During the last few years autonomous underwater vehicle (AUV) technology has evolved from concept demonstrators towards commercial products. The driving forces are the move for energy exploitation towards deeper waters, naval applications and the Internet driven need for more intercontinental underwater communication cables. Other applications emerging for the future will be within environmental research and monitoring and deepwater exploration.Deepwater developments beyond the continental shelf will require the same level of survey data quality and intervention access as established for shallow water. The potential for cost savings is two folds.Firstly, there is a reduction in the survey cost it self and secondly there is a considerable cost saving by avoiding over design of subsea installations due to lack of sufficient documentation of the field. In this scenario, there is an increasing understanding that underwater robotics and in particular AUVs will play an important role in future survey and subsea engineering work.The AUV as a free swimming underwater survey sensor carrier has several advantages compared to cable controlled ROV's and deep towed systems:The paper prepared for the OCEANS'O4, Kobe, Japan will focus on the HUGIN AUV concept and field results from the North Sea and GOM.

Exploration on deeper water puts high requirements on underwater positioning for both DP operations and survey applications. Acoustic positioning systems are continuously improved to meet new requirements. Development carried out during the last years for the HUGlN AUV has brought new technology available for combining acoustic positioning with inertial navigation. Based on this the HAlN system is developed as an extension to the HiPAP and HPR systems. HAlN Position ReferenceThe HAlN system for vessel positioning is an aided inertial navigations system. The position drift that is inherent in Inertial Navigation Systems is limited by the acoustic position measurements relative to transponder(s) on the seabed. The system can be used both with SSEL or LBL position input. The HAlN provides an improved position of the vessel which both has increased accuracy and higher update rate than the original position from the acoustic measurements. This extends operational water depth and reduced battery consumption. Position output during acoustic dropout will be maintained. HAlN SubseaThe system is also available in a version for ROV positioning for survey applications. In this version the system also is interfaced to a Doppler velocity log and a pressure sensor. The complementary solutionAcoustic and Inertial positioning principles in combination is ideal, since they have complementary qualities. Acoustic positioning is characterised by relatively high and evenly distributed noise and no drift in the position, whilst inertial positioning has very low shortterm noise and relatively large drift in the position over time.The presentation at Oceans'04 will show the HAlN operational methods, benefits and accuracy figures.