GLOBAL IONOSPHERE MAPS OBTAINED FROM GLOBAL NAVIGATION SATELLITE SYSTEM (GNSS) DATA AND THEIR PERFORMANCE AFTER INTEGRATION OF SATELLITE ALTIMETRY MEASUREMENTS

7th International Scientific Conference - SGEM2007, www.sgem.org, SGEM2007 Conference Proceedings/ ISBN: 954-918181-2, June 11-15, 2007

ABSTRACT

Both the group and phase velocity of the signals of all space geodetic techniques
operating in the microwave band, is disturbed when they pass through the
ionosphere – an effect, which can be corrected only if the measurements are
carried out at two distinct frequencies. In this way also information about
the parameters of the ionosphere in terms of Total Electron Content (TEC)
values can be gained and used to correct single-frequency measurements and
to monitor the ionization processes. The classical input data for estimation of
Global Ionosphere Maps (GIM) is the “geometry-free” linear combination,
derived from dual-frequency GNSS observations. Their precision is particularly
associated with the network density and homogeneity and thus lowers over
the oceans. Dual-frequency satellite altimetry missions like Jason-1 provide
information about the ionosphere parameters above the sea surface but due
to the limited spread of the measurements and some open questions related to
the systematic errors, they are mainly used for cross-validation so far. In this
study we create two-hourly GIM from GNSS data and additionally introduce
satellite altimetry observations. The combination increases the accuracy of the
combined GIM over the seas and allows the independent estimation of the
systematic instrumental errors, affecting the two techniques.