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 refle ctivity 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 thr ee-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 r anges the effects of beam sampling the ice region lead to strong underestim ation. It is shown that improvements obtained by applying the range-depende nt bias adjustment procedure lead to remarkable reduction of inter-elevatio n bias. The coupling of range-dependent bias adjustment with a procedure fo r mean-field bias removal allows a significant reduction of radar-raingauge differences. (C) 2000 Elsevier Science Ltd. All rights reserved.