Simultaneous Doppler Spectra Measurements of the Backscattered Signal at Low Incidence Angles Using Microwave Radars and an Ultrasonic Underwater Wave Gauge

This paper presents the results of simultaneous Doppler spectra measurements by microwave radars and an underwater sonar during the expedition to a marine platform in the Black Sea near the Katsiveli settlement in October 2018. The measurements were carried out at small angles of incidence, so the scattering mechanism remains mostly quasi-specular and is well described by tangent plane approximation (Kirchhoff approximation). The Doppler spectrum model is the same for microwave radiation and an ultrasound. The modeled Doppler spectrum and a measured one are in agreement with each other. The variance of the vertical component of the orbital velocity and the total slope variance were retrieved from radar measurements and compared with the Doppler sonar measurements. The results are in good agreement. The string wave gauge and wind measurements are used in the experiments to control the effectiveness of algorithms used.