ABSTRACT
Combined spatial and temporal processing techniques are presented to enhance optical ranging in underwater environments. The performance of underwater light detection and ranging (lidar) is often limited by scattering. Previous work has demonstrated that both hybrid lidar-radar, which temporally modulates the amplitude of light, and optical spatial coherence filtering, which spatially modulates the phase of light, have independently reduced the effects of scattering, improving performance. The combined performance of the processing methods is investigated, and experimental results demonstrate that the combined filtering improves the performance of underwater lidar systems beyond what either method provides independently.
ABSTRACT
An optical vortex is used to enhance the ranging accuracy of an underwater pulsed laser ranging system. An experiment is conducted whereby an underwater object is illuminated by a pulsed Gaussian beam, and both the object-reflected and scattered light are passed through a diffractive spiral phase plate prior to being imaged at the receiver. An optical vortex is formed from the spatially coherent non-scattered component of the return, providing an effective way to discriminate the desired objected reflected light from the spatially incoherent scatter. Experimental results show that the optical vortex permits a spatially coherent ballistic target return to be more easily discriminated from spatially incoherent forward scattered light up to eight attenuation lengths. The results suggest new optical sensing techniques for underwater imaging or lidar.
