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

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Report No. 6945 BBN Systems and Technologies Corporation Table 5.3 Standardized Exposure Rating Hodel (Example). - STAMDAROIZEO EYPOSME RATING #ML, North Aloutin Ptming Aroe, Surfwe Layer Condition Source lnforrtion fror SYC #Idol, Ref. R.ng. - 300 l - ostirtod volw (c) - corstal area swce (f) - fishing firre source WCE Ominant BU, Fsl Fsh Seismic Array 20 160 Twin Outdrv.(c) 40 Twin Outdrv.(c) 40 Twin Qltdrv.(c) 40 Twin Wtdrv.(c) 40 13' HeLer (c) 630 13' Haler lc) 630 13' Haler (c) 630 13' Yhaler (c) 630 Tug/Eargo tc) 100 YO. SYCl N dB o* 1 101 l 20 106 0 20 106 e 20 106 e 20 106 RECEIVER DS Specin N/luFZ e Grey Hale 0.02 l Harbor See1 0.44 l Herbor Porp. 0.02 (1) e Stel.Soe Lion 0.21 l Grey Uhole 0.02 e Harbor See1 0.U e Herbor Porp. 0.02 (1) l Stel.Seo Lion 0.21 e Grey Uhele 0.02 l Harbor -1 0.44 Hearing 8U. Frl Frh l e 0.09 9 kHz Fr e l a e e 40 41 149 3 80- 15 40 56 111 130 e e e e e 0.7 30 15 00 00 106 20 e e e e e e e 0.09 9 0.7 40 40 105 20 SER, dB SER- Ref. Area SNC1 Trwler (f) 40 Herbor Porp. 0.02 Mote (11: Hearing characteristic for Cetifornie sea lion wed for Stellar sea Lion. 5.2.3 Results of model studies for selected planning areas The SNC and SER Models have been.set up in spreadsheet format to facilitate their use in developing predictions for noise ratings and mammal exposure ratings for specified area - source - species situations. Two seasonal conditions and four OCS planning areas of special interest - Chukchi Sea, Norton Basin, North Aleutian Basin, and Shumagin have been considered. For the Chukchi Sea, a summer condition of 50% ice cover and a winter condition of 100% ice cover have been used since these conditions are common and correspond to those for which TL data were available. For the remaining three areas, a late-spring/ summer condition and a late fall/early winter condition were considered. These are, respectively, the periods when ( 1 ) a strong surface layer is developed because of solar heating and high fresh water input, and (2) when the surface cools to produce a neutral or slightly negative temperature gradient and eventual ice formation in many areas. The ice cover conditions assumed for the non-Chukchi areas were 0% for spring/summer and 0 to 30% for late fall/early winter. The results of the model analyses are presented here in tabular form with the SNC results presented first followed by the SER summary =able. The SER analyses were made using the major source types identified in the SNC analyses together with some of the major species expected to be present based on the population distribution and density information presented in Section An SER rating was obtained for both a reference condition of 1 animal/lun"kd a condition using the expected population density based on information from
Report No. 6945 BBN Systems and Technologies Corporation Section 2'.1.3 for each potential source - specie$ encounter situation. Thus ratings are obtained for both the encounter sensitivity for a single animal and the specific potential for acoustic impact for the population within an area. The SER values obtained from the analysis are shown in bar graph format. to supplement the data presented in the tables. The SER Model is designed to show which species are potentially most influenced by a given noise source by developing high values when compared to the input SNCl value. If the SER value is comparable to, or less than the SNC1 value, the species is likely to be minimaly influenced as a result of a mismatch between the source noise spectrum and the species hearing sensitivity and/or a low species population density in the area being considered. A procedure was devised for summarizing the results of the SER analysis using three general ratings of low, medium and high. These ratings were established by statistically analyzing the output of the SER Model for all of the source species encounters examined in the 4 planning areas. The average and the standard deviation of the area SER values were determined for a total of 75 data points. The values ranged between 111 and 207 dB with a mean value of 159 dB. The standard deviation was 20 dB. With these results as a guide the general ratings were defined as Low - SER values 140 dB and lower Medium - SER values between 141 and 179 dB High - SER values 180 dB and higher. These values are designed to provide a broad ranking of source audibility for the various source - species encounters considered under standardized conditions. These SER ratings are not based on behavioral observations and are intended only as a means of ranking encounter situations where potential behavioral responses may occur. Only a limited number of behavioral studies are available to provide a means of calibrating this ranking scheme. Averaged results from gray whale disturbance studies using playback of several types of continuous noise from industrial sources (Malme et al. 1984) showed that 50% of the whales migrating through the test area avoided areas where sound levels were about 120 dB. Over 90% of the whales avoided the region near the source where sound levels were higher than 130 dB. Reviewing the results of the SER analysis for those areas where continuous source - gray whale encounters were considered provided the following results which show a comparison of the mean SER ratings with the mean of the received levels at the reference range of 300 m for the various sources considered (the number of samples and the standard deviation are also shown) : SER Rank N Mean SER(~B) SD Mean Lrl(dB) SD High 2 18 1 - 138 - Medium 8 167 - 8 125 ' 7 These results suggest that the SER ranking scheme is consistent with behavioral observations for at least one species. However, more acoustic
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on the ice. The single calves remai
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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. D. 1 HUMAN VOCALIZATION AND AU
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FIG. D. 3 ESTIMATED HEARING CHARACT
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