Stereoradar Meteorology: A Promising Technique for observation of Precipitation from a Mobile Platform

Abstract

This paper presents a new concept in the measurement of precipitation by radar. The principle consists of stereoscopic observations: the same precipitation cell is observed by two radars operating at the same attenuated frequency but following two different angles of view. For instance, a system of two around based 20 km-spaced radars operating in X-band may provide stereoscopic observations. But the present paper considers more particularly an airborne radar configuration where a dual beam antenna system, combined with the aircraft displacement, views a precipitation cell under two incidences. In the method developed, the signal of interest is the difference z1 ? z2 between the apparent radar reflectivities (in dBZ) observed store the two viewing angles. It is shown that a second-order differentiation of z1 ? z2 allows one to estimate the along track gradient in the attenuation coefficient ?K/?X. However, because this estimate is too noisy, a variational method is proposed to retrieve the K-field from the z1 and z2 observations. The validation of such a concept is then investigated on the basis of a numerical simulation. In consideration of a simple raincell model and realistic sampling of the apparent reflectivity fields z1 and z2, it is demonstrated that the K-field can be reliably retrieved in the range of values 0.5 to 7 dB km?1. The obtained K-field may then be used to correct the apparent reflectivities for attenuation, and achieve an estimate of the ?true? reflectivity Z. Another variational approach is subsequently proposed which draws benefit of the simultaneous knowledge of Z and K to achieve an improved estimate of the rainfall rate R. A numerical simulation is again used as a tool to test it. The last part of the paper discusses possible applications of the new concept developed. Some emphasis is placed on the stereoradar from space in competition with the techniques already proposed for measurement of rain from a spaceborne radar.