A GPM Dual Frequency DSD Retrieval Method Based on Linear Model for DSD Vertical Profile

摘要

d on the Global Precipitation Measurement (GPM) core satellite which will likely succeed the highly-successful Tropical Rainfall Measuring Mission (TRMM) satellite launched in 1997. It has been shown previously that the backward-iteration algorithm can be embedded within a single-loop feedback model. However, the single-loop model is unable to correctly estimate DSD profiles for a significant portion of global median-volume-diameter, D{sub}0, and normalized DSD intercept parameter, N{sub}w combinations in rain because of a multiple-value solution space. For the remaining D{sub}0, N{sub}w pairs, another retrieval method is necessary. This paper proposes an optimization technique to find those DSD profiles in the rain region that the single-loop model cannot correctly determine. The optimization method is based on a model that both N{sub}0 and log(N{sub}w) are linear vertical profiles, and that the profiles can be found using an optimization technique. Using those assumptions, the method finds the top and bottom D{sub}0, log(N{sub}w) values such that a cost function related to the input measured reflectivity and estimated measured reflectivity profiles is minimized. A random-restart method is used to generate random seed values for each optimization cycle. Example cases are shown to demonstrate the performance.