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4. An advanced spatial co-registration of cloud properties for the atmospheric Sentinel missions: Application to TROPOMI.

Author

Argyrouli, Athina, Loyola, Diego, Romahn, Fabian, Lutz, Ronny, García, Víctor Molina, Hedelt, Pascal, Heue, Klaus-Peter, and Siddans, Richard

Subjects
REFLECTANCE measurement, ALBEDO, METEOROLOGICAL satellites, INFRARED imaging, SPECTRAL imaging, INFORMATION retrieval, ORBITS (Astronomy)
Abstract

The retrieval of cloud parameters from the atmospheric Sentinel missions require Earth reflectance measurements from a set of spectral bands. Frequently, the ground pixel footprints of the involved spectral bands are not fully aligned and therefore, special treatment is required within the operational algorithms. This so-called inter-band spatial mis-registration of passive spectrometers is present when the Earth reflectance measurements in different spectral bands are captured by different spectrometers. The cloud retrieval algorithm requires reflectance measurements in the UV (ultraviolet)/VIS (visible) band, where the first cloud parameter (i.e., radiometric cloud fraction) is retrieved from the OCRA (Optical Cloud Recognition Algorithm) algorithm. In addition, Earth reflectances in the NIR (near-infrared) band are needed for the retrieval of two additional cloud parameters (i.e., cloud height and cloud albedo or cloud-top height and optical thickness) from the ROCINN (Retrieval of Cloud Information using Neural Networks) algorithm. In the former TROPOMI (TROPOspheric Monitoring Instrument)/S5P (Sentinel-5 Precursor) retrieval, a co-registration scheme of the derived cloud parameters from the source band to the target band based on pre-calculated mapping weights from UV/VIS to NIR, and vice versa, is applied. In this paper we present a new scheme for the co-registration of the TROPOMI cloud parameters using collocated VIIRS (Visible Infrared Imaging Radiometer Suite)/SNPP (Suomi National Polar-orbiting Partnership) information. A great benefit of the new co-registration scheme based on the VIIRS data is that it improves the overall quality of the TROPOMI cloud products and, in addition, it allows the re-construction of the cloud parameters on the first UV/VIS detector pixel, which was impossible with the former scheme based on the static mapping tables. The latter practically means that a significant number of valid data points are added to the TROPOMI cloud, total ozone, SO2 and HCHO product since November 26th 2023 (orbit 31705), when the UPAS version 2.6 with the new co-registration scheme was activated operationally. From a comparison analysis between the two techniques, we found that the largest differences mainly appear for inhomogeneous scenes. From a validation exercise of TROPOMI against VIIRS in the across-track flight direction, we found that the old co-registration scheme tends to smooth out cloud structures along the scanline, whereas such structures can be maintained with the new scheme. The need to implement a similar inter-band spatial co-registration scheme is foreseen for the Sentinel-4/MTG-S (Meteosat Third Generation - Sounder) and Sentinel-5/MetOp-SG (Meteorological Operational Satellite - Second Generation) missions. In the case of Sentinel-4 instrument, the external cloud information will originate from collocated FCI (Flexible Combined Imager) data, on board the MTG-I (Meteosat Third Generation - Imager) satellite. [ABSTRACT FROM AUTHOR]

Published
2024
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5. Emissions of Sulphur Dioxide (SO2) from Coal-Fired Power Plants in Serbia and Bosnia-Herzegovina: First Attempts of a Validation of TROPOMI Satellite Products with Airborne In Situ Measurements

Author

Huntrieser, Heidi, primary, Klausner-Harlaß, Theresa, primary, Aufmhoff, Heinfried, primary, Baumann, Robert, primary, Fiehn, Alina, primary, Hedelt, Pascal, primary, Gottschaldt, Klaus-Dirk, primary, Lutz, Ronny, primary, Mrazovac Kurilić, Sanja, primary, Podraščanin, Zorica, primary, Ilić, Predrag, primary, Theys, Nicolas, primary, Jöckel, Patrick, primary, Loyola, Diego, primary, Makroum, Ismail, primary, Mertens, Mariano, primary, and Roiger, Anke, primary

Published
2023
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6. EXOTIME: searching for planets and measuring Pdot in sdB pulsators

