ZDR measurement considerations for a fast scan capability radar

This paper discusses the possibility of incorporating differential reflectivity ( Z DR ) measurement in Doppler radars having fast scan capability, without compromising the accuracy of the spectral moment estimates. The presently established technique of Z DR measurement using alternate sampling of horizontally and vertically polarized signals ( H and V ) has long acquisition time and reduced maximum unambiguous velocity. It is shown that Z DR acquisition time can be reduced significantly by simultaneously sampling H and V signals and range averaging, which does not compromise spectral moments estimation capability and volume update time. An analysis of variance of Z DR suggests that accurate estimation of Z DR at scan rates of 18° s −1 is possible only if correlation between simultaneously received horizontally and vertically polarized echoes is better than 0.995. A theoretical investigation of all the factors that contribute to the decorrelation established that this indeed is the case for rain media. A scheme for Z DR measurement is suggested which uses +45° and −45° polarized transmissions alternately and simultaneous reception of H and V signals to compensate for bias error due to propagation. Further, a method for nearly eliminating the bias error due to receiver mismatch is suggested.