'simultaneous Localisation and Tracking' Onboard Auvs with Multistatic Sonar Data

Multistatic Sonar Systems (MSS) based on manned or stationary systems provides necessary performance for Anti Submarine Warfare (ASW) surveillance operations. Sufficiently accurate sensor models are implemented in data fusion algorithms in order to exploit the added-value of the multiple aspects on the target. The logical follow-on is to use them to control the sensors, leading to an MSS based on AUVs [1,8]. This autonomous MSS has to cope with severe communication constraints, either as a direct result of the environment or for tactical reasons. For example, covertness can assist in detecting smart targets when being obliged to evade a multistatic network of unknown topology. We focus on an important step towards a persistent and covert autonomous multistatic system which is to maintain navigation & timing accuracy onboard the receiving AUVs by using the active acoustic transmissions of the multistatic sources plus their echoes from the ensonified environment. Therefore, we combine navigation and tracking strategies in a two-step algorithm, called „Simultaneous Localisation and Tracking‟ (SLAT): First, we identify stationary contacts using available bistatic tracking & data fusion algorithms as well as „standard‟ navigational data from AUVs. The latter is gained from an inertial navigation system, Doppler velocity log (DVL) and depth sensor. Then, we extent the Multihypothesis Tracking (MHT) to generate target tracks and state estimation of the sensors and the environment. We evaluate SLAT with data from the sea trial GLINT‟10 executed with NURC‟s AUVs and sensor arrays. The performance is measured by comparing localisation accuracy for an EchoRepeater (E/R) track. SLAT even works if the DVL data are not used! This means that SLAT can be used to realize a covert (non-emitting) receiving AUV which is able to maintain a sufficient self-localisation by utilising the acoustic transmissions and their echoes quasi as an “underwater-GPS”.