Evaluation of Alternative Procedures for Atmospheric Absorption Adjustments during Noise Certification. Volume III. Tables of Atmospheric-Absorption Losses.
DYTEC ENGINEERING INC LONG BEACH CA
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The work reported here extends that in FAA-RD-77-167, December 1977, to the problem of adjusting actual aircraft noise 13-octave-band spectra measured at 0.5-s intervals. Test-day spectra are used to calculate, PNL, PNLT, EPNL, AL, and SEL. The test-day spectrum at the time of PNLTM and at the time of ALM are adjusted to acoustical-reference conditions using the atmospheric-absorption method in American National Standard ANS S1.26-1978 and applied, using measurements of air temperature and relative humidity at various heights above the ground, by integrating over the frequency range of the passband of ideal filters and by calculating the absorption at the exact band center frequencies only. SAE ARP866A is also used with the vertical-profile temperaturehumidity data and with data at 10.0 m to determine adjustments from test to reference conditions. The adjustment methods are applied to noise data from 9 aircraft. Volume I describes the analyses and results of the study. Volume II presents the computer program that was developed and illustrates its use with a test case. Volume III presents tables of attenuation due to atmospheric absorption over a 300-m path. Attenuatons were calculated using ANS S1.26-1978 for pure tones at band center frequencies and for 3 noise spectral slopes by a band-integration method, and using SAE ARP866A. For each of the 5 methods, the tables cover 34 air temperatures from 2 to 35C, 10 relative humidities from 10 to 100 percent, and 24 nominal band center frequencies from 50 to 10,000 Hz. Author
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