Doppler Spectrum of the Signal Backscattered at Low Incidence Angles from the River with Constant Current: Model and Experiment

A simple method to calculate the wave spectrum in the presence of the constant river current is presented. The formation of the Doppler spectrum of the microwave radar signal backscattered from the water surface at low incidence angles is modeled. Measurements of the water surface backscatter at low incidence angles were performed using a Ka-band Doppler radar from the bridge over the Oka river in Nizhny Novgorod in June-October of 2019. Incidence angles varied from nadir to 25° during experiments. In this paper the results of comparison of experimental data processing and the model Doppler spectrum are presented. It is shown that the “simple” model that describes the wave spectrum and Doppler spectrum in the presence of the constant current allows to get results that are similar to experimental measurement yet differ especially in the case of sounding along the current. New measurements for different conditions will help to modify the model.