Kenneth Gade

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 at 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.

Signal processing for AUV based interferometric synthetic aperture sonar

This paper presents signal processing techniques particularly suited for interferometric Synthetic Aperture Sonar (SAS) systems onboard Autonomous Underwater Vehicles (AUV) (or other platforms carrying high grade navigation systems). The signal processing is applied to data collected in a controlled rail experiment at Elba Island, Italy, using a wideband interferometric SAS and an Inertial Navigation System (INS). We evaluate different strategies in fusing sonar micronavigation by the Displaced Phase Center Antenna (DPCA) technique with Aided INS (AINS). We obtained highest navigation accuracy using DPCA as aiding sensor into the AINS, then using raw DPCA surge and sway in combination with the AINS attitude and position. Coarse cross correlation based bathymetry and full resolution interferometry (based on the interferogram) is tested on the full swath and objects. Coarse bathymetry is more reliable than the interferogram technique. Phase wraparounds are avoided by estimating the coarse bathymetry first, then using the full resolution phase estimates as correction. Although much work remains, this technique does show a clear potential in improving object classification ability.

A Non-singular Horizontal Position Representation

Position calculations, e.g. adding, subtracting, interpolating, and averaging positions, depend on the representation used, both with respect to simplicity of the written code and accuracy of the result. The latitude/longitude representation is widely used, but near the pole singularities, this representation has several complex properties, such as error in latitude leading to error in longitude. Longitude also has a discontinuity at ±180°. These properties may lead to large errors in many standard algorithms. Using an ellipsoidal Earth model also makes latitude/longitude calculations complex or approximate. Other common representations of horizontal position include UTM and local Cartesian ‘flat Earth’ approximations, but these usually only give approximate answers, and are complex to use over larger distances. The normal vector to the Earth ellipsoid (called n -vector) is a non-singular position representation that turns out to be very convenient for practical position calculations. This paper presents this representation, and compares it with other alternatives, showing that n -vector is simpler to use and gives exact answers for all global positions, and all distances, for both ellipsoidal and spherical Earth models. In addition, two functions based on n -vector are presented, that further simplify most practical position calculations, while ensuring full accuracy.

Positioning accuracy for the HUGIN detailed seabed mapping UUV

HUGIN is an untethered underwater vehicle (UUV) intended for bathymetric data collection for detailed seabed surveying. The HUGIN sensor suite, consisting of standard commercially available navigation sensors and a multibeam echosounder, is reviewed with respect to accuracy and important characteristics. A Kalman filter for post processing integration of UUV sensors and survey vessel sensors is described. We present a complete error budget and discuss the resulting positioning accuracy of the digital terrain model that has been achieved with the HUGIN UUV. Finally we show how the claimed positioning accuracy has been verified.

INTEGRATED CAMERA-BASED NAVIGATION

Gade, Brita Helene Hafskjold; Jalving, Bjorn; Hagen, Per Espen; Gade, Kenneth. Integrated Camera-Based Navigation. Journal of navigation (Print) 2000 ;Volum 53.(2)

The Seven Ways to Find Heading

Gade, Kenneth. The Seven Ways to Find Heading. Journal of navigation (Print) 2016 ;Volum 69.(5) s. 955-970