Clutter suppression and classification using twin inverted pulse sonar (TWIPS)

Abstract

This paper describes the detection and classification of targets against clutter by distinguishing between linear and nonlinear scatterers and, further, by distinguishing those nonlinear targets that scatter energy at the even-powered harmonics from those that scatter in the odd-powered harmonics. This is done using twin inverted pulse sonar (TWIPS), which can also, in some manifestations, require no range correction (and therefore does not require the a priori knowledge of the environment needed for most remote detection technologies). The method applies, in principle, to a range of sensor technologies, including the use of radar to distinguish between circuitry, metal and soil; Light Detection and Ranging (LIDAR) to detect combustion products; and Magnetic Resonance Imaging (MRI). A sonar application is demonstrated, detecting objects in bubbly water (including in the wake of a ship of 3953 gross register tonnage). A manmade sonar that can operate in bubbly water is relevant: Cold War sonar is not optimized for the shallow coastal waters that typify many current operations. The US Navy use dolphins in such waters. TWIPS arose as a demonstration that echolocation was possible in bubbly water in response to a video showing dolphins generating bubble nets when hunting: if echolocation were impossible in these nets, then during this hunt, the dolphins would have blinded their sonar.

Quantification of undersea gas leaks from carbon capture and storage facilities, from pipelines and from methane seeps, by their acoustic emissions

“…One should also note that the inversion inherently assumes a zero bubble generation rate for all bubble sizes with a natural frequency outside of the bandwidth of the detected signal. Iterative solutions (for example, by replacing the zero bubble counts outside of that bandwidth with smooth extrapolations of the population trend) can be tested for stability; the tendency for the number of large bubbles to decrease with increasing bubble size in many bubble populations supports the logic of this approach (Leighton et al 2010).…”

Dolphin-Inspired Target Detection for Sonar and Radar

“…Fish will have been identified by the fact that they are strong in P − but weak in P + [In practice, because bubbles are such powerful scatterers, enhancing their scatter using P + is not difficult, and this technique is now routinely used in biomedical imaging (Burns et al, 2006); however suppressing their scatter using P − is not so simple, and Leighton et al, (2010) used the function P − /P + to achieve this]. Although in principle it is not required, the interpretation of the signals is aided by filtering the returned signals around the first harmonic before subtraction (to form P 1− ), and filtering them around the second harmonic before addition (to form P 2+ ).…”

“…We proposed that a sonar signal might be able to distinguish between fish and bubble clutter if it consisted of two closely-spaced pulses that were identical except that the second had opposite polarity with respect to the first, a scheme we called TWIPS (the Twin Inverted Pulse Sonar) (Leighton, 2004;Leighton et al, 2010).…”

“…The panels show the result of processing (c) in a conventional sonar manner, (d) using the P−/P+ TWIPS function, and (e) using the P+ TWIPS function. For details on the processing and the colour scale, see Leighton et al (2010).…”

Do dolphins benefit from nonlinear mathematics when processing their sonar returns?

“…The authors previously proposed a form of sonar signal (TWIPS: twin inverted pulse sonar) that could work in bubble clouds, consisting of pairs of pulses that were identical except that one was inverted with respect to the other, that could detect targets in bubbly water if the signal processing were to make use of nonlinear mathematics (Leighton 2004). TWIPS worked in simulation, tanks tests and finally sea trials, detecting targets in the wakes of a ferry and a commercial ship of 3953 and 4580 gross register tonnage, respectively (Leighton et al 2010(Leighton et al , 2011. However, while these TWIPS pulses were successful, there is no conclusive evidence that the types of pulses devised for that study are used by any type of dolphin (Leighton et al 2010;Finfer et al 2012).…”