InSAS´00: interferometric SAS and INS aided SAS imaging

This paper presents results of an experiment carried out in Elba Island (Italy), aimed at investigating wideband interferometric synthetic aperture sonar (InSAS). A 20 m underwater rail with a multi-axis motion actuator (MAMA) was used to introduce controlled distortions in the sonar trajectory during its displacement along the rail. The sonar operated between 120 kHz and 180 kHz and consisted of two 32 channel receiver arrays, of length L=26.7 cm, vertically separated by 21 cm, and of three transmitters spaced along-track at L/2. A very high grade inertial navigation system (INS), of the 0.1 nm/hr class was used to sense the sonar motion. Raw sonar and INS data were collected under various pre-determined distortions, e.g. ±1° sinusoidal yaw, for offline analysis. Multi-aspect insonification of different objects were also carried out using a turntable in order to assess the benefit for object classification. High navigational accuracy is obtained by combining INS motion estimates with those derived from the DPCA (displaced phase centre antenna), making very high resolution SAS imagery possible. Images with along-track resolution gains of Q=50-100 compared to that of the physical array are obtained in the presence of ±1° sinusoidal yaw