Figure 1.
Map of Australia (a) with expansion of northwest Australia (b). Additional expansions of the southern ((c); off Point Samson) and northern ((d); off Broome) sites and positions of seismic sail lines.
Figure 1.
Map of Australia (a) with expansion of northwest Australia (b). Additional expansions of the southern ((c); off Point Samson) and northern ((d); off Broome) sites and positions of seismic sail lines.
Figure 2.
Map of all acoustic sensor deployments for (a,d) pressure, (b,e) ground motion and (c,f) particle motion for the northern (left images) and southern (right images) experimental sites. Sensors notations (stars) are colour coded with the respective seismic sail lines they recorded. Seismic survey at the southern site was conducted as a racetrack design where the airgun array was only operated during sail lines at the western end of the track (coloured lines running north northwest to south southeast to the left of the images).
Figure 2.
Map of all acoustic sensor deployments for (a,d) pressure, (b,e) ground motion and (c,f) particle motion for the northern (left images) and southern (right images) experimental sites. Sensors notations (stars) are colour coded with the respective seismic sail lines they recorded. Seismic survey at the southern site was conducted as a racetrack design where the airgun array was only operated during sail lines at the western end of the track (coloured lines running north northwest to south southeast to the left of the images).
Figure 3.
Pressure power spectra measured almost directly underneath airgun array (red) and at 190 m (blue).
Figure 3.
Pressure power spectra measured almost directly underneath airgun array (red) and at 190 m (blue).
Figure 4.
Power spectral density of pressure signals from the airgun array as recorded by a USR throughout an individual seismic sail line operated at the northern ((a), closest point of approach, ≈12 m horizontal range, 18 September) and southern ((b), closest point of approach, ≈190 m horizontal range, 21 September) sites. The white lines mark the start and end of airgun operations along the seismic line.
Figure 4.
Power spectral density of pressure signals from the airgun array as recorded by a USR throughout an individual seismic sail line operated at the northern ((a), closest point of approach, ≈12 m horizontal range, 18 September) and southern ((b), closest point of approach, ≈190 m horizontal range, 21 September) sites. The white lines mark the start and end of airgun operations along the seismic line.
Figure 5.
Proportion of unsaturated to total signals within logarithmic horizontal range brackets for: (
a) particle motion at the northern (red) and southern (black) sites; and (
b) pressure only for USR instruments with pre-amp/secondary gain (dB) settings of −40/0 (red), −20/0 (blue), 0/0 (black), 0/20 (magenta), 20/0 (green) and 20/20 (cyan). The expected working ranges for each sensor can be found in
Table 1.
Figure 5.
Proportion of unsaturated to total signals within logarithmic horizontal range brackets for: (
a) particle motion at the northern (red) and southern (black) sites; and (
b) pressure only for USR instruments with pre-amp/secondary gain (dB) settings of −40/0 (red), −20/0 (blue), 0/0 (black), 0/20 (magenta), 20/0 (green) and 20/20 (cyan). The expected working ranges for each sensor can be found in
Table 1.
Figure 6.
Received levels of the airgun array signal with range for the southern (black) overlaid with northern (red) sites for: (a) peak-to-peak pressure level; (b) sound exposure levels; (c) mean-square sound pressure levels; (d) maximum magnitude ground acceleration; (e) and maximum magnitude particle acceleration. Mean values at each range (all data) interpolated along log10(range) (continuous blue line), together with the 95% confidence intervals (dotted blue lines) are shown along with the fitted curve (Equation (2)) using all data as the red curve.
Figure 6.
Received levels of the airgun array signal with range for the southern (black) overlaid with northern (red) sites for: (a) peak-to-peak pressure level; (b) sound exposure levels; (c) mean-square sound pressure levels; (d) maximum magnitude ground acceleration; (e) and maximum magnitude particle acceleration. Mean values at each range (all data) interpolated along log10(range) (continuous blue line), together with the 95% confidence intervals (dotted blue lines) are shown along with the fitted curve (Equation (2)) using all data as the red curve.
Figure 7.
