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Abstract-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.

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.

The ambition of getting one common tool for a great variety of navigation tasks was the background for the development of NavLab (Navigation Laboratory). The main emphasis during the development has been a solid theoretical foundation with a stringent mathematical representation to ensure that statistical optimality is maintained throughout the entire system_ NavLab is implemented in Matlab. and consists of a simulator and an estimator

A magnetic compass has too large a heading error for many applications, and it is often not obvious how to achieve an accurate heading, in particular for low-cost navigation systems. However, there are several different methods available for finding heading, and their feasibility depends on the given scenario. Some of the methods may seem very different, but they can all be related and categorised into a list by studying the vector that each method is using when achieving heading. A list of possible methods is very useful when ensuring that all relevant methods are being considered for a given application. For practical navigation, we have identified seven different vectors in use for heading estimation, and we define seven corresponding methods. The methods are magnetic and gyrocompass, two methods based on observations, multi-antenna Global Navigation Satellite Systems (GNSS), and two methods based on vehicle motion. K E Y WO R D S1. Heading estimation.2. Categorisation of methods. 3. Vectors.