A coupled Land Atmosphere Radiative-Transfer Model (LA-RTM) for multi-frequency passive microwave remote sensing: development and application over Wakasa Bay and the Tibetan Plateau

Abstract

Multi-frequency passive microwave sensors herald a new dawn for combined land and atmosphere observations. Past efforts to utilize microwave remote sensing of atmosphere and land surface have proceeded by treating these two areas in a parallel fashion. In this research, a unified approach is presented that can be used to improve both quantitative and qualitative understanding of land and atmosphere constituents. A coupled Land Atmosphere Radiative-Transfer Model (LA-RTM) that can be used as a forward model in retrieval algorithms, or as an observation operator in data-assimilation schemes is developed. This model is validated using data collected during the 2003 Advanced Microwave Scanning Radiometer on board the Earth Observing Satellite (AMSR/AMSR-E) validation experiment over Wakasa Bay in Japan and the Coordinated Enhanced Observing Period (CEOP) dataset for the Tibetan Plateau collected in April and August 2004. These datasets comprise satellite (AMSR-R) observations, ground-based microwave radiometers (GBMRs) and radiosonde atmosphere soundings. In both sites, good agreement between simulated and observed brightness temperatures is demonstrated. To facil- itate fast retrievals, a retrieval scheme is proposed that uses LA-RTM as a forward model to generate a look-up table (LUT) for varying land-surface conditions. This LUT is used to retrieve soil-moisture and surface-roughness conditions for the target site. Using this scheme, retrieved soil moisture at in situ stations was shown to have fairly good agreement with observations.