A new scheme to estimate rain rate from an S-band polarimetric radar, immune with respect to DSD variability and radar calibration error

The S-band radar offers the advantage of providing a rainfall rate estimation from the Z-R relation, free of along path attenuation effects. However, the natural variability of the rain is another source of error that may be quite important. Such variability is fairly well described by the intercept parameter N0*, that should be accounted for in rain estimators, but cannot be determined in conventional algorithms. Standard multi-parameter relationships allowed by polarimetric techniques may remove this effect, but it is subject to radar calibration error.

The rain profiling algorithm ZPHI, initially developed to overcome the problem of attenuation for operational C- and X-band polarimetric radars, is proposed to solve the natural rain variability effect for S-band polarimetric radars. As a matter of fact, N0* is one of the key parameters retrieved by ZPHI. The rainfall rate is then expressed as a function of N0* and of the specific attenuation, but is still subject to calibration error. The retrieved rain rate is statistically compared with a second estimator, in order to determine the calibration error with a 0.1 dB accuracy. The delivered rain rate is then immune to both rain variability and calibration error.

First results from the application of ZPHI with S-band polarimetric radar data are shown to illustrate these properties, and compared with conventional rain rate estimators. Some inter-comparisons are also operated with raingauge data.