The effectiveness of monostatic and bistatic deployment of low frequency active sonar

The simplest means of exploiting low frequency active sonar involves the deployment of both transmitter (Tx) and receiver (Rx) from a single platform, albeit at potentially different depths. If a second Rx array (at a different location) is available, then it is of interest to determine the benefit of deploying it in such a position as to receive echoes in a bistatic geometry. This paper illustrates the relative merits of monostatic and bistatic geometries in terms of the evasion probability for area and barrier searches, which in turn depend on the area coverage of a single transmission (or sequence of transmissions), and the lateral sweep width, respectively. Detection probabilities are calculated by generating signal excess surfaces (vs target range, depth and bearing) for a given sonar geometry. The deployment geometry is first optimised by choosing it so as to maximise the total area in which a target can be detected. Coupled to the theoretical optimization of the relative geometries of transmitter and receivers is the practicality of maintaining these geometries while undertaking operational tasks such as area search. Modelling has been undertaken to look at the effects of operational tasks and their interaction with submarine avoidance tactics. We illustrate the methodology by presenting results for a deep-water environment, namely the Greenland-Iceland-UK gap, assuming a transmission frequency of 2 kHz.