Enhanced extended range underwater imaging via structured illumination

In this article, the utility of structured illumination in order to enhance the contrast and subsequent range capability of an underwater imaging system is explored. The proposed method consists of transmitting a short pulse of light in a grid like pattern that consists of multiple, narrow, delta-function like beams. The grid pattern can be arranged in either a one-dimensional line or an area as a two-dimensional pattern. Scanning the pattern in time results in the sequential illumination of the entire scene. The receiving system architecture imposes the exact same, grid-like pattern sensitivity on the reflected light with a simple subsequent superposition of the time-sequenced images. The system can be viewed as a parallel implementation of a Laser Line Scan System where multiple beams are projected and received instead of a single one. The performance enhancement over more conventional systems that project either a sheet or an area of light is compared for a challenging underwater environment via computer simulations. The resulting images are analyzed as a function of the spacing between the projected light beams to characterize contrast and resolution. The results indicate that reasonable gains are obtainable for close spacing between the beams while quite significant gains are predicted for larger ones. Structured illumination systems can therefore collect images more rapidly than systems that scan a single beam; however with concomitant trade-offs in contrast and resolution.