The effects of particle size distributions on cross‐spectral phase measurements in spatial interferometry

Abstract

Recent observations made with a 50‐MHz Doppler radar interferometer suggest that the presence of precipitation can introduce a bias when using the cross‐spectral phase in spatial interferometry that results in an overestimation of the horizontal wind. The process is akin to turbulent fading, which produces a temporal decorrelation in the time history of the complex radar voltages. In the case of precipitation it has been proposed that the size distribution of precipitation particles produces a similar effect. This paper examines the supposition by presenting further data obtained with the 50‐MHz Doppler radar. In addition, two simulations, one in the time domain and one in the frequency domain, have been created to test for any biases introduced by an exponential form of the drop size distribution. In the time domain case spectra are generated from simulated time series data, whereas in the frequency domain case the spectra are computed directly. Results from the simulations are given for both the cases of Bragg scatter from turbulent variations in the refractive index and Rayleigh scatter from precipitation particles. This work shows that precipitation does influence the cross‐spectral phase data and suggests that spatial interferometry measurements may provide a means of extracting information related to drop size distribution parameters.