The Research On Suppressing The Helicopter Noise Interference By Use Of Sonar Buoy

Aero sonar buoy is one of the major equipment that helicopter uses to detect underwatertarget, but when employed around the buoy, the helicopter’s radiation noise would interferethe sonar buoy to estimate the target bearing. Adaptive interference cancellation is applied tosolve the problem of how to suppress the helicopter noise interference effected on sonar buoy,and the adaptive cancellation on helicopter noise is also discussed.First, several methods of the target bearing estimation by sonar buoy based on vectorhydrophone is introduced; the acoustic wave propagation in the air-water interface, and themain path that noise propagated from the helicopter to the vector hydrophone is also analyzedin this dissertation. By analyzing and comparing the noise characteristics of helicopter andunderwater target, the influence of the estimating results caused by helicopter noiseinterference is being illustrated, when taking acoustic intensity average, histogram andweighted histogram as to estimate the target bearing.Considering practical application, the adaptive signal process based on the least meansquare error criterion (LMS) is chosen to implement the helicopter noise interferencecancellation. The LMS algorithm principle, together with its characteristics such asconvergence and maladjustment are presented. The moving target signal is simulated byinterpolating fitting method, which offers data source for further cancellation research.Two adaptive cancellation methods are proposed in the dissertation, using aerialhelicopter noise and the combined velocity as reference signal. The theory of these twomethods is introduced systemically and their cancellation effects are also analyzed viasimulation. The former enables the helicopter’s noise interference cancellation effectively inthe hovering or low-speed flight, but as the speed increases, its cancelling effect declinedrapidly; Except for the existence of the cancellation blind zone, the latter shows no affects onthe helicopter speed and is more suitable for the practical application.