Sea Technology

OCT 2013

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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cameras can provide information about the absolute position, size and speed of targets, which is crucial for classifying targets and characterizing their interaction with turbines. The strobe illumination provides crisp, synchronized images despite the high target velocities and low ambient light levels. While the use of full-spectrum, artifcial light may cause behavioral changes in marine animals, the acoustic camera can be used to characterize these effects and potentially trigger the optical cameras when targets move into the system's feld of view. a feld evaluation was undertaken. Tow tests of the camera system mounted to the imaging frame were performed August 13 to 16, 2012 in northern Admiralty Inlet. All tows were conducted by the University of Washington Applied Physics Laboratory's RV Jack Robertson. Testing occurred during periods of falling tidal currents on greater ebb and food to characterize performance during periods when biological focculent concentrations would likely be highest due to mobilization from the bed by intense tidal currents. During each tow, target images of fsh, eye charts Functional Range in Field and calibration squares were One of the key uncertainpositioned on the imaging frame ties of integrating the imaging at a distance of either 2.5, 3.5 system with a tidal turbine is or 4.5 meters from the cameras. the functional range for deAll tests were performed with tection (i.e., distinguishing a the targets at a depth of approxitarget from background), dismately 50 meters to match the crimination (i.e., distinguishing target turbine hub depth. Images between marine animals and were captured in blocks of 50 debris) and classifcation (i.e., pairs at rates of 5 to 10 frames taxonomic grouping) of marine per second under the following animals by the stereographic conditions: camera-target sepacameras. This functional range ration of 2.5 , 3.5 and 4.5 meestablishes where the imaging ters; relative water velocity of system should be deployed relanear-zero (free-drift) and about 2 tive to the turbine rotor. Another meters per second (tow); and opquestion is the relative effectivetical camera digital gain settings ness of the acoustical and optiof 0, 10 and 20 decibels. Imaging frame for camera testing. cal camera systems. The main The images captured in feld variables that could affect imagtrials were assessed both qualitaing system effectiveness are the tively and quantitatively. Qualitarget range, relative velocity of the target, attenuation of tatively, the targets were visible on all platforms, although, artifcial lighting by focculent, the cameras' digital gain and as expected, image clarity degrades with distance due to a behavioral effects of the artifcial lighting. combination of light attenuation, backscatter and increasing Given the diffculty of accurately simulating focculent pixel size. Higher digital gain is helpful for detecting targets and high relative velocities of targets in a laboratory setting, at greater distances but can obscure targets that are close 16 st / October 2013 www.sea-technology.com

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