Processing techniques for multi-spectral laser line scan images

Conventional underwater laser line scan systems have demonstrated their ability to provide clear, high resolution visual images of submerged objects by measuring the optical energy reflected by a large number of closely spaced points on the target. Operational experience has demonstrated, however, that bulk energy is only one characteristic of the reflected light field from which valuable information regarding the target can be extracted. In 1993 Raytheon Company designed and built a unique underwater laser line scan sensor that has four separate, independent optical receivers rather than the single receiver that is present in all previous laser line scan systems. The optical elements of these receivers are designed such that all four receivers view the same point on the target at all times. They all therefore simultaneously receive their optical signal from a single target element. By fitting the individual receivers with various filters and optical analyzers it is possible to measure a variety of different aspects of the light field that is reflected by the target. This allows a much more complete investigation of the interaction between the target and the incident laser illumination and understanding this interaction can lead to a much better understanding of the identity, condition, and characteristics of the target. This paper presents and discusses an example of how the multi-channel laser line scan sensor can be configured and used to measure the multi-spectral fluorescence signatures of underwater targets and how these fluorescence maps can be processed to extract useful information regarding the targets.