ADEOS-II/GLI snow/ice products — Part I: Scientific basis

Algorithms for retrieval of aerosol and snow/ice properties in polar and mid-latitude regions are described. These include (i) a cloud mask, (ii) a snow/sea ice discriminator, (iii) algorithms for retrieval of snow properties (snow grain size and impurities) and (iv) surface temperature of snow/ice and open ocean water. The cloud mask and snow/ice discriminator are used for cloud clearing as well as surface classification. For cloud-free pixels that are determined to be snow-covered an algorithm for retrieval of snow grain size and impurity concentration has been constructed. Radiative transfer simulations of the coupled atmosphere-surface system are used to construct lookup tables that are used in the retrieval process which proceeds by comparing measured top-of-the-atmosphere (TOA) radiances with synthetic values obtained from the lookup tables. These algorithms are designed to be applicable to polar and mid-latitude regions, but can easily be extended for use in other regions with seasonal and permanent snow-cover. The surface temperature retrieval algorithm consists of two parts: one for retrieval of the snow/ice surface temperature (IST), and another one for the retrieval of open-ocean surface temperature (SST). A multilinear regression technique is used to determine the empirical coefficients in the expression for the surface temperature, and Arctic radiosonde data are used in conjunction with radiative transfer models to simulate the sensor-measured radiances. The algorithms have been extensively tested against synthetic data, Moderate Resolution Imaging Spectroradiometer (MODIS), MODIS Airborne Simulator (MAS) and GLobal Imager (GLI) data as well as other data sources.