A NEW-GENERATION SIDE-SCAN SONAR

Sidescan images of the sea-floor usually suffer from artefacts caused by the attitude variations of the towed platform. In collaboration wit h IFREMER, we are designing a system that compensates for yaw, pitch a nd roll in real time, i.e. during the whole ping cycle. The 4 m long a ntenna is made of 3 arrays working at 110 kHz. It enables ranges up to 1000 m and the angular resolution is 0.25-degrees i.e. 1 m scan resol ution for a 250 m range. The transmit array is made of 36 elements wit h 80 mm spacing. There are two identical receiving arrays, containing 32 active pieces each, with 120 mm spacing. The duplication of the rec eiving channel will give a bathymetric capability. Data provided by an attitude station are used to control the numerical beam-steering perf ormed at transmit and during receive. On the other hand, 16 focal zone s have been set to achieve a constant along-track resolution of 1 m up to 250 m range. In addition, focusing reduces the side-lobes level. T he experimental results in water tank are in good agreement with the n umerical model. First data and images were gathered during a campaign at sea in November 93.