5.2.2. sound levels from high-frequency sources/media/nanoq/files... · jasco applied sciences...

JASCO Applied Sciences Underwater Sound Propagation Acoustics Technical Report

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5.2.2. Sound Levels from High-Frequency Sources Table 31 shows ranges to received sound levels between 200 and 100 dB re 1 µPa for the active hydrographic survey sources. Maps are not presented for these sources because modelling was not performed for the full area.

Table 31. Estimated threshold radii for engineered sources, based on geometric spreading loss and directional source characteristics.

SPL (dB re 1 µPa)

Radius (km)

Sonardyne Ranger, 18 to 36 kHz*

Kongsberg HiPap 500, 33 kHz*

Reson Seabat 8160, 50 kHz

Teledyne Odom Echotrac MKIII, 24 kHz

Kongsberg EM 302, 30 kHz

Kongsberg EM 1002, 95 kHz

Huntec DTS, 500 Hz to 8 kHz

Knudsen Chirp3260, 3.5 kHz

200 0.002 0.003 0.007 0.002 0.007 0.005 0.007 0.005 190 0.005 0.006 0.021 0.005 0.021 0.010 0.012 0.009 180 0.008 0.009 0.048 0.008 0.049 0.036 0.025 0.017 170 0.018 0.021 0.12 0.022 0.13 0.085 0.037 0.030 160 0.036 0.040 0.21 0.044 0.22 0.23 0.049 0.042 150 0.066 0.074 0.29 0.12 0.30 0.39 0.085 0.064 140 0.17 0.19 0.37 0.23 0.39 0.54 0.21 0.12 130 0.35 0.35 0.45 0.34 0.48 0.67 0.38 0.29 120 0.56 0.53 0.63 0.45 0.77 0.80 0.65 0.46 110 1.1 0.91 0.94 0.53 1.3 0.93 1.8 0.91 100 2.2 1.6 1.5 0.57 2.2 1.2 4.1 2.8 * Based on empirical spreading loss estimate measured by Warner and McCrodan (2011).

5.3. Regional Study Area Figures 33 to 37 show aggregate cumulative SEL over a 24 hour period for ConocoPillips’, Maersk’s, and Shell’s August seismic survey operations with different M-weighting filters applied.

Underwater Sound Propagation Acoustics Technical Report JASCO Applied Sciences

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Figure 33. Cumulative flat-weighted SEL over 24 hours for Maersk’s, ConocoPhillips’, and Shell’s seismic survey operations in August.*186 dB re 1 µPa2s denotes the cSEL injury threshold for pinnipeds. Bathymetry contours are labelled in metres.


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Figure 34. Cumulative LFC-weighted SEL over 24 hours for Maersk’s, ConocoPhillips’, and Shell’s seismic survey operations in August.*186 dB re 1 µPa2s denotes the cSEL injury threshold for pinnipeds. Bathymetry contours are labelled in metres.


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Figure 35. Cumulative MFC-weighted SEL over 24 hours for Maersk’s, ConocoPhillips’, and Shell’s seismic survey operations in August.*186 dB re 1 µPa2s denotes the cSEL injury threshold for pinnipeds. Bathymetry contours are labelled in metres.


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Figure 36. Cumulative HFC-weighted SEL over 24 hours for Maersk’s, ConocoPhillips’, and Shell’s seismic survey operations in August.*186 dB re 1 µPa2s denotes the cSEL injury threshold for pinnipeds. Bathymetry contours are labelled in metres.


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Figure 37. Cumulative PINN-weighted SEL over 24 hours for Maersk’s, ConocoPhillips’, and Shell’s seismic survey operations in August.*186 dB re 1 µPa2s denotes the cSEL injury threshold for pinnipeds. Bathymetry contours are labelled in metres.

