CRED Optical Validation Data collected on Galvez Bank, Territory of Guam; Saipan Island, and Thirty Five Fathom Bank,Commonwealth of Northern Mariana Islands, USA, in 2010 to support Benthic Habitat Mapping

Saipan, the largest of the Northern Mariana Islands, has a land area of 122 km2 and is approximately 20 km long and 9 km wide. The island consists of a volcanic core enveloped by younger coral reef-derived limestone formations. The island has the most diverse types of coral reefs and associated habitats in the Commonwealth. A fringing and barrier reef system protects the majority of the beaches along the western and coastal plains. The western side of the island is the most populated and the coral reefs along these areas are negatively affected by human activity. Continuing sediment and nutrient pollution combined with sporadic stressors such as outbreaks of crown-of-thorns starfish (COTS) (Acanthaster planci) and temperature-induced bleaching affect many of Saipan's western and southeastern reefs. Furthermore, coral habitat on two large offshore banks (18 km x 22 km) in water depths between 30 m and 60 m on the western side of Saipan are negatively affected by the anchorage of commercial and naval vessels. It is these two banks that were the subject of the study reported here. Optical validation data were collected the Tethered Optical Assessment Device (TOAD), a sled equipped with underwater video camera and lights. These data are used to provide optical information regarding benthic and fish communities. They have also been used to provide ground-truth validation for benthic habitat maps based on multibeam echosounder surveys, but these are presented in a separate product, available on the PIBHMC website. From December 3-16 2004, CRED personnel and contractors conducted towed video surveys in the Saipan Anchorage, CNMI aboard the 62-ft-long Carolinian, one of the vessels owned and operated by Saipan Crewboats, Inc., and regularly chartered by the U.S. Navy. Operations were conducted during daylight hours, with video data collected using a new underwater camera sled, designed and fabricated by Deep Ocean Engineering, Inc. (DOE). The camera sled was attached via umbilical cable to a control console located on board the Carolinian. The camera sled was deployed from the port or starboard side of the Carolinian depending on the prevailing current and wind conditions. A video display monitor mounted on the control console was used to monitor the position of the sled relative to the seafloor. Instructions to raise/lower the sled were relayed to CRED personnel on deck to maintain close proximity of the sled to the seafloor and to avoid collisions with seafloor highs. Equipment Description: The TOAD sled body is constructed from a shortened Phantom ROV body with a tail piece added for stability. It is equipped with a Deep Sea Power & Light Multi SeaCam 2060 color video camera, two 500 W DeepSea Power & 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. The video data are recorded to digital video cassette using a video recorder mounted in the control console. 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.

Data Files: Video data were recorded on video tape recorders and the position of the camera sled was recorded using a GPS signal and different software packages, as described above.

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 SB0401 the consecutive numbers started at SAI04001. Video tape labels and paper log forms are annotated with the tow name. Data recorded using Hypack software 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, and the extension "raw." For example, a file collected on Dec. 10, 2004 (Julian date 345) aboard the Carolinian starting at time 1935 would be 2004CA3451935.raw. Time Correlation: All times are based on UTC. Clocks were manually synchronized prior to starting data collection each day of operations.

Resource Description: Digital video imagery that is geo-referenced to navigation files.