming a more physical aerosol model. The OMI aerosol NN is a step ahead of OMCLDO2 because it primarily estimates an explicit aerosol layer height (ALH), and secondly an aerosol optical thickness τ for cloud-free observations. Overall, it was found that all the considered aerosol correction parameters reduce the biases identified in DOMINO-v2 over scenes in China with high aerosol abundance dominated by fine scattering and weakly absorbing particles, e.g. from [-20%:-40%] to [0 %:20 %] in summertime. The use of the retrieved OMI aerosol parameters leads in general to a more explicit aerosol correction and higher tropospheric NO2 VCD values, in the range of [0 %:40 %], than from the implicit correction with the updated OMCLDO2. This number overall represents an estimation of the aerosol correction strategy uncertainty nowadays for tropospheric NO2 VCD retrieval from space-borne visible measurements. The explicit aerosol correction theoretically includes a more realistic consideration of aerosol multiple scattering and absorption effects, especially over scenes dominated by strongly absorbing particles, where the correction based on OMCLDO2 seems to remain insufficient. However, the use of ALH and τ from the OMI NN aerosol algorithm is not a straightforward operation and future studies are required to identify the optimal methodology. For that purpose, several elements are recommended in this paper. Overall, we demonstrate the possibility of applying a more explicit aerosol correction by considering aerosol parameters directly derived from the 477 nm O2−O2 spectral band, measured by the same satellite instrument. Such an approach can, in theory, easily be transposed to the new-generation of space-borne instruments (e.g. TROPOMI on board Sentinel-5 Precursor), enabling a fast reprocessing of tropospheric NO2 data over cloud-free scenes (cloudy pixels need to be filtered out), as well as for other trace gas retrievals (e.g. SO2, HCHO).
- Published
- 2019
36. Minimizing aerosol effects on the OMI tropospheric NO2 retrieval - An improved use of the 477nm O2-O2 band and an estimation of the aerosol correction uncertainty
- Author
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Chimot, J.J., Veefkind, j. Pepijn, De Haan, Johan F., Stammes, Piet, and Levelt, Pieternel Felicitas
- Abstract
Global mapping of satellite tropospheric NO2 vertical column density (VCD), a key gas in air quality monitoring, requires accurate retrievals over complex urban and industrialized areas and under any atmospheric conditions. The high abundance of aerosol particles in regions dominated by anthropogenic fossil fuel combustion, e.g. megacities, and/or biomass-burning episodes, affects the space-borne spectral measurement. Minimizing the tropospheric NO2 VCD biases caused by aerosol scattering and absorption effects is one of the main retrieval challenges from air quality satellite instruments. In this study, the reference Ozone Monitoring Instrument (OMI) DOMINO-v2 product was reprocessed over cloud-free scenes, by applying new aerosol correction parameters retrieved from the 477 nm O2-O2 band, over eastern China and South America for 2 years (2006 2007). These new parameters are based on two different and separate algorithms developed during the last 2 years in view of an improved use of the OMI 477 nm O2-O2 band: 1. the updated OMCLDO2 algorithm, which derives improved effective cloud parameters, 2. the aerosol neural network (NN), which retrieves explicit aerosol parameters by assuming a more physical aerosol model. The OMI aerosol NN is a step ahead of OMCLDO2 because it primarily estimates an explicit aerosol layer height (ALH), and secondly an aerosol optical thickness τ for cloud-free observations. Overall, it was found that all the considered aerosol correction parameters reduce the biases identified in DOMINO-v2 over scenes in China with high aerosol abundance dominated by fine scattering and weakly absorbing particles, e.g. from [-20% V -40%] to [0% V 20%] in summertime. The use of the retrieved OMI aerosol parameters leads in general to a more explicit aerosol correction and higher tropospheric NO2 VCD values, in the range of [0% V 40%], than from the implicit correction with the updated OMCLDO2. This number overall represents an estimation of the aerosol correction strategy uncertainty nowadays for tropospheric NO2 VCD retrieval from space-borne visible measurements. The explicit aerosol correction theoretically includes a more realistic consideration of aerosol multiple scattering and absorption effects, especially over scenes dominated by strongly absorbing particles, where the correction based on OMCLDO2 seems to remain insufficient. However, the use of ALH and τ from the OMI NN aerosol algorithm is not a straightforward operation and future studies are required to identify the optimal methodology. For that purpose, several elements are recommended in this paper. Overall, we demonstrate the possibility of applying a more explicit aerosol correction by considering aerosol parameters directly derived from the 477 nm O2-O2 spectral band, measured by the same satellite instrument. Such an approach can, in theory, easily be transposed to the new-generation of space-borne instruments (e.g. TROPOMI on board Sentinel- 5 Precursor), enabling a fast reprocessing of tropospheric NO2 data over cloud-free scenes (cloudy pixels need to be filtered out), as well as for other trace gas retrievals (e.g. SO2, HCHO).
