Observations and statistical analysis of combined active–passive microwave space-borne data and snow depth at large spatial scales

Remote sensing based on active and passive microwave data represents a useful tool for studying the state of the cryosphere at high temporal resolution and large spatial scale. In particular, retrieving snow parameters from space-borne data can benefit hydrological, meteorological, and climatological applications. In this paper, we analyze the trend of Ku band backscatter coefficients measured by the NASA's Quick Scatterometer (QuikSCAT) and K and Ka band brightness temperatures measured by the Special Sensor Microwave Imager (SSM/I) with respect to snow depth values at different locations in the Northern hemisphere during the period 1999–2004. We also quantify, for the first time, the dynamic range of space-borne Ku band scatterometer data over snow covered areas at very large spatial scale in comparison to the range in passive microwave brightness temperatures. Also for the first time, we quantify the improvement on the snow depth retrieval related to the combined use of active and passive data and compare the results with those obtained using either only active or passive data. Finally, we report first results regarding an analysis involving X-band brightness temperatures, collected by the Advanced Microwave Scanning Radiometer for EOS (AMSR-E), aiming at understanding whether the improvements derived from using a combination of active and passive data are related to the use of a low frequency or to the different techniques used (e.g., active or passive).