USE OF A WEATHER RADAR FOR THE HYDROLOGY OF A MOUNTAINOUS AREA .2. RADAR MEASUREMENT VALIDATION

This paper investigates the validation of radar rainfall measurement i n a mountainous region by comparison with raingage data, Initially, th e comparison serves as a basis for defining the assessment factor intr oduced to correct the systematic bias often affecting radar data. Seve ral methods are available for determining the assessment factor and al l are shown to provide a similar result. Corrections for both beam blo ckage and vertical profile of reflectivity are also evaluated. Both co rrections provide an improvement in radar measurement accuracy. The va lidation of radar rainfall measurement is performed at the catchment s cale of a few hundred square kilometres and at an hourly time period, these conditions being consistent with hydrological needs. The referen ce rainfall is determined by interpolating data from a dense raingage network. The accuracy of the areal reference value is defined by its s tandard deviation. A validation criterion taking into account the accu racy of the reference value is introduced. Validation results show a g ood level of agreement between reference measurements and radar data a t the catchment scale. The confidence associated with the reference va lue suggests a combined use of radar and raingages based on the contro l of radar estimates by raingage measurements. (C) 1997 Elsevier Scien ce B.V.