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.
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References
Stephens, R. W. B., and Bate, A. E., Acoustical and Vibrational Physics (Arnold, London, 1966).
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Allen, C. H., Proc. World Cong. Radio Meteorol., 270, Boulder, Colorado, September 1964.
Millington, G., Electronics Lett., 1, 184 (1965).
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BLOGH, J., COOPER, D. Method for Measuring Wind Turbulence. Nature 220, 1118–1119 (1968). https://doi.org/10.1038/2201118a0
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DOI: https://doi.org/10.1038/2201118a0
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