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

Report No. 6945
BBN Systems and Technologies Corporation
Moving Source Corrections - These are correction factors that 'provide spatial
and temporal compensation for source motion.
Cm - a spatial correction factor that determines an average
level for the typical bell-shaped Lr curve generated when
a moving source passes by a fixed receiver. It is area
specific but not frequency dependent.
Tt - the travel time required for a specific source to travel
in a straight path past the receiver with a closest point
of approach (CPA) of 300 m. The length of the path (Rm)
is determined by the range at which L; is 20 dB lower
than at CPA.
Tt = 2( Rm/S) , where Ss. is the source speed.
Fluctuation Correction - This is a correction for fixed or moving sources
which do not have a constant output level.
Tf - The total effective time during which a specific source
is at or near maximum output during a time period
covering a full operating cycle or a representative
operating condition. For sources with a wide range of
output levels, the approximate method of determining L
can be used to eliminate the need to determine Tf
e q
(discussed elsewhere).
Tr - The reference time interval used to determine the
effective impact duration of a noise source - marine
mammal encounter. An interval of 2 hrs is used as
representing the average time interval that a moving
source would be within acoustic range of a receiver or a
moving mammal would be within acoustic range of a fixed
source .
Leq
- The sound level of a'fixed, constant amplitude source
that would have the same acoustic energy as a fluctuating
and/or moving source.
Pe - (Probability of Encounter) The probability that a
specific type of source will be found in a 1 km2 area
surrounding the receiver location.
From Eqn ( 19), Pe = ( 1+1 .77S)/At, where S is the average
speed of advance of the source In km/sec, if it is
moving, and At js the total area included in the modeling
procedure in km .