METHOD OF DETECTING UNDERWATER OBJECTS Russian patent published in 2013 - IPC G01S5/02 G01S15/66 

FIELD: radio engineering, communication.

SUBSTANCE: an underwater or surface ship is placed at a certain point on the ocean, said ship radiating a sound wave with power I_rad=5*10⁵ W/m², at frequency of f_sound=10 kHz. That radiation propagates in all directions and generates sound pressure of the order p₁=17 W/m² at a distance L_det=30 km from the ship. After reflection from an underwater object with reflection coefficient k_ref=10^-2 and owing to water compressibility, the sound wave creates a diffraction grating which corresponds to a cylindrical sound wave. High-frequency generators with power P_gen=500 MW, operating at frequency f_radio=10⁸ Hz, mounted on one group of airplanes, irradiate separate areas of the water surface with a narrow beam of radio waves. First-order reflection from the diffraction grating formed by the cylindrical sound wave results in reflected waves. Receivers propagating in the narrow radiation beam, mounted on another group of airplanes, with sensitivity of 3*10^-21 W, with antenna area S_ant=700 m², detect power of the received radiation of about 10^-19 W. Owing to that scattering occurs on the moving grating, the electromagnetic wave reflected therefrom is Doppler shifted by a value δf=100 Hz. Coordinates of the underwater object are determined from the detected diffraction radiation.

EFFECT: longer range of detecting underwater objects.

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