Remote sensing of lower-middle-thermosphere temperatures using the N2 Lyman-Birge-Hopfield (LBH) bands

The scientific and societal importance of short-term changes in the thermosphere-ionosphere (T-I) system highlights a need to better understand short-term changes in the thermosphere. For collision avoidance, this need becomes increasingly important as the number of low-earth-orbiting satellites increases because geomagnetic activity can cause dramatic, unexpected increases in satellite drag. The thermospheric density changes responsible for changes in drag depend primarily on changes in the thermospheric temperature. However, for collision avoidance, the specification of drag could also be problematic during quiet periods when the number of satellites and the uncertainties in their orbits are large. While temperatures and densities at higher altitudes (greater than or similar to 250 km) have been extensively studied and modeled, there is a knowledge gap for densities at lower-middle-thermosphere altitudes (less than or similar to 200 km). At these lower altitudes, the primary sources of thermospheric density data, in situ and drag data from satellites, are rarely available. Remote sensing of temperatures and composition by NASA's Global-scale Observations of the Limb and Disk (GOLD) mission can help fill this gap. The GOLD mission produces disk images of neutral temperature, a key parameter for understanding neutral density in the lower-middle thermosphere. However, while disk images of the temperature have been available since the launch of GOLD, recent improvements to its observational capability that are relevant to data interpretation may not be widely known. Also, other temperature retrieval techniques than GOLD's have been published. Comparisons indicate that GOLD's technique gives the most consistent results and yields the lowest uncertainties. This paper discusses both temperature retrieval techniques and issues in interpreting GOLD's images of temperatures.