The Study On Sound Propagation Of Horizontally Varying Sound Velocity Profiles Underneath The Rough Arctic Sea-ice

In recent years,due to global warming,sea ice is gradually melting.Arctic underwater acoustics has become a new research hotspot.The value of Arctic underwater acoustics in the fields of transportation,resource surveying,climate change characterization,etc.is becoming more and more prominent.The study of Arctic underwater acoustics is of great significance.The Arctic Ocean has unique properties relative to other oceans.Most of the Arctic Ocean is covered by sea ice all year round.It has a unique positive gradient sound velocity profile and double duct sound velocity profile.This thesis focuses on range-dependent under-ice acoustic propagation in the Arctic Ocean.In this thesis,firstly,based on the sea ice draft data collected by National Snow and Ice Data Center from 1960 to 2005 by upward looking sonar,the morphological characteristics of the bottom of the Arctic sea ice are analyzed.The statistical parameters of the data are calculated and analyzed.Based on the data,a random rough surface model used to describe the bottom of the sea ice is established,and the validity of the model is verified by comparing the statistical parameters of the data and the model.Secondly,assuming that the lower surface of rough sea ice is a random rough surface with Gaussian distribution,the full-wave model OASES is used to calculate the sea ice reflection coefficient,and numerically analyze the variation of sea ice reflection coefficient with ice thickness and roughness,acoustic frequency,and incident angle.Finally,using the SVP data from the 9th Chinese National Arctic research expedition,the research of the acoustic propagation characteristics of horizontally varying sound velocity profiles in the Arctic is carried out.By OASES-BELLHOP,the sound propagation model is established,and the analyses of the ray trace and transmission loss are carried out.From both the typical Arctic sound velocity profile and double duct sound velocity profile,the acoustic propagation characteristics of the horizontally varying sound velocity profile under the rough sea ice are analyzed by comparing the simulation results of the horizontally constant and horizontally varying sound velocity profiles.In addition,the influence of sea ice with different roughness on the underwater acoustic propagation characteristics is analyzed.The results show that when the sound velocity profile changes horizontally,the bending degree and direction of the sound ray,the depth of the sound ray reversal point will change accordingly,which in turn affects factors such as the angle of the sound ray incident on the ice-water interface and the number of interactions with the sea ice,thus changing the spatial distribution of sound energy.The attenuation of sound energy increases or decreases,and the horizontal propagation distance changes.Horizontal variation of sound velocity profile has certain non-negligible effects on sound propagation.The rougher the sea ice is,the faster the sound energy in the surface channel decays,and the horizontal propagation distance becomes smaller,while the sound energy in the SOFAR channel is almost unaffected.