French Frigate Shoals is a large open atoll located at 23.75N, 166.2W. Tern Island is the
largest island at FFS and was enlarged by the U.S. Navy just prior to World War II; numerous other small islets exist.
The total land mass is only 0.23 sq. km but the large reef and adjacent banks include 733 sq. km of coral habitat
less than 100 m in depth.
Mobile fauna 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 fish count and biomass maps where
benthic habitat classification has been completed. 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 & 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 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 02/20/02and 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 and Ronald Hoeke
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 3-letter designator for the island area, "FFS" in
this case followed by a five-digit tow number. The first two digits indicate the last two digits of the calendar
year, i.e., "02" is used for this cruise, which took place in 2002. The last three numbers indicate the consecutive
number of the tow for that island and year, and start on the next hundred for subsequent cruises in that year to the
same island. During TC0207 the consecutive numbers started at 026. Video tape labels, the navigation files (*.glo)
and paper log forms are all annotated with the tow name. 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,
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 geo-referenced to navigation files