Optical validation data were collected using the Tethered Optical Assessment Device (TOAD), a sled equipped with underwater video camera, still 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 TOAD was deployed from a pot hauler mounted on the starboard side of the fantail on NOAA Ship Townsend Cromwell. It was lowered slowly to the bottom by the deck crew with the use of a capstan. The TOAD 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 TOAD was a MiniBat 8820 unit manufactured by Guideline, and was towed by the ship at 1-2 knots while remotely guided from the ship using adjustable wing controls to keep the unit close to the underwater substrate. The TOAD was damaged during the cruise on 02/20/02, and subsequent tows were conducted as drift deployments. 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 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 is a camera sled based on the Guildline MiniBat model 8820 tow body. The frame was configured with a single Sony DCR-PC110 Digital Video Camera in a modified Gates underwater housing, a Canon Power Shot G1 Still Camera (modified by CRED engineers) in an Ikelite housing rated to 60 m slaved to an Ikelite DS-50 strobe, and two 500 W DeepSea Power and Light model 710-0400601 underwater lights. The Canon camera had a custom-built timer that enabled the user to select a constant time interval (ranging from approximately 5 seconds to 2 minutes) between photographs. An interval of 30 seconds was typically selected, which, assuming a mean velocity for the camera sled of of 1.5 knots, resulted in one photograph approximately every 20 m. Photograph resolution is 2048 x 1536 pixels and file names are assigned sequentially and automatically by the camera, starting at 100-0000 after the camera's memory is cleared. The MiniBAT pressure sensor and wing controller were also mounted on the frame but the pressure sensor was not operational. After damage to the TOAD on 02/20/02 and the sled's wings were not installed thereafter. The cable between the sled and the surface was an underwater load-bearing electrical cable. The TOAD computers were located in the Electronics Lab of the Townsend Cromwell. The electronics box containing the power switches was secured to the ship's fantail, and all other TOAD surface components were secured in the ship's wet lab.
Name & address of person collecting data: Joyce Miller & Ron Hoeke NOAA IRC NMFS/PIFSC/CRED 1845 WASP Blvd., Building 176 Honolulu, HI 96818
Data Files: Video data were recorded on two video tape recorders. Still photos were recorded on digital camera and downloaded to the TOAD computer after the tow. 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 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 TC0201 (NOAA Ship Townsend Cromwell's 1st cruise in calendar year 2002) the consecutive tows at Ofu started at OFU02001. For following cruises, the tow numbers will increment by 100, so the first tow on the next cruise to Ofu in 2002 will be tow number OFU02100. Video tape labels, the navigation files (*.glo) and paper log forms are annotated with the tow name and number, e.g., OFU02001. If the navigation file is edited during processing the file name has a suffix 'a' added. For example, for a navigation data file named OFU02001a.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, 'OFU02001a.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.
Resource Description: Digital video images that are geo-referenced to navigation files.
Still photographs, collected every 30 seconds and averaging approximately 20m horizontal spacing between them, were analyzed using a point count method. 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. 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 described in the file BenthicHabitatClassificationCodes_Metadata.xls. 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.
List of navigation files: The following are shape files compatible with ESRI GIS software. Each item in the list a set of files used by ArcView/ArcGIS to display and access the associated data. Each item in the list has associated .shp, .dbf, and .shx files. They may additionally have .prj, .sbn, and .sbx files if the project's projection requires it. List of Navigation files: ofu02001a.glo ofu02002b.glo ofu02003a.glo