Design Considerations of Mid-range Bi-static System for Bottom Scatterer Imaging

In mid-range and mid-depth environment, scattering from seafloor features is hard to be recognized because of weak echo to noise ratio and time-variant environment. In this paper, challenges in bi-static bottom scatterer imaging system are illustrated through SWellEx96 data processing. Instead of using a conventional beamformer, a high resolution beamformer, deconvolved conventional beamformer (an iterative method origins from image restoration), is utilized to process broadband signal in SWellEx96 experiment to achieve better performance, with narrow mainlobe and lower sidelobes. With the SWellEx96 data for bottom imaging, we find that the main problem concerns with insufficient signal to noise ratio (SNR). In order to improve the signal processing gain, a vertical source array is used rather than a point source, which can be steered to specific angles to ensonify different regions. Then the scatterer image of the whole region can be formed by several strip images. Moreover, as the beam is focused on the bottom, multipath effect, like the surface reflection can be greatly decreased.