A new GapFiller system using front-scan sonar technology coupled with SHADOWS

SHADOWS is a high-performance side-scan sonar imaging system. To fill the gap at nadir, a GapFiller is developed by IXSEA. The GFS is a GapFiller using the front-scan sonar technology. It aims to fill the unsonified area of SHADOWS, which is forty-five meters wide, to ensure a good overlap between the two systems and allow the registration of the two different images. This is made possible thanks to the inertial navigation system PHINS. This system is distinguished from other GapFiller systems using multibeam sonar, indeed the kind of images obtained is noticeably different. Instead of observing the depth and bathymetric data, the images are sonar type ones. The design of the arrays has been integrally conceived by the IXSEA team, using d₃₃-technology and an integrated reflector architecture. Finally, without any treatment other than the beam forming, the theoretical resolution obtained on the entire gap is under 40 cm, with a total physical encumbrance under 80 cm. If a traditional coherent synthesis is not allowed by the geometry of the system, an appropriate treatment provided by using an accurate and highly performant inertial navigation system (PHINS) improve significantly the resolution of the GFS. In fact instead of a linear synthesised array, this original treatment formed a bidimensional phased-array antenna. An analytic determination of the theoretical resolution depending on the pointing direction has been performed. The results are very satisfactory and predict a significant improvement of the resolution. In fact the resolution now depends on the pointing direction and with a ten-ping synthesis the resolution at 5 meters is around 25 cm and under 15 cm at 10 meters achieving this way the nominal resolution of SHADOWS.