Improved thermospheric neutral density models are required to better predictLEO satellite orbits. This research describes a new method to estimate the densityusing a tomography-based approach, where the orbit states of satellitesserve as the measurements. The variational equation for the semimajor axis dueto perturbing drag acceleration is used to relate the change in osculating specificmechanical energy of the orbit to the integrated density over the orbit.Using several such measurements from a number of satellites, one can estimatethe density scale factor (i.e. a correction to an assumed density model). Theproblem considered here uses measurements from 100 satellites and solves forthe spatially resolved global density scale factor discretized over 324 grid elementsspanning 300 to 500 km altitude. This ill-posed problem is solved usingTikhonov regularization, with the 3D gradient chosen as the regularization operator,resulting in a penalty on the spatial smoothness of the estimated density.Preliminary simulation results show that the true time-averaged density can bereconstructed to within approximately 10%, using only simulated ground-basedtracking measurements separated over 5 orbital revolutions.
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