Stereoradar Meteorology: A New Unified Approach to Process Data from Airborne or Ground-Based Meteorological Radars

Abstract

The concept of stereoradar in meteorology was first proposed by Testud and Amayenc. It consists of radar observations of a precipitation cell from two viewing angles, using an attenuated frequency. The initial inspiration of the technique lays in the development of the ELDORA/ASTRAIA project, a dual-beam X-band airborne Doppler radar developed in common by NCAR and CRPE (Centre de Recherche en Physique de I?Environnement), and devoted to the observation of the three-dimensional dynamics of deep convection. At X band in severe weather the observed radar reflectivity may be severely corrupted by along-path attenuation. The stereoradar analysis was first conceived as a procedure to correct the observed reflectivity for attenuation. In July and August 1991, CRPE and NOAA collaborated to realize the first dual-beam airborne Doppler radar. Several scientific flights were accomplished in Florida in the framework of the CaPE (Convection and Precipitation/Electrification)experiment. These flights provide an excellent opportunity to validate the stereoradar concept on real data since (i) intense rain cells inducing strong X-band attenuation could be sampled by the dual-beam airborne radar, and (ii) ground truths were available from the three research radars (CP-2, CP-3, and CP-4) deployed on the ground by NCAR in CaPE. The object of this paper is to propose a new formulation for the stereoradar analysis that is simpler, more general, and numerically more stable than the previous one, because it implies now a first-order differentiation of the data field. The new processing is applied to a real dataset from the above-mentioned CaPE experiment. The first application to real data presented in this paper tends to demonstrate the great potential of this technique, not only to correct the apparent reflectivities for along-path attenuation but also to determine the specific attenuation field associated with a precipitation core. It should be emphasized that the stereoradar analysis achieves this retrieval without making any assumption about the size distribution or phase of the hydrometeors.