AUTONOMOUS UNDERWATER VEHICLES

Autonomous underwater vehicles have enormous potential for studying the world's oceans. Several major AUV programs are presently under way in Europe that will provide extensive data gathering capability for various research missions. These AUV designs and their sensor systems are described in the following section.

The British government's Department of Trade and Industry (DTI) is sponsoring a collaborative effort by Marconi Underwater Systems, Ltd. (MUSL), Moog Controls, Chelsea Instruments, and Alupower/Alcan International to produce an autonomous underwater vehicle specifically for oceanographic research. The Oceanographic Data Acquisition System (ODAS) AUV makes extensive use of off-the-shelf hardware, including advanced torpedo technology, and thus is an excellent example of military-to-civilian conversion. End use of the AUV is to collect data to ocean depths of 100 m while transmitting under the polar ice cap. Sensor design maximizes reliability and performance in the hostile environment (Neal 1992).

Core sensors include the most commonly measured oceanographic parameters, conductivity, temperature, and depth (CTD), and also chlorophyll-a fluorescence. Core sensors will require five data channels, two channels for housekeeping, and nine data channels for externally mounted sensors that would be mission specific, that is, fluorimeters, nephelometers, and transmissometers. Table 2.3 provides range, accuracy, and resolution specifications for the ODAS sensors.

Table 2.3
ODAS AUV Sensor Suite Specifications

Environmental design considerations include minimum air temperature, thermal shock, icing, fouling, low temperature sealing integrity, and corrosion. To withstand Arctic operations, circuit designs are rated to -40C operational and -65C storage. Sensors and filters are highly stable, and are designed for cold temperatures and thermal shocks.

AUVs are being developed by the Institute of Oceanographic Sciences' Deacon Laboratory (IOSDL) as part of the Autosub project of the United Kingdom's National Environment Research Council (NERC). Deacon Laboratory is leading this project. The Autosub project will involve the development of three AUVs (Babb 1993). The first is the Demonstrator Test Vehicle, which will be a full ocean depth (6,000 m) demonstration and learning AUV. Additional long-term concepts under consideration include DOLPHIN (Deep Ocean Long Path Hydrographic Instrument), a 6,000 m depth capable AUV that would follow a vertically undulating path taking oceanographic measurements in the water column and a range target of 7,000 km, surfacing every 30 km to fix its position by global positioning satellite (GPS) and transmit its data. Another AUV concept is DOGGIE (Deep Ocean Geological and Geophysical Instrumented Explorer), which would be used for geological survey using acoustic imaging sensors of the seabed.

Development of the DOLPHIN AUV during the next decade represents an ideal technique for automatic wide-area hydrographic data collection in the deep oceans and under ice. By conducting comprehensive surveys across ocean basins, DOLPHIN would complement surface observations using satellites, buoys at fixed locations, and other measurement platforms. DOLPHIN is designed to provide a set of measurements with sufficient accuracy and resolution (water density resolved to 1E-5) that when assimilated, along with other data, into four-dimensional models, would permit computation of global transport of heat and moisture by the oceans, a critical factor in global change.

DOGGIE would be a geologic survey vehicle that could provide highly detailed maps using acoustic imaging sensors of the seabed for a total track length of 1,000 km in a 50 km x 70 km rectangle. Specific study sites would include hydrothermal vent fields associated with ore deposits near midocean ridges. Because it is designed as a multisensor vehicle, DOGGIE carries side scan sonars, a subbottom profiler, a magnetometer, and chemical sensors. This AUV is therefore capable of providing a wealth of data on geophysical and geological properties of particular sites.

In addition to its activities under the U.K.'s Autosub project, IOSDL is also leading an EC Marine Science and Technology (MAST II) program with six other European partners (including IFREMER). This has the title "Advanced Systems Research for Unmanned Autonomous Underwater Vehicles" and is focussed on generic subsystems research. This is almost certainly the same program referred to during the WTEC team's visit to IFREMER in Toulon, France. IFREMER representatives mentioned then that they are engaged in an EC project to develop key technologies for a 6,000 m abyssal survey vehicle (ASV) for survey and mapping of deep ocean regions. Subsequent correspondence from IFREMER (November 1993) noted that this project tends towards the same objectives as the DOGGIE AUV. IFREMER quoted a figure for total funding of approximately $2.5 million for the EC-supported ASV project, which will result in a feasibility study and preliminary design in 1995.


Published: June 1994; WTEC Hyper-Librarian