Transoceanic underwater acoustic propagation modeling and diffraction effect
Transoceanic underwater acoustic propagation refers to the physical process that low-frequency sound waves interact with the deep ocean environment continuously on a large-scale,over a distance of 10000 km.It is the theoretical basis for acoustic detection at ultra-long range.The cumulative effect of the change in water sound velocity causes the diffraction,which is an important physical phenomenon in transoceanic acoustic propagation and leads to significant changes in acoustic propagation paths,arrival angles and acoustic propagation loss.This phenomenon transforms the"acoustic shadow zone"caused by the seafloor topography into an"acoustic illumination zone"and makes it possible to detect the acoustic signal of the event,which propagates over long distances.A three-dimensional underwater acoustic propagation model is constructed in the Cartesian coordinate system to improve the spatial resolution of the traditional acoustic propagation model in the cylindrical coordinate system.The model simulates a sound field with a constant spatial resolution,either near or far.Then,the accuracy of the model is validated by comparing the simulation results with the analytical solution derived from the method of images via Acoustical Society of America slope topography benchmark problems.The Tonga submarine volcano which erupted on 15 January 2022,was used as an example.A model was created to simulate volcanic T-wave propagation across the Pacific Ocean to the Atlantic Ocean,over 16000 km.The results show that T-waves excited by a volcano in the Pacific bypass the southern end of the South American continent and arrive at the mid-Atlantic along the non-great circular path,eventually being detected by the hydrophone triplet H10N at Asunción Island.Comparing simulation results under various waveguide conditions indicates that the variation of sound velocity in the ocean near Antarctica is the main reason for the horizontal bending of sound rays.The quantitative results show that accounting for the cumulative effect of water sound velocity variation,the reduction of sound propagation loss would be over 60 dB in the horizontal plane at 850 m depth and in the vertical profile at the range of 10000 km-16500 km.The diffraction caused by the changes in water sound velocity is the main reason that underwater acoustic observation systems are able to receive acoustic signals propagating through the oceans.
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