CHARGE DENSITIES IN THE IONOSPHERE FROM RADIO DOPPLER DATA

Abstract

A method is described whereby the directly observable radial velocities of a missile relative to a ground receiver?both in a radio-Doppler electronic system of tracking?may be compared to radial velocities determined by vacuum-trajectory formulae and the differences converted to ionization densities at the levels through which the rocket is passing. Basically, DOVAP1 is an instrumentation system which continuously compares the phase of two radio-frequency signals transmitted from a ground station to another ground station?one signal directly, the other by way of the rocket. The continuous variation in phase difference as a function of time is the well-known Doppler effect and is proportional to the missile velocity in the transmitter-missile-receiver path. If the transmitter and receiver are coincident, the measured velocity is twice the radial velocity of the missile relative to the receiver. 1Doppler velocity and position. The fact that the DOVAP system depends upon phase comparison for the data source permits errors to be introduced if the missile passes through regions in which the phase velocity of the radio frequency signal varies from assumed vacuum-velocity propagation. If the inherent accuracy of the DOVAP system is utilized to obtain initial conditions (velocities and position) in an electrically undisturbed portion of the atmosphere above the region of appreciable density, a very accurate vacuum trajectory may be computed, from which radial velocities to the ground receiver can be calculated and compared with observed DOVAP radial velocities when the rocket passes through charged regions of the atmosphere. The differences in radial velocities may then be used to compute ion or equivalent electron densities. This method was used to compute ion densities for several missiles fired at the White Sands Proving Ground, New Mexico. Results gave density maximums of 0.747 ? 1011 for the D layer at 38 miles, 1.69 ? 1011 for the E layer at 56 miles, and 11.4 ? 1011 for the F2 layer at 201 miles (all densities in ions per cubic meter).