Delory, E., André, M., Navarro-Mesa, J.L., van der Schaar, M. Evaluation of a multistatic sonar to detect silent surfacing sperm whales using the group’s chorus Proceedings of the Sea Tech Week, Brest, France, Oct 2006 Resum: Sperm Whales are highly vocal and can be localised with passive sonar, but, when at or near the surface, they tend to stop vocalising and thus are undetectable, i.e. when they are most at risk of collisions with maritime vessels. Regrettably, ship-borne active solutions have proven inefficient due to the short detection range and the ships’ high-speeds. Our objective in this paper is to evaluate the efficiency of an original passive sonar solution that would use vocalising whales’ clicks at depth as acoustic sources to detect silent whales. This solution could be a non-invasive complementary component of a more complex passive localisation Whale Anti-Collision System (WACS). To this aim, a simulation tool for 3D acoustic propagation was designed where a wideband N2D ray solution of the wave equation simulates a passive solution consisting of an arbitrary number of active acoustic sources, an illuminated object, and a receiver all positioned in a three-dimensional space with arbitrary bathymetry. Simulations show the application of the concept for the Canary Islands case, with an estimated detection range upper bound of the order of a kilometre. Projecte: Noise pollution effects on cetaceans