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

Report No. 6945
BBN Systems and Technologies Corporation
Lr3
-
= The received level at the reference range (300 m) in the 1/3
octave band with the highest level above the hearing threshold
(dB re 1 pPa) (see Fig. 5.2).
Ss = The level of hearing threshold at the center frequency of Lr3 (dB
re 1 pPa).
BWeff = The audible bandwidth, i.e the frequency band where the received
level at the reference range is above the hearing threshold of
given species (kHz).
For the usual case where the high frequency limit of the band of audibility is
more than a decade above the lower limit, the high frequency limit alone may
be used in Eqn. (26) with less than 0.5 dB error. This is useful in applications
where the lower limit of the range of audiblity is not easily defined
because of lack of accurate hearing threshold data. The acoustic terms,
Lr3-Ss and BWeff, in the model are designed to provide an output approaching 0
for cases where the received level spectrum becomes equal to the hearing
threshold and/or the audible bandwidth becomes very small. The bandwidth
correction term is calculated using kiloHertz rather than Hertz, as in the
usual application, in order to obtain more conveniently scaled values of SER.
An example of a spreadsheet layout for the SER Model is shown in Table
5.3. The table includes supplementary information on the effective bandwidth
and highest 1/3 octave band of the source. It also shows comparable information
for the region of maximum sensitivity on the hearing curve, defined as
shown in Fig. 5.2. The following summary is given to explain the terminolgy
used in applying the SER Model:
Standardized Exposure Rating Model
(Description of terms and data entering procedure)
Source - This is a summary of parameters from the SNC Model
results which are used in the SER procedure; see Table
5.2 and its description for details.
Receiver (species) - Specific species name
D, - Average density of the species in the model reference
area (~umber/km~)
Hearing Bandwidth - The dominant hearing range of a species as defined by a
10 dB amplitude range centered on the frequency of
maximum sensitivity.
Frl - The lowest frequency where the hearing sensitivity is
within 10 dB of the maximum.
Frh - The highest frequency where the hearing sensitivity is
within 10 dB of the maximum.