Improvements in the tropospheric refraction correction for range measurement

Abstract

The retardation of a satellite’s radio signal by the Earth’s troposphere and stratosphere is significant even when no bending of the signal path occurs, as in the zenith direction. The resulting error in range or Doppler data is generally estimated by assuming rectilinear propagation through a model atmosphere based on conditions at the tracking station. The two-quartic model of atmospheric refractivity that is used here (‘dry’ and ‘wet’ components) was derived earlier by the author from studies of meteorological balloon data, with parameters chosen to yield the right mean range correction at the zenith. Errors develop at very low elevation angles, partly because ( a ) the precise shape of the refractivity profile, involving temperature and water vapour irregularities, becomes important, and ( b ) signal path bending effects become significant. Corrections for the path curvature effect are presented, and possible ways of improving the profile model are discussed.