Richard Mills, of Kongsberg Maritime, discusses survey class AUVs and USVs.
Workers ready Hugin AUV. Photo from Kongsberg Maritime.
The autonomous underwater vehicle (AUV) market has reached a level of maturity over the past five years, where operators expect the vehicles to perform.
A modern state-of-the-art survey class AUV must be able to do many things, including collecting high resolution data and navigating accurately. The most recent iteration of the Hugin AUV developed by Kongsberg Maritime does those tasks well, but developments are underway to that could potentially change the way in which surveys are conducted.
This will see AUVs able to operate even more autonomously from their motherships, with the use of unmanned surface vehicles (USVs).
The Hugin AUV system evolved from a test and development platform back in the early 1990s, to a complete survey system, complete with a range of payload sensors, for autonomous or supervised operations.
It has a common architecture with its little brother Munin. They have the same control processors and algorithms; common user interfaces for mission planning and dive management; common navigation hardware and in-situ processing and they also share the same payload control.
It is the control elements that bring commercial value to the AUV and enable it to meet the requirements of a survey class vehicle. For example, an AUV can collect high resolution sensor data, but if the navigation accuracy is poor, the data has no value.
The Hugin vehicle control and guidance systems rely on high specification sensors, such as the Honeywell HG9900 inertial measurement unit (IMU). The raw output from the accelerometers and gyroscopes is fed into NavP, Kongsberg Maritime’s on-board navigation processor. NavP combines the IMU raw data with inputs from the doppler velocity log (DVL) and other external sources.
A well-planned survey pattern can minimize the error budget by having reciprocal tracks. Under ideal autonomous operating conditions, Hugin and Munin AUVs running with a DVL aided IMU can demonstrate a capability on the order of 0.05% of distance travelled in a straight line over a flat bottom.
For many commercial applications, external position updates such as USBL (ultra short base line) are used to limit the error budget of the navigation system. With Hugin, tracking the AUV with a HiPAP positioning system has required the mother ship to remain in acoustic range, usually within 4000-5000m of the AUV. This provides the best position updates for the AUV, but also provides a level of control and real-time data feedback for quality control purposes.
Hugin AUV on the surface.
Kongsberg’s AUVs are capable of using terrain navigation and underwater transponder protocol (UTP) to improve autonomous navigation accuracy. Terrain navigation requires known bathymetry of the survey area loaded onto the AUV as a digital terrain map (DTM). It also needs an onboard sensor such as multibeam echo sounder and some seafloor features of vertical extent. The position accuracy is determined by the quality of the DTM.
UTP is a feature within NavP. The AUV communicates with a seafloor transponder that has been deployed and boxed-in before the mission. When the AUV interrogates the transponder it calculates the range from the transponder, reducing position error over time.
For some applications, supervision of the AUV is essential. To enable operators to conduct concurrent activities, Kongsberg has begun developing an USV. Using a USV to supervise a Hugin could release the mothership from tracking the AUV making it possible for concurrent activity to occur.
Working with the Norwegian Defence Research Establishment, Kongsberg is developing ODIN, a new type of USV. It is a modular system comprising a control processor that can accept external inputs for navigation, positioning and situational awareness. Inputs may include GPS, infrared cameras and radar. The control output is fed through a mechanical interface to the vessel’s propulsion and steering. The ODIN concept is that it can be integrated with almost any hull with a variety of navigation, safety and survey sensors.
The first ODIN will conduct simple waypoint based survey missions. The control system and architecture leverages the Hugin operating system, adding more external sensor capabilities, particularly for collision avoidance. Future developments include in-mission autonomous generation of waypoints and routes for tasks such as AUV supervision.
To work with Hugin, the USV will be equipped with a HiPAP system and a marine broadband radio (MBR). The AUV position updates, supervision and data link route through the HiPAP with the MBR effectively working as a virtual Ethernet cable to the operator on the mothership or shore.
ODIN will be supervised by an operator; either on the mothership via the MBR, or onshore via satellite communications. Autonomous collision avoidance will override any mission plan or AUV following. The operator will also retain full control for safety purposes.
These topics will be explored at Oceanology International North America 2017 (held in San Diego in February) in a paper Marine Robotics: Survey Class AUVs and USVs.
The first generation USV to be tested is a survey boat. Long-term plans include the development of an AUV tender capable of not only tracking an AUV for over-the-horizon mission supervision, but also to launch and recovery the AUV autonomously.
Richard Mills is director sales – Marine Robotics at Kongsberg Maritime. His previous experience includes a similar role at International Submarine Engineering in Canada.