Protonospheric electron concentration profiles

Abstract

The local electron concentration has been calculated along portions of the orbit of OGO 1, based on ‘differential Doppler frequency’ and Faraday polarization rotation measurements of harmonic radio beacon transmissions. Since it is not possible to make these calculations with sufficient accuracy for most satellite orbits, an extensive error analysis is included, to establish the sources and magnitudes of the uncertainties in the computations. Order-of-magnitude improvement over satellites in low earth orbit is achieved with the very eccentric orbit of OGO 1 and by using a combination of Faraday and differential Doppler techniques. Values of protonospheric electron concentration have been obtained between altitudes of about 6000 and 15,000 km on a number of orbits. The uncertainties in the computed values result principally from scaling errors in the Faraday polarization rotation angle and from horizontal gradients in the ionosphere; they typically total less than ±600 electrons/cm³. A number of concentration profiles are shown and are compared with direct probe measurements, with whistler results, and with extrapolated values of electron concentration obtained from Alouette 1 near 1000 km.