IONOSPHERIC ELECTRON-DENSITY PROFILES OBTAINED WITH THE GLOBAL POSITIONING SYSTEM - RESULTS FROM THE GPS MET EXPERIMENT/

The Global Positioning System Meteorology (GPS/MET) experiment, which placed a GPS receiver in a low-Earth orbit tracking GPS satellites set ting behind the Earth's limb, has collected data from several thousand s of occultations since its launch in April 1995. This experiment demo nstrated for the first time the use of GPS in obtaining profiles of el ectron density and other geophysical variables such as temperature, pr essure, and water vapor in the lower atmosphere. This paper discusses some of the effects of the ionosphere, such as bending and scintillati on, on the GPS signal during occultation. It also presents a set of io nospheric profiles obtained from GPS/MET using the Abel inversion tech nique, and compares these profiles with ones obtained from the paramet erized ionospheric model (PIM) and with ionosonde and incoherent scatt er radar measurements. Statistical comparison of NmF2 values obtained from GPS/MET profiles and nearby ionosondes indicates that they agree to about similar to 20% (1-sigma) in a fractional sense. The high vert ical resolution, characteristic of the occultation geometry, is reflec ted in the GPS/MET profiles which reveal ionospheric structures of ver y small vertical scales such as the sporadic E.