New Calibration Formula for Radar–Rainfall Relationships Analysis

Abstract

A unipolar ground-based weather radar is a widely-used instrument for rainfall measurement. These radar measurements, however, need to be calibrated for more accurate rainfall estimation. This article introduces a new calibration approach using time-stepwise processing of reflectivity–rainfall rate (\(Z{-}R\)) relationship. Based on the previous work utilizing the radar–rainfall relationship, this article hypothesizes that the rainfall measurement from a ground based radar are affected by the distance from radar, altitudes and rainfall time duration. Unipolar ground-based radar data sets for two consecutive years with 77 occurrences of rainfall from 39 stations in calibration window of three hours as well as the corresponding rainfall measured from registered rain gauges were used in this study. The results indicated that it is better to use the radar–rainfall relationship \(Z=aR^{b}\) in view of the altitude effect (\(H\)) and empirical coefficient (\(c\)), such that \(Z=aR^{b}H^{c}\). The changes in the distance from the radar and duration of precipitation were evidently significant. For radar–rainfall relationship individually, the values of the determination coefficient \(R^{2}\) made up from 0.88 to 0.97, and those for this relationship in view of the altitude effect (\(H\)) were from 0.70 to 0.97. It is therefore concluded that the use of other effective parameters (distance from radar, altitude and rainfall time duration) leads to optimum accuracy of the \(Z{-}R\) relationship.