5.4. Sound Propagation Beyond the Regional Study Area Table 32 lists the maximum-over-depth rms SPL at each of the four receiver locations in Figure 5 from each of the source locations in the same map. Figure 38 shows sound levels as a function of range and depth along the four transects connecting the Maersk 4240 in3 airgun array to each receiver location. Levels are given in SEL units (dB re 1 μPa2s) which can be assumed to be equal to or greater than rms SPL (see section 3.8).


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(a)

(c)

(b)

(d)

Figure 38. Range-depth sound level contour plots for sounds from the Maersk 4240 in3 airgun array propagating to receivers R1 (a), R2 (b), R3 (c), and R4 (d). Sound levels are in units of SEL (dB re 1 μPa2s), which are assumed to be numerically greater than rms SPL (see Section 3.8).

Table 32. Maximum-over-depth rms SPL at the 4 receivers for airgun operations from ConocoPhillips, Maersk, and Shell airguns surveys.

Receiver

rms SPL (dB re 1 μPa)

S1 S2 S3 S4 S5 R1 120.9 126.7 127.2 127.1 122.4 R2 129.3 121.1 122.8 123.7 117.2 R3 125.2 122.2 128.1 123.0 115.4 R4 116.9 111.8 116.5 119.8 106.8


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6. Summary The results of this sound propagation modelling study show the greatest underwater sound levels associated with Maersk’s planned activities are those generated by the 4240 in3 airgun array, which dominates the sound levels from the sources on the hydrographic survey vessel. The sound levels from the airgun array exceed the NMFS injury criteria of 180 and 190 dB re 1 µPa at maximum ranges of 730 m (R95% of 590 m) and 180 m (R95% of 170 m), respectively. By comparison, the maximum ranges for these thresholds are 50 m and 18 m for the sources on the hydrographic survey vessel. The maximum range from the airgun array to the behavioural threshold of 160 dB re 1 µPa rms is 6.3 km (5.4 km R95%). These maximum propagation ranges correspond to model Scenario 1, with water properties representative of conditions in July. The ranges to the impact criteria drop less than 3% using a water column sound speed profile for conditions in August. The difference between the sound speed profile in July compared to August does not significantly affect the overall sound propagation. Ranges to the above stated impact thresholds are also slightly reduced when the source is moved to a deeper water location (as considered in Scenarios 2 and 3) because at these ranges sound disperses more freely and attenuates more rapidly than in shallow water. Bathymetry strongly influences sound propagation. The modelled sound fields are asymmetric due to the variability of the bathymetry throughout the region, but also due to the directionality of the source.

Based on the criteria for injury from multiple pulses, that is cSEL values of 198 dB re 1 µPa2s for cetaceans and 186 dB re 1 µPa2s for pinnipeds (Southall et al., 2007), the cumulative and aggregate cumulative sound exposure levels indicate the potential for injury remains localized within 2.5 kilometres range of the modelled Maersk survey lines. Inside the Tooq block, the total areas ensonified to cumulative levels at or above the M-weighted injury criteria are 23.8 km2 (low-frequency cetaceans), 5.5 km2 (mid-frequency cetaceans), 1.9 km2 (high-frequency cetaceans), and 57.9 km2 (pinnipeds).

The water column sound speed profile used in the model is a typical arctic profile that causes sound to be refracted upwards away from the seafloor and supports propagation to very long ranges. The model transects that extend beyond the regional study area show received sound exposure levels of 128 dB re 1 µPa2s can be expected over 500 km away from the seismic survey areas.


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Literature Cited Aerts, L., M. Blees, S. Blackwell, C. Greene, K. Kim, D. Hannay, and M. Austin. 2008. Marine mammal monitoring

and mitigation during BP Liberty OBC seismic survey in Foggy Island Bay, Beaufort Sea, July-August 2008: 90-day report. Prepared by LGL Alaska Research Associates Inc., LGL Ltd., Greeneridge Sciences Inc. and JASCO Applied Sciences Ltd. for BP Exploration Alaska.

