Bistatic Bottom Scattering And Reverberation Modelling And Statistical Analysis

Bottom reverberation is formed by the superposition of the scattering signals generated by a large number of bottom scatters at the receiving position,which is dominant in the echo of shallow water.Reverberation is regarded as interference in active sonar and should be suppressed,in our under water topography,reverberation is a signal which contains useful information.Scattering characteristics of the sea bottom can be inferred from the reverberation,which can be used to estimate bottom topography.This is the inverse problem,and it needs to be supported by the forward problem.The forward problem studies the process of source signals illuminate the bottom,then scattered and received by the receiving sensor.Forward model of scattering and reverberation is established to solve the problem.At present,the model researches mainly focus on the modelling of monostatic scattering,which studies the influencing factors of backscattering.With the widely application of the bistatic sonar system,the forward scattering and reverberation modeling becomes urgent,however,the modeling researches of low frequency bistatic sonar system is relatively less.This paper is devoted to the scattering and reverberation modelling and studying it's the statistical characteristics of a low frequency bistatic sonar system,which can be applied to the forward scattering and backward scattering.Aiming at low frequency bistatic sonar system and based on the scattering model which uses the small slope approximation,this paper studies the bottom scattering strength at different incident angles,scattered angles and bistatic angles,and also studies the influence of significant topography and different roughness of the bottom on the scattering strength.By studying the variation of scattering strength distribution of undulating seafloor and compared to the flat seafloor,it is concluded that the scattering strength will increased if the terrain slope is steeper and decreased if the slope becomes gentle.By studying the effects of the properties of the sediments(2D roughness spectrum strength,2D roughness spectrum index,density of the sediment,complex sound velocity of compression wave and shear wave)on the bottom scattering strength,it is concluded that 2D roughness spectrum strength is the key factor affecting the bottom scattering strength.Based on the scattering model above,combined with the acoustic propagation model in the ocean,a bistatic reverberation model is established,in which the signal is transmitted by a vertical line array and is received by a horizontal line array.And we studied the reverberation distribution with different bottom roughness and significant topographies.By simulation,we studied the reverberation distribution and statistical characteristics of shallow water and deep sea in detail,when the vertical array points to different angles to transmit signalsBy processing the experiment data,we obtain the reverberation distribution of bistatic sonar system in which the signal is transmitted by the vertical line array and received by the horizontal line array,and the simulation results are compared to preliminarily verify the feasibility of the reverberation model.The research work of this paper supports the imaging of bottom topography by establishing scattering and reverberation model to solve the forward problem.