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The Grand Canyon model validation is joint effort by the Federal Aviation Administration and the National Park Service to provide the most accurate modeling of the noise environment in the Canyon. In the summer of 1999 a team of NPS and FAA personnel conducted a study to measure air tour noise and the detectibility of that noise. The NPS and the FAA are currently comparing the actual detectibility of the noise to that predicted by numerical models.
Lateral Attenuation is the term used to describe the difference in sound heard directly underneath the aircraft compared to the sound heard to the side at the same slant distance. Physical influences on lateral attenuation are the ground characteristics, the physical placement of the engines on the airframe, and the usage of high-lift devices (i.e. flaps and slats). In the image at the right, a DC-9 test aircraft is passing through a microphone array suspended from one of two 200 foot cranes during a NASA-sponsored Lateral Attenuation flight test.