Areal Rainfall Estimates Using Differential Phase

Abstract

A radar polarimetric method for areal rainfall estimation is examined. In contrast to the polarimetric algorithm based on specific differential phase KDP, the proposed method does not require rain-rate estimation from KDP inside the area of interest, but it utilizes only values of total differential phase ΦDP on the areal contour. Even if the radar reflectivity and differential phase data inside the area are corrupted by ground clutter, anomalous propagation, biological scatterers, or hail contamination, reliable areal rainfall estimate is still possible, provided that correct ΦDP estimates are available at a relatively small number of range locations in or at the periphery of the contour of this area. This concept of areal rainfall estimation has been tested on the Little Washita River watershed area in Oklahoma that contains 42 densely located rain gauges. The areal rainfall estimates obtained from the polarimetric data collected with the 10-cm Cimarron radar are in good agreement with the gauge data, with the standard error of about 18%. This accuracy is better than that obtained with the algorithm utilizing areal averaging of pointwise estimates of KDP inside the watershed area.