IDENTIFICATION OF VERTICAL PROFILES OF RADAR REFLECTIVITY FOR HYDROLOGICAL APPLICATIONS USING AN INVERSE METHOD .1. FORMULATION

The vertical variability of reflectivity in the radar beam is one of t he main sources of error in estimating rainfall intensity. This vertic al variability, which has several origins, is characterized globally b y a function called ''vertical profile of reflectivity.'' The impact o f this vertical profile of reflectivity on the radar measurement is qu antified by incorporating this function in the radar equation. It is t hen possible to specify the influence of the characteristics of the ra dar, the distance, and the vertical profile on errors in estimating ra in rates at the ground level. A method for determining the vertical pr ofile of reflectivity is then described. This procedure requires the u se of radar images from at least two different elevation angles. It is based on the evolution of the ratio of reflectivities (reflectivity a t high elevation divided by reflectivity at a lower elevation angle) v ersus distance. The ratio evolution is closely related to the vertical profile of reflectivity and to the conditions of radar operation. An inverse solution method is used to identify the vertical profile of re flectivity corresponding to the observed ratio of reflectivities. The advantages and limitations of the proposed method are discussed.