Results from trials of a planar, incoherent, synthetic aperture sonar for underwater imaging
ABSTRACT Synthetic aperture sonar (SAS) techniques can yield high-resolution images with a small physical array. Their application in the underwater environment is usually confined to the deployment and synthesis of linear apertures. Incoherent SAS processing is a suboptimal approach compared with coherent SAS processing as the absence of phase information results in an inferior along-track resolution and a higher sidelobe level. The absence of phase information implies that incoherent processing is not constrained by phase-aliasing. Incoherent SAS can accommodate non-uniform inter-ping spacing and is tolerant to trajectory estimation errors of the order of the range-compressed pulse length. This presents new opportunities for a robust surveying system. Apertures of nonlinear shapes can be synthesised depending on the nature and requirement of the specific application and environment. Surveys can be conducted with minimal hardware deployment, such as by a diver. On the basis of this concept, tank trial results of a 3-dimensional incoherent SAS technique utilising the synthesis of 2D apertures are presented. Broadband pulses are employed to achieve optimal survey resolution. The feasibility of this technique is demonstrated for both monostatic and single-transmit, multiple-receive configurations. Practical results are shown for arbitrary-surface apertures sampled at non-uniformly separated positions.
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ABSTRACT: Over the past 20 years, sonar imaging technology particularly for the high-technology sector has been a focus of research, in which many developed countries, especially those with coast lines, have been competing with each other. It has seen a rapid development with increasing widespread applications that has played an important and irreplaceable role in underwater exploration with great prospects for social, economic, scientific, and military benefits. The fundamental techniques underlying sonar imaging, including multi-beamforming, synthetic-aperture and inverse synthetic-aperture sonar, acoustic lensing, and acoustical holography, are described in this paper. This is followed by a comprehensive and systematic review on the advantages and disadvantages of these imaging techniques, applicability conditions, development trends, new ideas, new methods, and improvements in old methods over recent years with an emphasis on the situation in China, along with a bold and constructive prediction to some development characteristics of sonar imaging technology in the near future in China. The perspectives presented in this paper are offered with the idea of providing some degree of guidance and promotion of research on sonar imaging technology.Chinese Journal of Oceanology and Limnology 06/2013; · 0.58 Impact Factor