Mapping the acoustic reflectivity of underwater objects using reconstructive tomography

• Main Authors: Ferguson, B.G., Wyber, R.J.
• Format: Conference Proceeding
• Language: English
• Subjects: Acoustic measurements; Acoustic reflection; Acoustic scattering; Acoustic signal detection; Object detection; Oceanic engineering and marine technology; Sonar detection; Sonar measurements; Tomography; Underwater tracking
• ISSN: 0197-7385
• DOI: 10.1109/OCEANS.2008.5151804

Topical issues in oceanic engineering are the remediation of marine environments through the removal of unexploded ordnance and the countering of sea mines that threaten the freedom of the seas, especially the freedom of naval manoeuvre in littoral waters. The acoustic reflectivity properties of these potentially dangerous objects are of fundamental interest as active sonar systems are used to detect their presence in the underwater environment. The target strength of an insonified object defines the fraction of the incident sonar signal that is reflected or scattered backwards by the object. In general, the target strength of underwater objects is aspect dependent, so measurements are required over a complete (360deg) range of insonification angles. To achieve this for inert ordnance and exercise mines, a monostatic sonar (where the acoustic source and receiver are collocated at a large distance from the object) is fixed and the object is slowly rotated about its vertical axis in a dam environment. For each insonification angle, the echo returned from the object is composed of a number of components corresponding to discrete reflective regions (or highlights) on the object. Recent advances in ultra wideband sonar transducer technology enable these components to be resolved in the time domain. A further advance is to apply tomographic reconstruction techniques to the echo data to form an acoustic reflectivity map of the object. The map shows the shape of the object and the positions of various acoustic highlights.