Atmospheric Propagation Studies up to 30 September 1970

Abstract

Abstract : The phase-path (doppler) sounder array was expanded to operate at two sounding frequencies simultaneously. Particular emphasis was given to the study of ionospheric background motions having periods longer than 5 minutes or so. It was found that the power spectra of the phase-path variations show the effect of a varying Vaisala frequency with height, probably modified by the effects of viscosity. It has also pointed out the potential of the doppler technique to measure the parameters of the neutral gas structure at ionospheric altitudes. Cophase analysis of phase-path records following Saturn-Apollo launches indicate that rocket generated infrasound is trapped at ionospheric heights by a wave- guide mechanism. Ionospheric motions detected by the doppler array following a large earthquake are found to have a phase velocity equal to that of seismic Rayleigh waves of the same period and to arrive from the direction of the epicenter. A study of the spatial coherence of ionospheric motions indicates reflection point separations of the order of 60 km are sufficient for noise decorrelation up to periods of 30 min; and separations of 90 to 100 km for periods longer than 30 min. Preliminary analysis of microbarograph records following some of the French tests of 1970 show arrivals of long period gravity waves with phase velocities of the order of 550 m/sec.