Dual Frequency Sonar - pre study and field experiment

With the ambition to improve future MCM operations the dual frequency sonar was studied by simulations and experiments. The hypothesis that buried objects will be visible to low frequency SAS only, while proud objects are visible to both low and high frequency SAS was tested. A ray tracing model was developed for simulating a dual frequency SAS. This model indicated that the reflected energy from buried targets was reduced when the center frequency was increased. In addition, SAS images indicated that the major structures were not lost when comparing with results from fullfield modeling and field data processing. In the experiments a new receiver array for low frequency SAS and a sidescan sonar for high frequency imaging were deployed and tested at the rail based SAS facility in Djupviken. The test experiments indicated that the new equipment was working as expected. Objects were identified using both the low frequency SAS and the high frequency sidescan sonar. Signal processing code for detection and separation of proud and buried objects was implemented and tested on both simulated and experimental SAS images. Buried objects were segmented and separated from proud object using the dual frequency processing.