Empirical SWE retrieval using airborne microwave and in situ snow measurements

We examine the response of microwave brightness temperatures to snow water equivalent over a wide range of snowpack conditions observed during the Cold Land Processes Experiment (CLPX) in 2002 and 2003. Spatially intensive measurements of snow were collected over the CLPX study areas within the Colorado Rocky Mountains. The NOAA Earth System Research Laboratory´s Polarimetric Scanning Radiometer (PSR) was operated to obtain coincident high-resolution (150-500 m) multiband microwave imagery of the snowpack. Together, a robust data set of over 2300 collocated in situ and remotely sensed observations were obtained for this analysis. For each point we modeled brightness temperatures using observed snow properties and the Helsinki University of Technology (HUT) snow emission model. Using observed and modeled data, we developed multiple regression algorithms to retrieve snow water equivalent (SWE). The algorithms use brightness temperature differences between 10.7, 18.7, and 21.5 GHz with 37 GHz and 89 GHz. Results show that the CLPX microwave data are consistent with a) historically established data and, b) after removal of cases with macro vegetation or possible wet snow, with theoretically derived curves for microwave dependence on SWE.