LEO (Low Earth Orbit) missions such as CHAMP and GRACE carrying a dual frequency GPS receiver onboard, offer a good chance to derive vertical electron density profiles by using the radio limb sounding technique. This technique has proved to be a powerful tool for remote sensing the Earth's neutral atmosphere and ionosphere by analyzing GPS radio occultation data obtained from the GPS/MET instrument, flown on the Microlab-1 LEO satellite.
The German CHAMP satellite was successfully launched from the Russian launch site Plessetsk by a COSMOS rocket on July 15, 2000.
The main scientific objectives of this geo-science mission are related to precise gravity and magnetic field measurements and atmosphere/ionosphere sounding by using GPS radio occultation techniques.
Whereas the first neutral gas limb sounding measurements onboard CHAMP were obtained on February 11, 2001, the first ionospheric occultations were measured on 11 April 2001.
CHAMP - Challenging Minisatellite
Payload for Geophysical Research.
Source: GFZ Potsdam, NASA, T. Althaus