Estimation of Snow Water Equivalent from Passive Microwave Remote Sensing Data (SSM/I) in Tibetan Plateau

摘要

So far, there is not an operational algorithm to estimate the snow water equivalent from passive microwave remote sensing data (SSM/I) in the Tibetan Plateau. In this study the SSM/I brightness temperature data in January 1993 are used to estimate SWE at this region. The frequencies of SSM/I data are used to retrieval snow depth are 19 and 37GHz in horizontal polarization. The results have shown all existing algorithms overestimated the snow depth in the Tibetan plateau. This paper analyzed the reasons of overestimation of snow depth from several aspects, such as the water content of snowpack, large water bodies (e.g. lakes), and the abnormal field snow depth data. After eliminating some futile data (including the passive microwave brightness temperature values and snow depth data in the weather stations), an improved algorithm has been established to retrieval the snow depth from the difference of 19 and 37GHz brightness temperature in horizontal polarization. Here, snow density is obtained by a time function of fresh snow density. The snow depth and density were converted to the snow water equivalent, and are regarded as the ground truth. In finally, the TB vertically polarized differences of 19 and 37GHz are regressed with the SWE. Using the statistical method, a simple and practical algorithm is developed to estimate the snow water equivalent from the differences of 19 and 37GHz in vertical polarization.