Laser projection photogrammetry and video system for quantification and mensuration

This paper describes a novel photogrammetric laser/video system suited for a variety of underwater quantification and mensuration applications. The system is comprised of a purpose-built frame to which are mounted a roll/pitch motion reference sensor, video camera, and three microlasers. Orientation of the three lasers provides for optical triangulation, which allows computation of range at specific location in the field-of-view. From this information and that derived from the motion sensor, the spatially variant magnification can be determined over the entire field-of-view using a simple algorithm. A variety of parameters can then be estimated using image-processing techniques, including perspective overlays, range to a point or location, scale in any region of the image, and area measurements. Specialized image processing algorithms can be added to provide object recognition, tracking, and other information. The specification of each component (i.e., laser wavelength and power, camera sensitivity and resolution, and dynamic range) and mounting geometry are determine based on the specific application and needed accuracy. The system can be mounted for use on any subsea vehicle or platform and provides a low cost automated approach for obtaining quantitative information from standard undersea video. Currently, the application software allows for post-processing of the video information but could be modified to process the video information real-time. The first application of this system will be used by Washington State Department of Fish and Wildlife researchers onboard DSV DELTA. The system may prove valuable for estimating the abundance of commercially and recreationally exploited groundfish species within a transect area conducted off the coast of Washington State. This non-intrusive, direct observation technique affords a means to estimate the density of certain benthic fish species in high relief areas that currently cannot be sampled using routine trawl survey techniques. The system may prove useful in other scientific and industrial applications. Laboratory and field data are provided to demonstrate system output and performance, as well as an error analysis summary. Future hardware and software enhancements to provide a means of geocoding or georeferencing the images that would support orthorectification and mosaicking of the transect images are described.