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Feasibility of Airborne Laser Devices for Pelagic Fish Surveys
The proposed work will employ an existing shore-mounted laser device which will attempt to detect moored artificial targets. The experiment is intended to test the ability of the device to detect and discriminate between yellowfin tuna and swordfish models deployed at different depths and orientations. Four artificial targets designed to represent the sizes of tunas and swordfish commonly caught by Hawaii longliners will be constructed. Research will focus on whether these species can be distinguished from one another in lidar generated images, and what the effect of other factors - depth, water clarity, surface state - might have on such discrimination. The results will show whether it might be feasible to develop lasers for use in pelagic fisheries research. The proposed research will provide target strengths of targets at different depths, and generate data necessary to design a practical laser device.
A final project report published as part of the
SOEST-JIMAR publication series:
Sibert, Program Manager
Dr. Christian Schoen
Detection Limit Technology, Inc.
531 Cooke Street
Honolulu, Hawaii 96813
Phone (808) 593-8677
FAX (808) 593-1735
The following is an excerpt from the project's final report published in 1996 as a UH-SOEST publication, entitled Feasibility of Dual Mode Lidar for Pelagic Fish Surveys, C. Schoen and J. Sibert, SOEST Pub. 96-02, JIMAR 96-301
The purpose of this final report is three-fold: first, to review the results of tests conducted by Science Application International Corporation (SAIC); second, to show how these results might be applied to fisheries applications; and finally, to describe the best direction for the technology in an R&D and commercial market. A brief summary of these points follows.
The SAIC lidar field test conducted at the NRaD TRANSDEC tank in San Diego resulted in fish identification at a depth of 76 feet in turbid water with K = 0.147-m (this corresponds to 205-foot depths in blue water where K = 0.055-m ). The test also distinguished between tuna and swordfish, but not between like species such as bluefin and yellowfin tuna. Fish detection depth exceeded 109 feet (294 feet for blue water) and data extrapolation showed it to be possible to 450 feet (in blue water). Analysis of current fish behavior data shows that for detection and identification of yellowfin tuna, for instance, the detection system must exceed 150 feet during daylight hours and average 300 feet for a likely probability of detection. These results indicate that lidar systems may have some application in pelagic fisheries research, but that tools for routine areal surveys will require further development.
Comparison of lidar vs. passive systems such as hyperspectral imaging yields interesting results. Lidar enables detection to depths approximately twice as deep as are possible with hyperspectral systems (passive systems will not detect deeper than 150 feet in blue water), has comparable resolution, has better than an order of magnitude greater search volume per exposure due to its natural spread with depth, and comparable power and size requirements. Its most probable commercial application would be for deployment on fish-spotting helicopters flying from ocean fleets.
The hardware subcomponents used in the field test were 3-5 years old. Newer technology is less expensive and more sensitive. A hardened prototype capable for helicopter deployment and test could be built with confidence in less than one year for under $200,000. Production systems could be built for 60% of this price. These systems could be assembled with an open framework to allow for further RED development. In particular, the most interesting application would be to combine hyperspectral and lidar. Using the fluorescence signatures of fish, there is strong evidence that "like species" (yellow and bluefin tuna) fish may be differentiated at depths greater than 300 feet by their dissimilar colors (fluorescence).
The systems are feasible for commercial development and sale if the price could be held under $300,000. These systems would also allow for further development as a tool for the R&D developer at the university for open ocean studies. With the open architecture, small changes to the system could make it a powerful ocean chemistry analysis system. The dual use of the system is readily apparent.
This page updated August 15, 2006