Thermospheric Temperature Derived from ARGOS Observations of N2 Lyman-Birge-Hopfield Emission (original) (raw)

2001

Abstract

Thermospheric temperature can be inferred from the rotational temperature of N2 in far-ultraviolet Lyman-Birge-Hopfied (LBH) emission, if the band shapes are measured with sufficient spectral resolution. The Advanced Research and Global Observations Satellite (ARGOS), launched February 1999, includes the High-resolution Ionospheric and Thermospheric Spectrograph (HITS), a far-ultraviolet sensor with 1-Å resolution well-suited to measure global N2 temperatures. Owing to the low sensitivity of HITS, many spectra include bins with low numbers of photon counts. Consequently, standard χ2 minimization techniques cannot accurately fit band shapes, since Poisson rather than Gaussian statistics apply. Approaches for temperature retrievals using the LBH (1-1) band are presented that properly address the statistical difficulties. One technique rebins the band into two colors, then derives effective temperature from a color ratio; the other two methods retrieve temperature from the band shape using Levenberg-Marquardt C-statistic minimization. Effective thermospheric temperature and exospheric temperature are derived from HITS 200 km stare spectra acquired June 25, 2000 using these techniques. MSIS temperature estimates at 200 km are higher than temperatures derived from HITS by ~140 K (latitudinally-averaged).

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