Carnes, M.R. 2009. Description and Evaluation of GDEM-V 3.0. NRL Memorandum Report 7330-09-9165. US Naval Research Laboratory, Stennis Space Center, MS. 21 p

Codispoti, Louis A., and Kravitz, Joseph H. 1968. Oceanographic Cruise Summary, Baffin Bay-Davis Strait-Labrador Sea, Summer 1967. Informal rept. 3 Sep-14 Oct 1967. Naval Oceanographic Office NSTL Station MS.

Collins, M.D. 1993. The split-step Padé solution for the parabolic equation method. J. Acoust. Soc. Am. 93:1736–1742.

Collins, M.D., R.J. Cederberg, D.B. King, and S.A. Chin-bing. 1996. Comparison of algorithms for solving parabolic wave equations. J. Acoust. Soc. Am. 100:178–182.

Dragoset, W. H. 1984. A Comprehensive Method for Evaluating the Design of Airguns and Airgun Arrays. paper presented at the 16th Annual Proc. Offshore Tech. Conf., vol. 3, pp. 75–84.

Francois R.E. and G.R. Garrison. 1982a. Sound absorption based on ocean measurements: Part I: Pure water and magnesium sulfate contributions. JASA 72:896-907.

Francois R.E. and G.R. Garrison. 1982b. Sound absorption based on ocean measurements: Part II: Boric acid contribution and equation for total absorption. JASA 72:1879-1890.

Funk, D., D. Hannay, D. Ireland, R. Rodrigues, and W. Koski. 2008. Marine mammal monitoring and mitigation during open water seismic exploration by Shell Offshore Inc. in the Chukchi and Beaufort Seas, July–November 2007: 90-day report. Prepared by LGL Alaska Research Associates Inc., LGL Ltd., and JASCO Research Ltd. for Shell Offshore Inc, Nat. Mar. Fish. Serv., and U.S. Fish and Wild. Serv.

Greene, C.R., Jr. 1997. Physical acoustics measurements. Richardson, W.J. (ed.). Northstar Marine Mammal Monitoring Program, 1996: Marine Mammal and Acoustical Monitoring of a Seismic Program in the Alaskan Beaufort Sea. LGL Rep. 2121-2. Report from LGL Ltd., King City, ON, and Greeneridge Sciences Inc., Santa Barbara, CA, for BP Explor. (Alaska) Inc., Anchorage, AK, and Nat. Mar. Fish. Serv., Anchorage, AK, and Silver Spring, MD, pp. 3-1 to 3-63.

Hannay, D.E., and R. Racca. 2005. Acoustic Model Validation. Technical report for Sakhalin Energy Investment Company by JASCO Research Ltd.

Henriksen, N., Higgins, A.K., Kalsbeek, F. & Pulvertaft, T.C.R. 2000: Greenland from Archaean to Quaternary. Descriptive text to the Geological map of Greenland, 1:2 500 000. Geology of Greenland Survey Bulletin 185, 93 pp .

Ireland, D.S., R. Rodrigues, D. Funk, W. Koski, and D. Hannay. 2009. Marine mammal monitoring and mitigation during open water seismic exploration by Shell Offshore Inc. in the Chukchi and Beaufort Seas, July–October 2008: 90-day report. Prepared by LGL Alaska Research Associates Inc., LGL Ltd., and JASCO Applied Sciences Ltd. for Shell Offshore Inc, Nat. Mar. Fish. Serv., and U.S. Fish and Wild. Serv.

Landro, M. 1992. Modelling of Gi Gun Signatures. Geophysical Prospecting 40, 721–747.

Laws, M., L. Hatton, M. Haartsen. 1990. Computer Modelling of Clustered Airguns. . First Break 8, 331–338.

Lurton, X. 2002. An Introduction to Underwater Acoustics: Principles and Applications. Springer, Chichester, U.K. pp 347.

MacGillivray, A.O. 2006. An Acoustic Modelling Study of Seismic Airgun Noise in Queen Charlotte Basin. MSc Thesis. University of Victoria, Victoria, BC. 98 p.