Author

Lutz, Ronny, Schuh, Sonja, and Silvotti, Roberto

Subjects
Astrophysics - Earth and Planetary Astrophysics, Astrophysics - Solar and Stellar Astrophysics
Abstract

We review the status of the EXOTIME project (EXOplanet search with the TIming MEthod). The two main goals of EXOTIME are to search for sub-stellar companions to sdB stars in wide orbits, and to measure the secular variation of the pulsation periods, which are related to the evolutionary change of the stellar structure. Now, after four years of dense monitoring, we start to see some results and present the brown dwarf and exoplanet candidates V1636 Ori b and DW Lyn b., Comment: 4 pages, 4 figures, published in "The Modern Era of Helio- and Asteroseismology", eds. M. Roth and K. Uytterhoeven

Published
2013
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7. The EXOTIME targets HS0702+6043 and HS0444+0458

Author

Lutz, Ronny, Schuh, Sonja, and Silvotti, Roberto

Subjects
Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Earth and Planetary Astrophysics
Abstract

Pulsations in subdwarf B (sdB) stars are an important tool to constrain the evolutionary status of these evolved objects. Interestingly, the same data used for this asteroseismological approach can also be used to search for substellar companions around these objects by analyzing the timing of the pulsations by means of a so-called O-C diagram. Substellar objects around sdB stars are important for two different reasons: they are suspected to be able to influence the evolution of their host-star and they are an ideal test case to examine the properties of exoplanets which have survived the red giant expansion of their host stars., Comment: Part of PlanetsbeyondMS/2010 proceedings http://arxiv.org/html/1011.6606v1

Published
2010
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8. The EXOTIME project: a status report on PG 1325+101 (QQ Vir)

Author

Benatti, Serena, Silvotti, Roberto, Claudi, Riccardo U., Schuh, Sonja, Lutz, Ronny, Kim, Seung-Lee, Janulis, Rimvydas, Paparò, Margit, Baran, Andrzej, and Østensen, Roy

Subjects
Astrophysics - Solar and Stellar Astrophysics
Abstract

After the discovery of V391 Peg b, the first planet detected around a post Red Giant phase star (Silvotti et al. 2007), the EXOTIME (EXOplanet search with the TIming MEthod) project is focused on the search for new planets with similar characteristics. The aim of the project is to organize a global observing network to collect as much data as possible for a sample of five subdwarf B (sdB) stars and share them in order to obtain a more precise analysis. These evolved pulsators may have extremely regular oscillation periods. This feature makes these stars suitable to search for planetary companions with the timing method as in the case of pulsars. In this contribution we present the project and some preliminary results for the star PG 1325+101 (QQ Vir) after the first two years of activity., Comment: Proceedings of the 4th HELAS Conference (Lanzarote, 1-5 Feb. 2010), Astron. Nachrichten, in press

Published
2010

9. EXOTIME: searching for planets around pulsating subdwarf B stars

Author

Schuh, Sonja, Silvotti, Roberto, Lutz, Ronny, Loeptien, Bjoern, Green, Elizabeth M., Ostensen, Roy H., Leccia, Silvio, Kim, Seung-Lee, Fontaine, Gilles, Charpinet, Stephane, Francoeur, Myriam, Randall, Suzanna, Rodriguez-Lopez, Cristina, van Grootel, Valerie, Odell, Andrew P., Paparo, Margit, Bognar, Zsofia, Papics, Peter, Nagel, Thorsten, Beeck, Benjamin, Hundertmark, Markus, Stahn, Thorsten, Dreizler, Stefan, Hessman, Frederic V., Dall'Ora, Massimo, Mancini, Dario, Cortecchia, Fausto, Benatti, Serena, Claudi, Riccardo, and Janulis, Rimvydas

Subjects
Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Earth and Planetary Astrophysics
Abstract

