Temporal fluctuations in vertical thermocline structure and depth span(on a time scale of 30 to 40 min)are shown to affect the arrival angle,and focusing ofmeasured broadband(22–28 kHz)non-surface-interacting acousti...Temporal fluctuations in vertical thermocline structure and depth span(on a time scale of 30 to 40 min)are shown to affect the arrival angle,and focusing ofmeasured broadband(22–28 kHz)non-surface-interacting acoustic signals at a depth of^100m.Measurements were taken in the PacificMissile Range Facility near Kauai island,Hawaii,for a source-receiver range of 1.0 km.The arrival time and angular spread of acoustic beams are obtained for measured signals using a plane wave beamformer with a-prior gaussian weighting.The weighting process reduces ambiguity in angularmeasurements due to spatial aliasing from a vertical arraywith element spacing d much greater than half the acoustic wavelength(λa/2)of the highest frequency in the broadband signal.Over two full periods of thermocline oscillation,2 times of high and 2 times of lowisotherm depth are selected to show fluctuations in angular beam spreading,focusing,and the robustness of the weighted beamformer routine.To benchmark the performance of the weighted beamformer,a twodimensional(2D)Parabolic Equation(PE)model calculates the angular signal spread and focusing using parameters to satisfy spatial sampling requirements for broadband beamforming.In the absence of spatial aliasing,beamforming the output of the 2D PE can be conducted without weighting.Comparison of measured and modeled results shows less than a degree of difference in the angular beam spread of direct,bottom reflected,and refracted paths.It is shown that a vertical array with d﹥﹥(λa/2)and gaussian weighting can resolve changes in angular spread and beam focusing as a function of vertical isotherm displacement.展开更多
A tide model (named DN1.0), which contains 12 principal constituents over China seas and the Northwest Pacific is estimated by along-track harmonic analysis with TOPEX/Poseidon altimetry data taken from 1993 to 2002. ...A tide model (named DN1.0), which contains 12 principal constituents over China seas and the Northwest Pacific is estimated by along-track harmonic analysis with TOPEX/Poseidon altimetry data taken from 1993 to 2002. CSR3.0, FES95.2 and DN1.0 are used respectively to detide the data for the time series of sea level anomaly (SLA) in the Yellow Sea, East China Sea, South China Sea and Northwest Pacific. The SLA curves and the power spectral density show that the major components that exist in SLA in China seas arise from the error of the tide models.展开更多
基金supported by the Office of Naval Research(ONR)Code 322OA [N00014-13-1-0306]
文摘Temporal fluctuations in vertical thermocline structure and depth span(on a time scale of 30 to 40 min)are shown to affect the arrival angle,and focusing ofmeasured broadband(22–28 kHz)non-surface-interacting acoustic signals at a depth of^100m.Measurements were taken in the PacificMissile Range Facility near Kauai island,Hawaii,for a source-receiver range of 1.0 km.The arrival time and angular spread of acoustic beams are obtained for measured signals using a plane wave beamformer with a-prior gaussian weighting.The weighting process reduces ambiguity in angularmeasurements due to spatial aliasing from a vertical arraywith element spacing d much greater than half the acoustic wavelength(λa/2)of the highest frequency in the broadband signal.Over two full periods of thermocline oscillation,2 times of high and 2 times of lowisotherm depth are selected to show fluctuations in angular beam spreading,focusing,and the robustness of the weighted beamformer routine.To benchmark the performance of the weighted beamformer,a twodimensional(2D)Parabolic Equation(PE)model calculates the angular signal spread and focusing using parameters to satisfy spatial sampling requirements for broadband beamforming.In the absence of spatial aliasing,beamforming the output of the 2D PE can be conducted without weighting.Comparison of measured and modeled results shows less than a degree of difference in the angular beam spread of direct,bottom reflected,and refracted paths.It is shown that a vertical array with d﹥﹥(λa/2)and gaussian weighting can resolve changes in angular spread and beam focusing as a function of vertical isotherm displacement.
基金Supported by Open Research Fund Program of the Key Laboratory of Geospace Environment and Geodesy, Ministry of Education, China (No.1469990324233-03-04).
文摘A tide model (named DN1.0), which contains 12 principal constituents over China seas and the Northwest Pacific is estimated by along-track harmonic analysis with TOPEX/Poseidon altimetry data taken from 1993 to 2002. CSR3.0, FES95.2 and DN1.0 are used respectively to detide the data for the time series of sea level anomaly (SLA) in the Yellow Sea, East China Sea, South China Sea and Northwest Pacific. The SLA curves and the power spectral density show that the major components that exist in SLA in China seas arise from the error of the tide models.
