Dual-polarimetric radar applications at Kwajalein Atoll, RMI

The dual-polarization weather radar on Kwajalein Island in the Republic of the Marshall Islands (KPOL) is currently one of the only full-time (24/7) operational S-band dual-polarimetric (DP) radars in the tropics. Through the use of KPOL DP fields and disdrometer data from Kwajalein, the Precipitation Office at NASA's Goddard Space Flight Center (GSFC) has developed applications for quality control (QC), absolute reflectivity calibration, and rainfall estimation to be applied in a near real-time operational environment. Data studies in light rain/drizzle show that KPOL DP measurements (from 2006 and later) meet or exceed quality thresholds for these applications as determined by consensus of the radar community. While the methodology for development of such applications is well documented, tuning of specific algorithms to the particular regime and observed drop size distribution requires a comprehensive testing and adjustment period to ensure high quality products. Presented are algorithm descriptions and results from multiple case studies at Kwajalein in which QC, absolute reflectivity calibration, and rain rate estimation were performed. Also described is a unique approach to calibrate the differential reflectivity field when vertically oriented scans are not available. Results show the following: 1) DP-based QC is superior to the legacy Tropical Rainfall Measuring Mission (TRMM) QC algorithm, especially in the detection and mitigation of ground clutter; 2) absolute reflectivity calibration can be performed using observations of light rain via a published integration technique; 3) DP-based calibration results are within ± 1 dB as compared to independent measurements; and 4) multi-parameter DP algorithm rain rates are higher in reflectivity cores than rates determined from traditional radar and rain gauge probability matching Z-R relationships.