Optical validation data were collected using a Tethered Optical Assessment Device (TOAD), an underwater sled equipped with an underwater digital video camera and lights. Data were collected in American Samoa, around the islands of Ofu and Olosega to support Benthic Habitat Mapping efforts during NOAA Ship Oscar Elton Sette cruise OES0402, from February 4-14, 2004.
These data provide optical observations that will be correlated with bathymetry and acoustic backscatter imagery to develop a benthic habitat map of Ofu and Olosega. Refer to supplemental information for description of instrument and survey.
Ofu and Olosega Islands are part of the Manu'a Island group in American Samoa, situated approximately 100 km northeast of Tutuila and 20km west of Ta'u. Centered at 14.17 degrees S, 169.65 degrees W, the twin islands have very little human settlement. Ofu and Olosega are steep, volcanic high islands that lie only 75 m apart and are connected by a bridge and road built across the shallow reef flat. Shallow multibeam mapping was conducted in 2004 and revealed approximately 60 km2 of previously uncharted bank top (greater than 300 m) that extends 0.2 to 2 km from shore and then drops abruptly to oceanic depths. An underwater portion of the National Park of American Samoa, which has exceptionally prolific coral growth, is located on the south shore of Ofu Island. 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 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 the port J-frame mounted amidships on the NOAA Ship Oscar Elton Sette. At each station the ship was positioned with the wind on the port 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 using a capstan. The operator monitored a live video feed from the camera and began recording data on a video tape recorder. 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 port side 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 and 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. 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: Joyce Miller NOAA IRC NMFS/PIFSC/CRED 1845 WASP Blvd., Building 176 Honolulu, HI 96818 Data Files: Video data were recorded on a video tape recorder. The position of the camera sled was recorded in WGS-84 using Guildline MiniBat In-Tow data acquisition software and a data feed from a shipboard Northstar Chartplotter. File naming convention: Each tow is given a name consisting of a three-letter designator for the island area, followed by a two-digit year and a three-digit tow number, which increments by one for each new tow around that island. During OES0402 (NOAA Ship Oscar Elton Sette's 2nd cruise in calendar year 2004) the consecutive tows at Tutuila started at TUT04000. For following cruises, the tow numbers will increment by 100, so the first tow on the next cruise to Tutuila in 2004 will be tow number TUT04100. Video tape labels, the navigation files (*.glo) and paper log forms are annotated with the tow name and number, e.g., TUT04012. If the navigation file is edited during processing the file name has a suffix 'a' added. For example, for a navigation data file named TUT04012a.glo, the 'a' would indicate that 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, 'TUT04012a.glo.met. Time Correlation: All times are based on UTC. Two clocks were manually synchronized prior to starting data collection; the clock in the video character generator that was used to annotate the video tape, and the clock in the TOAD data acquisition computer. 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.
ground condition
Please acknowledge the NOAA Coral Reef Ecosystem Division, Pacific Islands Fisheries Science Center as the source of this information.
NOAA IRC
NMFS/PIFSC/CRED
1845 WASP Blvd., Building 176
e-mail preferred
Pacific Island Benthic Habitat Mapping Center, Coral Reef Ecosystem Division (CRED), Pacific Islands Fisheries Science Center (PIFSC), NOAA
Unspecified
Complete
The horizontal position accuracy for the camera sled position is estimated at plus or minus 100 meters. There are three primary sources of this error. The ship's positioning is based on GPS SPS, often called standalone or non-differential GPS positioning. SPS has a measured accuracy of under 5 meters. The position of the GPS antenna is used; no attempt is made to translocate this position to that of the tow block from which the camera is deployed. The difference between the tow block and the antenna is about 14 meters. The largest source of error is uncertainty associated with the sled's position relative to the tow block.
After a tow was completed the video tape data was reviewed by spot-checking the master to verify that data were recorded. A backup copy of the tape is made at that time as well. Navigation data were copied from the acquisition computer to the data archive. A metadata extractor (gloFilter.py, version 3/17/06) was run to summarize the navigation data and test for errors. If errors were detected in a record, a copy of the data file was made (the 'a.glo' file mentioned above), that record was automatically flagged as invalid, and corrections were made if possible. This file's header was updated to document what type of processing occurred. A metadata file was recorded in the data archive in the same location as the navigation data. Processed navigation data were then imported to ArcGIS 9.x.
These data are not to be used for navigational purposes. NOAA makes no warranty regarding these data, expressed or implied, nor does the fact of distribution constitute such a warranty. NOAA cannot assume liability for any damages caused by any errors or omissions in these data, nor as a result of the failure of these data to function on a particular system.
Each comma-delimited record contains information on the UTC date and time, latitude, longitude, velocity north and east of the ship, water depth of the seafloor below the transducer (to find the total depth from the water surface to the seafloor add 5 m to these values to account for the depth of the tranducer) layback, and wing angle. List of navigation files: The shapefiles showing camera sled tracks listed below consist of a collection of files with the names listed below, followed by these extensions: .dbf, .shp, .shx, and .prj. All file types are necessary to properly displaying the source data. List of Navigation files: ofu04002.glo ofu04003.glo ofu04011a.glo ofu04012.glo ofu04013.glo ofu04014.glo ofu04017.glo ofu04018.glo ofu04019.glo ofu04024.glo ofu04025.glo ofu04026.glo ofu04027a.glo
