Propagation measurements in shock-ionized media

The effect of shock induced ionization on electromagnetic waves is investigated by means of some propagation experiments conducted in Hotshot II, a hypersonic wind tunnel at AEDC, Tullahoma, Tennessee. The purpose of the experiments was qualitative evaluation of the relative effects of hypervelocity ionization on the commonly used frequencies, thereby verifying at least the trends indicated by theoretical studies. From measured values of pressure and temperature inside the tunnel, the resulting free electron density is calculated using Gilmore's tables and the electron collision frequency estimated. Using these parameters, the wave attenuation is computed and compared with the observed results. The experimental results in general exceed the computed values. The factors, introduced by the operation of the tunnel itself, that effect the experiment and other uncertainties related to estimating the RF parameters are discussed in the light of the results.