- Published
- 2019
37. Trends and trend reversal detection in two decades of tropospheric NO2 satellite observations
- Author
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Georgoulias, Aristeidis K., A, Ronald J., Stammes, Piet, Boersma, K. Folkert, and Eskes, Henk J.
- Abstract
In this work, a ~ 21-years self-consistent global dataset from four different satellite sensors with a mid-morning overpass (GOME/ERS-2, SCIAMACHY/ENVISAT, GOME-2/Metop-A and GOME-2/Metop-B) is compiled to study the long-term tropospheric NO2 patterns and trends. The GOME and GOME-2 data are corrected relative to the SCIAMACHY data in order to reproduce what SCIAMACHY would measure if it was in orbit for the period 4/1996–9/2017. The highest tropospheric NO2 concentrations are seen over urban, industrialized and highly populated areas and over ship tracks in the oceans. Tropospheric NO2 has generally decreased during the last two decades over the industrialized and highly populated regions of the Western World (e.g. average decrease of the order of ~ 49 % over the U.S., the Netherlands and the U.K., ~ 36 % over Italy and Japan and ~ 32 % over Germany and France) and increased over developing regions (e.g. average increase of ~ 160 % over China and ~ 33 % over India). It is suggested here that linear trends cannot be used efficiently worldwide for such long periods. Tropospheric NO2 is very sensitive to socioeconomic changes (e.g. environmental protection policies, economic recession, warfare, etc.) which may cause either short term changes or even a reversal of the trends. The application of a method capable of detecting the year when a reversal of trends happened shows that tropospheric NO2 concentrations switched from positive to negative trends and vice versa over several regions around the globe. A country-level analysis revealed clusters of countries that exhibit similar positive-to-negative or negative-to-positive reversals while 29 out of a total of 64 examined megacities and large urban agglomerations experienced a trend reversal at some point within the last two decades.
- Published
- 2018
38. Directionally dependent Lambertian-equivalent reflectivity (DLER) of the Earth's surface measured by the GOME-2 satellite instruments.
- Author
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Tilstra, Lieuwe G., Tuinder, Olaf N. E., Wang, Ping, and Stammes, Piet
- Subjects
SURFACE of the earth ,ZENITH distance ,GEOSTATIONARY satellites ,RADIATIVE transfer - Abstract
In this paper we introduce the new concept of directionally dependent Lambertian-equivalent reflectivity (DLER) of the Earth's surface retrieved from satellite observations. This surface DLER describes Lambertian (isotropic) surface reflection which is extended with a dependence on the satellite viewing geometry. We apply this concept to data of the GOME-2 satellite instruments to create a global database of the reflectivity of the Earth's surface, providing surface DLER for 26 wavelength bands between 328 and 772 nm as a function of the satellite viewing angle via a second-degree polynomial parameterisation. The resolution of the database grid is 0.25 ∘ by 0.25 ∘ , but the real, intrinsic spatial resolution varies over the grid from 1.0 ∘ by 1.0 ∘ to 0.5 ∘ by 0.5 ∘ down to 0.25 ∘ by 0.25 ∘ by applying dynamic gridding techniques. The database is based on more than 10 years (2007–2018) of GOME-2 data from the MetOp-A and MetOp-B satellites. The relation between DLER and bi-directional reflectance distribution function (BRDF) surface reflectance is studied using radiative transfer simulations. For the shorter wavelengths (λ<500 nm), there are significant differences between the two. For instance, at 463 nm the difference can go up to 6 % at 30 ∘ solar zenith angle. The study also shows that, although DLER and BRDF surface reflectances have different properties, they are comparable for the longer wavelengths (λ>500 nm). Based on this outcome, the GOME-2 surface DLER is compared with MODIS surface BRDF data from MODIS band 1 (centred around 645 nm) using both case studies and global comparisons. The conclusion of this validation is that the GOME-2 DLER compares well to MODIS BRDF data and that it does so much better than the non-directional LER database. The DLER approach for describing surface reflectivity is therefore an important improvement over the standard isotropic (non-directional) LER approaches used in the past. The GOME-2 surface DLER database can be used for the retrieval of atmospheric properties from GOME-2 and from previous satellite instruments like GOME and SCIAMACHY. It will also be used to support retrievals from the future Sentinel-5 UVNS (ultraviolet, visible, near-infrared, and short-wave infrared) satellite instrument. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
39. Restoring the top-of-atmosphere reflectance during solar eclipses: a proof of concept with the UV absorbing aerosol index measured by TROPOMI.
