The land surface reflectance is a fundamental climate data record at the basis of the derivation of other climate data records and a key parameter in the understanding of the land-surface-climate processes. Here, we compared the surface reflectance product to reference reflectance determined from Top of atmosphere reflectance corrected using accurate radiative transfer code and very detailed measurements of the atmosphere obtained over the AERONET sites which allows to test for a large range of aerosol characteristics; formers being important inputs for atmospheric corrections. The application of this method necessitates the definition of a very detailed protocol for the use of AERONET data especially as far as size distribution and absorption are concerned, so that alternative validation methods or protocols could be compared.Thus, we defined a protocol to use the AERONET data. To correctly take into account the aerosol model, we used the aerosol microphysical properties provided by the AERONET network including size-distribution (%Cf, %Cc, rf, rc, σr, σc), complex refractive indices and sphericity. We selected 704 AERONET sites with sufficient data. To be useful for validation, the aerosol model should be readily available anytime, which is rarely the case due to satellite overpassing time (no almucantar protocol measurement + partial cloud cover…). We used regressions for each microphysical parameters using as parameter τ440 and α (Angström coefficient). Comparisons with the AERONET dataset indicate uncertainties up to 30% less than while using directly Dubovik's 2002 approach for each parameter (with τ550 only). In term of surface reflectance retrieval, for a mean loaded atmosphere with t550 less than 0.25, the maximum uncertainty is 0.0025 corresponding to a relative uncertainty U (in the MODIS RED channel) of less than 1% for ρsurf > 0.10. The result can be easily generalized to other satellites i.e. VIIRS, Landsat 8 and Sentinel 2 (the former are part of CEOS ESA/NASA ACIX project (Doxani et al, 2018). The conclusion is that the new protocol, using τ440 and α , gives uncertainties lower than 30% in red channels and 15% in blue channels than the previous one.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- 0402 Agricultural systems;
- 0426 Biosphere/atmosphere interactions;
- 0430 Computational methods and data processing;
- 0480 Remote sensing;