Estimation of Raindrop Size Distribution from Polarimetric Radar Measurements at Attenuating Frequency Based on the Self-Consistency Principle

A method for estimating three parameters of a gamma raindrop size distribution model and rainfall rate from polarimetric radar at attenuating frequency was developed. The algorithm was developed based on the self-consistency principle but was expanded to take into account the attenuation effect by describing the interrelation between polarimetric measurements along the range profile. The proposed method does not require any assumptions of relationship among raindrop size distribution (DSD) parameters or simplifications of equations that describe relationship between the axis ratio and diameter of raindrops, which have been used in previous studies. Moreover, the proposed algorithm needs no external reference data such as two-dimensional video disdrometer (2DVD) measurements for attenuation corrections because it retrieves the co-polar and differential specific attenuation from the interrelation among the polarimetric measurements.

The performance of this algorithm was evaluated by comparison with optical disdrometers and a weighing precipitation gauge. The evaluation of the algorithm showed that the retrieved three DSD parameters of raindrops, reflectivity, and differential reflectivity from actual C-band polarimetric radar data have fairly good agreement with those obtained by surface measurements. Moreover, the rainfall rates retrieved using this algorithm have comparable precision with those estimated from the specific differential phase (Kdp), and outperform those estimated through the so-called Z–R relationship, particularly during heavy rainfall.