A Novel Hybrid Approach for the Identification of Clear Air and Rain Echoes in the 205 MHz ST Radar Spectrum

Stratosphere–troposphere (ST) wind profiler radar (WPR) installed at Cochin, India, is a clear air VHF Doppler radar system designed for continuous wind velocity measurements under all-weather conditions. Clear air WPRs detect backscattered signals due to Bragg scattering from small irregularities in the refractive index caused by turbulence. The 205-MHz frequency band is able to detect both clear air and rain echos, simultaneously. Due to the large spectral width and merging of clear and rain echoes during rainy periods, the conventional signal processing techniques become inept at distinguishing the two echoes. An innovative hybrid approach is applied in this study to mitigate the ambiguity in identifying clear air and rain echoes separately. A combination of an exponentially modified Gaussian model and a pure Gaussian model is used to fit the raw spectrum in the hybrid approach adaptively. The data adaptive fitting procedure adopted can identify two distinct peaks during the rainy period, and the fitting process reduces to a single peak during non-rainy periods. Furthermore, the number of peaks is confirmed by locating the number of zero-crossings (NZCs) of the power gradient of the fit data. This unique approach is applied in the 205-MHz ST radar framework for the first time to solve the issue of multiple peaking in the ST radar spectrum.