Received levels of the airgun array signal averaged in logarithmic range bins with horizontal range for the northern (blue) and southern (red) sites for peak-to-peak pressure level (a), sound exposure level (b), mean-square sound pressure level (c), maximum magnitude ground acceleration (d), and maximum magnitude particle acceleration (e) levels.
Figure 7.
Received levels of the airgun array signal averaged in logarithmic range bins with horizontal range for the northern (blue) and southern (red) sites for peak-to-peak pressure level (a), sound exposure level (b), mean-square sound pressure level (c), maximum magnitude ground acceleration (d), and maximum magnitude particle acceleration (e) levels.
Figure 8.
Peak-to-peak pressure levels (a), sound ex-posure levels (b), mean-square sound pressure levels (c) and pressure peak gradient (d) for the northern (N = left) and southern (S = right) sites, shown as a function of logarithmic horizontal range and azimuth (y-axis, o) from tow direction (assumed array symmetrical, 0° is ahead). The white lines encapsulate measured data bounds. Gridding used linear interpolation.
Figure 8.
Peak-to-peak pressure levels (a), sound ex-posure levels (b), mean-square sound pressure levels (c) and pressure peak gradient (d) for the northern (N = left) and southern (S = right) sites, shown as a function of logarithmic horizontal range and azimuth (y-axis, o) from tow direction (assumed array symmetrical, 0° is ahead). The white lines encapsulate measured data bounds. Gridding used linear interpolation.
Figure 9.
Maximum values of horizontal (a), vertical (b), and magnitude (c) particle acceleration levels for the northern (N = left) and southern (S = right) sites, shown as a function of logarithmic horizontal range and azimuth (y-axis, °) from tow direction (assumed array symmetrical, 0° is ahead). The white lines encapsulate measured data bounds. The colour axes are common across panels. Gridding used linear interpolation.
Figure 9.
Maximum values of horizontal (a), vertical (b), and magnitude (c) particle acceleration levels for the northern (N = left) and southern (S = right) sites, shown as a function of logarithmic horizontal range and azimuth (y-axis, °) from tow direction (assumed array symmetrical, 0° is ahead). The white lines encapsulate measured data bounds. The colour axes are common across panels. Gridding used linear interpolation.
Figure 10.
Maximum values of horizontal (a), vertical (b), and magnitude (c), ground acceleration levels for the northern (N = left) and southern (S = right) sites, shown as a function of logarithmic horizontal range and azimuth (y-axis, °) from tow direction (assumed array symmetrical, 0° is ahead). The white lines encapsulate measured data bounds. The colour axes are common across panels. Gridding used linear interpolation.
Figure 10.
Maximum values of horizontal (a), vertical (b), and magnitude (c), ground acceleration levels for the northern (N = left) and southern (S = right) sites, shown as a function of logarithmic horizontal range and azimuth (y-axis, °) from tow direction (assumed array symmetrical, 0° is ahead). The white lines encapsulate measured data bounds. The colour axes are common across panels. Gridding used linear interpolation.
Figure 11.
Relationship between pairs of metrics, for the southern site (black dots) overlaid with the northern site (red dots) for sound exposure level against peak-to-peak pressure level (a), sound exposure level against mean-square sound pressure level (b), SEL against magnitude of ground acceleration (c), sound exposure level against magnitude of particle acceleration (d), and magnitude of particle acceleration against magnitude of ground acceleration (e).
Figure 11.
Relationship between pairs of metrics, for the southern site (black dots) overlaid with the northern site (red dots) for sound exposure level against peak-to-peak pressure level (a), sound exposure level against mean-square sound pressure level (b), SEL against magnitude of ground acceleration (c), sound exposure level against magnitude of particle acceleration (d), and magnitude of particle acceleration against magnitude of ground acceleration (e).
Table 1.
Instrument configurations, input signal tolerances, and expected operational ranges, including pre-amplifier gain (dB), the secondary gain (dB) applied in the digitizing electronics, and for the CMST-DSTO instruments: calculated maximum peak pressure (kPa and dB re 1 µPa), the maximum voltage at the hydrophone output.
