A programa calculates speed of sound for a temperature range of 0 to 30 degrees C and relative humidity 0 to 100% RH.
The algorithm is based on the approximate formula published in JASA [1993] by Owen Cramer, "The variation of the specific heat ratio and the speed of sound in air with temperature, pressure, humidity, and CO2 concentration."
f (t, p, xw, xc) = a0
+ a1 t + a2 t2
+ (a3 + a4 t + a5
t2) xw + (a6+ a7 t + a8 t2)p + (a9 +a10 t +a11
t2) xc + a12 xw2
+ a13 p2 + a14 xc2
+ a15 xw p xc where the t is the celsius temperature, p is the pressure, xw is the water vapor mole fraction, and xc is the carbon dioxide mole fraction.
The coefficients are:
a0 = 331.5024
a1 = 0.603 055
a2 = -0.000 528
a3 = 51.471 935
a4 = 0.149 587 4
a5 = -0.000 782
a6 = -1.82 * 10-7 a7 = 3.73 * 10-8 a8 = -2.93 * 10-10 a9 = -85.209 31
a10 = -0.228 525
a11 = 5.91 * 10-5 a12 = -2.835 149
a13 = -2.15 * 10-13 a14 = 29.179 762
a15 = 0.000 486
xw = h f psv / p where h is the relative humidity expressed as a fraction, f is the enhancement factor, and psv is the saturation vapor pressure of water vapor in air.