In 2007, a companion with planetary mass was found around the pulsating subdwarf B star V391 Pegasi with the timing method, indicating that a previously undiscovered population of substellar companions to apparently single subdwarf B stars might exist. Following this serendipitous discovery, the EXOTIME (http://www.na.astro.it/~silvotti/exotime/) monitoring program has been set up to follow the pulsations of a number of selected rapidly pulsating subdwarf B stars on time-scales of several years with two immediate observational goals: 1) determine Pdot of the pulsational periods P 2) search for signatures of substellar companions in O-C residuals due to periodic light travel time variations, which would be tracking the central star's companion-induced wobble around the center of mass. These sets of data should therefore at the same time: on the one hand be useful to provide extra constraints for classical asteroseismological exercises from the Pdot (comparison with "local" evolutionary models), and on the other hand allow to investigate the preceding evolution of a target in terms of possible "binary" evolution by extending the otherwise unsuccessful search for companions to potentially very low masses. While timing pulsations may be an observationally expensive method to search for companions, it samples a different range of orbital parameters, inaccessible through orbital photometric effects or the radial velocity method: the latter favours massive close-in companions, whereas the timing method becomes increasingly more sensitive towards wider separations. In this paper we report on the status of the on-going observations and coherence analysis for two of the currently five targets, revealing very well-behaved pulsational characteristics in HS 0444+0458, while showing HS 0702+6043 to be more complex than previously thought., Comment: Contribution to: The Fourth Meeting on Hot Subdwarf Stars and Related Objects, 20 - 24 July 2009, Shanghai, China, published 03/2010 by Ap&SS (Open access publication). 12 pages, 14 figures, 5 tables

Published
2010
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10. Comparison of Cloud Parameters from GOME-2 and Assessment of Cloud Impact on Tropospheric NO2 and HCHO Retrievals

Author

Argyrouli, Athina, primary, Lutz, Ronny, additional, Romahn, Fabian, additional, Molina García, Víctor, additional, Loyola, Diego, additional, Seo, Sora, additional, Valks, Pieter, additional, De Smedt, Isabelle, additional, Boersma, Folkert, additional, Tilstra, Lieuwe Gijsbert, additional, Stammes, Piet, additional, and Compernolle, Steven, additional

Published
2023
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12. Assessing the quality of the Sentinel-5p TROPOMI cloud products and their reprocessing using ground-based Cloudnet data

Author

Compernolle, Steven, primary, Argyrouli, Athina, additional, Lutz, Ronny, additional, Sneep, Maarten, additional, Lambert, Jean-Christopher, additional, Fjaeraa, Ann Mari, additional, Granville, José, additional, Hubert, Daan, additional, Keppens, Arno, additional, Loyola, Diego, additional, O'Connor, Ewan, additional, Pinardi, Gaia, additional, Rasson, Olivier, additional, Romahn, Fabian, additional, Stammes, Piet, additional, Verhoelst, Tijl, additional, and Wang, Ping, additional

Published
2023
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13. Intercomparison of Sentinel-5P TROPOMI cloud products for tropospheric trace gas retrievals

Author

Latsch, Miriam, primary, Richter, Andreas, additional, Eskes, Henk, additional, Sneep, Maarten, additional, Wang, Ping, additional, Veefkind, Pepijn, additional, Lutz, Ronny, additional, Loyola, Diego, additional, Argyrouli, Athina, additional, Valks, Pieter, additional, Wagner, Thomas, additional, Sihler, Holger, additional, van Roozendael, Michel, additional, Theys, Nicolas, additional, Yu, Huan, additional, Siddans, Richard, additional, and Burrows, John P., additional

Published
2022
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14. Global Ozone Monitoring Experiment-2 (GOME-2) Daily and Monthly Level 3 Products of Atmospheric Trace Gas Columns

Author

Chan, Ka Lok, primary, Valks, Pieter, additional, Heue, Klaus-Peter, additional, Lutz, Ronny, additional, Hedelt, Pascal, additional, Loyola, Diego, additional, Pinardi, Gaia, additional, Van Roozendael, Michel, additional, Hendrick, François, additional, Wagner, Thomas, additional, Kumar, Vinod, additional, Bais, Alkis, additional, Piters, Ankie, additional, Irie, Hitoshi, additional, Kanaya, Yugo, additional, Takashima, Hisahiro, additional, Choi, Yongjoo, additional, Park, Kihong, additional, Chong, Jihyo, additional, Cede, Alexander, additional, Frieß, Udo, additional, Richter, Andreas, additional, Ma, Jianzhong, additional, Benavent, Nuria, additional, Holla, Robert, additional, Postylyakov, Oleg, additional, Rivera Cárdenas, Claudia, additional, and Wenig, Mark, additional

Published
2022
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16. Comparison of Cloud Parameters from GOME-2 and Assessment of Cloud Impact on Tropospheric NO2 and HCHO Retrievals.

