After decades of research and development, autonomous underwater vehicles (AUVs) are today becoming accepted by an increasing number of users in various military and civilian establishments. The number of AUV systems sold to civilian and military customers worldwide is well into triple digits. The bulk of these systems have been manufactured within the last five years, so the sector is in rapid growth.
AUVs provide a safe, cost-effective and reliable alternative to manned or remotely controlled systems. For military users, they can reduce the exposure of personnel and high-value assets to dangerous environments such as mine fields or enemy-controlled harbours and waterways. They also facilitate covert or clandestine information gathering behind enemy lines. For civilian users, the flexibility and agility of AUVs make them cost-effective sensor platforms, in particular in deeper water.
However, the actual autonomy of the vehicles in existence today is limited in many ways, restricting their potential uses. Further advances in AUV autonomy will enable new operations, such as covert, very long endurance missions (weeks) in unknown and/or hostile areas. While some experimentation is already taking place with e.g. under ice operations, the chance of failure is unacceptably high for many potential users. De-risking of long-endurance autonomous operations in unknown areas is thus an important goal for the AUV community.
The level of autonomy achieved by AUVs is chiefly determined by their performance in three areas:
Energy autonomy - reliable power sources and low power consumption for long-endurance missions.
Navigation autonomy - precise navigation and positioning with little or no position estimate error growth for extended periods of time.
Decision autonomy - the ability to sense, interpret and act upon unforeseen changes in the environment and the AUV itself.
These three areas should be addressed in a balanced fashion. In particular, navigation and decision autonomy are interlinked in various ways - the AUV's trajectory will affect navigation system and individual sensor performance, while the navigation system's performance will affect the AUV's ability to achieve the mission objectives. Actions taken by a decision autonomy subsystem can include changes to the vehicle trajectory, but also sensor configuration and utilization.
This chapter will focus on the latter two technology areas. For energy autonomy, the reader is referred to e.g. (Hasvold et al., 2006) or (Hagen et al., 2007).
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