Historically, operation of the mid-frequency active sonar in littoral regions has presented sonar operators with challenges due to the complex nature of the ocean acoustic environment in shallow waters. Although there are complex reasons for the appearance of clutter, research has shown that biological backscatter currently produces serious interference in midfrequency active sonar. This proposal will show that air bladders of small fish, which are found with great abundance in the ocean, have an acoustic resonant frequency that is within the current AN/SQS-53C echo-ranging band and cause serious performance degradation. It is proposed that the performance degradation resulting from fish swim bladders can be largely eliminated by exploiting the known resonant characteristics of biologics to transmit at frequencies away from that of the resonant biological backscattering. The objective of this proposal is to demonstrate the feasibility and efficacy of using a modified transmit spectrum (of currently unavailable bands) and an associated innovative in-situ analysis and selection method, to mitigate the resonant backscattering effects due to biologics on mid-frequency active sonar returns, in particular, the AN/SQS-53C.