Author

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 NO2 and HCHO tropospheric gases. [ABSTRACT FROM AUTHOR]

Published
2023
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17. Supplementary material to "Intercomparison of Sentinel-5P TROPOMI cloud products for tropospheric trace gas retrievals"

Author

Latsch, Miriam, primary, Richter, Andreas, additional, Eskes, Henk, additional, Sneep, Maarten, additional, Wang, Ping, additional, Veefkind, Pepijn, additional, Lutz, Ronny, additional, Loyola, Diego, additional, Argyrouli, Athina, additional, Valks, Pieter, additional, Wagner, Thomas, additional, Sihler, Holger, additional, van Roozendael, Michel, additional, Theys, Nicolas, additional, Yu, Huan, additional, Siddans, Richard, additional, and Burrows, John P., additional

Published
2022
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18. Global Ozone Monitoring Experiment-2 (GOME-2) daily and monthly level-3 products of atmospheric trace gas columns.

Author

Chan, Ka Lok, Valks, Pieter, Heue, Klaus-Peter, Lutz, Ronny, Hedelt, Pascal, Loyola, Diego, Pinardi, Gaia, Van Roozendael, Michel, Hendrick, François, Wagner, Thomas, Kumar, Vinod, Bais, Alkis, Piters, Ankie, Irie, Hitoshi, Takashima, Hisahiro, Kanaya, Yugo, Choi, Yongjoo, Park, Kihong, Chong, Jihyo, and Cede, Alexander

Subjects
TRACE gases, OZONE, AIR pollutants, WATER vapor, TROPOSPHERIC ozone, NITROGEN dioxide, SCIENTIFIC community
Abstract

We introduce the new Global Ozone Monitoring Experiment-2 (GOME-2) daily and monthly level-3 product of total column ozone (O 3), total and tropospheric column nitrogen dioxide (NO 2), total column water vapour, total column bromine oxide (BrO), total column formaldehyde (HCHO), and total column sulfur dioxide (SO 2) (daily products 10.15770/EUM_SAF_AC_0048, ; monthly products 10.15770/EUM_SAF_AC_0049,). The GOME-2 level-3 products aim to provide easily translatable and user-friendly data sets to the scientific community for scientific progress as well as to satisfy public interest. The purpose of this paper is to present the theoretical basis as well as the verification and validation of the GOME-2 daily and monthly level-3 products. The GOME-2 level-3 products are produced using the overlapping area-weighting method. Details of the gridding algorithm are presented. The spatial resolution of the GOME-2 level-3 products is selected based on the sensitivity study. The consistency of the resulting level-3 products among three GOME-2 sensors is investigated through time series of global averages, zonal averages, and bias. The accuracy of the products is validated by comparison to ground-based observations. The verification and validation results show that the GOME-2 level-3 products are consistent with the level-2 data. Small discrepancies are found among three GOME-2 sensors, which are mainly caused by the differences in the instrument characteristic and level-2 processor. The comparison of GOME-2 level-3 products to ground-based observations in general shows very good agreement, indicating that the products are consistent and fulfil the requirements to serve the scientific community and general public. [ABSTRACT FROM AUTHOR]

Published
2023
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19. Three-Dimensional Distribution of Biomass Burning Aerosols from Australian Wildfires Observed by TROPOMI Satellite Observations

Author

Lemmouchi, Farouk, primary, Cuesta, Juan, additional, Eremenko, Maxim, additional, Derognat, Claude, additional, Siour, Guillaume, additional, Dufour, Gaëlle, additional, Sellitto, Pasquale, additional, Turquety, Solène, additional, Tran, Dung, additional, Liu, Xiong, additional, Zoogman, Peter, additional, Lutz, Ronny, additional, and Loyola, Diego, additional

Published
2022
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29. An improved TROPOMI tropospheric NO2 research product over Europe

Author

Liu, Song, Valks, Pieter, Pinardi, Gaia, Xu, Jian, Chan, Ka Lok, Argyrouli, Athina, Lutz, Ronny, Beirle, Steffen, Khorsandi, Ehsan, Baier, Frank, Huijnen, Vincent, Bais, Alkiviadis, Donner, Sebastian, Dörner, Steffen, Gratsea, M., Hendrick, Francoise, Karagkiozidis, D., Lange, Kezia, Piters, Ankie, Remmers, J., Richter, A., Van Roozendael, M., Wagner, T., Wenig, M., and Loyola, Diego

