High performance Doppler-inertial navigation-experimental results

This paper presents experimental results from a number of performance verification sea tests of the MARPOS(R) Doppler-inertial navigation system jointly implemented by Maridan A/S, Denmark, and the Technical University of Denmark for use onboard the MARIDAN series of AUVs. MARPOS(R) is a dead-reckoning based navigation system, the core of which is a state-of-the-art ring laser gyro (RLG) and a Doppler velocity log (DVL). The system also integrates a very accurate CTD sensor suite and a high quality embedded differential GPS receiver used at the surface for position initialization, a priori sensor calibration and moving base alignment of the INS. A series of accuracy verification tests were performed at a sheltered shallow water test facility, using a small surface vessel to allow simultaneous logging of DGPS reference positions and Doppler-inertial based dead-reckoning navigation data. The proven accuracy was 0.10% of distance traveled for straight line trajectories and 0.02% for site surveys, where navigation was performed in a confined area, typically 1×1 km. Results from a number of surveys carried out by a MARIDAN 150 AUV have confirmed the operational efficiency and robustness of the system. Correlation of overlapping sidescan sonar imagery indicates that the operational performance of MARPOS(R) actually surpasses the outcome of the surface vessel tests. A probable cause is the inherently more stable platform provided by an AUV as opposed to a small surface vehicle which is subjected to wave induced motion and the often more extreme sound velocity variations of the surface water layers