Optimised acoustic detection system for detecting various underwater threats in a sensitive zone

An acoustic detection system for detecting targets that are at least partially submerged in a sensitive zone defined in relation to an infrastructure, the detection system comprising at least one multistatic detection group, each multistatic detection group defining a detection zone and having: a submerged transmitter (31) emitting at low frequencies; and a plurality of submerged receivers (32) comprising at least two receivers, each receiver of a given group forming, with the transmitter of the group, a bistatic pair generating an elementary detection zone (320) surrounding a shadow zone (321), the detection zone of the group being formed by the entire set of elementary detection zones of the receivers in the group, and the receivers being arranged in at least one layer. For at least one group of the system, the shape formed by the receivers in at least one layer of the group is at least partially circular, with a given radius (R), the inter-receiver distance (2a) between two adjacent receivers in the layer depending upon the distance (