Passive Microwave Retrieval of Vegetation Optical Depth and Soil Permittivity Over Snow Covered Surfaces at L-Band

To account for the impacts of snow on surface upwelling emission at the L-band microwave, this study employs a soil-snow-vegetation emission model to examine the retrieval errors associated with the simultaneous estimation of vegetation optical depth (VOD) and ground permittivity. The findings demonstrate that neglecting snow cover in retrievals can lead to an overestimation of VOD by approximately 30% and substantial error in ground permittivity, largely depending on the ground freeze-thaw status, snow density, and VOD. We utilize the Soil Moisture Active Passive (SMAP) satellite observations to retrieve VOD and compare it to the vegetation proxies such as AGB and tree height on a global scale. The results show consistent spatial patterns with the land cover types and dependencies with above-ground biomass (AGB) values and tree heights. The preliminary results offer promising possibilities to obtain global estimates of VOD and soil permittivity over snow-covered areas, where current SMAP observations are underutilized.