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

transcript

Defence Research andDevelopment Canada

Recherche et développementpour la défense Canada Canada

Francine Desharnais1, Marjo H. Laurinolli2, Alex E. Hay3, and Douglas J. Schillinger3

1DRDC Atlantic2JASCO Research Ltd

3Department of Oceanography, Dalhousie University

Defence R&D Canada • R & D pour la défense Canada

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

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)

Sample Sounds - Eubalaena Glacialis

trumpet

down cry +harmonics

low upsweep

down cry

gunshot

Localization methodology [Laurinolli, 2002]

• Aural detection

• Time delay estimates through spectrogram cross-correlation technique

• Localization with crossing of hyperbolae of equal time difference

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

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Laurinolli, F. Desharnais, D.J. Schillinger, Source levels of North Atlantic right whale sounds in the Bay of Fundy (unpublished)

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( f ) = A( f ) + 20η ( f )log10 υ

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

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

More references

• EC-SWAN (temporal and spatial fluctuations)

• Gully and Sable Bank

• Western Bank

• Bay of Fundy

• Classified literature

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

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)

Examples of Signal Excess (10 km)

Frequency band [Hz] 100-200 200-800

Source level [dB re 1 Pa @ 1 m] 175 160

Ambient noise level [dB] 82 72

Transmission loss [dB] 70 85

Signal excess [dB] 23 3

Range inferences

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

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

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