Measurements of the impedance at 7.75 Mc/s of an electrically short antenna in the ionosphere indicate that power is absorbed by some mechanism other than electromagnetic radiation. The importance of the radiation of energy as an electron pressure (electroacoustic) wave generated near the antenna is discussed, and it is shown that the calculated power radiated by this mechanism yields results in good agreement with the observations.

Ionospheric electron-density data were obtained from Faraday rotation measurements on a 73.6-Mc/s signal radiated from the Scout rocket NASA ST-7/P-21, launched from Wallops Island, Virginia, at 1238 EST on October 19, 1961. This Scout, a four-stage solid-fuel vehicle, created a severe ionospheric disturbance along its trajectory, since the third-and fourthstage propulsion periods occurred within the ionosphere. The receiving station was very close to the launch site, so that the 73.6-Mc/s propagation path was almost the same as the rocket flight path. At the same time, ionosonde records were obtained from a local sounding station. From a comparison between the results obtained from the ionosonde, the Faraday rotation method, and the high-altitude profile [Bauer and Jackson, 1962], an interpretation of the influence of the burning rocket on the ionosphere has been derived. It should be noted that the radio propagation technique is well suited for an investigation of this type, since the radio wave is initially propagated right through the disturbed region and it gradually moves out as the geometry of the rocket trajectory results in a sideways motion of the ray path. Thus, a rough estimate can be made of the nature and horizontal growth rate of the disturbance.The Faraday rotation measurement is essentially a measurement of the total number of electrons in a tube of unit cross-sectional area between the rocket and the ground, the axis of the tube being the line of propagation of the radio wave. The apparent local electron density at the rocket is derived from the rate at which this total electron content changes with rocket position. If the ionospheric profile is unchanged and if the rocket motion is radial, the rate of change measured represents the density at the rocket level. If the electron distribution is changing along the ray path, the measurements represent a combination of both the density at the rocket level and the change in total content along the ray path. Thus, in a disturbed ionosphere the apparent density measured can be either less or greater than the true density, depending on changes taking place at lower altitudes along the ray path. The apparent electron density derived from the Faraday rotation, and also the initial undisturbed electron-density profile obtained by reduction of the ionogram, are shown in Figure 1. Since the sideways displacement of the ray path with respect to the trajectory is an important consideration in the later discussion of the data, trajectory and typical ray paths are also included on the figure.The effects of the burning rocket on the apparent electron density can be seen to be as follows (where the regions A, B, and C referred to are indicated in the figure):A. Third-stage ignition occurred at an altitude of 120 km, and it resulted in very rapid and highly distorted Faraday cycles, which were interpreted as a large increase in local density. This is shown on the figure as a dashed curve, since an accurate measurement could not be derived from these distorted cycles...

A theoretical treatment of the electron displacement in the vicinity of a linear cylindrical antenna immersed in the ionosphere has been developed which explains the surprisingly thick ion sheaths that have been observed experimentally when large RF voltages are applied to the antenna. The force that displaces the electrons is obtained from numerical solutions to the nonlinear differential equation describing their motion, and the results are found to be consistent with the observations.

An analytical expression is derived for the probability distribution of the phase difference between two spaced antennas excited by a random fan of rays plus a specular component. From this expression, graphs showing the variation of the standard deviation as a function of the coherence ratio and the autocorrelation coefficient of the scattered part of the incident angular power spectrum are presented. Some consideration is given to the properties of the functions (cos x) and (a1a2 ) (where x is the phase difference and a,, a, are the amplitudes at each antenna) and of the covariance C(a1a,, cos x>.

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