- Author
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Trees, Victor, Wang, Ping, and Stammes, Piet
- Subjects
SOLAR eclipses ,ECLIPSES ,ATMOSPHERIC composition ,REFLECTANCE ,SURFACE of the earth ,PROOF of concept ,AEROSOLS - Abstract
During a solar eclipse the solar irradiance reaching the top of the atmosphere (TOA) is reduced in the Moon shadow. The solar irradiance is commonly measured by Earth observation satellites before the start of the solar eclipse and is not corrected for this reduction, which results in a decrease in the computed TOA reflectances. Consequently, air quality products that are derived from TOA reflectance spectra, such as the ultraviolet (UV) absorbing aerosol index (AAI), are distorted or undefined in the shadow of the Moon. The availability of air quality satellite data in the penumbral and antumbral shadow during solar eclipses, however, is of particular interest to users studying the atmospheric response to solar eclipses. Given the time and location of a point on the Earth's surface, we explain how to compute the obscuration during a solar eclipse, taking into account wavelength-dependent solar limb darkening. With the calculated obscuration fractions, we restore the TOA reflectances and the AAI in the penumbral shadow during the annular solar eclipses on 26 December 2019 and 21 June 2020 measured by the TROPOMI/S5P instrument. We compare the calculated obscuration to the estimated obscuration using an uneclipsed orbit. In the corrected products, the signature of the Moon shadow disappeared, but only if wavelength-dependent solar limb darkening is taken into account. We find that the Moon shadow anomaly in the uncorrected AAI is caused by a reduction of the measured reflectance at 380 nm , rather than a colour change of the measured light. We restore common AAI features such as the sunglint and desert dust, and we confirm the restored AAI feature on 21 June 2020 at the Taklamakan Desert by measurements of the GOME-2C satellite instrument on the same day but outside the Moon shadow. No indication of local absorbing aerosol changes caused by the eclipses was found. We conclude that the correction method of this paper can be used to detect real AAI rising phenomena during a solar eclipse and has the potential to restore any other product that is derived from TOA reflectance spectra. This would resolve the solar eclipse anomalies in satellite air quality measurements in the penumbra and antumbra and would allow for studying the effect of the eclipse obscuration on the composition of the Earth's atmosphere from space. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
40. Advances in Lidar Observations for Airborne Hazards for Aviation in the Framework of the EUNADICS-AV Project.
- Author
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Liu, D., Wang, Y., Wu, Y., Gross, B., Moshary, F., Apituley, Arnoud, Mona, Lucia, Papagiannopoulos, Nikolas, Rufenacht, Rolf, Wagenaar, Saskia, Stammes, Piet, de Laat, Jos, de Cerff, Wim Som, de Haij, Marijn, Marchese, Francesco, Falconieri, Alfredo, Haefele, Alexander, and Hervo, Maxime
- Subjects
LIDAR ,ARTIFICIAL satellites ,INFORMATION storage & retrieval systems ,AIR traffic control ,AIRSPACE (Law) - Abstract
The vulnerability of the (European) aviation system to the airborne hazards was evident during the Eyjafjallajökull volcanic eruption in 2010. For support of Air Traffic Control (ATC) many observations of the event were available from satellites, ground based instruments and airborne platforms, at pan-European scale. However, efficient use of the data for ATC proved difficult mainly due to sub-optimal aggregation and integrated assessment of the available information in near-real-time. The project EUNADICS-AV (European Natural Disaster Coordination and Information System for Aviation) aims to close this gap. The observational component of the project will make existing data products for airborne hazards more accessible, visible and used, and to foster tailored product development. Once assimilated into models and integrated in the EUNADICS-AV Data Portal these data can be the base to efficiently improve European airspace resilience to airborne hazards. Since 2010 new data products have become available specifically for for airborne hazard alerting and monitoring together with specific tailored products designed for replying to user needs and recommendations. This paper describes the EUNADICS-AV approach and will focus on the role of operational and research grade ground based lidars. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
41. Retrieval of tropospheric NO2 columns over Berlin from high-resolution airborne observations with the spectrolite breadboard instrument
- Author
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Vlemmix, Tim, Ge, Xinrui (Jerry), Goeij, Bryan T. G., Wal, Len F., Otter, Gerard C. J., Stammes, Piet, Wang, Ping, Merlaud, Alexis, Schüttemeyer, Dirk, Meier, Andreas C., Veefkind, J. Pepijn, and Levelt, Pieternel F.
