ALBERT

Description: Retrievals of marine boundary layer (MBL) cloud microphysical and optical properties, based on high spatial resolution observations from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), are presented. The research–level retrieval algorithm, which is modified from the MODIS Data Collection 6 (C6) operational algorithms, is documented. An ASTER specific cloud masking scheme is implemented and the derived cloud covers agree well with those from an independent scheme reported in a previous ASTER cloud cover study by (Zhao and Di Girolamo, 2006). The viability of the retrieval algorithm is shown by a comparison of retrieved cloud optical thickness τAaM and effective droplet radius reff,AaM with the co-located, operational MODIS retrievals for 48 MBL cloud scenes with different degrees of cloud heterogeneity. The input for the retrieval is provided by aggregated, atmospherically corrected ASTER cloud top reflectances γ^0.86,AaM and γ^2.1,AaM. By means of the subpixel cloud cover Csub, which is derived from the ASTER cloud mask at its native resolution, the data set is divided into 52,254 overcast and 47,538 partially cloudy pixels. PDFs and scatter plots of γ^0.86,AaM, γ^2.1,AaM, and τAaM agree well with the corresponding MODIS products with Pearson's product–moment correlation coefficients of R 〉 0.980. A comparison for pixels with Csub = 1.0 yields a high agreement between reff,AaM and the MODIS retrievals with R = 0.972. However, for partially cloudy pixels there are significant differences between both products which can exceed 10 μm. Moreover, it is shown that the numerous delicate cloud structures in the example MBL scenes, resolved by the high–resolution ASTER retrievals, are smoothed by the MODIS observations. The overall good agreement between the research–level ASTER results and the operational MODIS C6 products proves the feasibility of MODIS–like retrievals from ASTER reflectance measurements and provides the basis for future studies concerning the scale–dependency of satellite observations and 3–dimensional radiative effects.