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 Hi'ialakai HI0602, from February 26 to March 1, 2006.
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 degress 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 (less 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 new TOAD sled body used for the 2004 data collection is constructed from a shortened Phantom ROV body with a tail piece added for stability. It is equipped with a Deep Sea Power and Light Multi SeaCam 2060 color video camera, two 500 W DeepSea Power and Light Multi-SeaLite model 1050 underwater lights, a sonar altimeter to detect the height of the camera above the seafloor, a pair of parallel lasers to determine the size/scale of viewed objects, a compass to determine the sled heading and orientation, and a depth (pressure) sensor. The video signal from the sled is send via a coaxial conductor within a 200 m long and 127 mm diameter umbilical cable to a topside control unit. Name & address of person collecting data: Scott Ferguson NOAA IRC NMFS/PIFSC/CRED 1845 WASP Blvd., Building 176 Honolulu, HI 96818 Data Files: Video data were recorded to digital video cassette using a video recorder mounted in the control console. Video backups were made at the end of each day. Hypack Max (version 2.12A) hydrographic survey software was used to record GPS data, water depth, length of umbilical cable in the water, and camera sled information (height, heading, etc.), which provide ship and camera sled positions for the duration of individual tows. 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. For example, during HI0602 (NOAA Ship Hi'ialakai 2nd cruise in calendar year 2006) the consecutive tows at Ofu started at OFU06001. For subsequent cruises in the same year, the tow numbers will increment by 100, so the first tow on the next cruise to Ofu in 2006 will be tow number OFU06100. Video tape labels and paper log forms are also annotated with the tow name; if more than one tape is required for a tow, consecutive letters are added to the end of the tow number (OFU06100a, OFU06100b, OFU06100c...). Navigation files generated by Hypack Max follow the Hypack 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, followed by the extension .raw. For example, a file begun at 1935 on Dec. 10, 2004 (Julian date 345) aboard the Carolinian would be 2004CA3451935.raw. Time Correlation: All clocks were synchronized to UTC at the beginning of each day's operations. Two clocks were manually synchronized to GPS-derived times: the acquisition computer clock and the internal clock of the OSD-79 on-screen display unit. 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
Hypack Max includes a window for manual entry of the length of camera sled cable paid out, a utility to enter horizontal and vertical offsets between the GPS antenna and sheave over which the camera sled cable passes, and a built-in caternary function. Using these data, Hypack Max automatically estimates the camera sled's position. Analysis of tow data indicate that horizontal positional uncertainty associated with the location of the camera sled recorded in Hypack is plus or minus 13 m.
After a tow was completed the video tape data was reviewed by spot-checking the tape to verify that data were recorded. Backups were made at the end of each day.Raw data files recorded time, horizontal position, and ship's heading information, and were copied from the acquisition computer to the data archive. Tow-specific metadata were recorded in the data archive in the same location as the raw data, in a spreadsheet that was then referred to in creating metadata records of each island where data were collected during the cruise. Raw data files were exported as comma-delimited text files which were then imported into ArcGIS 9.x and saved as shapefiles. Video still frames spaced 20 m apart were analyzed. For the analysis, five circles approximately 0.5 mm in diameter and spaced equidistantly were drawn in a horizontal line on a piece of clear plastic sheet taped to a computer monitor screen. For every still frame, within the center of each circle the substrate (rock, sand, rubble, etc.) living cover (seagrass, scleractinian [stony] coral, macroalgae, etc) and growth morphology of coral colonies (branching, encrusting, etc) were identified. Classification information was recorded on a spreadsheet for each camera tow according to the codes and include the type of substrate, living cover (if any), and dominant variation in relief seen in the image. The substrate within the first circle is recorded under the column labeled S1 while the living cover and coral growth morphology within the same circle are recorded under the columns labeled C1 and CM1. Data from the second circle are recorded under columns S2, C2, CM2 and so on. Spreadsheets with benthic classification data from video analysis are attributed to the appropriate tow track shapefile and along-track location. Color coding is then applied to highlight features of interest, such as the percentage of the seafloor covered by living corals or other benthic fauna found at each location or different types of substrate.
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 the UTC date and time, latitude, longitude, altitude, vehicle depth, and water depth. 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. OFU06001-010 (10 files)