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Malme, C.I., P.W. Smith, and P.R. Miles. 1986. Characterisation of Geophysical Acoustic Survey Sounds. Prepared by BBN Laboratories Inc., Cambridge, for Battelle Memorial Institute to the Minerals Management Service, Pacific Outer Continental Shelf Region, Los Angeles, CA.

Marlowe, James. 1968. Unconsolidated marine sediments in Baffin Bay. Journal of Sedimentary Petrology. 38(4):1065-1078.

McCauley, R.D., M.-N. Jenner, C. Jenner, K.A. McCabe, and J. Murdoch. 1998. The response of humpback whales (Megaptera novaeangliae) to offshore seismic survey noise: preliminary results of observations about a working seismic vessel and experimental exposures. Austral. Petrol. Prod. & Explor. Assoc. J. 38:692-707.

O’Neill, C., D. Leary, and A. McCrodan. 2010. Sound Source Verification. (Chapter 3) In Blees, M.K., K.G. Hartin, D.S. Ireland, and D. Hannay. (eds.) Marine mammal monitoring and mitigation during open water seismic exploration by Statoil USA E&P Inc. in the Chukchi Sea, August–October 2010: 90-day report. Prepared by LGL Alaska Research Associates Inc., LGL Ltd., and JASCO Applied Sciences Ltd. for Statoil USA E&P Inc., Nat. Mar. Fish. Serv., and U.S. Fish and Wild. Serv.

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Teague, W.J., M.J. Carron, and P.J. Hogan. 1990. A comparison between the Generalized Digital Environmental Model and Levitus climatologies. J. Geophys. Res. 95(C5):7167-7183.

Warner, G., and A. McCrodan. 2011. Underwater Sound Measurements. (Chapter 3) In: Hartin K.G., L.N. Bisson, S.A. Case, D.S. Ireland, and D. Hannay. (eds.) 2011. Marine mammal monitoring and mitigation during site clearance and geotechnical surveys by Statoil USA E&P Inc. in the Chukchi Sea, August–October 2011: 90-day report. LGL Rep. P1193. Rep. from LGL Alaska Research Associates Inc., LGL Ltd., and JASCO Research Ltd. for Statoil USA E&P Inc., Nat. Mar. Fish. Serv., and U.S. Fish and Wild. Serv. 202 pp, plus appendices.

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Glossary 1/3-octave band levels

Frequency resolved SPLs in non-overlapping passbands that are 1/3 of an octave wide (where an octave is a doubling of frequency). Three adjacent 1/3-octave bands make up one octave. 1/3-octave bands become wider with increasing frequency.

90% energy window Time interval over which the cumulative energy rises from 5% to 95% of the total pulse energy, abbreviated with the symbol T90. This interval contains 90% of the total pulse energy.

absorption Dissipation of sound energy through viscosity or chemical reactions.

attenuation The acoustic energy loss due to absorption and scattering.

azimuthal The horizontal angular component of direction.

bar Pressure unit equal to 100 kPa, which is approximately equal to the atmospheric pressure on Earth at sea level. 1 Bar is equal to 106 Pa or 1011 µPa.

broadband sound level The total sound pressure level measured over a specified frequency range. If the frequency range is unspecified, it is understood to be the entire measurement range.

broadside Perpendicular to the travel direction of the source array.

compressional wave A mechanical vibration wave where the direction of particle motion is parallel to the direction of propagation. Compressional waves are sometimes referred to as P-waves in the field of geophysics.

decibel A logarithmic unit of the ratio of a quantity to a specific reference level (abbrev. dB).

endfire Parallel to the travel direction of a source array.

ensonified Exposed to sound.

far-field The zone where, to an observer, sound originating from an array of sources (or a spatially-distributed source) appears to radiate from a single point in space. The distance to the acoustic far-field increases with frequency.

frequency Rate of oscillation measured in units of cycles-per-unit-time: e.g. 1 Hertz (abbrev. Hz) = 1 cycle / second.