Table 1.
Instrument configurations, input signal tolerances, and expected operational ranges, including pre-amplifier gain (dB), the secondary gain (dB) applied in the digitizing electronics, and for the CMST-DSTO instruments: calculated maximum peak pressure (kPa and dB re 1 µPa), the maximum voltage at the hydrophone output.
Instrument | Pre-Amplifier Gain (dB) | System Gain (dB) | Maximum Peak Pressure (kPa) | Maximum Peak Pressure Level (dB re 1 µPa) | Maximum Voltage (V) | Expected Working Range (m) |
---|
USR | −40 | 0 | 1451.2 | 243.2 | 230 | <200 |
USR | −20 | 0 | 145.1 | 223.2 | 23 | 100–400 |
USR | 0 | 0 | 14.5 | 203.2 | 2.3 | 200–1000 |
USR | 0 | 20 | 4.6 | 193.2 | 0.727 | 500–1500 |
USR | 20 | 0 | 1.5 | 183.2 | 0.23 | >1000 |
USR | 20 | 20 | 0.1 | 163.2 | 0.023 | >4000 |
GS-M20 pressure | 20 | 0–18 | | | | Unknown |
GS-M20 particle motion | 20 | 0–18 | | | | Unknown |
Table 2.
Description of acoustic metrics quantified for individual discharges of the 2600 cui airgun array.
Table 2.
Description of acoustic metrics quantified for individual discharges of the 2600 cui airgun array.
Metric (Abbreviation) | Description | Units | Derivation |
---|
Mean-square sound pressure level (SPL) | , to the specified reference value, p02, in decibels, here taken over the time for 90% of total signal energy to pass (T90%). | dB re 1 μPa2 | where Lp is mean-square sound pressure level, T90% is the signal length, is signal plus noise, and T5 and T95 are the times where 5% and 95% of the cumulative (signal plus noise) has passed and is 1 µPa. |
Peak-to-peak pressure level (P-P) | Twenty times the logarithm (base 10) of the ratio of pressure difference between the compressional and rarefactional pressure within the signal (not necessarily consecutive peaks) using the appropriate reference value | dB re 1 μPa | , where is the peak-to-peak level, p is sound pressure, t is time, is peak-to-peak pressure, and is 1 µPa. |
Sound exposure level (SEL) | Ten times the logarithm (base 10) of the ratio of time-integrated (over the 90% energy duration) squared pressure, less ambient noise contribution, to the reference exposure. | dB re 1 μPa2·s | , where Ep is the time-integrated pressure, p is pressure, s and n denote signal and noise, respectively, T5 and T95 are time points bracketing the 90% energy duration, and Tn and Tn + T denote a period away from the signal where the noise is stationary. T = T95 − T5. = 1 µPa2·s. |
Peak pressure gradient (PPG) | Twenty times the logarithm (base 10) of the peak-to-peak pressure, divided by the time taken for this pressure difference to occur, using the appropriate reference value. | dB re 1 μPa·s−1 | is 1 µPa. |
Max. hor. particle acc. (MxHPA) | Twenty times the logarithm (base 10) of the maximum magnitude of each of the horizontal particle acceleration vectors | dB re 1 µms−2 | of 1 µms−2 |
Max. vert. particle acc. (MxVPA) | Twenty times the logarithm (base 10) of the maximum vertical particle acceleration | dB re 1 µms−2 | of 1 µms−2 |
Max. particle acc. 3-axis (MxMPA) | Twenty times the logarithm (base 10) of the maximum magnitude of the vector sum of the X, Y, and Z particle acceleration values (where X, Y, and Z are north, east, and vertical vectors). | dB re 1 µms−2 | of 1 µms−2 |
Max. hor. ground acc. (MxHGA) | Twenty times the logarithm (base 10) of the maximum magnitude of the vector sum of the two horizontal ground acceleration vectors | dB re 1 µms−2 | of 1 µms−2 |
Max. vert. ground acc. (MxVGA) | Twenty times the logarithm (base 10) of the maximum vertical ground acceleration | dB re 1 µms−2 | of 1 µms−2 |
Max. ground acc. 3-axis. (MxMGA) | Twenty times the logarithm (base 10) of the maximum magnitude of the vector sum of the X, Y, and Z ground acceleration values (where X, Y, and Z are north, east, and vertical vectors) | dB re 1 µms−2 | of 1 µms−2 |
Table 3.
