Analysis on the characteristics of phase difference sequence in super wide coverage multi-beam echo sounder

The ocean is much more than 70% of the surface on the Earth, many kinds of mineral resources and natural gas exist under seafloor. Before mining for them we need detail terrain information of the seafloor. Multi-beam echo sounder is one of the current major equipments to obtain bathymetry of ocean, whose working principle is to estimate the DOA (Direction of Arrival) and TOA (Time of Arrival) of echo from each footprint on the seabed, and then to get the depth. To obtain super wide coverage of oblique incident angle, a phase detection method, such as the array separation method, is often used. The phase based detection method is to locate the zero-crossing of the phase difference curve through function fitting and then to achieve the DOA estimation of echo. In order to fit better the phase difference curve, the paper presents a theoretical analyzing of the phase difference sequence in super wide coverage multi-beam echo sounder. In this paper, based on output of FFT beam-former, a mathematical expression of phase difference sequence in multi-beam-former has been derived. The relation between the shape of the phase difference curve, the extent of non-confusion region, zero-crossing point position and the acoustical center's distance of two sub-arrays, number of sub-array's hydrophones, sloping angle of array, beam index has been discussed. Simulation based on a model assumption has been performed to verify the derived conclusions. The research results show that the theoretical mathematical expression matches simulation data and sea trial data very well.