This paper presents two methods for computing differential propagation phase shift (ϕDP) using time series data form a coherent radar with alternate switching between two linear but orthogonal polarizations. An analysis of the statistical error in ϕDP estimate shows that ϕDP can be estimated with less than 0.5° standard error using time and range averaging. To evaluate the usefulness of ϕDP for estimating rainfall rate (R) vis‐a‐vis the ZDR method, a discussion on the sensitivity of R to standard errors in ϕDP as well as ZH and ZDR is presented. It is shown that the relation, differential propagation phase constant Δϕ versus R, is relatively insensitive to drop size distribution (DSD) variations and thus can yield more accurate R estimate, even when a direct relationship between Δϕ and R is assumed. However, standard error in Δϕ estimate causes large inaccuracies of R at low values (R < 50 mmh−1), thus limiting its usefulness to higher rainfall rates. It is also shown that Δϕ can be used as a third remote measurable in conjunction with ZH and ZDR to determine a three parameter gamma DSD. Another use of Δϕ is likely to be in hydrometeor type identification, especially hail in severe storms.

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This paper discusses the possibility of incorporating differential reflectivity (ZDR) measurement in Doppler radars having fast scan capability, without compromising the accuracy of the spectral moment estimates. The presently established technique of ZDR 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 ZDR 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 ZDR suggests that accurate estimation of ZDR 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 ZDR 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.