- Abstract
This paper presents the retrieval method that was developed to derive tropospheric NO2 columns from UV/VIS spectral measurements obtained with the Spectrolite Breadboard Instrument during the AROMAPEX campaign in Berlin (April 2016). A typical DOAS retrieval approach is followed. For the calculation of air mass factors this study specifically focuses on the impact of the surface reflectance, which varies considerably from pixel to pixel over this urban region. Ground-based aerosol optical thickness measurements are used as prior information. It is shown that retrieved surface reflectance shows good agreement with those derived from Landsat 8 measurements performed on the same day. Furthermore we demonstrate that tropospheric NO2 columns retrieved for pairs of adjacent pixels are self-consistent in the sense that they do not show a substantial systematic dependence on surface reflectance, in contrast to differential slant column densities. Also some cases are identified to illustrate this on a pixel-by-pixel level. An error budget is provided to quantify the impact of various assumptions on the accuracy of the retrieval of surface reflectance and tropospheric NO2 columns. Both in the morning and afternoon flight a NO2 plume is observed stretching out over Berlin from West to East. Peak values between 15 × 1015 and 20 × 1015 molec/cm2 are detected, whereas – at much lower spatial resolution – OMI detects peak values between 9 × 1015 (first overpass) and 4 × 1015 molec/cm2 (second overpass).
- Published
- 2018
42. The importance of surface reflectance anisotropy for cloud and NO2 retrievals from GOME-2 and OMI
- Author
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Lorente, Alba, Boersma, K.F., Stammes, Piet, Tilstra, L.G., Richter, Andreas, Yu, Huan, Kharbouche, Said, and Muller, Jan Peter
- Subjects
Meteorologie en Luchtkwaliteit ,WIMEK ,Meteorology and Air Quality ,Life Science - Abstract
The angular distribution of the light reflected by the Earth's surface influences top-of-atmosphere (TOA) reflectance values. This surface reflectance anisotropy has implications for UV/Vis satellite retrievals of albedo, clouds, and trace gases such as nitrogen dioxide (NO2). These retrievals routinely assume the surface to reflect light isotropically. Here we show that cloud fractions retrieved from GOME-2A and OMI with the FRESCO and OMCLDO2 algorithms have an east-west bias of 10% to 50 %, which are highest over vegetation and forested areas, and that this bias originates from the assumption of isotropic surface reflection. To interpret the across-track bias with the DAK radiative transfer model, we implement the bidirectional reflectance distribution function (BRDF) from the Ross-Li semi-empirical model. Testing our implementation against state-of-the-art RTMs LIDORT and SCIATRAN, we find that simulated TOA reflectance generally agrees to within 1 %. We replace the assumption of isotropic surface reflection in the equations used to retrieve cloud fractions over forested scenes with scattering kernels and corresponding BRDF parameters from a daily high-resolution database derived from 16 years' worth of MODIS measurements. By doing this, the east-west bias in the simulated cloud fractions largely vanishes. We conclude that across-track biases in cloud fractions can be explained by cloud algorithms that do not adequately account for the effects of surface reflectance anisotropy. The implications for NO2 air mass factor (AMF) calculations are substantial. Under moderately polluted NO2 and backwardscattering conditions, clear-sky AMFs are up to 20% higher and cloud radiance fractions up to 40% lower if surface anisotropic reflection is accounted for. The combined effect of these changes is that NO2 total AMFs increase by up to 30% for backward-scattering geometries (and decrease by up to 35% for forward-scattering geometries), which is stronger than the effect of either contribution alone. In an unpolluted troposphere, surface BRDF effects on cloud fraction counteract (and largely cancel) the effect on the clearsky AMF. Our results emphasise that surface reflectance anisotropy needs to be taken into account in a coherent manner for more realistic and accurate retrievals of clouds and NO2 from UV/Vis satellite sensors. These improvements will be beneficial for current sensors, in particular for the recently launched TROPOMI instrument with a high spatial resolution.