Maximum levels measured at the northern and southern sites, and the horizontal range at which they occurred for peak-to-peak pressure level (P-P), sound exposure level (SEL), mean-square sound pressure level (SPL), pressure peak-gradient (PPG), seabed ground acceleration (maximum horizontal and vertical vectors and magnitude), and particle acceleration (maximum horizontal and vertical vectors and magnitude) levels, as defined in
Table 2.
Table 3.
Maximum levels measured at the northern and southern sites, and the horizontal range at which they occurred for peak-to-peak pressure level (P-P), sound exposure level (SEL), mean-square sound pressure level (SPL), pressure peak-gradient (PPG), seabed ground acceleration (maximum horizontal and vertical vectors and magnitude), and particle acceleration (maximum horizontal and vertical vectors and magnitude) levels, as defined in
Table 2.
| Northern Site | Southern Site |
---|
Measure and Unit | Level | Horizontal Range (m) | Level | Horizontal Range (m) |
---|
P-P (dB re 1 µPa) | 230 | 12 | 209 | 56 |
SEL (dB re 1 µPa2∙s) | 217 | 14 | 187 | 56 |
SPL (dB re 1 µPa2) | 218 | 14 | 191 | 5 |
PPG (dB re 1 µPa∙s−1) | 314 | 12 | 275 | 231 |
MxVGA (dB re 1 µms−2) | 147 | 60 | 142 | 68 |
MxHGA (dB re 1 µms−2) | 148 | 60 | 148 | 80 |
MxMGA (dB re 1 µms−2) | 149 | 60 | 149 | 80 |
MxVPA (dB re 1 µms−2) | 138 | 65 | 141 | 93 |
MxHPA (dB re 1 µms−2) | 141 | 65 | 141 | 99 |
MxMPA (dB re 1 µms−2) | 142 | 39 | 142 | 99 |
Table 4.
Received levels with 95% confidence limits (±) and sample size (n), for peak-to-peak pressure level (P-P), sound exposure level (SEL), mean-square sound pressure level (SPL), maximum magnitude ground acceleration (MxMGA), and maximum magnitude particle acceleration (MxMPA), with logarithmic range bin centred at 250, 500, and 1000 (m), for the two sites.
Table 4.
Received levels with 95% confidence limits (±) and sample size (n), for peak-to-peak pressure level (P-P), sound exposure level (SEL), mean-square sound pressure level (SPL), maximum magnitude ground acceleration (MxMGA), and maximum magnitude particle acceleration (MxMPA), with logarithmic range bin centred at 250, 500, and 1000 (m), for the two sites.
| 250 m | 500 m | 1000 m |
---|
| Northern | Southern | Northern | Southern | Northern | Southern |
---|
P-P | 193 ± 0.5 (99) | 204 ± 0.6 (18) | 184 ± 0.3 (501) | 197 ± 0.2 (244) | 171 ± 0.3 (899) | 188 ± 0.2 (1131) |
SEL | 173 ± 0.4 (99) | 181 ± 0.4 (18) | 164 ± 0.3 (501) | 176 ± 0.1 (244) | 152 ± 0.2 (899) | 168 ± 0.1 (1131) |
SPL | 176 ± 0.7 (99) | 185 ± 0.4 (18) | 165 ± 0.4 (501) | 180 ± 0.2 (244) | 150 ± 0.2 (899) | 172 ± 0.2 (1131) |
MxMGA | 127 ± 1.5 (24) | 134 ± 1.1 (18) | 119 ± 0.6 (128) | 127 ± 0.4 (116) | 111 ± 0.7 (210) | 118 ± 0.4 (213) |
MxMPA | 133 ± 0.8 (57) | na | 126 ± 0.6 (186) | 136 ± 0.2 (143) | 116 ± 0.3 (433) | 127 ± 0.20 (426) |
Table 5.
