Method for Measuring Wind Turbulence

Abstract

SHOCK waves in calm air travel with a velocity that is easily calculated to include the effects of temperature, humidity and the strength of the shock front¹. In turbulent air, however, the instantaneous velocity of a shock wave is modified by local wind conditions. The shock pressure wave produces a change in the refractive index of the air² which causes partial reflexion of electromagnetic waves, so it has been thought possible to track the shock wave using a Doppler radar, thereby enabling its velocity to be measured and the radial wind component to be ascertained. For this purpose Alien and Weiner³ have presented a theory to calculate the reflexion coefficient of electromagnetic waves from a sound shock front. Support for this theory has now been obtained using the Riccati form of the wave equation as suggested by Millington⁴. This indicates that a typical value for the power reflexion coefficient, for realizable shock waves at a range of a few hundred feet, is about −140 dB, assuming that the shock front is short compared with the radar wavelength.