Study Of The Microwave Emissivity Characteristics

Surface microwave emissivity is an important parameter to describe the ground microwave radiation characteristics, and a basis of inversion geophysical parameters with microwave remote sensing data. It is defined as the ratio of the microwave radiation from surface and blackbody thermal radiation with the same temperature as surface. The microwave emissivity is a function of structure, water content, and surface roughness. In this study, the half-month averaged emissivity over different land covers were estimated using Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) combined with IGBP (International Geosphere-Biosphere Project labels) land classification data under clear sky condition. The microwave emissivity has been compared with the estimated soil moisture and microwave vegetation index (MVI) from AMSR-E, NDVI (Normalized Difference Vegetation Index) from MODIS (Moderate Resolution Imaging Spectroradiometer), which aims to understand the intrinsic relationship among satellite products. The results show a high correlation between the AMSR-E microwave emissivity and other satellite products, which can validate the microwave emissivity dataset simply and quickly. Then we combine emissivity with land cover data to extract and analyze emissivity characteristics over different vegetation types and the Gobi Desert at different frequencies, polarization and their seasonal variation. The results show that the emissivity of vegetation increases along with the growing frequency, and declines with the growing of frequency in the snow region. In summer, the emissivity of vegetation at V polarization of89GHz is larger than0.944. The emissivity of vegetation is relatively stable and the polarization difference is low (<0.081) in summer. In the same area, the RMSE of emissivity summer time series is less than0.0072. In winter, emissivity decreases in snow covered area, especially for higher frequencies. Furthermore, with vegetation density increase, the emissivity increases and emissivity polarization difference decreases. In Gobi desert area, emissivity polarization difference decrease as the frequency increases, and the polarization difference is large (0.03-0.127). The H polarization emissivity increases with increasing frequency, but the V-polarized microwave emissivity is reduced with increasing frequency because of the body scattering. The results indicate that NDVI derived the good negative correlation with microwave emissivity polarization difference at37GHz.