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 in a mountainous region by comparison with raingage data, Initially, the comparison serves as a basis for defining the assessment factor introduced to correct the systematic bias often affecting radar data. Several methods are available for determining the assessment factor and all are shown to provide a similar result. Corrections for both beam blockage and vertical profile of reflectivity are also evaluated. Both corrections provide an improvement in radar measurement accuracy. The validation of radar rainfall measurement is performed at the catchment scale of a few hundred square kilometres and at an hourly time period, these conditions being consistent with hydrological needs. The reference rainfall is determined by interpolating data from a dense raingage network. The accuracy of the areal reference value is defined by its standard deviation. A validation criterion taking into account the accuracy of the reference value is introduced. Validation results show a good level of agreement between reference measurements and radar data at the catchment scale. The confidence associated with the reference value suggests a combined use of radar and raingages based on the control of radar estimates by raingage measurements. (C) 1997 Elsevier Science B.V.