I. Introduction
Most modern AxVs provide an aided inertial system (AINS) as their navigation solution. AINS systems are based around inertial measurement unit (IMU) aided by a Doppler velocity log (DVL), depth sensor and underwater or global positioning system [10]. Aiding sensors are needed to reduce the drift rate or periodically reset position estimates. Modern INS systems are specified as being capable of heading drift rates of less than 0.01 deg/hr [2]. High accuracy comes with higher cost, which is acceptable for non-expendable AxVs, but is not desired for expendable (one-shot) UUVs, which are taken into consideration in this paper. Although the cost factor eliminates the complete AINS solution from the equation, a basic sensor suite, e.g. compass and pressure sensor, remains as a minimal requirement.