Multistatic sonar for shallow water surveillance

During the eighties it became obvious that the passive sonar for surveillance for the more and more silent submarines was insufficient. Therefore, the research was directed towards active systems, and in 1995 the program "Multistatic Sonar" was initiated with the purpose to investigate if multistatic techniques could b used in the Baltic Sea. The program started with the development of equipment for experimental research. This equipment has later been used for investigations of important aspects on multistatic sonar, such as target strength, reverberation, detection and localisation. The equipment has been tested in measurements of the bistatic target strength and bottom reverberation. These tests, including both measuring technique and comparison with theoretical models, have given valuable experience for the further development of effective methods for a systematic determination of target strength and bottom reverberation. In order to improve the performance of active sonar in shallow waters, different signal shapes have bee studied. Measurements and calculations show that reverberation can be suppressed by a careful selection o the shape of the transmitted signal. Questions about range and velocity resolution and how well the different signal shapes cope with multipath propagation have been investigated. High resolution localisation with Match Field Processing (MFP) Technique developed for passive sonar, seems to be a promising method also for bistatic sonar. A prototype of a high precision GPS-controlled timer was built to demonstrate how the demand on the time synchronisation in multistatic scenario can be solved. Our research has given us a good knowledge about active sonar in the Baltic Sea and possibly also about multistatic surveillance. We suggest that operational multistatic tests should be performed with the existing passiv sonar as a receiver supplemented by an additional transmitter.