The Autonomous Underwater Vehicle is a REMUS 6000 type AUV of the company Hydroid. Unlike many other types of AUV, it does not consist of a continuous pressure hull but is based on a titanium frame. This construct carries the various pressue cases, the sensors and the buoyancy foam. The individual sensors, such as the echo sounders are each designed for depths of at least 6000 meters. The electronics of these sensors is either in its own pressure-tight titanium bottles or in the main electronics bottle of the vehicle. This cylindrical container includes all the electronics to the vehicle control. All components are attached to the titanium frame.
The compressive strength in the various systems is assured either by appropriately designed cases or by an oil compansation device.
The remaining space of the cigar-shaped body is "filled" with sections of syntactic foam. This high density foam ensures the buoyancy of the AUV. The individual foam sections are laminated to protect the material.
- Length: 4.00 m
- Diameter: 0.66 m
- Weight (Air): 880 kg
- Buoyancy (Water): 5 kg
- Mission Depth: 10 - 6000 m
- Speed: 2.5 - 4 kn
- Mission Time: up to 22 h (Sidescan Sonar) / up to 16 h (Multibeam Sonar)
- Max. Range: 120 km
- 2 Lithium-Ion battery packs provide the AUV power during a dive
- Each of the two batteries consists of 672 single cells and is secured in a pressure-tight titanium bottle
- Each of the two battery sets can provide 5.6 kWh
- Batteries are loaded by external software-controlled chargers
- external power supply is available
The following sensors are already integrated and part of the standard configuration:
- Seabird SBE 49 FastCat CTD (pumped CTD for determining conductivity, temperature and water pressure)
- Wet Labs ECO FLNTU fluorometer and turbidity sensor
- Edgetech 2200-MP 120/410 kHz sidescan sonar
- SeaBat Reson 7125 multibeam 200/400 kHz
The following sensors can be installed instead of the Multibeam echo sounder:
- AVT Pike camera (4 Megapixel, monochrome)
- Edgetech 2200-MP sub-bottom profiler 4-24 kHz
The following sensors can be installed on request:
- eH-sensor (in cooperation with Dr. Koichi Nakamura, Japan)
- Rockland Scientific microRider (measures turbulence microstructures)
Navigation / Vehicle control
The navigation of AUVs is mainly based on the INS (Inertial Navigation System). The INS is capable to determine acceleration and angular velocity in 3-dimensional space and it usually requires an initial position by GPS to dead reckon its own position. Since the INS is associated with an increasing error, the AUV requires an LBL transponder field (Long Base Line Positioning) in the working area. The transponders are calibrated from the ship to determine their exact position and depth. During the dive, the AUV measures both transponders and can thus determine its own position. This position supports the initial navigation system. A downward looking DVL (Doppler Velocity Log) stabilizes continuously the INS navigation by exact ground velocity values. The AUV depth is determeined by a separate pressure sensor. The above mentioned DVL provide the altitude (heigth above seabed), too. Once the AUV is surfaced and is within the WIFI range, it can be controlled from the ship. The vehicle can detect obstacles in its pre-field and escape upwards.
The following sensors support the AUV navigation:
- Kearfott INS
- Teledyne RDI Workhorse Navigator DVL (Doppler Velocity Log) 300 kHz
- Garmin GPS
- Paroscientific 8B7000 pressure sensor
- Imagenex 852 Echo Sounder (obstacle avoidance)
- Hydroid LBL transponder
Acoustic communication summarizes the entire data exchange under water. The AUV has echo sounder on top and on bottom respectively. With these transducers, the AUV can both communicate with the ships station and measure the transponder. Another acoustic transducer is installed on the ships hull. In addition to communicate with the vehicle the ship station can communicate with the transponders by using this echo sounder, too. During the dive, the vehicle transmits various status messages (including position, speed, temperature, depth, etc.). The AUV mission data can be changed very limited in this way.
Once the AUV appears out of the WI-FI reach, it first waits for a satellite position by GPS and then establishes a satellite connection to the peer on the research vessel. So that the team on board gets data the AUV status and position..
Smaller amounts of data to be downloaded by using the wireless LAN connection. More important, however, is this connection during launch and recovery of AUV. It can be controlled by means of this connection from the deck.
Deck Cable Communication
Once again the AUV in the container on board the research vessel, it is connected to the network of the ships station. The connection is used to download mission data, change vehicle parameters and access to the computers of the individual sensors. The data transfer rate is 100 Mbit/s.
The following emergency systems are integrated:
- In case of insufficient battery capacity an emergency system ensures surfacing of the AUV and the sending of SMS messages (status, position, etc.) via satellite.
- An emergency-weight can be dropped if the AUV has to surface quickly or it requires more buoyance.
- Safety depths can be defined to avoid hitting the ground.
- There are different algorithms in the vehicle code to ensure that the AUV can adequately respond to emergencies (eg AUV is stuck under a rock ledge, dropping the emergency weight, etc.).
- The AUV team is able to intervene via acoustic communication. If for example the weather is getting worse then the mission can be aborted. In the event that surfacing is not possible, it can be "parked" at a certain depth.