Parameters for fits over the full sampling range using Equation (2) at the northern and southern sites using
Figure 6 and the appropriate metric against horizontal range with correlation coefficient (
r2). Abbreviations defined in
Table 2.
Table 5.
Parameters for fits over the full sampling range using Equation (2) at the northern and southern sites using
Figure 6 and the appropriate metric against horizontal range with correlation coefficient (
r2). Abbreviations defined in
Table 2.
| Northern Site | Southern Site |
---|
| a | b | c | r2 | a | b | c | r2 |
---|
P-P | −30.73 | −0.00034 | 265.4 | 0.901 | −38.37 | −0.00014 | 303.4 | 0.945 |
SEL | −24.03 | −0.00094 | 226.5 | 0.928 | −28.79 | −0.00120 | 256.3 | 0.943 |
SPL | −29.84 | −0.00061 | 242.1 | 0.917 | −36.64 | −0.00076 | 283.7 | 0.921 |
MxMGA | −41.30 | 0.0011 | 231.3 | 0.704 | −35.48 | −0.00108 | 225.9 | 0.855 |
MxMPA | −34.52 | 0.0008 | 218.3 | 0.716 | −32.04 | −0.00028 | 223.2 | 0.952 |
Table 6.
Parameters for fits to metrics for northern and southern sites at short-range using horizontal-range limited curve fitting (Equation (1)), with correlation coefficient (
r2) for each fit and the maximum range used in the curve fitting. Abbreviations defined in
Table 2.
Table 6.
Parameters for fits to metrics for northern and southern sites at short-range using horizontal-range limited curve fitting (Equation (1)), with correlation coefficient (
r2) for each fit and the maximum range used in the curve fitting. Abbreviations defined in
Table 2.
| Northern Site | Southern Site |
---|
Metric | Max Range (m) | a | b | r2 | Max Range (m) | a | b | r2 |
---|
P-P | 300 | −30.24 | 265.81 | 0.905 | 200 | −19.69 | 245.90 | 0.819 |
SEL | 300 | −25.96 | 235.17 | 0.904 | 200 | −14.06 | 212.78 | 0.893 |
SPL | 300 | −30.69 | 250.05 | 0.824 | 200 | −15.82 | 220.14 | 0.888 |
PPG | 300 | −51.61 | 364.92 | 0.270 | 200 | 0.38 | 233.72 | 0.000 |
MxHPA | 1000 | −31.55 | 209.08 | 0.617 | 1000 | −24.37 | 199.65 | 0.427 |
MxVPA | 1000 | −28.14 | 195.91 | 0.438 | 1000 | −29.54 | 208.38 | 0.239 |
MxMPA | 1000 | −28.91 | 203.67 | 0.680 | 1000 | −27.06 | 208.92 | 0.632 |
MxHGA | 500 | −27.62 | 193.53 | 0.671 | 500 | −23.80 | 190.65 | 0.812 |
MxVGA | 500 | −22.01 | 172.24 | 0.464 | 500 | −23.57 | 184.60 | 0.807 |
MxMGA | 500 | −27.83 | 194.10 | 0.672 | 500 | −23.93 | 191.27 | 0.823 |
Table 7.
Parameters for fits to metrics for northern and southern sites at long horizontal range using Equation (2), with correlation coefficient (
r2) for each fit and the minimum range used in the curve fitting. Abbreviations defined in
Table 2.
Table 7.
