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

Report No. 6945
BBN Systems and Technologies Corporation
Assumptions for the SER Model
1. The SER values are obtained for species - source encounters which are
assumed to occur regularly; i.e., no weighting factors are included
for startle effects or for unusual source temporal patterns. These
can be included when more data become available. Note however that
normal source fluctuations are considered in the L calculation
which is part of determining SNC1.
eq
2. The maximum sound level above hearing threshold,
consider any weighting factor based on apparent lou Lri, ness. A value of
30 dB above threshold may be apparently louder if it occurs at a
frequency near the maximum hearing sensivity range than if it occurs
at a frequency much higher or lower than this range. In the present
model this loudness dependence is assumed to be independent of
frequency since data are not available to provide a better weighting
factor.
3. Species density values which have been used in the SER Model have
been assumed to apply over broad areas. In regions where high
concentrations exist the SER values would be proportionally higher.
Ranking potential acoustic interaction
The Standardized Noise Contribution Model (SNC) and the Species Exposure
Rating Model (SER) were developed during the study to rank the acoustic energy
output of a wide variety of sources and provide a rating for the acoustic
interaction potential of the various ,source - species encounters that are
possible in a given area. The information developed using these models,
presented previously in Tables 5.4 through 5.11, has been summarized in Table
6.2 for each of the four OCS Planning Areas that were studied in detail.
A simplified three level ranking system was used in summarizing the SER
results. In this system a "High" ranking indicates a high probability of
acoustic interaction because of a good match between species hearing and
source output bandwidths together with a sufficient number of animals in the
area. A "Low" ranking indicates a large mismatch between hearing and source
bandwidths and/or a small number of animals in the area. The numerical
criteria used in determining an assigned rank are given in Note (1) of the
table. These criteria were developed from a statistical analysis of all of
the SER results as discussed previously in Section 5.2.3.
The ranking order shown in Table 6.2 indicates that the baleen whales as
represented in the study by the gray and fin whales have a high probability of
being influenced by noise from most of the sources used in the analysis. This
is a consequence of their assumed low frequency hearing sensitivity which is
believed to overlap the output frequency range of most man-made sources (and
also most natural sources). Some high rankings also occurred among the
odontocetes and pinnipeds studied. These were for killer whales, harbor
porpoise, Dall's Porpoise, fur seals, and harbor seals; all for tanker