CRED Optical Validation Data at French Frigate Shoals, 2004, to Support Benthic Habitat Mapping

French Frigate Shoals is a large open atoll located at 23.75N, 166.2W. Tern Island is the largest island at FFS and was enlarged by the U.S. Navy just prior to World War II; numerous other small islets exist. The total land mass is only 0.23sq. km but the large reef and adjacent banks include 733 sq. km of coral habitat less than 100 m in depth. Optical validation data were collected using the Tethered Optical Assessment Device (TOAD), a sled equipped with underwater video camera and lights. These data are used to provide ground-truth validation that for benthic habitat maps based on multibeam echosounder surveys. Camera sled deployments were conducted at night, usually between 1800 and midnight. Each tow was usually limited to 20 minutes of bottom time at a given location in order to allow for more tows to be conducted in a given work area and thus increase the spatial distribution of the observations. The camera sled was deployed from lower arm of the starboard J-frame on the NOAA Ship Hi'ialakai. At each station the ship was positioned with the wind on the starboard side and drifted downwind; occasional light turns were applied to the ship's screws if necessary to reduce the ship's motion. The TOAD was lowered slowly to the bottom by the deck crew. The operator monitored a live video feed from the camera and began recording data on two video tape recorders. When the camera reached bottom the deck crew was notified by radio to stop lowering. The operator continued to monitor the vehicle and provided commands to raise or lower it to keep the camera just above the bottom. Equipment Description: The TOAD was deployed from the lower arm of the vessel's J-frame. The TOAD is a camera sled based on the Guildline MiniBat model 8820 tow body. The frame has been extensively modified from its original configuration and was configured with a single ROS model 54-00100-13 color underwater video camera and two 500 W DeepSea Power & Light model 710-0400601 underwater lights mounted on the original sled frame. The MiniBat pressure sensor and wing controller was also mounted on the frame but no wings were installed. Cable between the sled and the surface consisted of an underwater electrical cable (cable 1, blue in color) with a separate load-bearing line to support the sled frame. The electrical cable was clipped to the line at regular intervals upon deployment and removed upon recovery. The load-bearing line was led to the starboard capstan on the aft deck. All TOAD surface components were located in the Dry Lab in an equipment rack on the after bulkhead. After operations began we learned that the sled's pressure sensor was not working. Name & address of person collecting data: John Rooney NOAA IRC NMFS/PIFSC/CRED 1845 WASP Blvd., Building 176 Honolulu, HI 96818 Data Files: Video data were recorded on two video tape recorders. The position of the camera sled was recorded using Guildline MiniBat In-Tow data acquisition software. File naming convention: Each tow is given a name consisting of a 3-letter designator for the island area followed by a two-digit year and three-digit tow number. For example, during HI0401 the first tow was called FFS04001. Video tape labels, the navigation files (*.glo) and paper log forms are all annotated with the tow name. If the navigation file is edited during processing the file name has a suffix "a" added. For example, one of the navigation data files is named "FFS04001a.glo". Metadata were extracted from the navigation data and recorded to a file with the same name as the navigation file except that a file type of ".met" was appended; for example, "FFS04001a.glo.met" Time Correlation: All times are based on UTC. Two clocks were set manually synchronized prior to starting data collection; the clock in the video character generator that was used to annotate the video tape and the TOAD data acquisition computer clock was used to annotate the navigation (*.glo) files. These clocks were set to UTC at the beginning of each evening's operations and then compared to one another prior to (and during) each tow. There were problems maintaining synchronization of the TOAD computer clock during this cruise. See the problems section for a description. (Problems with data could be described here.)

Resource Description: Digital video images that are geo-referenced to navigation files.