- Published
- 2018
43. Restoring the top-of-atmosphere reflectance during solar eclipses: a proof of concept with the UV Absorbing Aerosol Index measured by TROPOMI.
- Author
-
Trees, Victor, Wang, Ping, and Stammes, Piet
- Abstract
Solar eclipses reduce the measured top-of-atmosphere (TOA) reflectances as derived by Earth observation satellites, because the solar irradiance that is used to compute these reflectances is commonly measured before the start of the eclipse. Consequently, air quality products that are derived from these spectra, such as the ultraviolet (UV) Absorbing Aerosol Index (AAI), are distorted or undefined in the shadow of the Moon. The availability of air quality satellite data in the penumbral and antumbral shadow during solar eclipses, however, may be of particular interest to users studying solar eclipses and their effect on the Earth's atmosphere. Given the time and location of a point on the Earth's surface, we explain how to compute the eclipse obscuration fraction taking into account wavelength dependent solar limb darkening. With the calculated obscuration fractions, we restore the TOA reflectances and the AAI in the penumbral shadow during the annular solar eclipses on 26 December 2019 and 21 June 2020 measured by the TROPOMI/S5P instrument. We verify the calculated obscuration with the observed obscuration using an uneclipsed orbit. In the corrected products, the signature of the Moon shadow disappeared. Not taking into account solar limb darkening, however, would result in a maximum underestimation of the obscuration fraction of 0.06 at 380 nm on 26 December 2019, and in a maximum Moon shadow signature in the AAI of 6.7 points increase. We find that the Moon shadow anomaly in the uncorrected AAI is caused by a reduction of the measured reflectance at 380 nm, rather than a color change of the measured light. We restore common AAI features such as the sunglint and desert dust, and we confirm the restored AAI feature on 21 June 2020 at the Taklamakan desert by measurements of the GOME-2C satellite instrument on the same day but outside the Moon shadow. We conclude that the correction method of this paper can be used to detect real AAI rising phenomena and has the potential to restore any other product that is derived from TOA reflectance spectra. This would resolve the solar eclipse anomalies in satellite air quality measurements in the penumbra and antumbra, and would allow for studying the effect of the eclipse obscuration on the composition of the Earth's atmosphere from space. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
44. Effects of clouds on the UV Absorbing Aerosol Index from TROPOMI.
- Author
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Kooreman, Maurits L., Stammes, Piet, Trees, Victor, Sneep, Maarten, Tilstra, L. Gijsbert, de Graaf, Martin, Stein Zweers, Deborah C., Wang, Ping, Tuinder, Olaf N. E., and Veefkind, J. Pepijn
- Subjects
- *
AEROSOLS , *ZENITH distance , *AREA measurement , *EXTREME value theory - Abstract
The ultraviolet (UV) Absorbing Aerosol Index (AAI) is widely used as an indicator for the presence of absorbing aerosols in the atmosphere. Here we consider the TROPOMI AAI based on the 340 nm /380 nm wavelength pair. We investigate the effects of clouds on the AAI observed at small and large scales. The large-scale effects are studied using an aggregate of TROPOMI measurements over an area mostly devoid of absorbing aerosols (Pacific Ocean). The study reveals that several structural features can be distinguished in the AAI, such as the cloud bow, viewing zenith angle dependence, sunglint, and a previously unexplained increase in AAI values at extreme viewing and solar geometries. We explain these features in terms of the bidirectional reflectance distribution function (BRDF) of the scene in combination with the different