Simulation-based analysis of rainrate estimation errors in dual-wavelength precipitation radar from space

A variety of major sources of rainrate retrieval errors in a conventional dual-wavelength radar technique (DWRT) as well as Ze-R method are analyzed based on simulations upon utilizing a disdrometer-measured raindrop size distribution (DSD) as well as vertical rain field structure (VRS) data collected by Tropical Rainfall Measuring Mission's (TRMM) precipitation radar (PR). A spaceborne dual-wavelength radar geometry comprising 13.6 and 35 GHz operating frequencies are considered in the simulations. Through first fold of the simulation, we statistically examined the significance of the VRS effect in the DWRT, which is found to be negligible. Next, we attempted to gauge relative sensitivities of the DWRT and Ze14 (at 13.6 GHz)-R method to the natural fluctuation of DSD. Statistical error analyses suggest some distinct lower bounds of rainrate retrieval accuracies of the two estimates. For instance, if the minimum sensitivity of 35-GHz radar is equivalent to about 10 dBZ and the rainrate is about 10 mm h⁻¹, DWRT shows ∼51% of improvement in the accuracy for 3-km range resolution, while it has ∼44% improvement for 1-km range resolution compared to the Ze14-R method. Finally, the effects of nonuniform rain field (NUR) and mismatching in the observed field-of-views (FOV) of the radars are analyzed. It is noticed that the NUR effect introduces small amount of enhancement in the errors comparing to that due to the effect of the DSD variation and/or the coupling of the Mie scattering effect, while mismatching in the FOV significantly enhances errors as well as biases in the DWRT estimates.