Sounding of the topside ionosphere/plasmasphere based on GPS measurements from 
CHAMP: Initial results

S. Heise, N. Jakowski, A. Wehrenpfennig, Ch. Reigber, and H. Luhr


Beside the GPS radio occultation measurements of the troposphere and ionosphere,
the CHAMP satellite tracks presently up to 8 GPS satellites simultaneously for
navigation. The received dual frequency GPS signals provide valuable information
on the ionization state of the topside ionosphere and plasmasphere. This paper
briefly describes a new developed model assisted technique to improve the three
dimensional electron density estimation above the CHAMP orbit from these GPS
measurements. Application of this assimilation algorithm provides a 2-D electron
density slice of the ionosphere/plasmasphere system within the CHAMP orbit plane
from the CHAMP altitude up to GPS orbit heights. We estimate the accuracy of the
GPS TEC calibration and perform a first validation by comparing the retrieved
electron density of the ionosphere/ plasmasphere slice at CHAMP altitude to
simultaneous electron density measurements of the Langmuir Probe onboard CHAMP. 

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Geophysical Research Letters, 29, 14, 1699, doi:10.1029/2002GL014738, 2002