ratios of diffuse and direct illumination of the surface at 340 and 380 nm. To reduce the dependency on the BRDF and homogenize the AAI distribution across the orbit, we present three different AAI retrieval models: the traditional Lambertian scene model (LSM), a Lambertian cloud model (LCM), and a scattering cloud model (SCM). We perform a model study to assess the propagation of errors in auxiliary databases used in the cloud models. The three models are then applied to the same low-aerosol region. Results show that using the LCM and SCM gives on average a higher AAI than the LSM. Additionally, a more homogeneous distribution is retrieved across the orbit. At the small scale, related to the high spatial resolution of TROPOMI, strong local increases and decreases in AAI are observed in the presence of clouds. The BRDF effect presented here is a first step – more research is needed to explain the small-scale cloud effects on the AAI. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
45. Structural uncertainty in air mass factor calculation for NO2 and HCHO satellite retrievals
- Author
-
Lorente, Alba, Boersma, K. Folkert, Yu, Huan, Doerner, Steffen, Hilboll, Andreas, Richter, Andreas, Liu, Mengyao, Lamsal, Lok N., Barkley, Michael, De Smedt, Isabelle, Van Roozendael, Michel, Wang, Yang, Wagner, Thomas, Beirle, Steffen, Lin, Jin-Tai, Krotkov, Nickolay, Stammes, Piet, Wang, Ping, Eskes, Henk J., Krol, Maarten, Marine and Atmospheric Research, Sub Ecology and Biodiversity, and Sub Atmospheric physics and chemistry
- Abstract
Air mass factor (AMF) calculation is the largest source of uncertainty in NO2 and HCHO satellite retrievals in situations with enhanced trace gas concentrations in the lower troposphere. Structural uncertainty arises when different retrieval methodologies are applied within the scientific community to the same satellite observations. Here, we address the issue of AMF structural uncertainty via a detailed comparison of AMF calculation methods that are structurally different between seven retrieval groups for measurements from the Ozone Monitoring Instrument (OMI). We estimate the escalation of structural uncertainty in every sub-step of the AMF calculation process. This goes beyond the algorithm uncertainty estimates provided in state-of-the-art retrievals, which address the theoretical propagation of uncertainties for one particular retrieval algorithm only. We find that top-of-atmosphere reflectances simulated by four radiative transfer models (RTMs) (DAK, McArtim, SCIATRAN and VLIDORT) agree within 1.5 %. We find that different retrieval groups agree well in the calculations of altitude resolved AMFs from different RTMs (to within 3 %), and in the tropospheric AMFs (to within 6 %) as long as identical ancillary data (surface albedo, terrain height, cloud parameters and trace gas profile) and cloud and aerosol correction procedures are being used. Structural uncertainty increases sharply when retrieval groups use their preference for ancillary data, cloud and aerosol correction. On average, we estimate the AMF structural uncertainty to be 42 % over polluted regions and 31 % over unpolluted regions, mostly driven by substantial differences in the a priori trace gas profiles, surface albedo and cloud parameters. Sensitivity studies for one particular algorithm indicate that different cloud correction approaches result in substantial AMF differences in polluted conditions (5 to 40 % depending on cloud fraction and cloud pressure, and 11 % on average) even for low cloud fractions (
- Published
- 2017
46. Deriving terrestrial cloud top pressure from photopolarimetry of reflected light
- Author
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Knibbe, Willem Jan J., de Haan, Johan F., Hovenier, Joop W., Stam, Daphne M., Koelemeijer, Robert B.A., and Stammes, Piet
