Research on the effect of the ground clutter on the measurement of the precipitation by the spaceborne millimeter wave precipitation radar

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For the design of the future millimeter wave spaceborne precipitation radar, such as the 35.5GHz radar onboard the GPM(Global Precipitation Measurement) mission, the adverse effects of the ground clutter in the antenna sidelobe area must be evaluated in order to precisely measure the precipitation echo from the antenna mainlobe area. Therfore it is indispensable to measure the precise values of the basic normalized radar scattering cross section σ^0 of the ground surface. The 35.5GHz step frequency polarimetric scatterometer is designed and developed to measure basic normalized radar scattering cross section of the ground surface. The scatterometer uses the vector network analyzer as the transmitter and receiver and two standard horn antennas are used for the transmitter and receiver antennas. The scatterometer is mounted on the top of the tower whose height is variable from 1 meter to 3 meters. The scattering cross section σ^0 of the soil varies as the soil surface roughness and soil moisture content changes. The complex dielectric constant which is the basic parameter to determine the value of σ^0 is the function of the soil moisture content. In order to measure the σ^0 of the soil surface as functions of the surface roughness and soil moisture content, the turn table is manufactured to mount a sample of the soil surface. The turn table rotates stepwisely by 360 degrees. The laser roughness meter and the instrument to measure complex dielectric constant are also prepared to measure soil roughness and soil complex dielectric constant, respectively. The normalized radar scattering cross section σ^0 of the soil is measured as a function of the incidence angle by varying the soil roughness and soil moisture content as parameters. The σ^0 values does not depend on soil roughness so much when the incidence angle is about 10 degrees and it increases as the soil moisture content increases.