Abstract
Abstract. In this study, a method is presented to retrieve the surface reflectance using the radiances measured at the top of the atmosphere for the two views provided by the Advanced Along-Track Scanning Radiometer (AATSR). In the first step, the aerosol optical depth (AOD) is obtained using the AATSR dual-view algorithm (ADV) by eliminating the effect of the surface on the measured radiances. Hence the AOD is independent of surface properties and can thus be used in the second step to provide the aerosol part of the atmospheric correction which is needed for the surface reflectance retrieval. The method is applied to provide monthly maps of both AOD and surface reflectance at two wavelengths (555 and 659 nm) for the whole year of 2007. The results are validated versus surface reflectance provided by the AERONET-based Surface Reflectance Validation Network (ASRVN). Correlation coefficients are 0.8 and 0.9 for 555 and 659 nm, respectively. The standard deviation is 0.001 for both wavelengths and the absolute error is less than 0.02. Pixel-by-pixel comparison with MODIS (Moderate Resolution Imaging Spectrometer) monthly averaged surface reflectances show a good correlation (0.91 and 0.89 for 555 and 659 nm, respectively) with somewhat higher values (up to 0.05) obtained by ADV over bright surfaces. The difference between the ADV- and MODIS-retrieved surface reflectances is smaller than ±0.025 for 68.3% of the collocated pixels at 555 nm and 79.9% of the collocated pixels at 659 nm. An application of the results over Australia illustrates the variation in the surface reflectances for different land cover types. The validation and comparison results suggest that the algorithm can be successfully used for both the AATSR and ATSR-2 (which has characteristics similar to AATSR) missions, which together cover a 17-year period of measurements (1995–2012), as well as a prototype for the Sea and Land Surface Temperature Radiometer (SLSTR) planned to be launched in the fall of 2015 onboard the Sentinel-3 satellite.
Highlights
The interest in global satellite observations of land properties for application in Earth system science and global climate research is growing (National Research Council, 2004)
The objective of the current paper is to describe and evaluate a different method for the retrieval of the land surface reflectance which is based on the use of the dual-view ca
The aerosol optical depth (AOD) retrieved using ADV is used as atmospheric correction to obtain the surface reflectance
Summary
The interest in global satellite observations of land properties for application in Earth system science and global climate research is growing (National Research Council, 2004). Surface albedo, defined as the ratio of upwelling to downwelling radiative flux at the surface (Lucht et al, 2000), is one of the most important variables controlling the surface radiation budget. It has been well recognized that the surface albedo is among the main radiative uncertainties in climate modeling (e.g., Hahmann and Dickinson, 2001; Wang et al, 2007). Snow-free albedo is especially important for land surface models that compute the exchange of energy, water, or carbon for various land use categories (Tasumi et al, 2008; Rechid et al, 2009). Surface albedo varies spatially and temporally as a result of both natural processes (e.g., vegetation growth, change in soil moisture content, snow aging) and human activity (e.g., deforestation, agriculture, burning).
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