Geoacoustic Inversion With Distributed Sensors

In shallow water,geoacoustic parameters such as sediment layers and thicknesses,density and attenuation coefficient have a great influence on the propagation of acoustic signals.The geoacoustic parameters of the sediments such as sound speed profile attenuation coefficient are difficult to measure in a direct way.So the method of geoacoustic inversion has been paid much attention.The method has been researched extensively using sound received on a vertical or horizontal line array(VLA/HLA).Most of the research prefers VLA due to its advantage of sampling the spatial variability of the acoustic fields with respect to the depth in the shallow water.In comparison,an HLA system provides significant advantages in practical aspects such as stability and ease of deployment.Both VLA and HLA require usually a dedicated ship to deploy the array and source to collect the data.Conducting such experiments is costly.With the development of underwater sensor network,it is anticipated in the future that many low-cost acoustic transceivers will be deployed in the ocean in the form of a distributed sensor network.Based on this,the paper proposes a geoacoustic inversion method using distributed sensors.The major work and contributions in this paper are given as follows:1)First of all,the method using distributed sensors is analyzed theoretically.When the source moves,there seems to be a different horizontal array with different array aperture at each position of the source.Different distances between source and sensors mean different incident angles which increases the diversity of spatial sampling.So compared with the traditional ways,the new method can get at least similar inversion results.2)The method using distributed sensors is applied to two different environments.Simulation results using genetic algorithm(GA)will be presented to compare with VLA and HLA,respectively.3)For the distributed sensors,the data received from two sensors may not be coherent due to the long distance between them.So frequency-coherent and phone-coherent inversion methods are applied to distributed sensors to find a more suitable method.4)The method using distributed sensors is applied to the SW06 experiment.The LFM signal received by the VLA is filtered and the data of the desired frequencies is extracted.Geoacoustic inversion is first carried out with VLA to verify the effectiveness of the data by comparing the results with the true values.Then the inversion method using distributed sensors is applied to the data for verifying the effectiveness of the method.