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

Most sound is actually transmitted to water within the 13-degree “cone”, especially in calm
conditions. Outside the cone most sound is reflected except where appropriately oriented faces
of waves and chop enable some sound to be transmitted across the air-water interface. The
sound that penetrates outside the cone does not penetrate deeply. The analysis conducted for
this project described in Appendix 1 and below treats the area ensonified as if the cone didn’t
exist. This simplifying assumption results in an overstatement of the amount of noise
transmitted into the water from the air-water interface and results in an overestimation of the
area affected by elevated noise levels in the water.
Exposures to elevated noise levels from aircraft overflight would be brief in duration (seconds)
as the aircraft passes overhead and would diminish rapidly due to the speed of the aircraft. For
example, Blackwell and Greene, in their study of underwater noise in the Cook Inlet near
Elmendorf AFB (2002, Figure 3C), found that a landing F-15 passing directly overhead only
generated underwater noise levels exceeding the ambient noise level for approximately three
seconds. The exposed animal would need to be nearly directly underneath the overflight in
order to be exposed to elevated noise levels from an aircraft overflight due to lack of or greatly
diminished transmission of sound into water at angles greater than 13 degrees from the vertical.
Furthermore, a noise would generally need to be louder than ambient (background) noise levels
in order to be perceived by the animal.
Blackwell and Greene (2002) also measured high ambient noise levels in the Knik Arm. They
found a 119 dB re 1 µPa average in-water reading adjacent to Elmendorf AFB while no
overflights were taking place. The same investigators measured ambient noise of 124 dB re 1
µPa at Point Possession (a nearby locality south of Anchorage) during a changing tide. An EA
for the Port of Anchorage reported noise levels on shipping days averaged 134–143 dB re 1 µPa
and the Knik Arm Bridge EIS (Underwater Measurements of Pile-Driving Sound) reported
background levels of 115–133 dB re 1 µPa. Additionally, KABATA et al. (2010) summarized a
variety of existing noise studies conducted within the Knik Arm and concluded that measured
background levels rarely are below 125 dB re 1 μPa, except in conditions of no wind and slack
tide. Ambient noise energy in the Knik Arm is typically concentrated at frequencies below 10
kHz (Blackwell and Greene 2002).
Of F-15 aircraft overflights measured in air and in water while on approach for landing at
Elmendorf AFB by Blackwell and Greene (2002), the sounds of overflight were detectable in
water in only two of the eleven overflights, one at 90 degrees (i.e., directly overhead) and one at
80 degrees overhead. The peak in-water noise measured was 134dB re 1 μPa for the F-15
landing straight overhead; the second measured overflight (at 80 degrees overhead) was 122 dB
re 1 μPa. The sounds from the remainder of the overflights could not be detected in the water.
The authors attributed this to two factors, angles exceeding 13 degrees from vertical, which
reduces penetration of sound energy into the water, and high ambient in-water noise. For those
events where aircraft noise was detectable in the water, it was only detectable for approximately
3 seconds.
F-22 aircraft have been based at JBER since 2007, when F-22s replaced the F-15E and one of the
F-15C squadrons that had been based at JBER. In 2010, the last remaining F-15 squadron
departed JBER, leaving the F-22 as the only fighter aircraft based at JBER. F-22 engines are more
powerful than those used in F-15 aircraft, and have the potential to be louder than engines of
Wildlife Analysis
Page 1-8
F-22 Plus-Up Environmental Assessment