An assessment of new satellite total density data for improving upper atmosphere models (original) (raw)
1999, Planetary and Space Science
The DTM series of atmospheric density models (Barlier et al., 1977; Berger et al., 1998) have been developed for atmospheric constituent representation and precise orbit computation. They are based upon satellite drag total density data which are implicitly averaged over one or more days.Our approach consists of refining the computation of the density model coefficients with more precise orbit computation, using the information contained in the tracking data. Satellite Laser Ranging (SLR) in case of Starlette (800 km) and GFZ-1 (380 km), Doppler-DORIS in case of SPOT2 (800 km).This has been verified by comparison of the new density values to Dynamic Explorer 2 (DE-2) measurements, as well as by precise orbit computation. In both cases, an improvement of a few percent has been achieved, showing the interest of the method.This study has been done in preparation for the new accelerometric mission CHAMP for which we prepare a new gravity field (GRIM5) using the orbit perturbation technique, as well as an improved density model, hence improving the drag modeling.
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Measuring atmospheric density using GPS-LEO tracking data
We present a method to estimate the total neutral atmospheric density from precise orbit determination of Low Earth Orbit (LEO) satellites. We derive the total atmospheric density by determining the drag force acting on the LEOs through centimeter-level reduced-dynamic precise orbit determination (POD) using onboard Global Positioning System (GPS) tracking data. The precision of the estimated drag accelerations is assessed using various metrics, including differences between estimated along-track accelerations from consecutive 30-h POD solutions which overlap by 6 h, comparison of the resulting accelerations with accelerometer measurements, and comparison against an existing atmospheric density model, DTM-2000. We apply the method to GPS tracking data from CHAMP, GRACE, SAC-C, Jason-2, TerraSAR-X and COSMIC satellites, spanning 12 years (2001–2012) and covering orbital heights from 400 km to 1300 km. Errors in the estimates, including those introduced by deficiencies in other modeled forces (such as solar radiation pressure and Earth radiation pressure), are evaluated and the signal and noise levels for each satellite are analyzed. The estimated density data from CHAMP, GRACE, SAC-C and TerraSAR-X are identified as having high signal and low noise levels. These data all have high correlations with anominal atmospheric density model and show common features in relative residuals with respect to the nominal model in related parameter space. On the contrary, the estimated density data from COSMIC and Jason-2 show errors larger than the actual signal at corresponding altitudes thus having little practical value for this study. The results demonstrate that this method is applicable to data from a variety of missions and can provide useful total neutral density measurements for atmospheric study up to altitude as high as 715 km, with precision and resolution between those derived from traditional special orbital perturbation analysis and those obtained from onboard accelerometers.
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