CRED Optical Validation Data at Oahu in the Main Hawaiian Islands, 2005, to Support Benthic Habitat Mapping

Oahu, which consists of the eroded remains of two connected volcanoes, covers 1554 sq. km and reaches a height of 1227 m at Mount Kaala. Located at 21 degrees 30'N, 157 degrees 55'W , has 180 km of shoreline and an estimated reef area of 504 sq. km (Hawaii Coral Reef Network). Oahu, by far the most densely populated of the island, had 836,231 residents in 1990 (three quarters of the state's population), mainly concentrated on the south shore. Like all of the Main Hawaiian Islands, it is considered a high island and contributes significant nutrient and sediment runoff to coastal waters. The island's dense population and commercial infrastructure increases the amount of sediment and nutrient runoff, and contributes to the runoff of polluting chemicals. Oahu has 0.82 sq. km (82 hectares) of marine protected areas. 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. The duration of each tow varied, but averaged about 40 minutes of bottom time at a given location. 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 equipped with an ROS model 54-00100-13 color underwater video camera as the primary data collection instrument. The ROS camera was mounted to point at approximately a 45 degree angle toward the seafloor. A Deep Sea Power and Light model 2050 MultiSeaCam low-light color video camera was also mounted on the sled and aimed straight ahead. The signal from this camera was fed to a second video monitor to provide warning of underwater obstructions the sled might be headed for. Illumination was provided by two 500 W DeepSea Power & Light Multi-SeaLite model 1050 underwater lights mounted on the original sled frame. The lights were located near the base and each side of the sled to provide the maximum possible horizontal distance from the ROS camera. An ORE Offshore model 4330B Multibeacon was attached to the sled to provide a response to acoustic interrogations sent by the Hi'ialakai's Model 4410D-01 Trackpoint II Plus Ultrashort Baseline acoustic tracking system. Cable between the sled and the surface consisted of a 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. 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 Hypack Max version 02.012a survey software. File naming convention: Each tow is given a name consisting of a 3-letter designator for the island area followed by a tow number. During HI0505 the consecutive numbers started at OAH05000. Video tape labels and paper log forms are annotated with the tow name. Data files recorded in Hypack software followed their CHS filename format consisting of the year, the first two letters of the platform name, the Julian date, and the hour and minute in which the file was started. For example, a file collected on July 18, 2005 (Julian date 199) aboard the Hi'ialakai starting at time 1935 would be 2005HI1991935. Time Correlation: All times are based on UTC. Four clocks were manually synchronized prior to starting data collection; the clock in the video character generator that was used to annotate the video tape, in one of the video cassette recorders, in the Trackpoint II system, and in the computer running the Hypack Max software. These clocks were set to UTC at the beginning of each evening's operations.

Resource Description: Digital video imagery that is geo-referenced to navigation files.