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The impact of noise on passive monitoring of marine mammals in the Bay of Fundy

The impact of noise on passive monitoring of marine mammals in the Bay of Fundy ... Ambient noise on the Scotian Shelf and the Bay of Fundy. Signal excess (some examples) ...

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The impact of noise on passive monitoring of marine mammals in the Bay of Fundy

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    Slide 1: The impact of noise on passive monitoring of marine mammals in the Bay of Fundy

    Francine Desharnais1, Marjo H. Laurinolli2, Alex E. Hay3, and Douglas J. Schillinger3 1DRDC Atlantic 2JASCO Research Ltd 3Department of Oceanography, Dalhousie University

    Slide 2:Outline

    Designing a system for the Bay of Fundy Feasibility study for passive detection SE = SL - (TL + AN) Transmission loss, source level Ambient noise on the Scotian Shelf and the Bay of Fundy Signal excess (some examples) Conclusions

    Slide 3:The problem

    North Atlantic right whales Bay of Fundy Deeper area of Bay Clay on top drift Summer/Fall Feasibility study with omnidirectional sensors (sonobuoys)

    Slide 4:Sample Sounds - Eubalaena Glacialis

    moan trumpet down cry + harmonics low upsweep down cry gunshot dB dB

    Slide 5:Localization methodology [Laurinolli, 2002]

    Aural detection Time delay estimates through spectrogram cross-correlation technique Localization with crossing of hyperbolae of equal time difference

    Slide 6:Transmission loss

    Scotian Shelf drift over sandstone Layer of LaHave clay in deeper basin Source depth 3 m Receiver depth 30 m 180 m water depth 150 & 500 Hz

    Slide 7:Source Level Determination

    Lower bound: 10-200 Hz: 175 dB re 1 ?Pa @ 1m 200-800 Hz: 160 dB re 1 ?Pa @ 1m A.E. Hay, M.H. Laurinolli, F. Desharnais, D.J. Schillinger, Source levels of North Atlantic right whale sounds in the Bay of Fundy (unpublished)

    Slide 8:Ambient noise - Key references for Scotian Shelf

    Piggott C.L. Piggott, “Ambient sea noise at low frequencies in shallow water of the Scotian Shelf,” J. Acoust. Soc. Am. 36, 2152-2163, 1964. 8.4 - 3100 Hz, 20 and 28 fathoms depths Ship noise edited out Main reference for Scotian Shelf L is noise spectrum in dB//1ubar, A and n are empirical constants, v is wind speed in miles/hour. A varies with season [Jan-Apr, May-Dec]. Wind 1.7,4.3,10.4,15.6,20,33 kn.L is noise spectrum in dB//1ubar, A and n are empirical constants, v is wind speed in miles/hour. A varies with season [Jan-Apr, May-Dec]. Wind 1.7,4.3,10.4,15.6,20,33 kn.

    Slide 9:Key references - cont’d

    Wenz G.M. Wenz, “Acoustic ambient noise in the ocean: spectra and sources,” J. Acoust. Soc. Am. 34, 1936-1956, 1962. Increase by 2.5 dB for shallow water 2-7 dB lower than Piggott Knudsen et al. Knudsen, V. O., Alford, R. S., and Emling, J. W., “Underwater ambient noise,” J. Mar. Res. 3, 410-429, 1948. Agrees closely with Wenz >500 Hz <500 Hz Wenz is closer to Piggott Wenz: Winds: 1.7,4.3,10.4,15.6,20,33 kn. Light and heavy shipping Knudsen: 0.4,1.7,4.3,10.4,15.6,20,33 knWenz: Winds: 1.7,4.3,10.4,15.6,20,33 kn. Light and heavy shipping Knudsen: 0.4,1.7,4.3,10.4,15.6,20,33 kn

    Slide 10:Key references - cont’d

    Zakarauskas et al. P. Zakarauskas, “Ambient noise in shallow water: a survey of the unclassified literature,” Defence Research Establishment Atlantic Technical Memorandum 86/207, 1986. P. Zakarauskas, D.M.F. Chapman and P.R. Staal, “Underwater acoustic ambient noise levels on the Eastern Canada continental shelf,” J. Acoust. Soc. Am. 87, 2064-2071, 1990. <1 kHz Grand Banks, Scotian Shelf, Flemish Cap, Laurentian Channel Winter and summer

    Slide 11:More references

    EC-SWAN (temporal and spatial fluctuations) Gully and Sable Bank Western Bank Bay of Fundy Classified literature

    Slide 12:Scotian Shelf Rules of Thumb

    20 Hz Seasonal finback cycle (in excess of 25 dB in winter) Shipping band (10-200 Hz) Moderate to high shipping on Wenz’ curves for shallow water EC-SWAN dataset for specific areas Short-term temporal fluctuations up to 10 dB, spatial fluctuations < 5 dB Wind band (>200 Hz) Piggott is good guide, Wenz and Knudsen too low Low fluctuations Very little data processed above 3 kHz Some information on temporal and spatial statistics Very little on depth dependence

    Slide 13:Bay of Fundy - unpublished

    < 200 Hz: Noise levels follow EC-SWAN data for moderate to heavy shipping. 200-800 Hz: Amongst the highest levels measured on Scotian Shelf at these frequencies Shallow water Wenz curves + 2 to 5 dB to account for spillage from high shipping noise Depth dependence Little based on modelling (energy-flux model)

    Slide 14:Examples of Signal Excess (10 km)

    Slide 15:Range inferences

    Slide 16:Conclusions

    Right whales can be detected well beyond 10 km in range in the 100-200 Hz band. Higher frequencies get lost in background noise ~10 km Shipping noise a significant factor - directional sensors desirable for added range

    Slide 18:Eastern Canada Shallow Water Ambient Noise survey (EC-SWAN)

    Slide 19:EC-SWAN

    12 month survey at 4 sites on shelf Sonobuoy data No attempt to extract ship-contaminated samples 10-2500 Hz (some to 32 kHz) Spatial and temporal statistics

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