Jamming cancellation of moving underwater targets
Publish date: 2005-01-01
Report number: FOI-R--1761--SE
Written in: Swedish
Jamming cancellation can reduce the ability of an adversary to conduct underwater information warfare of both misleading and jamming nature. In low conflict situations, jamming cancellation may be used for surveillance of ship routes and harbours, to improve the ability to detect unknown targets with weak signatures in a background of ship and ambient noise. A number of signal analysis methods for jamming cancellation have been studied and applied to data from a field trial. The methods are two MVDR methods (minimum variance distortionless response) of adaptive nature and two null-steering methods which require a priori information about target positions. The field trial included two vessels, each towing an acoustic source transmitting a 200 Hz tone. Signals were registered with a uniform linear array placed on the sea bottom. In a hypothesized scenario the vessels acted as a moving target and a jamming source, respectively. The purpose of the study was then to assess the ability of the methods to provide good target tracks in BTR (bearing time record) diagrams. In data sections where a pursuit of the target source predicted by theory is possible, the null steering methods suppress the jamming source and the target can be discerned. Narrow-band MVDR applied to the same data results in unsteady tracks from both sources, while broad-band MVDR only yields one track from the jamming source. The conclusion is that the null-steering methods are preferred over the MVDR methods when narrow-band sources are transmitting in shallow waters.