  Ionospheric tomography using GPS data has been reported in the literature and
even the application to radar altimeter calibration was succesfully carried out
in a recent work. We here present a new software tool, called Global
Ionospheric Stochastic Tomography software (GIST), and its powerful capability
for ingesting GPS data from different sources (ground stations, receivers on
board LEO for navigation and occultation purposes) and other data such as
altimetry data to yield global maps with dense coverage and inherent
calibration of the instruments. We show results obtained including 106 IGS
ground stations, GPS/MET low rate occultation data, TOPEX/POSEIDON GPS data
from the navigation antenna and NASA Radar Altimeter with the additional
benefit of a direct estimation of the NRA bias. The possibility of ingesting
different kinds of ionospheric data into the tomographic model suggest a way to
accurately monitor the ionosphere with direct application to single frequency
instrument calibration.
