Radio occultation measurements from the Australian microsatellite FedSat

The Australian Low Earth Orbit (LEO) microsatellite, FedSat (named to commemorate the centenary of the Australian Federation in 2001), was launched into orbit on December 14, 2002 from the Tanegashima Space Centre, Japan. A Global Positioning System (GPS) receiver was one of the instruments onboard. The received GPS signals can be used to investigate the ionospheric electron density and the atmosphere below FedSat's orbiting altitude, using radio occultation (RO) techniques. The RO technique developed involves a simplified form of the Abel transform using the slant total electron content (STEC) determined from radio signals that traverse below FedSat's orbiting altitude. Electron density profiles from the GPS RO data, recorded by the GPS receiver onboard the FedSat satellite, are determined for the first time. The technique combined with simultaneous occultation density profile extraction from different LEO satellites and satellite navigation systems has the potential to image near real-time 3-D structures of the ionospheric electron density.