Analysis and Ranking of the Acoustic Disturbance Potential of ...

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Report No. 6945 BBN Systems arid Technologies Corporation - similar single-engine airplane) was determined to cause hauled out harbor seals to vacate the beach most of the t,ime. [This estimate was based on observations for flyovers at ranges of about 120 m (Johnson 1977).] The response of walruses varies widely but they were reported to become alert and move into the water when "aircraftn approach within 1-1.5 km at altitudes varying from 150 to 1500 m (Salter 1979). If the aircraft is assumed to be a twin engine turboprop, an estimated received level of 100 dB is obtained using a slant range of 1 km. The overall ambient noise level on beaches often exceeds this value because of surf noise (see Fig. 3.10). This suggests that walruses are reacting to.visua1 stimuli rather than acoustic, or perhaps both. Alternatively, the observations may have been made on protected beaches with no surf and low ambient noise or for overflights with larger aircraft than that assumed in the analysis. Among the other Alaskan pinniped species that have been observed to react to aircraft, specific response thresholds have not been reported. Table 5.13. Airborne Sound Zone of Influence Estimates for Pinnipeds. Minimum slant range for probable disturbance by aircraft 1 Species Harbor Seal Pacific Walrus L, Criterion 2 110 dB 100 dB - - - Light 1-eng Prop Light 2-eng TProp 120 m 300 m B737-200 400 m B727 F-4C Military 420 m 1100 m Notes: (1) Range estimated by using Eq. (13) for Standard Day Conditions together with aircraft radiated noise data from Table A-3. (2) The Lr criterion for probable disturbance is determined by using observed response information from Sec. 2.4 and estimating the Lr in the dominant bandwidth for the aircraft type and range.
Report No. 6945 BBN Systems and Technologies Corporation 6. CONCLUSIONS AND RECOMMENDATIONS 6.1 Conclusions Major sound sources Sound energy in the Alaskan marine environment was classified as originating from five categories of sources: natural, biological, industrial, transportation, and cultural. With the exception of specific types of source concentrations, the noise source distribution was found to be generally diffuse with a relatively sparse average density. Four types of source concentrations were found: industrial sources associated with seasonal oil exploration and drilling activities in the Alaskan.Beaufort (and eventually. in other OCS areas); high density shipping and fishing vessel activities in marine transportation lanes and popular fishing areas; aircraft, shipping and cultural sources contributing near cities and smaller population centers; and natural seismic activity contributing in active volcanic zones. The highly distributed and relatively local effects of these noise sources were not easily shown on a large scale overlay to be used with the mammal distribution maps. Consequently, the required source distribution information was presented in tabular form showing source types, locations, numbers, and - acoustic characteristics. Table 6.1 shows the basic characteristics of examples of the major types of sources including both reported source levels as well as estimated equivalent source levels for those sources that have a time-varying output. The estimated source levels for large earthquakes can be seen to be higher than those of all the other sources. The high levels are mitigated by the generally long interval between events and by the predominantly low frequency range of the acoustic energy. Much of the sound energy is below the hearing range of most marine mammals, with the probable exception of baleen whales. The major area of volcanic and seismic activity in Alaska is the subduction zone along the Aleutian arc and the Alaska Peninsula. The North Aleutian and Shumagin Planning Areas include parts of this region. Seismic events of M6 to M7 are expected in this area at about a 2-year interval with production of loud underwater transients. Smaller scale events occur more frequently. Baleen whales are capable of producing very loud vocalizations as shown by the representative value in Table 6.1. When several whales are interacting in an area their frequent vocalizations produce a very high average sound level. Pinnipeds, while not as loud as whales, are often more numerous in a given area and also provide a signifioant contribution to underwater noise levels. The loudest man-made sound sources (excluding explosives) are air gun and vibroseis arrays. The source level shown for the air gun array is based on a power summation of the dominant bands in a 1/3 octave spectrum. The broadband pulse waveform peak is about 13 dB higher. The source level for the vibroseis is the maximum 1/3 octave band level obtained during the tone pulse sweep.
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H BOWERS BAW I ALEUTIAN ARC 3 STGEC
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A BEAUFORT SEA B U WCH SEA CHOPEaAS
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Report No. 6945 L 1 A. Baird's Beak
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A BEAUFCRT SEA B CHW(CH SEA CHOPEBA
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A BEAUFCRT SEA BWKQIYA DrnTONBAsw E
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A BEAUFORT SEA BCHlKCHSEA CHaeEansr
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on the ice. The single calves remai
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A 0EAUFaAT SEA BCHJKCH 9 A CHaPE BA
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BCmrcCHSEA CHOPEBnsw 0 NORTON 0Am E
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.. A BEWORT SEA B WKCH SEA CH)PEBAS
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FIG. 3.2 NOISE SPECTRA IN SHALLOW W
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Adapted From K.H. Jacob (1986) Cali
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FIG. 3.8 ESTIMATED OVERALL SOUND LE
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FIG. 3. Q UNDERWATER NOISE SPECTRA
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FIG- 3.1 1 STATISTICAL ANALYSIS OF
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FIG- 3-12 STATISTICAL ANALYSIS OF C
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-- Alr Gun Array + Vlbrosels -* Ice
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FIG. 3.14 REPRESENTATIVE SHIPS AND
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~ -- -- FIG. 3.1 7 REPRESENTATIVE R
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FIG. 3-18 REPRESENTATIVE CULTURAL S
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FIG. 4.1 CORRECTION TO 300 M REFERE
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A. 6. ~la~onca 011shwe. mm I C. MSI
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FIG. 4.1 1 AIR TO SHALLOW WATER SOU
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FIG. D. 1 HUMAN VOCALIZATION AND AU
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FIG. D. 3 ESTIMATED HEARING CHARACT
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