DIFFERENCES IN THE ACOUSTIC ECHOES FROM SUBMERGED ELASTIC SHELLS CONTAINING DIFFERENT FLUIDS

It is desirable to be able to distinguish between a submerged metal ob ject and one essentially composed of air-filled membranes, such as fis h. This target-identity problem has been addressed before. Another tar get-identity problem still to be addressed is that of distinguishing b etween a (water-tight) metal shell containing air inside and the same shell with defective seals that flood it with water, e.g. empty oil dr ums or old refrigerators that may be lying on the sea floor, before an d after becoming flooded. Debris of this type is apparently abundant i n many shallow coastal waters. The characterization would be done remo tely, by analysis of the acoustic echoes returned by these scatterers. We have constructed a predictive model that simulates the resonance e choes returned by a spherical steel shell (of various thicknesses), fi rst air-filled and then flooded with water. As a first approximation, the shell is assumed to be many characteristic dimensions away from th e seafloor. We then extract the spectrum of resonances in both cases a nd exhibit their extraordinary difference in features. These could the n be used to easily distinguish between both active signatures, remote ly and in situ.