Limitation on the use of spaceborne imaging SAR as rain radars

A SAR detecting rain can achieve only part of its resolution capability because of random drop motion. However, the most significant limitation for rain measurement with imaging SAR is surface clutter. The authors studied the possibility of using the X-SAR and the C-Band channel of SIR-C for rain measurement. Both SIR-C and X-SAR achieve adequate SNR at 60° incidence angle over the ocean. However, the signal-to-clutter ratio (SCR) over ocean precludes use of SIR-C and allows use of X-SAR off-vertical only for very heavy rains, and then only at high incidence angles. Calculations at vertical incidence look promising over forests. However, range-sidelobes lead to small SCR over oceans at both X- and C-bands. To get broad-swath rain measurement with SAR will require designing a radar with this as a goal, rather than using a radar designed for surface imaging