Semi Self-Motion Compensation for a Near-Range Synthetic Aperture Sonar

This paper describes a self-motion compensation technique for a near-range synthetic aperture sonar. We are developing a SBSAS (sub-bottom synthetic aperture sonar), intended for chemical ammunition exploration. Since chemical ammunition is about 20 cm diameter×70 cm length in size, and buried in the sedimentary layers, we chose a low frequency (15 kHz) and applied a synthetic aperture technique to obtain high-resolution (<15 cm). As the SBSAS is mounted on a small ship (<10 t), the platform is greatly affected by wind and waves, making it very difficult for the SBSAS to maintain constant velocity and direction as is needed for synthetic aperture processing. Furthermore, the SBSAS must keep near range in order to avoid refraction of the deposition layer. Therefore, it is strongly affected by the motion displacement of the surge. Although the conventional DPCA (displaced phase center antenna) technique performs selfmotion compensation using its own sonar echoes, it compensates only for the sway; the surge is negligibly small for long-range SAS. We developed a new DPCA semi self-motion compensation technique to compensate the surge for nearrange SAS, and call this technique the “MP (Multi Ping) DPCA”. The results of the simulation and sea trial are reported here. Classification: Signal processing