Electron densities from satellite antenna impedance

Impedance of satellite antennas has been measured throughout the orbits of several satellites by means of a standing wave system, which is a lumped-circuit equivalent to the slotted-line impedance-measurement technique. Impedance data from a recent satellite, ranging in altitude from 240 to 1,000 km (kilometers), have been used to calculate the electron density of the ionosphere. On the sunny side of the earth, this density was found to be a function of the latitude and altitude; on the dark side, it was found to be nearly a constant.