Most forms of swarm coordination require frequently updated relative position and posture information about at least all near neighbours. The Serafina project [1][2] considers comparatively small submersibles (40 cm in lengths) but in large numbers. This imposes constraints in terms of size and energy consumption of the components. It also requires high degrees of flexibility as the school configuration changes frequently and fast.

This article suggests a low-cost localization method which involves the communication system [3] and fuses information on the long-wave radio band with wide-band acoustic readings in order to generate range, bearing, and posture reading of all surrounding submersibles, i.e. all submersibles in sensing range. MLS- (maximum lengths sequence) signals are employed for high interference robustness and deployability even in cluttered environments which usually impose multiple specular reflections and possible resonance effects.

A number of physical experiments are discussed which tests for precision, sensing range, interference robustness, and motion sensitivity. All those experiments refer to inter- school localization. Absolute localization (with respect to external, global landmarks) need only to be solved for one of the submersibles in the school (as all internal, relative locations are known) and is not discussed in this article.

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