Measurement of scattering coefficient dependence on soil moisture content and surface roughness by 35 GHz polarimetric scatterometer

Polarimetric measurements of scattering coefficient sigma⁰ of a bare soil were performed changing a roughness of a soil surface and a soil moisture content using the 35 GHz polarimetric scatterometer. At Ka band, a few experimental results of sigma⁰ data are available. One of the purpose of this experiment is to obtain the surface backscattering characteristics to evaluate surface clutter interference with precipitation measurement from space using the Dual frequency Precipitation Radar (DPR, 13.8 GHz and 35.5 GHz), which is planned to be onboard the Global Precipitation Measurement (GPM) Mission core satellite to observe precipitation globally. In evaluation of surface clutter interference, sigma⁰ data for various surface conditions are needed, especially sigma⁰ dependence on soil moisture content and surface roughness. Another purpose of this experiment is to apply the measured sigma⁰ data to estimate a soil moisture content globally after the launch of the GPM core satellite. An angular scan range of the DPR is from nadir direction though the incidence angle of 8.4 degrees (with the 35.5 GHz radar) or 17 degrees (with 13.6 GHz radar), so the measured data by the DPR is useful to observe the earth surface condition globally. In this study, the roughness of the soil surface was measured with a laser profile meter to determine the roughness dependence of the scattering coefficient. A soil moisture content was measured comparing the weight of the soil before and after the heating of the soil. The soil was heated enough to contain no water. To increase the number of the independent samples for each experimental conditions (soil moisture content/surface roughness/incidence angle), azimuthal angle is changed like clockwork using the turntable of 2 m diameter. The system of the scatterometer is network analyzer based polarimeter