F-22 Plus-Up Environmental Assessment - Joint Base Elmendorf ...

estimated un-weighted SPL. It should be noted that odontocete hearing is not strong at low
frequencies (Southall et al 2007). Much of the noise energy generated by jet aircraft is at low
frequencies, and use of un-weighted SPL yields conservative estimates of noise impacts to
belugas. Transmission of sound from a moving airborne source to a receptor underwater is
influenced by numerous factors and has been studied extensively (Richardson et al. 1995, Young
1973, Urick 1972). In this wildlife analysis, twenty-six dB were added to SPL re 20 µPa to
convert to SPL re 1 µPa and, an additional 6 dB are added to account for doubling of sound
pressure as the sound rays cross the interface between air and water. Taking into account
sound metric conversion and the reflectance of noise energy at the air-water interface, noise
levels in water (SPL re 1 µPa) were calculated as being 35 dB higher than noise levels in air just
above the water’s surface (LA max re 20 µPa). Additional discussion on transmission of aircraft
noise into water is located in ‘Step 4: Establish area exposed to noise exceeding thresholds’.
Step 3: Establish threshold for potential effects. Calculated noise levels generated by F-22
aircraft in the Knik Arm do not exceed 137 dB SPL re 1 µPa, well below the threshold for
temporary hearing loss (195 dB re 1 µPa 2 -s) and permanent hearing loss (215 dB re 1 µPa 2 -s) for
non-pulse sound. However, such noise levels do have some probability of causing a behavioral
reaction such as area avoidance or alteration of natural behaviors.
The most appropriate acoustic threshold is currently the odontocete risk function, which
assesses the probability of a behavioral reaction from 120 dB SPL to 195 dB SPL for non-pulse
sound (U.S. Navy 2008). The risk function was derived by the U.S. Navy and NMFS to
determine effects from mid-frequency sonar. However, the odontocete risk function is currently
the best available science for predicting behavioral effects from intermittent, non-impulsive
(non-pulse) sound.
The risk function is used to estimate the percentage of an exposed population that is likely to
exhibit behaviors at a given received level of sound (NOAA 2009, NMFS 2009). For example, at
165 dB SPL (dB re: 1 μPa rms), the risk (or probability) of harassment is 50 percent, and NMFS
applies that 50 percent of the individuals exposed at that received level are likely to respond by
exhibiting behavior that NMFS would classify as behavioral harassment (NOAA 2009, NMFS
2009).
The values used in the odontocete risk function are based on three sources of data: Temporary
threshold shift (TTS) experiments conducted at Space and Warfare Systems Center (SSC) and
documented in Finneran, et al. (2001, 2003, and 2005; Finneran and Schlundt 2004);
reconstruction of sound fields produced by the USS SHOUP associated with the behavioral
responses of killer whales observed in Haro Strait and documented in NMFS (2005), DoN
(2004), and Fromm (2004a, 2004b); and observations of the behavioral response of North
Atlantic right whales exposed to alert stimuli containing mid-frequency components
documented in Nowacek et al. (2004).
The risk function represents a general relationship between acoustic exposures and behavioral
responses. The risk function, as currently derived, treats the received level as the only variable
that is relevant to a marine mammal’s behavioral response. However, we know that many other
variables—the marine mammal’s gender, age, and prior experience; the activity it is engaged in
during an exposure event, its distance from a sound source, the number of sound sources, and
whether the sound sources are approaching or moving away from the animal—can be critically
Wildlife Analysis
Page A1-2
F-22 Plus-Up Environmental Assessment