ATMOSPHERIC DENSITY MEASUREMENTS DERIVED FROM CHAMP/STAR ACCELEROMETER DATA

摘要

The STAR accelerometer on-board the German CHAMP satellite has provided precise global (+-87° latitude) measurements of non-gravitational accelerations at ～425 km altitude since its launch in July 2000. CHAMP also carries a GPS receiver that permits continuous tracking of the satellite, which makes possible the calibration of the accelerometer bias and scale factors, including their variation in time. The accelerometer measures the non-gravitational accelerations experienced by the spacecraft in three components, of which the along-track component mainly represents the atmospheric drag. By subtracting modeled accelerations for solar radiation pressure and Earth Albedo from the STAR observations, the drag acceleration is isolated, which is proportional to the atmospheric density. The density has been derived assuming negligible upper-atmosphere winds, thus the accuracy of the density measurements depends mainly on the uncertainty of the STAR calibration parameters and the upper-atmosphere winds. The accuracy of the densities therefore is a function of geomagnetic activity, an indicator for large wind amplitudes, and also latitude. Density is analyzed for the time period surrounding three geomagnetic storms occurring in 2002. The derived densities are then compared to several semi-empirical thermospheric density models, revealing the limitations of each. The results are further analyzed by binning as a function of season, latitude, local time, and solar activity. Finally, we will comment on the prospect of using the dual-accelerometers onboard the twin GRACE satellites, which were launched in March 2002, for similar studies.