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Acoustic sounding of rain

For remote measurements of rains, radars have been successfully used for many years. In the last decade, high- frequency acoustic radars (sodars) are being increasingly employed to measure the parameters of precipitation. They have a number of advantages over the conventional radars. In the present report, a new method of acoustic sounding of rain is described based on recording of the Doppler power spectra of falling raindrops comprised in the scattering volume with a high-frequency cw Doppler bistatic sodar. Differential acoustic scattering cross sections of a rigid spherical particle have been calculated with the use of the exact formulas of the Mie scattering theory as functions of the parameter p equals (pi) d/(lambda) , and the scattering angle (theta) , where d is the raindrop diameter and (lambda) is the acoustic radiation wavelength. Errors in reconstructing the normalized raindrop size distribution (NRSD) are numerically estimated. The NRSD's and the rain intensities reconstructed from raw spectra of real signals measured with cw bistatic Doppler sodars operating at frequencies of 5 and 40 kHz, respectively, are presented. The estimated rain intensities varied from 0.1 to 6.1 mm/h. The results obtained demonstrate that high-frequency sodars are very promising for measurements of rains.