Interferometric synthetic aperture sonar for high-resolution 3-D mapping of the seabed

Abstract

A technique is described and demonstrated for generating high-resolution 3-D images of the objects on the seabed, combining synthetic aperture sonar with bathymetric (interferometric) processing. This has applications in surveying of oil wells, pipelines and shipwrecks, and in defence in mine hunting. It is shown that the technique is very sensitive to platform motion errors, and ways are discussed by which the errors may be estimated and compensated. Practical results obtained with an experimental system in a test tank are presented and discussed, and a number of areas for further work are identified. 1 Introduction Sidescan sonars are now a widely accepted and important tool of ocean technology. Broadly, they fall into one of two classes: the short-range high-resolution systems working at a relatively high frequency (e.g. about 100kHz), and the long-range low-resolution systems working at 10kHz or less. The former have a wide range of applications in surveying of oil wells, pipelines and shipwrecks, and in defence in mine-hunting. The longer range systems such as GLORIA have contributed significantly to the study of the deep ocean floor. The original method of determining seabed topography is by means of an ship-mounted echo sounder, covering a given area in a raster fashion. This is slow

Shallow water height mapping with interferometric synthetic aperture sonar

“…Nevertheless this images provide only information in twodimensions, which is not sufficient for most underwater imaging applications. If the area observed is imaged by two synthetic apertures and a suitable looking angle, the information included in the phases can be used to obtain the third dimension and thus supply height estimation ( [1,3]). This is a know technique in synthetic aperture radar systems, but still a relatively unexplored concept in synthetic aperture sonar systems.…”

InSAS Interferogram Filtering Via A New Coupled PDE Method

“…Interferometric Synthetic Aperture Sonar (InSAS) provides a means of obtaining high resolution three-dimensional images of targets on the sea floor [1,2]. The interferogram obtained from InSAS always has much noise that disturbs the quality of the interferogram.…”

Phase Unwrapping via Graph Cuts

“…The need for phase estimation is common to many imaging techniques, from which we point up interferometric synthetic aperture radar and sonar (InSAR/InSAS) [3], [4], [5], [6], [7], [8], [9], magnetic resonance imaging (MRI) [10], [11], and optical interferometry [12]. In InSAR, as in InSAS, two or more antennas measure the phase between them and the terrain; the topography may then be inferred from the difference between those phases, relying on simple geometric reasoning.…”