Application of computed tomography to the acoustic imaging of sea mines at safe standoff distances

Abstract

Typical imaging sonars make use of very high frequencies and arrays with a large number of sensors to provide high angular resolution. With such arrays the spatial resolution degrades and high propagation losses occur as the sonar is moved away from the target being imaged and operational ranges are generally 5 m or less. An alternative imaging technique has been implemented using computed tomography in which the target is insonified with a broad beam from multiple aspects. The spatial resolution achievable with this method is determined only by the bandwidth of the test signal and not by the beamwidth of the sonar or the distance of the sonar from the target. Results are presented showing clear images of mines and mine-like objects in which a spatial resolution of better than 2 cm is achieved at a range of 60 m, even for low target strength mines. Features are evident in the images that are related to both the internal and external shape of the targets as well as structural waves propagating within the targets. This offers the potential to provide unambiguous classification of mines from long ranges, even in a harsh operational environment.