Numerical comparison of techniques for estimating Doppler velocity time series from coherent sea surface scattering measurements

A number of techniques for estimating the Doppler velocity time series from coherent sea surface scattering measurements are compared by observing their behaviour with computer simulated signals. These techniques include the finite difference instantaneous frequency estimator, the covariance moment estimation technique, tracking the peak of the short-time Fourier transform and tracking the peak of the cross Wigner–Ville time–frequency distribution. This comparison is achieved by examining the ability of each technique to track the instantaneous frequency of a unity amplitude, sinusoidal frequency law, complex exponential signal embedded in white Gaussian noise. The response of the estimators to various signal conditions, including low signal-to-noise ratios, high Doppler frequency excursions and high modulation frequencies, is investigated. Using the results, consideration is given to the suitability of each technique for estimating the magnitude, phase and power spectrum of the Doppler velocity time series. These are fundamental quantities required for studying sea surface scattering mechanisms and remotely sensing oceanographic properties.