Tomographic Imaging of Thermospheric Neutral Density Using UV Limb Scanning
Abstract
Limb scanning both parallel to and perpendicular to the orbit plane of low-Earth orbiting satellites has been used to characterize and study the distribution of ions and neutral species in the Earth's thermosphere and ionosphere. In particular, inversions of the perpendicular-viewing limb profiles observed by the Global Ultraviolet Imager (GUVI) on the NASA TIMED satellite, in approximately the East-West direction, have been validated against satellite drag inferred neutral density profiles and found to be in good agreement. However, comparisons against in-plane limb observations, in approximately the North-South viewing direction, have not have not been as favorable. To properly invert the UV emission profiles, one must account for volume emission rate gradients due to both density gradients and gradients caused by the variation of the solar zenith angle along the lines-of-sight of the observations. In the East-West direction the dominant source of the volume emission rate gradients is illumination gradients due to variation of the solar zenith angle, which was taken into account in the GUVI inversions. However, in the North-South viewing direction, density gradients are much larger than they are in the East-West direction and they too must be considered; when they are ignored inversions of the type used to interpret the GUVI observations fail to produce accurate results. But, in-plane limb scans over-sample the volume of space observed permitting tomographic inversion of the limb profiles to produce a two-dimensional reconstruction of the volume emission rate in the orbit plane beneath the satellite. We show the results of tomographic inversions of in-plane, North-South viewing, limb profiles that properly account for the volume emission rate gradients so that the density and illumination gradients can be disentangled to produce more accurate neutral densities. We also present results of tomographic fitting of topside scale-heights to extract exospheric temperatures. The tomographic inversions are shown to be in better agreement with the NRLMSISE-2000 model than single limb scan inversions that only include the variation of the solar zenith angle along the lines-of-sight.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMSA43B2142D
- Keywords:
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- 0355 ATMOSPHERIC COMPOSITION AND STRUCTURE Thermosphere: composition and chemistry;
- 0394 ATMOSPHERIC COMPOSITION AND STRUCTURE Instruments and techniques;
- 2419 IONOSPHERE Ion chemistry and composition;
- 3360 ATMOSPHERIC PROCESSES Remote sensing