Suppression of surface clutter interference with precipitation measurement from space by the Dual frequency Precipitation Radar

A new method to suppress the surface clutter interference with precipitation measurement from space by the Dual frequency Precipitation Radar (DPR, 13.8 GHz and 35.5 GHz) is introduced for the Global Precipitation Measurement (GPM) mission, which is planned in succession to the Tropical Rainfall Measuring Mission (TRMM). The DPR has very high sensitivity and its minimum detectable rain rate is designed to be 0.3mm/h(attained by the 35.5 GHz radar) at the rain top. In this study, the radiation pattern of the slotted wave guide planar phased array antenna was calculated by considering the Taylor distribution with random errors in excitation current. The signal (S) to clutter (C) power ratio (S/C ratio) was evaluated for the antenna pattern given by the Taylor distribution (designed peak side lobe level=-35 dB, n=6, ; these values are same as the TRMM PR), where the S means received power from rain scattering volume, and the C means the backscattered power from sea/land surface. A uniform rain rate of 0.3 mm/h was assumed for the calculation of signal S at 35.5 GHz and 0.5 mm/h for S at 13.6 GHz. A side lobe clutter interferes the rain echo severely when the strong side lobe illuminates the nadir direction, where the specular component of the scattering coefficient of sea/land surface is dominant. The introduced method to suppress the side lobe clutter is to tilt the antenna beam a few degrees in coordinate plane determined by the satellite flight direction and the nadir direction. The radiation pattern of the phased array antenna is characteristic in that the region of the strong side lobe arises in crisscross. By tilting the antenna beam, the strong side lobe illuminates the off nadir direction. So that makes it possible to suppress the side lobe clutter. Calculation results show that the surface clutter interference is suppressed well at the main beam tilt angle 2 degrees.