Retrieval of aerosol optical depth over land based on a time series technique using MSG/SEVIRI data

Abstract

Abstract.A novel approach for the joint retrieval of aerosol optical depth (AOD) and aerosol type, using Meteosat Second Generation -Spinning Enhanced Visible and Infrared Imagers (MSG/SEVIRI) observations in two solar channels, is presented. The retrieval is based on a Time Series (TS) technique, which makes use of the two visible bands at 0.6 µm and 0.8 µm in three orderly scan times (15 min interval between two scans) to retrieve the AOD over land. Using the radiative transfer equation for plane-parallel atmosphere, two coupled differential equations for the upward and downward fluxes are derived. The boundary conditions for the upward and downward fluxes at the top and at the bottom of the atmosphere are used in these equations to provide an analytic solution for the AOD. To derive these fluxes, the aerosol single scattering albedo (SSA) and asymmetry factor are required to provide a solution. These are provided from a set of six pre-defined aerosol types with the SSA and asymmetry factor. We assume one aerosol type for a grid of 1 • ×1 • and the surface reflectance changes little between two subsequent observations. A k-ratio approach is used in the inversion to find the best solution of atmospheric properties and surface reflectance. The k-ratio approach assumes that the surface reflectance is little influenced by aerosol scattering at 1.6 µm and therefore the ratio of surface reflectances in the solar band for two subsequent observations can be wellapproximated by the ratio of the reflectances at 1.6 µm. A further assumption is that the surface reflectance varies only slightly over a period of 30 min. The algorithm makes use of numerical minimisation routines to obtain the optimal solution of atmospheric properties and surface reflectance by selection of the most suitable aerosol type from pre-defined sets.A detailed analysis of the retrieval results shows that it is suitable for AOD retrieval over land from SEVIRI data. Six AErosol RObotic NETwork (AERONET) sites with different surface types are used for detailed analysis and 42 other AERONET sites are used for validation. From 445 collocations representing stable and homogeneous aerosol type, we find that >75 % of the MSG-retrieved AOD at 0.6 and 0.8 µm values compare favourably with AERONET observed AOD values, within an error envelope of ± 0.05 ± 0.15τ and a high correlation coefficient (R>0.86). The AOD datasets derived Published by Copernicus Publications on behalf of the European Geosciences Union. L. Mei et al.: Retrieval of aerosol optical depth over landusing the TS method with SEVIRI data is also compared with collocated AOD products derived from NASA TERRA and AQUA MODIS (The Moderate-resolution Imaging Spectroradiometer) data using the Dark Dense Vegetation (DDV) method and the Deep Blue algorithms. Using the TS method, the AOD could be retrieved for more pixels than with the NASA Deep Blue algorithm. This method is potentially also useful for surface reflectance retrieval using SEVIRI observations. The current paper focuses on AOD retrieval ...

Effect of Heat Wave Conditions on Aerosol Optical Properties Derived from Satellite and Ground-Based Remote Sensing over Poland

“…The surface properties are estimated for particular conditions: during relatively cloud-free reference days (cloud cover over Poland < 0.6) which exhibit a low AOD (<0.15 at 550 nm), based on top-of-atmosphere (TOA) reflectance measured by the SEVIRI detector. However, even for low AODs, the elimination of influence of atmospheric components (in particular atmospheric aerosols) on the reflectance measured by satellite is still essential, thus several approaches to tackle this topic were proposed (e.g., [41,42]). In the algorithm used here, instead of the golden section search method and parabolic interpolation, an approach based on applying the optimal interpolation method [43] is used with the additional ground based sources of AOD data, that allow a reduction of the typical uncertainties related to the aerosol background estimation, and hence improve the AOD SEVIRI retrieval.…”

Mapping Surface Broadband Albedo from Satellite Observations: A Review of Literatures on Algorithms and Products

“…The atmospheric correction was shown to have an accuracy equivalent to that of the MODIS products, within 20% of the AOD values. To improve the temporal resolution of the AOD estimation, Mei et al [77] developed an algorithm to simultaneously retrieve the AOD and surface reflectance by assuming that both the aerosol and the surface reflectance are stable in the three consecutive SEVIRI observations, which shows good agreement with in situ measurements.…”

Retrieval of Aerosol Optical Depth from Optimal Interpolation Approach Applied to SEVIRI Data

“…The next algorithm, the Oxford-Ral Aerosol and Cloud (ORAC) scheme, uses an optimal estimation approach and allows the retrieved AOD, aerosol effective radius and surface albedo to vary simultaneously to calculate the retrieved state with the maximum probability, whilst accounting for both measurements and a priori data and uncertainties in both [23]. The retrieval developed by Mei et al [24] is based on a time-series technique, which makes use of two visible bands at 0.6 and 0.8 μm in three orderly scan times. In this case, the surface properties estimation technique takes into account the assumption that the ratio of the reflectance in the solar band for two subsequent observations may be well approximated by the ratio of the reflectance at 1.6 μm.…”