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

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Report No. 6945 BBN Systems and Technologies Corporation . The time duration required for the CPA sequence must also be compared to the reference period. This is done as a separate correction process. Received levels significantly below the level at CPA do not contribute much to the total energy received during the CPA sequence. By neglecting contributions 20 dB or more below the level at CPA, it is possible to calculate a specific time required for completion of the sequence as determined by the speed of the source. The range from the receiver at which the received level is 20 dB below that at CPA is obtained using the measured or modeled TL characteristics. The effective time duration of the CPA sequence is approximately equal to the travel time required for the source to cover two of the 20 dB range intervals or: where Rm = Maximum effective range where TL is 20 dB greater than at CPA (km) S = Speed of the source (km/sec) When these modifications are incorporated into the SNC Model, Eqn (20) can be rewritten as follows: SNC = Ls - TLr - Cm + 10 Log{(Tt)(Tf)(Pe)(Ns)} dB re 1 vPa at 300 m (22) Eq. (22) was used to calculate the SNC ratings for the major sources identified in the study for each of four OCS planning areas - Chukchi, Norton Basin, North Aleutian and Shumagin. The effect of two different sound propagation conditions was also considered if appropriate. In order to simplify the analysis, the procedure followed previously in presenting a summary of source level characteristics is also used here in that the dominant bandwidths and maximum 1/3 octave band levels are used rather than the full 1/3 octave spectra. The SNC Model spreadsheet layout is shown in the example in Table 5.2. (Complete tabular SNC results for all of the areas studied are presented in the next section in combination with the SER Model results.) The following description gives detailed information on the organization and terminology of the SNC tables. Standardized Noise Contribution Model (Description of terms and data entering procedure) Source - Description of category or specific name of source. Type - Fixed (remains stationary), Local (moves less than 600 m in 2 hours), Moving (moves more than 600 m in 2 hours) Dominant Bandwidth - The frequency band including the 1/3 octave Band with the highest level in the source level spectrum and bounded by the 1/3 octave bands with levels within 10 dB.
Report No. 6945 BBN Systems and Technologies Corporation Table 5.2. Standardized Noise Contribution Model (ExampIe). STWDARDIZED NOISE tOllTRlBuT1OU -EL, North Aleutian Plaming Area, Surface Layer Condition Ref. areas used in mdel (km-2): Total overall, 149000 ; Coastal (c), 3600 ; Fishing (f), Ref.Range,3Wm;Uax.EffectiveRange;ships,aircraft(km)- 27 0.9 (e - estinsted) Ref. 300 m Uov.Srce.Corr. source (area) Type speed Dominant nu, nz Max 113 0ct.H~ D.0nd. Ux l/3 Area TravTime (kts) fmin fnsx ~sl,d8 freq. Ls2,dB Lr1,dB Lr2,dB Cm,d0 TtlTr Tug/Barge (c) mvng 10 100 12500 171 630 162 129 120 -11 1 Twin Outdrv.(c)mvng 20 40 16000 167 500 156 125 114 -11 0.73 U400 ; Airports (a), 78 Fluc. Equiv. Encntr. Exp. SNC ratings Corr. Level Prob. Nun. D.0nd Ux 1/3 TflTr Lq.dB Pe N SNC1,dB SNC2 e 1 118 9.4E-03 5 105 % e e 0.8 112 1.S-02 15 106 95 e e 13' Whaler (c) mvng 20 630 8000 159 4000 153 117 111 -11 0.73 0.8 104 l.S-02 20 W 93 e e Trawler(f) mvng 5 40 1000 157 100 147 115 105 -11 1 1 104 5.1E-04 20 84 74 Trawler(f) mvng 10 40 4000 169 160 158 127 116 -11 1 1 116 9.8E-04 Drillship fixed 20 800 174 63 167 132 125 0 1 1 132 6.E-06 e Dredge (AP.1 fixed 50 630 185 160 178 143 136 0 1 0.8 142 6.E-06 e Seismic Array mvng 5 20 160 216 50 210 174 168 -11 1 0.005 140 l.2E-04 (300 m) 0. 737-200 (a) mvng 400 100 800 135 125 130 121 116 -10 0.0012 1 82 7.E-02 fmin - the center frequency of the lowest frequency 1/3 octave within the 10 dB limit. fmax - the center frequency of the highest frequency 1/3 octave within the 10 dB limit. Lsl - the power sum of the 1/3 octave band levels in the dominant bandwidth expressed in dB re 1 pPa at 1 m. Maximum 1/3 Octave Band - The 1/3 Octave Band with the highest level in the source level spectrum. freq. - the center frequency of this band. Ls2 - the sound level in this band in dB re 1 pPa at 1 m. Reference Lrl - The received level in the dominant band at a range of 300 m from the source in the area chosen for the model. Lr2 - The received level in the maximum 1/3 octave band at a range of 300 m from the source.
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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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FIG. D. 1 HUMAN VOCALIZATION AND AU
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FIG. D. 3 ESTIMATED HEARING CHARACT
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