Subjects
troposphere, TROPOMI, NO2, Air Quality
Abstract

Launched in October 2017, the TROPOspheric Monitoring Instrument (TROPOMI) aboard Sentinel-5 Precursor provides the potential to monitor air quality over point sources across the globe with a spatial resolution as high as 5.5 km × 3.5 km (7 km × 3.5 km before 6 August 2019). The DLR nitrogen dioxide (NO2) retrieval algorithm for the TROPOMI instrument consists of three steps: the spectral fitting of the slant column, the separation of stratospheric and tropospheric contributions, and the conversion of the slant column to a vertical column using an air mass factor (AMF) calculation. In this work, an improved DLR tropospheric NO2 retrieval algorithm from TROPOMI measurements over Europe is presented. The stratospheric estimation is implemented using the STRatospheric Estimation Algorithm from Mainz (STREAM), which was developed as a verification algorithm for TROPOMI and does not require chemistry transport model data as input. A directionally dependent STREAM (DSTREAM) is developed to correct for the dependency of the stratospheric NO2 on the viewing geometry by up to 2×1014 molec./cm2. Applied to synthetic TROPOMI data, the uncertainty in the stratospheric column is 3.5×1014 molec./cm2 in the case of significant tropospheric sources. Applied to actual measurements, the smooth variation of stratospheric NO2 at low latitudes is conserved, and stronger stratospheric variation at higher latitudes is captured. For AMF calculation, the climatological surface albedo data are replaced by geometry-dependent effective Lambertian equivalent reflectivity (GE_LER) obtained directly from TROPOMI measurements with a high spatial resolution. Mesoscale-resolution a priori NO2 profiles are obtained from the regional POLYPHEMUS/DLR chemistry transport model with the TNO-MACC emission inventory. Based on the latest TROPOMI operational cloud parameters, a more realistic cloud treatment is provided by a Clouds-As-Layers (CAL) model, which treats the clouds as uniform layers of water droplets, instead of the Clouds-As-Reflecting-Boundaries (CRB) model, in which clouds are simplified as Lambertian reflectors. For the error analysis, the tropospheric AMF uncertainty, which is the largest source of NO2 uncertainty for polluted scenarios, ranges between 20 % and 50 %, leading to a total uncertainty in the tropospheric NO2 column in the 30 %–60 % range. From a validation performed with ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements, the new DLR tropospheric NO2 data show good correlations for nine European urban/suburban stations, with an average correlation coefficient of 0.78. The implementation of the algorithm improvements leads to a decrease of the relative difference from −55.3 % to −34.7 % on average in comparison with the DLR reference retrieval. When the satellite averaging kernels are used to remove the contribution of a priori profile shape, the relative difference decreases further to ∼ −20 %.

Published
2021

30. An improved TROPOMI tropospheric NO<sub>2</sub> research product over Europe

Author

Liu, Song, primary, Valks, Pieter, additional, Pinardi, Gaia, additional, Xu, Jian, additional, Chan, Ka Lok, additional, Argyrouli, Athina, additional, Lutz, Ronny, additional, Beirle, Steffen, additional, Khorsandi, Ehsan, additional, Baier, Frank, additional, Huijnen, Vincent, additional, Bais, Alkiviadis, additional, Donner, Sebastian, additional, Dörner, Steffen, additional, Gratsea, Myrto, additional, Hendrick, François, additional, Karagkiozidis, Dimitris, additional, Lange, Kezia, additional, Piters, Ankie J. M., additional, Remmers, Julia, additional, Richter, Andreas, additional, Van Roozendael, Michel, additional, Wagner, Thomas, additional, Wenig, Mark, additional, and Loyola, Diego G., additional

Published
2021
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31. Global Ozone Monitoring Experiment-2 (GOME-2) Daily and Monthly Level 3 Products of Atmospheric Trace Gas Columns.

