Parameter estimation for multistatic active sonar using extended fixed points

The main task of multistatic active sonar is the localisation and tracking of objects of interest (targets). Therefore, a precise knowledge of the parameters of the multistatic scenario is mandatory. These are the positions of the acoustic sources, the times of transmission, as well as the position and heading of the own sonar sensor. Reflections from so called "fixed points" can be used to improve knowledge about these parameters. A fixed point can be a wreck or geographical feature (e.g. a small island) with known position. In general these fixed points consist of multiple scattering points, thus, the assumption of a point-like target is not fulfilled. In this paper we discuss the impact that an extension of the fixed point has on the estimation process and derive a method within the Kalman filter measurement update to incorporate knowledge about the extension in the estimation approach. Results will be discussed for simulated data.