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The Mineral Aerosol Profiling from Infrared Radiances (MAPIR) algorithm retrieves vertical dust concentration profiles from cloud-free Infrared Atmospheric Sounding Interferometer (IASI) thermal infrared (TIR) radiances using Rodgers' optimal estimation method (OEM). We describe the new version 4.1 and evaluation results. Main differences with respect to previous versions are the Levenberg–Marquardt modification of the OEM, the use of the logarithm of the concentration in the retrieval and the use of Radiative Transfer for TOVS (RTTOV) for in-line radiative transfer calculations. The dust aerosol concentrations are retrieved in seven 1 km thick layers centered at 0.5 to 6.5 km. A global data set of the daily dust distribution was generated with MAPIR v 4.1 covering September 2007 to June 2018 , with further extensions planned every 6 months. The post-retrieval quality filters reject about 16 % of the retrievals, a huge improvement with respect to the previous versions in which up to 40 % of the retrievals were of bad quality. The median difference between the observed and fitted spectra of the good-quality retrievals is 0.32 K , with lower values over oceans. The information content of the retrieved profiles shows a dependence on the total aerosol load due to the assumption of a lognormal state vector. The median degrees of freedom in dusty scenes (min 10 µm AOD of 0.5) is 1.4. An evaluation of the aerosol optical depth (AOD) obtained from the integrated MAPIR v 4.1 profiles was performed against 72 AErosol RObotic NETwork (AERONET) stations. The MAPIR AOD correlates well with the ground-based data, with a mean correlation coefficient of 0.66 and values as high as 0.88. Overall, there is a mean AOD (550 nm) positive bias of only 0.04 with respect to AERONET, which is an extremely good result. The previous versions of MAPIR were known to largely overestimate AOD (about 0.28 for v 3). A second evaluation exercise was performed comparing the mean aerosol layer altitude from MAPIR with the mean dust altitude from Cloud–Aerosol LIdar with Orthogonal Polarization (CALIOP). A small underestimation was found, with a mean difference of about 350 m (standard deviation of about 1 km) with respect to the CALIOP cumulative extinction altitude, which is again considered very good as the vertical resolution of MAPIR is 1 km. In the comparisons against AERONET and CALIOP, a dependence of MAPIR on the quality of the temperature profiles used in the retrieval is observed. Finally, a qualitative comparison of dust aerosol concentration profiles was done against lidar measurements from two ground-based stations (M'Bour and Al Dhaid) and from the Cloud–Aerosol Transport System (CATS) instrument on board the International Space Station (ISS). MAPIR v 4.1 showed the ability to detect dust plumes at the same time and with a similar extent as the lidar instruments. This new MAPIR version shows a great improvement of the accuracy of the aerosol profile retrievals with respect to previous versions, especially so for the integrated AOD. It now offers a unique 3 -D dust data set, which can be used to gain more insight into the transport and emission processes of mineral dust aerosols. [ABSTRACT FROM AUTHOR]

A-train satellite data, acquired during the Calbuco volcano (Chile) sub-Plinian eruption in April 2015, are discussed to explore the complementarity of spaceborne observations in the microwave (MW), thermal infrared (TIR), and visible wavelengths for both near-source plume and distal ash clouds. The analysis shows that TIR-based detection techniques are not suitable near the volcanic vent where rising convective columns are associated with large optical depths. Detection and parametric estimates of near-source tephra mass loading and plume height from MW radiometric data, available 69 min after the eruption onset, are proposed. Results indicate a maximum plume altitude of about 21 km above the sea level and an ash mass of $3.65 \times 10^{10}$ kg, in agreement with mass values obtained from empirical formulas, but less than proximal–distal mass deposit of $1.86 \times 10^{11}$ kg. This discrepancy may be explained by extrapolating Advanced Technology Microwave Sounder-based estimates to 6 h, thus obtaining a total mass of about $1.90 \times 10^{11}$ kg. Distal volcanic cloud retrievals are derived from TIR imagery and results show a good agreement between Moderate-Resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS) retrievals of total mass taking into account the overpass time shift. If only the overlapping pixels between MODIS and VIIRS are considered, the respective estimates are $1.90 \times 10^{9}$ kg and $1.80 \times 10^{9}$ kg. TIR radiometric estimates of distal ash cloud height and mass loadings are also compared with Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations lidar retrievals. For low-to-medium optically thick ash cloud, average Cloud-Aerosol Lidar with Orthogonal Polarization-derived mass loading is about 0.8 g/m2 against 0.4 g/m2 from VIIRS and 1.4 g/m2 from MODIS. [ABSTRACT FROM AUTHOR]

