Implementation and Evaluation of VPR Correction Methods Based on Multiple Volume Scans
Earth and related Environmental sciences
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The use of radar measurements to monitor and quantify rainfall is limited by errors and uncertainties in the estimation of surface precipitation. Weather radars use different elevation angles to measure the reflectivity of hydrometeors and from these measurements, the precipitation at surface level can be estimated. Due to the earth's curvature the height of the volume sampled by the radar increases with the distance, and the measurements get less and less representative of surface conditions. Another important error is due to the vertical variation of the radar reflectivity. This non-uniformity of the vertical profile of reflectivity is caused by the growth, melting and evaporation of precipitation (Joss and Waldvogel, 1990). In particular, the melting produces an enhancement of reflectivity in the melting layer known as the bright band. This effect is much more present in vertical reflectivity profiles (VPR) of stratiform precipitation than in the convective ones. Various methods have been proposed in literature to correct radar measurements from those errors. These methods consist in estimating the shape of the representative vertical profile of reflectivity and to use it for extrapolating reflectivity measurements aloft towards ground level. This representative profile can be determined by using climatological profiles, local profiles at short distances from the radar (Kitchen et al.; 1994; Germann and Joss,2002) or by means of an inverse theory (Andrieu and Creutin, 1995; Vignal et al.; 1999). In the present work a simple VPR method, aimed for operational use, has been implemented. It is based on the identification of an average VPR by using volume reflectivity data at short range. The method is onldy applied to the stratiform areas. A version of the Steiner algorithm adapted to the Belgian climate is used for separating stratiform zones from convective zones. A criterion for the applicability of the average VPR is imposed to filter out unrealistic profiles. When the average VPR is discarded, a climatological profile is used. The radar observations are available from a C-band Doppler radar located in the south of Belgium (Wideumont) and operated by the Royal Meteorological Institute of Belgium (RMI). The radar performs a 5-elevation scan every 5 minutes and a 10-elevation scan every 15 minutes. Both scans are used to obtain the best precipitation estimates and accumulation maps. The evaluation is based on daily accumulations. These accumulations are first adjusted with gauge measurements from the automatic network operated by the hydrological service of the Walloon region. The verification is then performed by comparing with measurements from the RMI climatological network. The final goal is to develop the optimal VPR correction method for operational use.
CitationVazquez, M.; Goudenhoofdt,E.; Delobbe, L. (2010). Implementation and Evaluation of VPR Correction Methods Based on Multiple Volume Scans. , Issue Proc. 6th European Conf. on Radar in Meteorology and Hydrology: Adv. in Radar Applications, IRM,