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geoacoustic Relating to the acoustic properties of the seabed.

intensity Sound energy flowing through a unit area perpendicular to the direction of propagation per unit time.

M-weighting The process of band-pass filtering loud sounds to reduce the importance of inaudible or less-audible frequencies for broad classes of marine mammals.

Parabolic Equation (PE) method

A computationally-efficient solution to the acoustic wave equation that is used for modelling transmission loss (TL). The PE approximation simplifies the computation of TL by neglecting the back-scattered component of the acoustic field. This component is very small for most ocean-acoustic propagation problems.

peak sound pressure level Maximum instantaneous sound pressure, expressed in decibels, sometimes referred to as zero-to-peak level. Peak-to-peak level is the difference between the maximum and minimum instantaneous sound pressures, expressed in decibels.

percentile Value below which an event occurs some percentage of the time. The nth percentile level gives the level below which the signal is n% of the time.

permanent threshold shift (PTS) Permanent loss of hearing sensitivity due to excessive noise exposure. PTS is considered auditory injury.

power spectrum density The acoustic signal power per unit frequency as measured at a single frequency (units µPa2/Hz).

power spectrum density level The dB level (10log10) of the power spectrum density, usually presented in 1 Hz bins (units dB re 1 µPa2/Hz).

pressure (hydrostatic) The pressure at any given depth in a static liquid that is the result of the weight of the liquid acting on a unit area at that depth, plus any pressure acting on the surface of the liquid (SI unit Pa).

pressure (acoustic) The deviation from the ambient hydrostatic pressure caused by a passing sound wave (SI unit Pa). Also referred to as overpressure.

pulsed sound Discrete sounds with very short durations (less than a few seconds). Sounds with longer durations are called continuous sounds.

rms sound pressure The root-mean-square average of the instantaneous sound pressure (symbol Lp) as measured over some specified time interval (symbol T90). The 90% energy time window


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(T90) is typically used for pulse sounds. Consequently, the rms SPL for pulse sounds is often referred to as the 90% rms SPL (Lp90).

shear wave A mechanical vibration wave where the direction of particle motion is perpendicular to the direction of propagation. Shear waves are sometimes referred to as S-waves in the field of geophysics. Shear waves only propagate in solid media, such as sediments or rock. Shear waves in the seabed can be converted to compressional waves in water at the water-seabed interface.

signature Pressure signal generated by a particular source.

sound A time-varying pressure disturbance that is generated by mechanical vibration waves travelling through a fluid medium (e.g., air or water).

sound exposure level (SEL) A measure of the total sound energy contained in one or more pulses. SEL is measured in units of dB re 1 µPas.

sound pressure level (SPL) The decibel ratio of sound pressure to some reference pressure. Numerically, the dB level is equal to 20×Log10(P/Pref), where P is the sound pressure and Pref is the reference pressure. In underwater acoustics, the standard reference pressure is 1 µPa and the units of SPL are written: dB re 1 μPa. Unless otherwise stated, SPL refers to the root mean square (rms) sound pressure.

spectrum The representation of an acoustic signal in terms of its power (or energy) distribution versus frequency (see Power Spectrum Density).

source level (SL) The SPL that would be measured at 1 metre distance from a point-like source that radiates the same total amount of sound power as an actual source. Source levels are expressed in units of dB re 1 μPa at 1 m.

surface duct The upper portion of the water column where the sound speed profile gradient causes sounds to constantly turn upwards and therefore reflect off the surface, resulting in comparatively long range sound propagation with little loss.

temporary threshold shift (TTS) Temporary loss of hearing sensitivity due to excessive noise exposure.

transmission loss (TL) The dB reduction in sound level that results from the spreading of sound away from an acoustic source, subject to the influence of the surrounding environment. Also referred to as propagation loss.

wavelength Distance over which a wave completes one cycle of oscillation, abbreviated with the symbol λ.

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