Radar-acoustic hybrid detection system for rapid detection and classification of submerged stationary articles

摘要

A region of water is insonifed with a series of pulses. A synthetic apeture radar (SAR) is flown about the region and images the water surface above the sonified area. The radar has a carrier frequency (F_r) the acoustic source has a nominal carrier frequency of F_a. This acoustic frequency F_a is selected such that the acoustic wavelength is nearly, or exactly, half the wavelength of the radar carrier F_r where modified by the Sine of the incident of angle. Also practical are those acoustic wavelengths that are integer multiples of the wavelength that is half the radar wavelength. This arrangement will result in the Bragg condition in portions of the radar image of the water surface. The pulse repetition frequency (PRF) of the radar and the acoustic sources are equal (or can be such that the acoustic PRF is an integer multiple of the radar PRF), and locked in phase together by a radio frequency link between the SAR and the sonar transmitter. The sonar signal is repeatable and coherent with the radar signal. As a result, the SAR image can be processed, eliminating random surface wave motion, to detect and classify the structures that underlie the water surface.