The proof-of-concept for raindrop size distribution retrieval using combined dual-frequency radar DFR

Source abstract

Accurate retrieval of raindrop size distributions (DSDs) is essential for understanding cloud and precipitation microphysics. The dual-frequency ratio (DFR) measured by dual-frequency radars is independent of the normalized intercept parameter (Nw) and depends solely on the mass-weighted mean diameter (Dm). This characteristic makes DFR a powerful parameter for DSD retrieval. However, the DFR–Dm relationship is subject to a dual-solution ambiguity, particularly for smaller particles. This study demonstrates that W-band reflectivities obtained through scattering simulations based on measured raindrop size distributions, combined with the DFR(Ka, W) constraint, effectively mitigate the DFR(X, Ka)–Dm dual-solution ambiguity. The results demonstrate that incorporating the DFR(Ka, W) constraint substantially reduces the DFR–Dm ambiguity, raising the proportion of data with a unique Dm solution from 35.38 % (DFR(X, Ka) alone) to 87.5 %. The proposed framework shows potential advantages over conventional approaches, particularly for weak echoes (< 20 dBZ), where conventional methods fail but the proposed framework maintains robust accuracy. This proof-of-concept study provides a reference framework for future three-frequency radar DSD retrieval.