Ga. Hajj et Lj. Romans, IONOSPHERIC ELECTRON-DENSITY PROFILES OBTAINED WITH THE GLOBAL POSITIONING SYSTEM - RESULTS FROM THE GPS MET EXPERIMENT/, Radio science, 33(1), 1998, pp. 175-190
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.