Author

Ka Lok Chan, Valks, Pieter, Heue, Klaus-Peter, Lutz, Ronny, Hedelt, Pascal, Loyola, Diego, Pinardi, Gaia, Van Roozendael, Michel, Hendrick, François, Wagner, Thomas, Kumar, Vinod, Bais, Alkis, Piters, Ankie, Hitoshi Irie, Hisahiro Takashima, Yugo Kanaya, Yongjoo Choi, Kihong Park, Jihyo Chong, and Cede, Alexander

Subjects
COLUMNS, TRACE gases, OZONE, WATER vapor, NITROGEN dioxide, TROPOSPHERIC ozone, AIR pollutants
Abstract

We introduce the new GOME-2 daily and monthly level 3 product of total column ozone (O3), total and tropospheric column nitrogen dioxide (NO2), total column water vapour, total column bromine oxide (BrO), total column formaldehyde (HCHO) and total column sulphur dioxide (SO2). The GOME-2 level 3 products are aimed to provide easily translatable and userfriendly data sets to the scientific community for scientific progress as well as satisfying public interest. The purpose of this paper is to present the theoretical basis as well as the verification and validation of the GOME-2 daily and monthly level 3 products. The GOME-2 level 3 products are produced using the overlapping area weighting method. Details of the gridding algorithm are presented. The spatial resolution of the GOME-2 level 3 products is selected based on sensitivity study. The consistency of the resulting level 3 products among three GOME-2 sensors is investigated through time series of global averages, zonal averages, and bias. The accuracy of the products is validated by comparing to ground-based observations. The verification and validation results show that the GOME-2 level 3 products are consistent with the level 2 data. Small discrepancies are found among three GOME-2 sensors, which are mainly caused by the differences in instrument characteristic and level 2 processor. The comparison of GOME-2 level 3 products to ground-based observations in general shows very good agreement, indicating the products are consistent and fulfil the requirements to serve the scientific community and general public. [ABSTRACT FROM AUTHOR]

Published
2022
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32. Validation of the Sentinel-5 Precursor TROPOMI cloud data with Cloudnet, Aura OMI O2-O2, MODIS, and Suomi-NPP VIIRS

Author

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

33. An improved tropospheric NO2 column retrieval algorithm for TROPOMI over Europe

Author

Liu, Song, Valks, Pieter, Pinardi, Gaia, Xu, Jian, Chan, Ka Lok, Argyrouli, Athina, Lutz, Ronny, Beirle, Steffen, Khorsandi, Ehsan, Baier, Frank, Huijnen, Vincent, Bais, Alkiviadis, Donner, Sebastian, Dörner, Steffen, Gratsea, Myrto, Hendrick, François, Karagkiozidis, Dimitris, Lange, Kezia, Piters, Ankie J. M., Remmers, Julia, Richter, Andreas, Roozendael, Michel, Wagner, Thomas, Wenig, Mark, and Loyola, Diego G.

Abstract

Launched in October 2017, the TROPOspheric Monitoring Instrument (TROPOMI) aboard Sentinel-5 Precursor provides the potential to monitor air quality over point sources across the globe with a spatial resolution as high as 5.5 km × 3.5 km (7 km × 3.5 km before 6 August 2019). The nitrogen dioxide (NO2) retrieval algorithm for the TROPOMI instrument consists of three steps: the spectral fitting of the slant column, the separation of stratospheric and tropospheric contributions, and the conversion of the slant column to a vertical column using an air mass factor (AMF) calculation. In this work, an improved tropospheric NO2 retrieval algorithm from TROPOMI measurements over Europe is presented. The stratospheric estimation is implemented using the STRatospheric Estimation Algorithm from Mainz (STREAM), which was developed as a verification algorithm for TROPOMI and does not require chemistry transport model data as input. A directionally dependent STREAM (DSTREAM) is developed to correct for the dependency of the stratospheric NO2 on the viewing geometry by up to 2 × 1014 molec/cm2. Applied to synthetic TROPOMI data, the uncertainty in the stratospheric column is 3.5 × 1014 molec/cm2 for polluted conditions. Applied to actual measurements, the smooth variation of stratospheric NO2 at low latitudes is conserved, and stronger stratospheric variation at higher latitudes are captured. For AMF calculation, the climatological surface albedo data is replaced by geometry-dependent effective Lambertian equivalent reflectivity (GE_LER) obtained directly from TROPOMI measurements with a high spatial resolution. Mesoscale-resolution a priori NO2 profiles are obtained from the regional POLYPHEMUS/DLR chemistry transport model with the TNO-MACC emission inventory. Based on the latest TROPOMI operational cloud parameters, a more realistic cloud treatment is provided by a clouds-as-layers (CAL) model, which treats the clouds as uniform layers of water droplets, instead of the clouds-as-reflecting-boundaries (CRB) model, in which clouds are simplified as Lambertian reflectors. For the error analysis, the tropospheric AMF uncertainty, which is the largest source of NO2 uncertainty for polluted scenarios, ranges between 20 % and 50 %, leading to a total uncertainty in the tropospheric NO2 column in the 30–60 % range. From a validation performed with ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements, the improved tropospheric NO2 data shows good correlations for nine European urban/suburban stations with an average correlation coefficient of 0.78. The implementation of the algorithm improvements leads to a decrease of the relative difference from −55.3 % to −34.7 % on average.

