Vehicles

Looking at the current situation in AUV technology (see Figure 1), there are currently over 50 different types of AUVs in research and commercial operation, just a few of these systems are: Hydroid's REMUS (USA), Bluefin Robotics Corporation's Odyssey (USA), Woods Hole's ABE (USA), FAU's (USA), Boeing's, Oceaneering's and Fugro's Echo Ranger (USA), Kongsberg Simrad's Hugin 3000 (Norway), Sias-Patterson's Fetch (USA), University of Southampton's AUTOSUB (England), Alive and Swimmer (France), and Hafmynd's Gavia (Iceland). Of these autonomous underwater vehicles all but a few of them are 100 percent powered. Three of these vehicles are torpedo shaped (see Figure 2) and move without power. These are the Webb Research Corporation's Slocum glider (the name Slocum commemorated the first person who sailed around the world solo, Joshua Slocum), University of Washington's Applied Research Laboratory's "Seaglider", and Scripps Institution of Oceanography "Spray" (Spray was the name of Joshua Slocum's boat when he sailed around the world) currently sold by Bluefin

Robotics Corporation. These three vehicles are from the United States of America and have the ability to do studies in glide mode.

These vehicles glide slowly down to a specified depth and then back to the surface using a buoyancy control system tracing a saw-tooth profile, observing data such as temperature and conductivity versus depth. When the vehicle is at the surface, positioning is obtained via GPS and communication between the vehicle and the home base is via satellite. The three gliders are small semi-torpedo shaped AUVs that control their forward motion by the glide path taken and changing buoyancy. Wings allow steerable gliding, thus horizontal propulsion.

Underwater Vehicles

Fig. 1. 1) Woods Hole Oceanographic Institution, USA: Autonomous Benthic Explorer (ABE), 2) ECA, France: ALISTAR 3000, 3) Boeing, Oceaneering and Fugro, USA: ECHO RANGER, 4) Bluefin Robotics, USA: BLUEFIN 21, 5) Southampton Oceanography Center, Great Britain: AUTOSUB, 6) Florida Institute of Technology, USA: TUVAAQ, 7) Kongsberg-Simrad, Norway: HUGIN 3000, 8) Atlas Maridan, Germany: M600, 9) Hydroid, USA: REMUS, 10) Cybernetix, France: ALIVE, 11) Cybernetix, France: SWIMMER, 12) Autonomous Undersea Systems Institute, USA: SAUV.

Fig. 1. 1) Woods Hole Oceanographic Institution, USA: Autonomous Benthic Explorer (ABE), 2) ECA, France: ALISTAR 3000, 3) Boeing, Oceaneering and Fugro, USA: ECHO RANGER, 4) Bluefin Robotics, USA: BLUEFIN 21, 5) Southampton Oceanography Center, Great Britain: AUTOSUB, 6) Florida Institute of Technology, USA: TUVAAQ, 7) Kongsberg-Simrad, Norway: HUGIN 3000, 8) Atlas Maridan, Germany: M600, 9) Hydroid, USA: REMUS, 10) Cybernetix, France: ALIVE, 11) Cybernetix, France: SWIMMER, 12) Autonomous Undersea Systems Institute, USA: SAUV.

The Slocum glider, the Seaglider and Bluefin's glider Spray are excellent at the tasks they are designed to do (i.e., very long term, very little power, slow cruising of the ocean's water column), but they are limited as to the type of payloads they can carry, and they have no active propulsion for times that require more than buoyancy thrust (e.g., control of the vehicle at the surface). These autonomous underwater gliders each change their buoyancy to be able to travel horizontally in the ocean's water column using the lift on their wings, like a normal glider does to convert vertical velocity into forward motion. These vehicles are not capable of traveling in a horizontal path as would a typical propeller vehicle but follow a saw-tooth path as the vehicle descends or ascends.

Fig. 2. 1) Spray, 2) Seaglider, 3) Slocum Glider (Photos courtesy of Bluefin, Applied Physics Laboratory, University of Washington and Webb Research Corporation)

These three underwater gliders were designed specifically for long term sampling and easy deployment and recovery by a minimal crew (i.e., one to three people) on any size boat or ship. Consequently, this requires a design that has minimal space for instrumentation and is limited in its function/capabilities. These vehicles are relatively inexpensive, typically less than the cheapest powered AUV's (e.g., $100,000 for the EcoMapper AUV by YSI Inc.), costing less than a week and a half of ship time for a research vessel.

With respect to these gliders four basic sampling modes exist: 1) vertical sampling where the forward motion of the vehicle counters any local currents to maintain position, 2) horizontal saw-tooth sampling where the forward motion allows for the vehicle to obtain information both vertically and horizontally, 3) array sampling where multiple gliders form a distribution of sampling instruments covering an entire region, and 4) long life and repeat sampling over an extended duration.

Spray and Slocum Battery/Electric Gliders

The Slocum Battery (Webb et al., 2001) and Spray Gliders (Sherman et al., 2001) have been optimized for missions in shallow coastal environments. Each of these vehicles uses battery power to control the buoyancy.

The Slocum Battery is controlled by different methods. The pitch and roll is controlled by translating and rotating the internal battery packs. A rudder controls the turning rate and the pitch moment and the buoyancy at the surface are aided by the inflation of an airbladder. The Slocum battery uses an efficient shallow water single stroke pump to move water in and out of the vehicle for volume control. The communication and GPS antennas are embedded in a vertical stabilizer, which rises above the ocean surface when the vehicle is pitched forward (Griffiths, 2002). Additionally, "the yaw moment for steering is achieved by mounting the wings aft of the center of buoyancy, and when rolled, the lateral component of lift creates a yaw moment" (Webb et al., 2001). Slocum Battery/Electric Specifications (Webbresearch, 2008a)(Griffiths, 2002)

• Depth Range: 4 - 200 m (coastal model or 1000 m (1 km model)

• Energy: alkaline batteries

• Navigation: GPS, internal dead reckoning, altimeter

• Sensor Package: conductivity, temperature, depth

• Communications: RF modem, Iridium satellite, ARGOS, Telesonar modem Spray (Spray, 2008a)

• Payload: 3.5 to 51.8 kg depending on the glide ratio between 19

and 25 degrees

• Energy: Primary lithium sulfuryl chloride batteries

• Range: 3500 to 4700 km depending on the glide ratio.

• Navigation: GPS, and internal dead reckoning, altimeter

• Sensor Package: Sensors used include: Precision Measurement

Engineering CTD; modified

Sea Bird 41 CP CTD with seawater pump; Sea Point Optical Backscatter Sensor; Sea Point Chlorophyll Fluorometer; Tritech PA200 acoustic altimeter for bottom avoidance; and Sontek Argonaut-SGP 750-kHz Acoustic Doppler Current Profiler. • Communication: Iridium satellite

The Spray glider (see Figures 3 and 4) is similar to the Slocum Battery Glider but with a more hydrodynamic shape giving it about fifty percent less drag than the Slocum Battery (Sherman et al., 2001). The Spray was targeted for long-range up to 4700 km and down to 1500 meters depth by optimizing the use of energy. Use of a high-pressure reciprocating pump with external bladders makes the vehicle similar to the ALACE floats (Davis et al., 1992).

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