The area between the islands of Maui County is a heavily transited and utilized waterway. Vessels engaged in inter-island commerce, recreational and commercial fishing, and a host of recreational whale watchers, sailors, divers, surfers, beachgoers and others take advantage of them every day, making them an important economic, and somewhat stressed, environmental resource. The area features a wide shelf top with depths ranging from 50 - 80 m that is relatively sheltered from large swell by the surrounding islands, but is often exposed to strong currents. During the last glacial maximum ca. 21,000 years ago, sea level was estimated to range from 130-135 m lower than it is today, creating a single large island called "Maui Nui". The insular shelf between the modern Maui County islands was above sea level for thousands of years, exposing this limestone structure to karst processes. Subsequent sea level rise and Holocene reef growth accentuated the karst topography resulting in the solution basins and rims, and reef pinnacles seen in the modern bathymetry. The combination of wave sheltering and high flow regimes led to the development of the largest known black coral beds in Hawaii, and well-developed hermatypic coral reefs that may extend deeper than those recently reported from Pulley Ridge off Florida (Jarrett et al., 2005). At the same time, the complex bathymetry divides the area into a number of separate pinnacles, ridge lines, and solution basins that may harbor their own unique suite of environmental parameters and biological communities. In addition to the extensive and already discovered rich reef and snapper communities, it has been suggested that the convoluted surface of the shelf may provide habitat and serve as a refugia for other marine organisms. Populations that have been severely and negatively affected in shallower waters closer to shore by polluted runoff from land, heavy fishing and spearfishing pressure, and other anthropogenic impacts, may be sustained by
the unique and more isolated features of this area. It is important to understand the environmental significance of this shelf and to map particularly fragile or important areas so that they can be managed and protected appropriately. It should be noted that the rugged nature of the seafloor would make deployment of photographic camera sleds at 1-5 m above bottom a high risk operation and damage to the tow body would be likely. Thus, the ability to fly the laser line scan equipment at higher altitudes above bottom makes use of this sensor on the Maui Nui shelf very desirable.
Laser line scan data were collected during cruise HI-06-14 aboard the NOAA Ship Hi'ialakai. The Northrop Grumman SM-2000 Laser Line Scan (LLS) system, which is owned and operated by Science Applications International Corporation (SAIC), was leased for this test. The LLS system was towed for about 24 hours over the seafloor in the channels between the islands of Maui, Lanai, and Molokai. The altitude of the LLS instrument was set at 8 m above the seafloor for the duration of the deployment. During testing the LLS towfish struck and underwater ledge resulting in the loss of the instrument.
Equipment Description - During a 3-day mobilization, SAIC and ships personnel, aided by commercial welders, mounted a towing winch on the centerline, at the forward edge, of the Hi'ialakai's fantail. A large-diameter sheave was hung from the center of the A-frame at the ship's stern, with the towcable from a dedicated tow winch run over it. Six consoles were set up along the aft bulkhead of the Hi'ialakai's dry lab to operate the tow vehicle and winch, provide navigation information, operate an IXSEA GAPS acoustic ultrashort baseline navigation system (USBL) used to track the position of the tow vehicle, and provide data processing capabilities. A hinged pole mount for the USBL transducer was welded to the port side of the Hi'ialakai on the after end of the 01 deck. The mount was designed to enable the pole to be lifted out of the water during transit periods. Once the ship was in position to begin laser line scan surveying, the pole was lowered into a vertical position and held in place with guy wires. The LLS instrument was mounted on a Focus 1500 remote operated tow vehicle (ROTV) which provides a stable platform that can be maneuvered along survey tracklines and provides a coordinated uplink of sensor and instrumentation data over a fiber optic tow cable. The altitude of the focus ROTV was tracked using a Klein sidescan system.
Name & address of person collecting data
1845 WASP Blvd., Building 176
Honolulu, HI 96818
Data Files - Laser Line Scan data as well as information from peripheral equipment such as the IXSEA Gaps system were recorded on two separate computers and an external hard drive. The LLS data were recorded in 168 different files in a proprietary "OIC" format and averaged 0.53 Gb per file. OIC file names start with a designation for the survey line number, followed by the Julian year, day and time, with each of these separated by periods, and followed by the ".oic" filename extension. All times are based on UTC.
Resource Description: Digital video imagery that is geo-referenced to navigation files.