Phase difference technology apply to the sounding of broadband multi-beam bathymetry sonar

摘要

The sounding method and accuracy of multi-beam bathymetric sonars are being continuously researched, and many traditional multi-beam bathymetric algorithms have been proposed, such as: the Energy Centre method, the WMT method, the BDI method, etc. Some of these methods have a high precision of sounding in the mirror area, while some have a high precision of sounding in the non- mirror area. If we combine these methods and apply them to high-frequency shallow-water multi-beam sonar, the precision of sounding reaches a satisfactory level. Besides the sounding precision, the sounding resolution (the number of sounding points) is also an important indicator for multi-beam bathymetric sonar. The sounding resolution of a traditional bathymetric algorithm mainly depends on the number of pre-formed beams, which restricts the improvement of sounding resolution. In this paper, differential phase technology will be applied to broadband multi-beam bathymetric sonar, which not only ensures the accuracy of sounding, but also greatly improves the sounding resolution by dozens of times or even a hundred times as compared to a traditional bathymetric algorithm. Hence, more detailed acoustic images can be obtained without increasing the frequency of multi-beam bathymetric sonar. This is possible by using differential phase technology for underwater topography, which is advantageous for small target detection. The paper also analyzes various important factors which affect the differential phase technique, such as additive noise, baseline de-correlation and beam footprint of the seabed. In addition, it also gives the theoretical curve of sounding accuracy changing with the signal pulse width, SNR, grazing angle and other factors. Finally, we find that even under high SNR conditions, differential phase technology is still able to maintain a good sounding performance, even when we reduce the number of received array elements. This lays a good foundation for studying low frequency multi-beam bathymetric sonar.