Removal of the nπ ambiguity in observations of total electron content

Abstract

Two of the main sources of error in converting observations of the Faraday rotation angle of a signal from a geostationary satellite into total electron content ( N T ) are the uncertainty in the baseline—corresponding to the initial polarisation—and the uncertainty in the total number of rotations—the ‘ nπ ambiguity’. A new method of resolving the nπ ambiguity, through the use of critical frequency data, is described. The method has been applied to data obtained at Sydney from Syncom 3. Results suggest that this comparatively simple method is quite reliable. The same method has been used to estimate the zero for absolute measurements of N T . It appears to give consistent results but yields a value which is rather different from that calculated on the basis of data previously published on Syncom 3.