Near Real-Time Monitoring of the Ionosphere Using Dual Frequency GPS Data in a Kalman Filter Approach

Abstract

The ionosphere is an important source of errors for the GPS signals that travel through
the ionosphere on their way to the ground-based receivers by introducing a frequency dependent
path delay proportional to the total electron content (TEC) along the signal path. For dualfrequency
GPS receivers, the ionospheric effects can be accounted for by taking advantage of the
dispersive nature of the ionosphere in the microwave region of the electromagnetic spectrum,
while for the single frequency GPS receivers the ionospheric effects can be minimized by modeling
them using, for example, empirical or physics-based ionospheric models. On the other hand, the
errors imposed by the ionosphere on the GPS signals can provide important temporal and spatial
information about the electron density distribution in the ionosphere. Besides the ionospheric
errors, there are some other sources of errors that can affect the GPS signals, such as the satellite
and receiver instrumental biases, carrier phase ambiguities, multipath effects, clock errors, orbital
errors, tropospheric errors, but which can be compensated for, estimated, or neglected depending
on the particular application. In this paper, we are only concerned with the ionospheric effects on
the GPS signals, and describe a Kalman filter-based algorithm for near real-time estimation of the
line-of-sight and vertical ionospheric TEC and of the combined satellite and receiver instrumental
biases, using data from dual-frequency GPS receivers.