Experimental evidence of signal-optical noise interferencelike effect in underwater amplitude-modulated laser optical radar systems.

We report experimental evidence that in an amplitude-modulated laser optical radar system for underwater 3D imaging the observed contrast oscillations as a function of the modulation frequency originate from an interferencelike effect between target signal (V) over cap (T) and water backscattered radiation (V) over cap (W). The demonstration relies on the ability to perform a direct measurement of (V) over cap (W) in a 25 m long test tank. The proposed data processing method enables one to remove the contribution of water backscattering from the detected signal and drastically reduce signal fluctuations due to the medium. Experiments also confirm the possibility to improve the signal to optical noise ratio and contrast by increasing the modulation frequency. (C) 2008 Optical Society of America