Clutter suppression and classification using twin inverted pulse sonar in ship wakes

Abstract

Twin inverted pulse sonar (TWIPS) is here deployed in the wake of a moored rigid inflatable boat (RIB) with propeller turning, and then in the wake of a moving tanker of 4580 dry weight tonnage (the Whitchallenger). This is done first to test its ability to distinguish between scatter from the wake and scatter from the seabed, and second to test its ability to improve detectability of the seabed through the wake, compared to conventional sonar processing techniques. TWIPS does this by distinguishing between linear and nonlinear scatterers and has the further property of distinguishing those nonlinear targets which scatter energy at the even-powered harmonics from those which scatter in the odd-powered harmonics. TWIPS can also, in some manifestations, require no range correction (and therefore does not require the a priori environment knowledge necessary for most remote detection technologies).

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

“…As with TWIPS (Leighton et al 2010(Leighton et al , 2011, such effectiveness at discrimination is seen as its primary advantage, an enhancement of the ability to detect the target in the first place (prior to classifying it) being a secondary, lesser advantage. Figure 8 compares the ROC curve for BiaPSS processing of this dolphin-like pulse for tank data (figure 8a) and for simulation (figure 8b) (using the simulation method described by Chua et al (2012)).…”

“…Consequently, fish would represent substantially linear targets to dolphins. However, man-made sonar could be designed to use the frequencies where nonlinear scatter can be excited from targets; for example, in the detection of sea mines in coastal waters (Leighton et al 2010(Leighton et al , 2011. Extension of the technique to radar might allow the possibility of using nonlinearities to distinguish between electronics and soil, e.g.…”

“…Note that a ROC curve only gives a measure of the detection performance and not the ability to provide classification. Leighton et al (2010Leighton et al ( , 2011 found that TWIPS was very effective at task (i), and could generate some improvements at task (ii).…”

“…Such processing will not lead to the complete removal of nonlinear components, but only serve to suppress them partially. This approach can be regarded as a generalization of the TWIPS principle (Leighton et al 2010(Leighton et al , 2011, with TWIPS corresponding to the choice of G = −1, albeit that, in that instance, the roles of P + and P − are reversed. The website where the data can be obtained is listed in the acknowledgements.…”

“…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).…”