Niihau, the oldest of the Main Hawaiian islands along with Kauai, is also the second smallest, at 182 sq. km, and the
smallest inhabited Hawaiian island. Located at 21 degrees 55'N, 160 degrees 10'W, it is the furthest from the magma-producing hotspot
which formed the island chain. The island lies only 21 km west-northwest of Kauai, but the islands are separated by a
channel 1097 m deep. Niihau reaches a height of 390 m, has 72 km of shoreline, and an estimated reef area of 60 sq. km
(Hawaii Coral Reef Network). The island is privately owned and was inhabited by 230 people in 1990. Like all of the
Main Hawaiian islands, it is considered a high island and contributes significant nutrient and sediment runoff to
coastal waters. Niihau has no designated marine protected areas.
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 that 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 lower arm of the starboard J-frame on the NOAA Ship Hi'ialakai. 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 TOAD was lowered slowly to the bottom by the deck crew. The
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 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 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. An ORE Offshore model 4330B
Multibeacon was attached to the sled to provide a response to acoustic interrogations sent by the Hi'ialakai's Model
4410D-01 Trackpoint II Plus Ultrashort Baseline acoustic tracking system. 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:
1845 WASP Blvd., Building 176
Honolulu, HI 96818
Data Files: Video data were recorded on two video tape recorders. The position of the camera sled was recorded using
Hypack Max version 02.012a survey software.
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 three-digit tow number. During HI0505 the consecutive numbers started at OAH05000. Video tape labels and paper log forms are
annotated with the tow name. Data files recorded in Hypack software followed their 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. For example, a file collected on July 18, 2005 (Julian date 199) aboard the Hi'ialakai starting at time 1935
would be 2005HI1991935.
Time Correlation: All times are based on UTC. Four clocks were manually synchronized prior to starting data collection;
the clock in the video character generator that was used to annotate the video tape, in one of the video cassette
recorders, in the Trackpoint II system, and in the computer running the Hypack Max software. 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.