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All figures (14)
FIG. 11. (Color online) Measured (signs), approximated by an empirical curve (dotted) and numerically modeled (WNI – solid, PE – dashed) transmission loss at 14 Hz. The source ESD level is estimated from the transmitted signal model to be 213 dB re 1 lPa2 s /Hz at 1 m.
FIG. 10. Energy spectrum density of the signal from the airgun array at 1 m from the array center modeled for the far field.
TABLE I. Geoacoustic parameters of the seafloor model used for numerical modeling of sound propagation.
FIG. 12. (Color online) Low-pass (<20 Hz) filtered airgun signals received on a bottom-mounted hydrophone at different distances from the signal source. The waveforms are aligned at the arrival time of high-frequency waterborne waves (vertical dotted line). The dashed line indicates the arrival times of the head wave propagating along the interface of the rigid basement at a depth of approximately 1000 m below the seafloor.
FIG. 1. (Top) Transmission loss over semi-cemented calcarenite without bulk acoustic attenuation and (bottom) modulus of Green’s function. The circles indicate the critical frequencies of modes 1-4 with corresponding wave numbers.
FIG. 3. Group velocities of modes 1–4 versus frequency calculated for the primary model of a shallow water acoustic channel over calcarenite. Modal attenuation is gray-scale coded. Values above 0.2 dB/km are shown as a dotted line.
FIG. 2. (Color online) Imaginary versus real part of the horizontal wave number for modes 1 to 4 calculated for the primary model of a shallow water acoustic channel with an elastic seabed. The dashed lines indicate real wave numbers at the critical frequencies given by Eq. (1). The signal frequency varied from 4 to 40 Hz.
FIG. 13. (Color online) (Top) Transmission loss as a function of frequency determined from airgun signals measured by receiver 1 at a distance of approximately 40 km (dotted line). Values of low SNR (below 1 dB) are not shown. The solid line is a numerical prediction using the WNI method and a range-independent bathymetry model with the geoacoustic parameters given in Table I. The dashed line shows the numerical prediction by the PE method applied to the same acoustic environment model but with the rangedependent bathymetry shown by the dashed line in Fig. 8. (Bottom) Same as top figure but for the signal measured at receiver 2. The PE numerical prediction shown here used the bathymetry model shown by the dashed line (2) in Fig. 8.
FIG. 4. Attenuation of modes 1 to 3 versus water depth and frequency calculated for the primary model of the acoustic channel.
FIG. 5. Reflection coefficient from a 1 m layer of cap rock overlaying semicemented calcarenite versus grazing angle and frequency.
FIG. 8. (Color online) Bathymetry along the acoustic paths: (1) from receiver 1 to the starting point (southernmost) of inshore transect A; (2) from receiver 2 to the starting point of inshore transect A; and (3) from receiver 3 to the starting point of offshore transect B. Bathymetry data were taken from the Australian bathymetry and topography grid (Geoscience Australia, 2009). The dashed lines show piecewise linear approximation of the bathymetry profiles used for PE modeling of transmission loss.
FIG. 6. Attenuation of modes 1 to 4 in a shallow water channel over an elastic seabed with (solid lines) and without (dashed lines) 1 m layer of cap rock overlaying semi-cemented calcarenite.
FIG. 7. Location of the hydrophone array (1 to 4) and the easternmost inshore (A) and offshore (B) seismic transects in Bass Strait. The white circle shows the location of a 100 m borehole made as part of a geotechnical survey.
FIG. 9. Spectrogram of a 40-s recording fragment made on receiver 1 showing five airgun signals from the inshore transect.
Journal Article
•
DOI
•
Characteristics of sound propagation in shallow water over an elastic seabed with a thin cap-rock layer.
[...]
Alec J. Duncan
1
,
Alexander Gavrilov
,
Robert D. McCauley
,
Iain Parnum
,
Jon M. Collis
- Show less
+1 more
•
Institutions (1)
Curtin University
1
11 Jul 2013
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Journal of the Acoustical Society of America