“Quasi-Period” Signal Processing Technique for Doppler Sodar Measurements

Abstract

An approach for estimating the first and second moments of the spectrum of a narrowband signal, which will be called the ?quasi-period? technique, is described. This method is based on the statistical properties of the instantaneous frequency of a quasi-sinusoidal signal. The probability density function of the instantaneous frequency is determined by the first two moments of the spectrum only and does not depend on its shape. Using statistics of the instantaneous frequency, it is possible to compensate for the bias of the mean frequency by noise and to define an objective criterion for identifying data with an inadequate signal-to-noise ratio. Using model signals with known spectra as well as a sinusoidal signal and additive noise, an evaluation of the accuracy of this method for estimating the mean frequency was obtained. The use of this technique in sodar systems for wind measurements allows better identification of interfering data and measurement of the wind variance in addition to its mean value, both during one profile and averaging over a number of profiles.