Properties of Doppler Spectra of the Reflected Signal in the Presence of Constant Current

There are a number of methods of currents measurements, including both in situ and remote sensing methods. HF Doppler radars are widely used to monitor currents from the shore. They are operating in the middle incidence angles, when the scattering is assumed to be resonant. The influence of currents on the Doppler spectrum in case of sounding at small incidence angles is not so well studied. In this paper the result of data processing of the experiments with Doppler radars installed at the opposite sides of the bridge over river are presented. The measurements were carried out at small incidence angles, when the backscattering mechanism is quasi-specular. The dependences of the main parameters of the Doppler spectrum on the azimuth angle were constructed for three schemes of measurements. It is shown that the use of the kurtosis coefficient and the coefficients of skewness to describe the Doppler spectrum makes it possible to determine the direction of wave propagation relative to the direction of the current. The goal of this paper is to provide experimental data to remote sensing scientists, to discuss the results obtained and future experiments.