- Published
- 2000
- Full Text
- View/download PDF
47. In-orbit Earth reflectance validation of TROPOMI on board the Sentinel-5 Precursor satellite.
- Author
-
Tilstra, Lieuwe G., de Graaf, Martin, Wang, Ping, and Stammes, Piet
- Subjects
REFLECTANCE ,SPECTRAL reflectance ,SOLAR spectra ,SURFACE of the earth ,INSTRUMENT flying ,RADIATIVE transfer - Abstract
The goal of the study described in this paper is to determine the accuracy of the radiometric calibration of the TROPOMI instrument in flight, using its Earth radiance and solar irradiance measurements, from which the Earth reflectance is determined. The Earth reflectances are compared to radiative transfer calculations. We restrict ourselves to clear-sky observations as these are less difficult to model than observations containing clouds and/or aerosols. The limiting factor in the radiative transfer calculations is then the knowledge of the surface reflectance. We use OMI and SCIAMACHY surface Lambertian-equivalent reflectivity (LER) information to model the reflectivity of the Earth's surface. This Lambertian, nondirectional description of the surface reflection contribution results in a relatively large source of uncertainty in the calculations. These errors can be reduced significantly by filtering out geometries for which we know that surface LER is a poor approximation of the real surface reflectivity. This filtering is done by comparing the OMI/SCIAMACHY surface LER information to MODIS surface BRDF information. We report calibration accuracies and errors for 21 selected wavelength bands between 328 and 2314 nm , located in TROPOMI spectral bands 3–7. All wavelength bands show good linear response to the intensity of the radiation and negligible offset problems. Reflectances in spectral bands 5 and 6 (wavelength bands 670 to 772 nm) have good absolute agreement with the simulations, showing calibration errors on the order of 0.01 or 0 %–3 %. Trends over the mission lifetime, due to instrument degradation, are studied and found to be negligible at these wavelengths. Reflectances in bands 3 and 4 (wavelength bands 328 to 494 nm), on the other hand, are found to be affected by serious calibration errors, on the order of 0.004–0.02 and ranging between 6 % and 10 %, depending on the wavelength. The TROPOMI requirements (of 2 % maximal deviation) are not met in this case. Trends due to instrument degradation are also found, being strongest for the 328 nm wavelength band and almost absent for the 494 nm wavelength band. The validation results obtained for TROPOMI spectral band 7 show behaviour that we cannot fully explain. As a result, these results call for more research and different methods to study the calibration of the reflectance. It seems plausible, though, that the reflectance for this particular band is underestimated by about 6 %. A table is provided containing the final results for all 21 selected wavelength bands. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
48. Improved SIFTER v2 algorithm for long-term GOME-2A satellite retrievals of fluorescence with a correction for instrument degradation.
- Author
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van Schaik, Erik, Kooreman, Maurits L., Stammes, Piet, Tilstra, L. Gijsbert, Tuinder, Olaf N. E., Sanders, Abram F. J., Verstraeten, Willem W., Lang, Rüdiger, Cacciari, Alessandra, Joiner, Joanna, Peters, Wouter, and Boersma, K. Folkert
- Subjects
ALGORITHMS ,FLUORESCENCE ,ARTIFICIAL satellites - Abstract
Solar-induced fluorescence (SIF) data from satellites are increasingly used as a proxy for photosynthetic activity by vegetation and as a constraint on gross primary production. Here we report on improvements in the algorithm to retrieve mid-morning (09:30 LT) SIF estimates on the global scale from the GOME-2 sensor on the MetOp-A satellite (GOME-2A) for the period 2007–2019. Our new SIFTER (Sun-Induced Fluorescence of Terrestrial Ecosystems Retrieval) v2 algorithm improves over a previous version by using a narrower spectral window that avoids strong oxygen absorption and being less sensitive to water vapour absorption, by constructing stable reference spectra from a 6-year period (2007–2012) of atmospheric spectra over the Sahara and by applying a latitude-dependent zero-level adjustment that accounts for biases in the data product. We generated stable, good-quality SIF retrievals between January 2007 and June 2013, when GOME-2A degradation in the near infrared was still limited. After the narrowing of the GOME-2A swath in July 2013, we characterised the throughput degradation of the level-1 data in order to derive reflectance corrections and apply these for the SIF retrievals between July 2013 and December 2018. SIFTER v2 data compare well with the independent NASA v2.8 data product. Especially in the evergreen tropics, SIFTER v2 no longer shows the underestimates against other satellite products that were seen in SIFTER v1. The new data product includes uncertainty estimates for individual observations and is best used for mostly clear-sky scenes and when spectral residuals remain below a certain spectral autocorrelation threshold. Our results support the use of SIFTER v2 data being used as an independent constraint on photosynthetic activity on regional to global scales. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
