93-169
Higher-Order Ionospheric Effects On The Gps Observables And Means Of Modeling Them
Sassan Bassiri and George A. Hajj
Abstract
Based on realistic modeling of the electron density of the ionosphere and using a dipole moment approximation for the earth magnetic field, we are able to estimate the effect of the ionosphere on the GPS signal for a ground user. The lowest-order (1/f2) effect, which is of the order of .1-30 meters of zenith group delay, is subtracted out by forming a linear combination of the dual frequencies of the GPS signal. One is left with second- (1/f 3) and third-order (1/f 4) effects which are estimated typically to be ~0-2 cm, and ~0-2 mm at zenith respectively, depending on the time of day, time of year, the solar cycle and the relative geometry of the magnetic field and the line of sight. Given the total electron content along a line of sight, we derive an approximation to the second-order term which is accurate to -90% within the magnetic dipole moment model; this approximation can be used to reduce the second-order term to the millimeter level, thus, potentially improving precise positioning in space and on the ground. The induced group delay, or phase advance, due to second- and third-order effects are examined for two ground receivers located at equatorial and mid-latitude regions tracking several GPS satellites.
* Department of Electrical Engineering, Sharif University of Technology, Tehran, Iran.
**Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109.