Parameters for fits to metrics for northern and southern sites at long horizontal range using Equation (2), with correlation coefficient (
r2) for each fit and the minimum range used in the curve fitting. Abbreviations defined in
Table 2.
| Northern Site | Southern Site |
---|
Metric (Levels) | Min Range (m) | Type | a | b | c | r2 | Min Range (m) | Type | a | b | c | r2 |
---|
P-P | 200 | 1 | −30.55 | −0.00035 | 264.8 | 0.897 | 200 | 1 | −38.73 | −0.00012 | 304.6 | 0.946 |
SEL | 200 | 1 | −23.48 | −0.00098 | 224.8 | 0.926 | 200 | 1 | −29.04 | −0.00118 | 257.1 | 0.943 |
SPL | 200 | 1 | −29.14 | −0.00067 | 239.9 | 0.914 | 200 | 1 | −37.03 | −0.00074 | 285.0 | 0.921 |
PPG | 200 | 1 | −33.54 | 328.4 | 0.00 | 0.185 | 200 | 2 | −22.5 | 292.9 | 0 | 0.109 |
MxHPA | 400 | 2 | −25.87 | 189.7 | 0.00 | 0.597 | 1000 | 1 | −34.10 | −0.00004 | 227.2 | 0.886 |
MxVPA | 400 | 2 | −27.44 | 191.2 | 0.00 | 0.623 | 1000 | 1 | −33.00 | −0.00022 | 220.0 | 0.772 |
MxMPA | 400 | 2 | −26.56 | 194.0 | 0.00 | 0.632 | 1000 | 1 | −32.86 | −0.00021 | 225.8 | 0.932 |
MxHGA | 50 | 2 | −16.48 | 159.9 | 0.00 | 0.709 | 50 | 2 | −22.25 | 183.3 | 0.00 | 0.893 |
MxVGA | 50 | 2 | −10.23 | 134.9 | 0.00 | 0.482 | 50 | 2 | −16.56 | 160.0 | 0.00 | 0.823 |
MxMGA | 50 | 2 | −32.98 | 206.9 | 0.00 | 0.690 | 50 | 2 | −44.78 | 253.7 | 0.00 | 0.848 |
Table 8.
Statistics of linear fits for the correlations shown including first and second coefficients of the linear regression fit (a and b), correlation coefficient, standard error (SE) and the 95% confidence error of the first coefficient of the linear fit. Abbreviations are defined in
Table 2.
Table 8.
Statistics of linear fits for the correlations shown including first and second coefficients of the linear regression fit (a and b), correlation coefficient, standard error (SE) and the 95% confidence error of the first coefficient of the linear fit. Abbreviations are defined in
Table 2.
| Northern Site | Southern Site | All Data |
---|
Pair | a | b | r2 | SE-O | 95% CI-a | a | b | r2 | SE-O | 95% CI-a | a | b | r2 | SE-O | 95% CI-a |
---|
SEL/P-P | 0.98 | 19.9 | 0.88 | 4.29 | 0.0030 | 0.93 | 28.70 | 0.97 | 2.43 | 0.0014 | 0.96 | 23.4 | 0.94 | 3.52 | 0.0015 |
SEL/SPL | 1.06 | −12.1 | 0.95 | 2.93 | 0.0021 | 1.06 | −7.99 | 0.97 | 2.62 | 0.0015 | 1.12 | −17.1 | 0.95 | 3.45 | 0.0014 |
SEL/MxMGA | 0.96 | −43.1 | 0.60 | 9.31 | 0.0017 | 1.06 | −54.45 | 0.87 | 6.00 | 0.0080 | 0.97 | −46.6 | 0.74 | 8.01 | 0.0084 |
SEL/PPG | 0.92 | 83.1 | 0.16 | 24.47 | 0.0173 | 0.53 | 134.17 | 0.12 | 21.09 | 0.0121 | 0.70 | 110.9 | 0.13 | 23.28 | 0.0118 |
SEL/MxMPA | 0.74 | −1.01 | 0.64 | 7.32 | 0.0082 | 0.87 | −23.09 | 0.93 | 3.13 | 0.0037 | 0.74 | −1.8 | 0.77 | 6.06 | 0.0043 |
MxMPA/MxMGA | 1.07 | −18.01 | 0.64 | 6.99 | 0.0329 | 1.13 | −25.25 | 0.87 | 4.15 | 0.0124 | 1.16 | −23.0 | 0.80 | 5.25 | 0.0132 |