Adjustment of range-dependent bias in radar rainfall estimates

Due to the vertical variability of reflectivity and radar sampling geometry, radar rainfall estimation is necessarily subject to biases that are range-related. These range-related errors mirror the vertical structure of reflectivity field as it is perceived by the radar at various ranges. This study focuses on range-dependent biases that arise at mid-ranges (30-70 km) due to the requirement of using relatively high elevation radar scans to avoid ground effects. Rainfall data for the Warden Hill weather radar in UK, both unadjusted and adjusted for range-related effects, are evaluated for a three-year period. Quantitative analysis is splitted into two distinct stages: i) radar-only evaluation, and ii) radar-gauge comparison along the range. Effects of bright band are recognizable at close ranges, while at farther ranges the effects of beam sampling the ice region lead to strong underestimation. It is shown that improvements obtained by applying the range-dependent bias adjustment procedure lead to remarkable reduction of inter-elevation bias. The coupling of range-dependent bias adjustment with a procedure for mean-field bias removal allows a significant reduction of radar-raingauge differences. (C) 2000 Elsevier Science Ltd. All rights reserved.