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In bistatic acoustic scattering wave testing, there will be strong direct blast interference , An algorithm based on vector sensor adaptive signal processing that rejecting of direct blast interference in bistatic sonar has been studied, through computer simulation the effectiveness of this algorithm was demonstrated. Simulation test results show that when the space angle of interference and signal greater than 5 deg, the object scattering signal can be effectively estimated with six elements of vector sensor array Introduction In recent years, bistatic or multistatic acoustic scattering testing becomes an effective way of object acoustic characteristics study, because the characteristics of bistatic or multistatic target scattering wave provide more information about the target than the characteristics of monostatic target acoustic scattering wave [1-3], but the testing of bistaic acoustic scattering has the problem of direct blast interference [4][5]. Fig.1 is diagrammatic sketch of direct blast interference in bistatic acoustic testing. In bistatic acoustic testing configuration, the transmitter and the receiver are separated at a certain distance, the transmission loss of direct blast signal is smaller than the signal scattered by underwater object for the direct blast signal transmits directly from transmitter to receiver. When direct blast and object scattering signals arrive at the receiver at the same time, the object scattering signal is impossible to be extracted from the strong direct blast interference. Fig.1. Direct blast interference in bistatic acoustic testing Recently, the problem of direct blast rejection in bistatic acoustic testing has gained great interest of study. Normally, we use conventional beamforming to separate two signals that arriving from different directions, but this method fails under the condition that interference is much stronger than the signal. Adaptive filtering is another way of interference rejection [4][5][6], through the adaptive null steering processor, the direct blast interference could be suppressed. The performance of this method depends greatly on the beamwidth of conventional beamforming, when the space angle of interference and signal smaller than one beamwidth, namely the object scattering signal and the direct blast interference are in the same receiving beam, adaptive filtering cannot reject the interference accurately. Many studies have shown that acoustic vector sensor could provide higher directional gain International Power, Electronics and Materials Engineering Conference (IPEMEC 2015) © 2015. The authors Published by Atlantis Press 29 compared with hydrophone [7], so the vector sensor array could provide higher directional gain against reverberation with small aperture. In this paper, an algorithm based on vector sensor signal processing and adaptive signal processing has been studied, this algorithm fully integrated the benefits of adaptive filtering and vector sensor array signal processing, which could reject the direct blast interference effectively with small array aperture. Principle of Direct Blast Rejection based on Vector Sensor adaptive Array Processing The principal of adaptive array processing is steering the lowered or null response of a receiving beam pattern in the direction of interference, the width of the null depends on the array beamwidth, when space angle of interference and signal smaller than one beamwidth but not in the same direction, adaptive array processing could reject the interference but also decreased the power of the desired signal. Vector sensor array could provide higher directional gain against reverberation with small aperture, based on that, we can use the adaptive array processing to suppress the direct blast interference and use the vector sensor array processing to increase the gain of the signal to reverberation. Fig.2 is the block diagram of adaptive filtering vector sensor array processing rejecting direct blast interference, in which, CBF means conventional beamforming. The vector sensor array element space is d in bistatic testing. The acoustic vector sensor measure the acoustic pressure and velocity of the scattering wave, there are three channel in one acoustic vector.  is the DOA of direct blast interference, which can be accurately obtained through surface positioning system. The DOA of object scattering signal and direct blast are different, the signal received by receiver array is expressed as ) (t S t i , the signal processing flow of direct blast rejection algorithm is:

Rejection Of Direct Blast Interference Based on Vector Sensor adaptive Array Processing