Alamagan is located approximately in the middle of the Mariana Archipelago, with a land area of 11.2 square km and
features an active volcano. Feral pigs, goats, and cattle are causing extensive damage to terrestrial ecosystems, and
these terrestrial effects are likely linked to the marine environment through runoff and sedimentation. The reef
communities at Alamagan are noticeably less developed than those observed at Guguan Island, which lies only 26 km to
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 & 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 an underwater electrical cable (cable 2, black in color) with an internal kevlar strength member
to support the sled frame. The cable was led from the camera sled over a 22-inch diameter sheave hung from the
J-frame, and from there around a gypsy head mounted on the alternate CTD winch, amidships on the vessel's port side.
All TOAD surface components were located in the Dry Lab in an equipment rack on the after bulkhead.
Name & address of person collecting data:
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 3-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 Alamagen Island the designator is
"ALA." During OES0307 (NOAA Ship Oscar Elton Sette's 7th cruise in calendar year 2003) the consecutive numbers started
at ALA03000. Video tape labels, the navigation files (*.glo) and paper log forms are annotated with the tow name and
number, e.g., ALA03002. If the navigation file is edited during processing the file name has a suffix 'a' added. For
example, for a navigation data file named "ALA03002a.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, 'ALA03002a.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.