Published
2021

34. Validation of the Sentinel-5 Precursor TROPOMI cloud data withCloudnet, Aura OMI O2–O2, MODIS, and Suomi-NPP VIIR

Author

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

35. An improved TROPOMI tropospheric NO2 research product over Europe

Author

Liu, Song, Valks, Pieter, Pinardi, Gaia, Xu, Jian, Chan, Ka Lok, Argyrouli, Athina, Lutz, Ronny, Beirle, Steffen, Khorsandi, Ehsan, Baier, Frank, Huijnen, Vincent, Bais, Alkiviadis, Donner, Sebastian, Dörner, Steffen, Gratsea, Myrto, Hendrick, François, Karagkiozidis, Dimitris, Lange, Kezia, Piters, Ankie J. M., Remmers, Julia, Richter, Andreas, Van Roozendael, Michel, Wagner, Thomas, Wenig, Mark, and Loyola, Diego G.

Subjects
ddc
Published
2020

36. Validation of the Sentinel-5 Precursor TROPOMI cloud data with Cloudnet, Aura OMI O<sub>2</sub>–O<sub>2</sub>, MODIS, and Suomi-NPP VIIRS

Author

Compernolle, Steven, primary, Argyrouli, Athina, additional, Lutz, Ronny, additional, Sneep, Maarten, additional, Lambert, Jean-Christopher, additional, Fjæraa, Ann Mari, additional, Hubert, Daan, additional, Keppens, Arno, additional, Loyola, Diego, additional, O'Connor, Ewan, additional, Romahn, Fabian, additional, Stammes, Piet, additional, Verhoelst, Tijl, additional, and Wang, Ping, additional

Published
2021
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38. Validation of Sentinel-5p TROPOMI cloud data with ground-based Cloudnet and other satellite data products

Author

Compernolle, Steven, primary, Argyrouli, Athina, additional, Lutz, Ronny, additional, Sneep, Maarten, additional, Lambert, Jean-Christopher, additional, Fjaeraa, Ann Mari, additional, Granville, José, additional, Hubert, Daan, additional, Keppens, Arno, additional, Loyola, Diego, additional, O'Connor, Ewan, additional, Rasson, Olivier, additional, Romahn, Fabian, additional, Stammes, Piet, additional, Verhoelst, Tijl, additional, and Wang, Ping, additional

Published
2021
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40. Intercomparison of Cloud Products based on S5P/TROPOMI Level 1b Data Version 1 and the updated Version 2

Author

Latsch, Miriam, primary, Richter, Andreas, additional, Burrows, John P., additional, Wagner, Thomas, additional, Sihler, Holger, additional, van Roozendael, Michel, additional, Loyola, Diego, additional, Valks, Pieter, additional, Argyrouli, Athina, additional, Lutz, Ronny, additional, Veefkind, Pepijn, additional, Eskes, Henk, additional, Sneep, Maarten, additional, Wang, Ping, additional, and Siddans, Richard, additional

Published
2021
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41. Supplementary material to "An improved tropospheric NO<sub>2</sub> column retrieval algorithm for TROPOMI over Europe"

Author

Liu, Song, primary, Valks, Pieter, additional, Pinardi, Gaia, additional, Xu, Jian, additional, Chan, Ka Lok, additional, Argyrouli, Athina, additional, Lutz, Ronny, additional, Beirle, Steffen, additional, Khorsandi, Ehsan, additional, Baier, Frank, additional, Huijnen, Vincent, additional, Bais, Alkiviadis, additional, Donner, Sebastian, additional, Dörner, Steffen, additional, Gratsea, Myrto, additional, Hendrick, François, additional, Karagkiozidis, Dimitris, additional, Lange, Kezia, additional, Piters, Ankie J. M., additional, Remmers, Julia, additional, Richter, Andreas, additional, Van Roozendael, Michel, additional, Wagner, Thomas, additional, Wenig, Mark, additional, and Loyola, Diego G., additional