49. Validation of the Sentinel-5 Precursor TROPOMI cloud data with Cloudnet, Aura OMI O2-O2, MODIS and Suomi-NPP VIIRS.
- Author
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Compernolle, Steven, Argyrouli, Athina, Lutz, Ronny, Sneep, Maarten, Lambert, Jean-Christopher, Fjæraa, Ann Mari, Hubert, Daan, Keppens, Arno, Loyola, Diego, O'Connor, Ewan, Romahn, Fabian, Stammes, Piet, Verhoelst, Tijl, and Ping Wang
- Subjects
ATMOSPHERIC composition ,SPACE-based radar ,STRATOCUMULUS clouds ,GROUND penetrating radar ,RADIANCE - Abstract
Accurate knowledge of cloud properties is essential to the measurement of atmospheric composition from space. In this work we assess the quality of the cloud data derived from Copernicus Sentinel-5 Precursor (S5P) TROPOMI radiance measurements: cloud top height and cloud optical thickness (retrieved with the S5P OCRA/ROCINN_CAL algorithm), cloud height (S5P OCRA/ROCINN_CRB and S5P FRESCO) and radiometric cloud fraction (all three algorithms). The analysis combines: (i) the examination of cloud maps for artificial geographical patterns, (ii) the comparison to other satellite cloud data (MODIS, NPP-VIIRS and OMI O
2 -O2 ), and (iii) ground-based validation with respect to correlative observations (2018-04-30 to 2020-02-27) from the CLOUDNET network of ceilometers, lidars and radars. Peculiar geographical patterns were identified, and will be mitigated in future releases of the cloud data products. Zonal mean latitudinal variation of S5P cloud properties are similar to that of other satellite data. S5P OCRA/ROCINN_CAL agrees well with NPP VIIRS cloud top height and cloud optical thickness, and with CLOUDNET cloud top height, especially for the low (mostly liquid) clouds. For the high clouds, S5P OCRA/ROCINN_CAL cloud top height is below the cloud top height of VIIRS and of CLOUDNET, while its cloud optical thickness is higher than that of VIIRS. S5P OCRA/ROCINN_CRB and S5P FRESCO cloud height are well below the CLOUDNET cloud mean height for the low clouds, but match on an average better with the CLOUDNET cloud mean height for the higher clouds. As opposed to S5P OCRA/ROCINN_CRB and S5P FRESCO, S5P OCRA/ROCINN_CAL is well able to match the lowest CTH mode of the CLOUDNET observations. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
50. Comparison of south-east Atlantic aerosol direct radiative effect over clouds from SCIAMACHY, POLDER and OMI–MODIS.
- Author
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de Graaf, Martin, Schulte, Ruben, Peers, Fanny, Waquet, Fabien, Tilstra, L. Gijsbert, and Stammes, Piet
- Subjects
GENERAL circulation model ,AEROSOLS ,POLARISCOPE ,SOLAR radiation ,BIOMASS burning ,ATMOSPHERIC models - Abstract
The direct radiative effect (DRE) of aerosols above clouds has been found to be significant over the south-east Atlantic Ocean during the African biomass burning season due to elevated smoke layers absorbing radiation above the cloud deck. So far, global climate models have been unsuccessful in reproducing the high DRE values measured by various satellite instruments. Meanwhile, the radiative effects by aerosols have been identified as the largest source of uncertainty in global climate models. In this paper, three independent satellite datasets of DRE during the biomass burning season in 2006 are compared to constrain the south-east Atlantic radiation budget. The DRE of aerosols above clouds is derived from the spectrometer SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY), the polarimeter Polarization and Directionality of the Earth's Reflectances (POLDER), and collocated measurements by the spectrometer Ozone Monitoring Instrument (OMI) and the imager Moderate Resolution Imaging Spectroradiometer (MODIS). All three datasets confirm the high DRE values during the biomass season, underlining the relevance of local aerosol effects. Differences between the instruments can be attributed mainly to sampling issues. When these are accounted for, the remaining differences can be explained by a higher cloud optical thickness (COT) derived from POLDER compared to the other instruments and a neglect of aerosol optical thickness (AOT) at shortwave infrared (SWIR) wavelengths in the method used for SCIAMACHY and OMI–MODIS. The higher COT from POLDER by itself can explain the difference found in DRE between POLDER and the other instruments. The AOT underestimation is mainly evident at high values of the aerosol DRE and accounts for about a third of the difference between POLDER and OMI–MODIS DRE. The datasets from POLDER and OMI–MODIS effectively provide lower and upper bounds for the aerosol DRE over clouds over the south-east Atlantic, which can be used to challenge global circulation models (GCMs). Comparisons of model and satellite datasets should also account for sampling issues. The complementary DRE retrievals from OMI–MODIS and POLDER may benefit from upcoming satellite missions that combine spectrometer and polarimeter measurements. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
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