On the impact of the atmosphere in passive microwave remote sensing of land surface parameters

Data from the SGP97 Experiment and a coupled soil emission-atmosphere radiative transfer model were used to quantify the atmospheric effects on land surface parameter retrieval. Using vertical profiles of air temperature and humidity obtained from radiosonde ascends, the atmospheric contributions to the top of the atmosphere (TOA) brightness temperatures for frequencies ranging from 1.4 to 37 GHz were calculated. In order to derive surface emissivities, the solution of the radiative transfer equation was inverted. Surface emissivities obtained from SSM/I and ESTAR measurements were compared to in situ measurements of volumetric soil moisture. It was found that SSM/I measurements over sparsely vegetated areas could be used to discriminate wet, normal, and dry soil moisture conditions. Atmospheric corrections did not improve the retrieval. Moreover, it was shown that for the retrieval of cloud and atmospheric parameters from 19 GHz measurements, the surface emissivity and therefore soil moisture have to be accurately known.