The top-of-the-atmosphere (TOA) reflectances of the Visible Infrared Imaging Radiometer (VIIRS) M9 channel and the Moderate Resolution Imaging Spectroradiometer (MODIS) 26 channel have been simulated using the libRadtran radiative transfer model and the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) Vertical Feature Mask data. The simulated data were analyzed to quantify the performance differences between the VIIRS M9 and the MODIS 26 channels. Analysis of simulated clear-sky TOA reflectances showed that compared MODIS channel 26, the VIIRS M9 channel always performs better in reducing background reflectance regardless of latitude, season, surface type, vapor content or surface elevation. For mid-latitude, sub-Arctic and tropical regions the VIIRS M9 channel reduce the background reflectance by approximately 66.7%, 52.6% and 41.5%, respectively over the surface type of sandstone, compared to MODIS channel 26. Simulations for cloudy skies showed that both stratus and cumulus clouds contribute less to VIIRS M9 and MODIS band 26 TOA reflectances. Analysis of observed MODIS, VIIRS and CALIOP data was consistent with the simulated results. The VIIRS M9 decreases clear-sky background reflectance by as much as 35.96% and non-cirrus cloud reflectance by 29.86% compared with the MODIS channel 26. The observed reflectances of MODIS and VIIRS cirrus channels for clear-sky, non-cirrus cloud, and cirrus cloud are 0.0133 and 0.0095, 0.020 and 0.015, 0.084 and 0.067 respectively. [ABSTRACT FROM AUTHOR]

• Continuous timeseries of spectral irradiance are needed to study plant photobiology. • Atmospheric water-vapour & ozone column thickness affect daily spectral irradiance. • Photon ratios affecting plant photobiology varied on a daily and seasonal basis. • Proxy model development for photon ratios would facilitate result interpretation. Plants rely on spectral cues present in their surroundings, generated by the constantly changing light environment, to guide their growth and reproduction. Photoreceptors mediate the capture of information by plants from the light environment over a wide range of wavelengths, but despite extensive evidence that plants respond to various light cues, only fragmentary data have been published showing patterns of diurnal, seasonal and geographical variation in the spectral composition of daylight. To illustrate patterns in spectral photon ratios, we measured time series of irradiance spectra at two distinct geographical and climatological locations, Helsinki, Finland and Gual Pahari, India. We investigated the drivers behind variation of the spectral photon ratios measured at these two locations, based on the analysis of over 400 000 recorded spectra. Differences in spectral irradiance were explained by different atmospheric factors identified through multiple regression model analysis and comparison to spectral irradiance at ground level simulated with a radiative transfer model. Local seasonal and diurnal changes in spectral photon ratios were related to solar elevation angle, atmospheric water-vapour content and total ozone column thickness and deviated from their long-term averages to an extent likely to affect plant photobiology. We suggest that future studies should investigate possible effects of varying photon ratios on terrestrial plants. Solar elevation angle especially affects the patterns of B:G and B:R ratios. Water vapour has a large effect on the R:FR photon ratio and modelled climate scenarios predict that increasing global temperatures will result in increased atmospheric water vapour. The development of proxy models, utilising available data from weather and climate models, for relevant photon ratios as a function of solar elevation angle and atmospheric factors would facilitate the interpretation of results from past, present and future field studies of plants and vegetation. [ABSTRACT FROM AUTHOR]