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Atmospheric Effects on the Speed of Sound

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The small-signal speed of sound in humid air is calculated from a model which includes the real-gas effects from the equation of state for humid air and the vibrational dispersion due to N2, O2, and CO2 relaxation. Other atmospheric effects such as dispersion due to viscothermal and rotational relaxation, heat radiation, propagation along the air-ground boundary, the density gradient, turbulence, aerosols and fogs are considered and found to be unimportant for frequencies between 1 Hz and 5 MHz at one atmosphere. The uncertainty in predicting the sound speed varies between 0.22 msec at -90 C to 0.05 msec at 90 C. Experimental results in humid air at 20 C and 30 C are in excellent agreement with the model. For the propagation frequency of 20 Hz, it is found that the presently used sound-ranging formula, c 20.06 x square root of T sub s, where T sub s .75t sub v .25t 273.2 t sub v virtual temperature, differs by up to 0.5 msec over the range -60 C to 60 C. A correction to the sonic temperature determination is suggested which results in deviations of less than 0.05 msec over the temperature range from -60 C to 50 C and for relative humidities from 5 to 100. Author

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Technical rept.

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Prepared in cooperation with Texas Univ. at El Paso. Dept. of Physics. DOI: 10.21236/ADA076060



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