SAMI: A low‐frequency wideband prototype for synthetic aperture mapping and imaging

A low‐frequency wideband (6–12 kHz) prototype has been developed in the framework of the SAMI (synthetic mapping and imaging) project. The prototype uses a subsurface towed fish. One transmitting array and two parallel receiving arrays 2 m long were installed on the tow‐fish. Each array is associated to a synthetic aperture sonar channel. Thanks to the use of suitable transmitted signals (linear period modulated chirps), array synthesis could simply be achieved in the time domain; pulse compression and azimuthal matched filtering could be separated in order to reduce the processing complexity. Synthetic image resolution was measured at sea using reflectors on a frame; the results obtained were comparable to the predicted performance: 0.5×0.15 m. The cross correlation between both synthetic aperture channels output was used for measuring the elevation of the sea bottom reverberation cells. Synthetic aperture maps were then produced. Real‐time processing was achieved on board the vessel for a swath of 500 m...