Published
2021
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42. An improved tropospheric NO2 column retrieval algorithm for TROPOMI over Europe

Author

Liu, Song, primary, Valks, Pieter, additional, Pinardi, Gaia, additional, Xu, Jian, additional, Chan, Ka Lok, additional, Argyrouli, Athina, additional, Lutz, Ronny, additional, Beirle, Steffen, additional, Khorsandi, Ehsan, additional, Baier, Frank, additional, Huijnen, Vincent, additional, Bais, Alkiviadis, additional, Donner, Sebastian, additional, Dörner, Steffen, additional, Gratsea, Myrto, additional, Hendrick, François, additional, Karagkiozidis, Dimitris, additional, Lange, Kezia, additional, Piters, Ankie J. M., additional, Remmers, Julia, additional, Richter, Andreas, additional, Van Roozendael, Michel, additional, Wagner, Thomas, additional, Wenig, Mark, additional, and Loyola, Diego G., additional

Published
2021
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43. Operational trace gas column observations from GOME-2 on MetOp

Author

Valks, Pieter, Heue, Klaus-Peter, Liu, Song, Lutz, Ronny, Zimmer, Walter, De Smedt, Isabelle, Pinardi, Gaia, Theys, N., Lerot, Christophe, Van Roozendael, Michel, and Beirle, Steffen

Subjects
remote sensing, ozone, GOME-2, trace gases, satellite, air quality
Published
2019

44. Supplementary material to "Validation of the Sentinel-5 Precursor TROPOMI cloud data with Cloudnet, Aura OMI O2-O2, MODIS and Suomi-NPP VIIRS"

Author

Compernolle, Steven, primary, Argyrouli, Athina, additional, Lutz, Ronny, additional, Sneep, Maarten, additional, Lambert, Jean-Christopher, additional, Fjæraa, Ann Mari, additional, Hubert, Daan, additional, Keppens, Arno, additional, Loyola, Diego, additional, O'Connor, Ewan, additional, Romahn, Fabian, additional, Stammes, Piet, additional, Verhoelst, Tijl, additional, and Wang, Ping, additional

Published
2020
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45. Validation of the Sentinel-5 Precursor TROPOMI cloud data with Cloudnet, Aura OMI O<sub>2</sub>-O<sub>2</sub>, MODIS and Suomi-NPP VIIRS

Author

Compernolle, Steven, primary, Argyrouli, Athina, additional, Lutz, Ronny, additional, Sneep, Maarten, additional, Lambert, Jean-Christopher, additional, Fjæraa, Ann Mari, additional, Hubert, Daan, additional, Keppens, Arno, additional, Loyola, Diego, additional, O'Connor, Ewan, additional, Romahn, Fabian, additional, Stammes, Piet, additional, Verhoelst, Tijl, additional, and Wang, Ping, additional

Published
2020
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46. Validation of Sentinel-5p retrieved cloud height data using ground-based radar/lidar measurements from the CLOUDNET network

Author

Compernolle, Steven, primary, Argyrouli, Athina, additional, Lutz, Ronny, additional, Sneep, Maarten, additional, Granville, José, additional, Hubert, Daan, additional, Keppens, Arno, additional, Verhoelst, Tijl, additional, Fjaeraa, Ann Mari, additional, Loyola, Diego, additional, O'Connor, Ewan, additional, and Lambert, Jean-Christopher, additional

Published
2020
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49. Evaluation of TROPOMI cloud products for NO2 retrievals

Author

Latsch, Miriam, primary, Richter, Andreas, additional, Burrows, John P., additional, Wagner, Thomas, additional, Silher, Holger, additional, van Roozendael, Michel, additional, Loyola, Diego, additional, Valks, Pieter, additional, Argyrouli, Athina, additional, Lutz, Ronny, additional, Veefkind, Pepijn, additional, Eskes, Henk, additional, Sneep, Maarten, additional, Wang, Ping, additional, and Siddans, Richard, additional

Published
2020
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