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 Justin Eickmeier,Mohsen Badiey.Influence of Short Time-Scale Water-Column Temperature Fluctuations on Broadband Signal Angular Beam Spreading[J].Journal of Marine Science and Application,2018,(2):216-223.[doi:10.1007/s11804-018-0020-x]
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Influence of Short Time-Scale Water-Column Temperature Fluctuations on Broadband Signal Angular Beam Spreading


Influence of Short Time-Scale Water-Column Temperature Fluctuations on Broadband Signal Angular Beam Spreading
Justin Eickmeier Mohsen Badiey
Justin Eickmeier Mohsen Badiey
College of Earth, Ocean and Environment, University of Delaware, Newark, DE 19716, USA
ThermoclineBeamformingSpatial aliasingHigh-frequencyShallow waterBroadbandParabolic equation
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 of measured broadband (22-28 kHz) non-surface-interacting acoustic signals at a depth of~100 m. Measurements were taken in the Pacific Missile 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 angular measurements due to spatial aliasing from a vertical array with 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 low isotherm 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.


Apel JR, Badiey M, Chiu CS, Finnette S, Headrick R, Kemp J, Lynch JF, Newhall A, Orr MH, Pasewark BH, Tielbuerger D, Turgut A, von der Heydt K, Wolf S (1997) An overview of the 1995 SWARM shallow-water internal wave acoustic scattering experiment. IEEE J Ocean Eng 22(3):465-500. https://doi.org/10.1109/48.611138
Aubry A, Derode A, Roux P, Tourin A (2007) Coherent backscattering and far-field beamforming in acoustics. J Acoust Soc Am 121:70-77. https://doi.org/10.1121/1.2400662
Badiey M, Song A, Smith KB (2012) Coherent reflection from surface gravity water waves during reciprocal acoustic transmissions. J Acoust Soc Am 132(4):EL290-EL295. https://doi.org/10.1121/1.4747815
Badiey M, Eickmeier J, Song A (2014) Arrival-time fluctuations of coherent reflections from surface gravity water waves. J Acoust Soc Am 135(5):EL226-EL231. https://doi.org/10.1121/1.4871577
Beron-Vera FJ, Brown MG (2009) Underwater acoustic beam dynamics.J Acoust Soc Am 126(1):80-91. https://doi.org/10.1121/1.3139901
Bondor VG, Grebenyuk YV, Sabynin KD (2009) The spectral characteristics and kinematics of short-period internal waves on the Hawaiian shelf. J Atmos Oceanic Phys 45(5):641-651. https://doi.org/10.1134/S0001433809050077
Carbone NM, Hodgkiss WS (2000) Effects of tidally driven temperature fluctuations on shallow-water acoustic communications at 18 kHz.IEEE J Ocean Eng 25(1):84-94. https://doi.org/10.1109/48.820739
Colosi JA, Flatte SM, Bracher C (1994) Internal-wave effects on 1000-km oceanic acoustic pulse propagation:simulation and comparison with experiment. J Acoust Soc Am 96(1):452-468. https://doi.org/10.1121/1.411331
Cox H, Zeskind R, Owen M (2003) Robust adaptive beamforming. IEEE Trans Acoust Speech Signal Process 35(10):1365-1376. https://doi.org/10.1109/TASSP.1987.1165054
Deane GB (2001) Environmental factors that affect acoustic propagation and underwater communications in the surf zone. J Acoust Soc Am 109(5):2449. https://doi.org/10.1121/1.4744681
Flatte SM, Dashen R, Munk W, Watson K, Zachariasen F (1979) Sound transmission through a Fluctuating Ocean. Cambridge U. P, New York, pp 50-60
Hinich MJ (1978) Processing spatially aliased arrays. J Acoust Soc Am 64(3):792-794. https://doi.org/10.1121/1.382044
Jensen B, Kuperman WA, Porter MB, Schmidt H (2011) Parabolic equations. In:Computational ocean acoustics. Springer, New York, pp 457-467
Karjadi EA, Badiey M, Kirby JT, Bayindir C (2012) The effects of surface gravity waves on high-frequency acoustic propagation in shallow water. IEEE J Ocean Eng 37(1):112-121. https://doi.org/10.1109/JOE.2011.2168670
Kinsler LE, Frey AR, Coppens AB, Sanders JV (1999) Fundamentals of acoustics. John Wiley & Sons, Berkeley, pp 70-80
Lee OS (1961) Observations on internal waves in shallow water. J Limnol Oceanogr 6(3):312-321. https://doi.org/10.4319/lo.1961.6.3.0312
Li J, Stoica P (2005) Robust adaptive beamforming. John Wiley & Sons, Hoboken, pp 50-60
Möser M (2004) Engineering acoustics:an introduction to noise control.Springer Germany, Berlin, pp 44-50
Moura J, Lourtie I (eds) (1993) Acoustic signal processing for ocean exploration. Springer Netherlands, Dordrecht, pp 79-114
Porter MB, Bucker HP (1987) Gaussian beam tracing for computing ocean acoustic fields. J Acoust Soc Am 82(4):1349-1359. https://doi.org/10.1121/1.395269
Smith K (2001) Convergence, stability, and variability of shallow water acoustic predictions using a split-step Fourier parabolic equation model. J Comput Acoust 9(1):243-285. https://doi.org/10.1142/S0218396X01000401


Received date:2017-06-01;Accepted date:2017-12-27。
Foundation item:This research was supported by the Office of Naval Research (ONR) Code 322OA[N00014-13-1-0306].
Corresponding author:Justin Eickmeier,jeickmei@udel.edu
Last Update: 2018-10-11