ISSN 2070-7401 (Print), ISSN 2411-0280 (Online)
Sovremennye problemy distantsionnogo zondirovaniya Zemli iz kosmosa


Sovremennye problemy distantsionnogo zondirovaniya Zemli iz kosmosa, 2021, Vol. 18, No. 1, pp. 175-187

On the problem of river flow influence on the Doppler spectrum of reflected radar signal at small angles of incidence

M.S. Ryabkova 1 , V.Yu. Karaev 1 , M.A. Panfilova 1 , Yu.A. Titchenko 1 , E.M. Meshkov 1 , E.M. Zuikova 1 
1 Institute of Applied Physics RAS, Nizhny Novgorod, Russia
Accepted: 22.10.2020
DOI: 10.21046/2070-7401-2021-18-1-175-187
The Doppler spectrum of reflected microwave radar signal contains information about the movement of the scattering surface. For small angles of incidence, the Kirchhoff method is used to describe backscattering, and in the framework of a two-scale model of the scattering surface, the reflection occurs on sections of the wave profile oriented perpendicular to the incident radiation. The width and shift of the Doppler spectrum depend on the second order statistical moments of surface waves. The current leads to wave spectrum transformations and changes in statistical characteristics, which can be used to measure the speed and direction of the current. To test this hypothesis, a river was chosen where the direction and speed of the current can be easily measured. To define the spectrum formed on a constant current, the concepts of effective wind speed and effective wind direction were introduced. The dependence of the wave spectrum on the angle between the wind direction and the current direction was obtained. This allowed calculating the second-order statistical moments that are necessary for obtaining the Doppler spectrum. Dependences of the width and shift of the Doppler spectrum on the azimuthal angle and direction of sensing were calculated, an assessment of the influence of the current velocity on the Doppler spectrum was performed. It is shown that the existing azimuthal dependences of the backscattering cross-section, width and shift of the Doppler spectrum allow suggesting several approaches (algorithms) to the problem of determining the velocity and direction of the current. Thus, the analysis confirmed that the problem of determining the speed and direction of the current from the Doppler spectrum measured at small angles of incidence is potentially solvable.
Keywords: current velocity, current direction, width and shift of the Doppler spectrum, Kirchhoff approximation, two-scale model of scattering surface, small incidence angles, wind waves
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