1. International Reference Ionosphere 1990;Bilitza;URSI/COSPAR, NSSDC/WDC-A-R&S,1990
2. Comparison between IRI and GPS-IGS derived electron content during 1991–97: First results;Bilitza;Physics and Chemistry of the Earth,1998
3. Ionospheric tomograp helps resolve GPS ambiguities On The Fly at distances of hundreds of kilometers during increased geomagnetic activity;Colombo,2000
4. Resolving carrier-phase ambiguities on-the-fly, at more than 100Km from the nearest reference, with the help of ionospheric tomography;Colombo,1999
5. IGS products for the ionosphere;Feltens,1998