Estimates of Spaceborne Precipitation Radar Pulsewidth and Beamwidth Using Sea Surface Echo Data

Calibration consistency between Ku-band radars flown on the Tropical Rainfall Measuring Mission's (TRMM's) precipitation radar (PR) and the global precipitation measurement (GPM) mission's dual-frequency PR (DPR) can be attained by the use of the normalized radar cross section (NRCS) or σ
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over the oceans. With the use of the sea surface echo (SSE) data obtained from the spaceborne PRs, this article aims to estimate the radar parameters of pulsewidth and beamwidth and to evaluate the bias in the NRCS estimates caused by the discrete range sampling. Since the SSE shape is closely related to the received pulsewidth and the two-way cross-track beamwidth, those parameters are individually estimated from the SSE shapes. The SSE shapes are also used to evaluate the impact of the discrete range sampling on the NRCS statistics. The pulsewidth and beamwidth estimated from the SSEs compare well with the level-1 values and accurately reflect changes in the configuration of the radars. The NRCS statistics in GPM version 06 show that the calibration consistency between GPM KuPR and TRMM PR is evaluated within the range of -0.39 to +0.03 dB (-0.48 to +0.11 dB) with (without) the peak correction.