HUGIN AUV Research Articles

Using Terrain Navigation to Improve Marine Vessel Navigation Systems

AbstractTerrain navigation has been used extensively by underwater vehicles in the last decade. By comparing bathymetric measurements with a digital terrain model (DTM), one can estimate a global position of a vehicle underwater, where GPS signals are unavailable. With the increasing threat of GPS signal jammers and spoofers to marine vessels, GPS-independent techniques are becoming more interesting for surface vessels as well. This paper explores the idea and challenges of using terrain navigation to detect GPS spoofing and as a substitute position source during GPS jamming. A robust navigation system is suggested based on a GPS-aided INS augmented by terrain navigation. The INS and terrain navigation system of the HUGIN AUV was adapted to a surface vessel and tested in two experiments on the coast of Norway in scenarios simulating GPS jamming. The results from the experiments clearly indicate the feasibility of such a system, if a DTM of the area is available and the terrain is well suited for terrain navigation.

Synthetic aperture sonar imaging of breaking internal wave structures

In October 2012, the Centre for Maritime Research and Experimentation (CMRE) conducted the ARISE’12 trials from the NATO research vessel Alliance, off of Elba island, Italy. During this trial, data were collected by the Norwegian Research Defence Establishment (FFI) using a HUGIN AUV with interferometric synthetic aperture sonar (SAS). Large visible structures in the SAS images and in the SAS bathymetries were caused by features in the water column, called boluses, which formed after breaking internal wave events. Variation in backscattered intensity from the seabed was caused by focusing of sound by the bolus and errors in bathymetry by the changes in phase as the acoustic energy moved through the lower sound speed bolus. A ray model and a 3D parabolic equation (PE) model were used to simulate the effects of the bolus on the acoustic field incident on the bottom and results compared favorably with SAS data. Models for the change in bolus size and speed as it propagated upslope also gave reasonable comparison to estimates obtained from SAS intensity images. [The work performed by APL was supported by the US Office of Naval Research.]

Autofocus of synthetic aperture sonar data using the phase adjustment by contrast enhancement algorithm

Imagery from synthetic aperture systems often suffers from imperfect image formation due uncertainties in the collection geometry or environmental parameters. Autofocus techniques aim to estimate and subsequently eliminate the effect of these uncertainties‐‐‐automatically adjusting focus parameters to obtain a “better” image. Typically, autofocus algorithms will optimise for reduced Doppler phase gradients or improved image contrast. The phase adjustment by contrast enhancement (PACE) algorithm belongs to the second class and was first proposed for use in synthetic aperture radar (SAR) autofocus. The algorithm is somewhat unusual for a contrast optimisation in that it avoids lengthy computation through directly solving the equations for optimum contrast. This advance allows for rapid autofocus without the need for complicated iterative optimisers. We compare results from using the PACE algorithm on local region of strip‐map synthetic aperture sonar (SAS) data collected with the HUGIN AUV and compare against a benchmark phase gradient autofocus (PGA) algorithm. We also demonstrate the effect of using the algorithm in circular SAS imagery, something not currently possible with standard PGA‐based autofocus.

A MODEL-BASED OCEAN CURRENT OBSERVER FOR 6DOF UNDERWATER VEHICLES

The problem of ocean current estimation for 6DOF underwater vehicles is considered in this paper. A model-based observer for ocean current estimation is proposed and it is shown how the performance of underwater vehicles can be improved by incorporating the ocean current estimates in the controller. The results are illustrated with a simulation case study with the HUGIN AUV.

A Toolbox of Aiding Techniques for the HUGIN AUV Integrated Inertial Navigation System

Modern AUV designs must handle submerged autonomous operation for long periods of time. The state of the art solution embedded in the HUGIN AUVs is a Doppler Velocity Log (DVL) aided Inertial Navigation System (INS) that can integrate various forms of position measurement updates. In autonomous operations, position updates are only available in limited periods of time or space, thus the core velocity aided inertial navigation system must exhibit high accuracy. However, position uncertainty of a DVL aided inertial navigation system will eventually drift off, compromising either mission operation or requirements for accurate positioning of payload data. To meet the requirements for a range of military and civilian AUV applications, the HUGIN vehicles come with a flexible and powerful set of navigation techniques. Methods for position updates include GPS surface fix, DGPS-USBL, Underwater Transponder Positioning (UTP) and bathymetric terrain navigation. Based on synthetic aperture sonar technology, a potentially revolutionary accurate velocity measurement is under development. HUGIN also comes with a navigation post-processing system (NavLab), which can be applied to increase navigational integrity and maximize position accuracy.