Simulation and field evaluation of the effects of raindrops on coherent Doppler wind lidar spectrum

Coherent Doppler wind lidar can simultaneously detect wind and rain parameters via the double-peak feature in the Doppler wind spectrum, formed by the difference in vertical velocity between aerosols and raindrops. This study aims to establish a theoretical and analytical framework for the synergistic influence of the single-particle effect and the raindrop spectral distribution on the Doppler wind spectrum. A Mie and vector complex ray model (VCRM) combined with the data from raindrop spectra measured by a micro rain radar, and an elastic lidar is proposed to estimate the atmospheric backscattering and extinction coefficients of raindrops. The observable atmospheric conditions characterizing the double-peak Doppler wind spectrum were quantitatively resolved using a validated theoretical model and measured raindrop spectral data. In a comparative experiment between single- and double-peak cases, when the aerosol backscattering intensity approaches the magnitude of the raindrop scattering intensity, the double-peak feature in the frequency spectrum emerges. Furthermore, using the Joss empirical raindrop spectral model, critical raindrop spectral parameters that can arise in the double-peak wind Doppler spectrum are suggested based on different background aerosol backscattering coefficients. When the aerosol extinction coefficient is of order 10^{- 5}m^-1, double-peak spectra can be observed for fine rainfall with a rate of 1.4 to 100 mm/h, widespread rainfall with a rate of 14.8 to 100 mm/h, and thunderstorms with a rate of 82 to 100 mm/h, respectively. The rates are decreased to 0.1-1.4 mm/h, 0.1-14.8 mm/h, and 0.1-82.1 mm/h, for fine rainfall, widespread rainfall, and thunderstorms, respectively, when the aerosol extinction coefficient is of order 10^{- 6}m^-1. It is worth noting that there are order-of-magnitude differences in the spectral parameters of raindrops required to trigger the double-peak feature across different precipitation systems, even for the same combination of aerosol concentration and rainfall intensity.