January 2015
Spotlight Summary by Jonathan J. Makela
Advanced mesospheric temperature mapper for high-latitude airglow studies
The Earth’s mesosphere and lower thermosphere, the region of the atmosphere near 100-km altitude, represent the boundary between our world and space. The mesosphere is the coldest region of the atmosphere, with temperatures as low as 180 K frequently observed. Wave and tidal processes are important in this region of the atmosphere as momentum is transferred and deposited, which has a profound effect on the overall general circulation of the upper atmosphere. Waves of interest in the mesosphere can have horizontal wavelengths ranging from 10s to 100s of kilometers and periods as short as 10s of minutes. The occurrence of polar mesospheric, or noctilucent, clouds at this height range are thought to potentially be a tracer for climate change. Despite its importance, the mesosphere is one of the least-well studied regions of our atmosphere. It is too high for meteorological balloons to reach and too low for satellites to fly through. Sounding rockets can obtain direct measurements of the physical properties of the mesosphere, but they are expensive and provided very limited spatial and temporal measurements, limiting their usefulness for understanding the complex dynamics of the mesosphere. Remote sensing from satellite platforms can provide a useful mean view of the global properties of the mesosphere, but again, provide little information on dynamics. Thus, the study of the dynamics of the mesosphere lies in the domain of the ground-based remote sensor.
Being able to resolve properties of the mesosphere with high spatial and temporal resolution is critical to properly characterizing dynamical features present. This is where the Advanced Mesospheric Temperature Mapper (AMTM) developed by Pautet et al. excels. By observing several emission lines associated with the well-known hydroxyl (OH) bands, this instrument can estimate the temperature of the mesosphere at around 87-km altitude. The emission lines observed by the AMTM were chosen such that the instrument would perform well, even in the presence of strong aurora, which contaminate observations made by previous mesospheric temperature mappers. The AMTM is fronted by a 120° wide-angle fish-eye lens, and temperature and emission intensity measurements are obtained at a spatial resolution of about 500 m over more than 25,000 km2. Thanks to improvements in InGaAs detector technology, the AMTM can do this with excellent accuracy – less than 4 K – with about a factor of six improvement in temporal cadence and factor of four improvement in spatial resolution when compared to previous instruments making comparable measurements. Indeed, the AMTM was cross-calibrated to the well-proven mesospheric lidar system operated by Utah State University with impressive results.
The AMTM is a robust instrument that will provide a new view of fundamental processes at the boundary between our world and space. It can be operated remotely for long periods of time, which is fortunate when it is deployed to such harsh environments as the South Pole, where our understanding of upper atmospheric wave dynamics is minimal. The AMTM opens up a new window into understanding our environment in unprecedented detail.
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Being able to resolve properties of the mesosphere with high spatial and temporal resolution is critical to properly characterizing dynamical features present. This is where the Advanced Mesospheric Temperature Mapper (AMTM) developed by Pautet et al. excels. By observing several emission lines associated with the well-known hydroxyl (OH) bands, this instrument can estimate the temperature of the mesosphere at around 87-km altitude. The emission lines observed by the AMTM were chosen such that the instrument would perform well, even in the presence of strong aurora, which contaminate observations made by previous mesospheric temperature mappers. The AMTM is fronted by a 120° wide-angle fish-eye lens, and temperature and emission intensity measurements are obtained at a spatial resolution of about 500 m over more than 25,000 km2. Thanks to improvements in InGaAs detector technology, the AMTM can do this with excellent accuracy – less than 4 K – with about a factor of six improvement in temporal cadence and factor of four improvement in spatial resolution when compared to previous instruments making comparable measurements. Indeed, the AMTM was cross-calibrated to the well-proven mesospheric lidar system operated by Utah State University with impressive results.
The AMTM is a robust instrument that will provide a new view of fundamental processes at the boundary between our world and space. It can be operated remotely for long periods of time, which is fortunate when it is deployed to such harsh environments as the South Pole, where our understanding of upper atmospheric wave dynamics is minimal. The AMTM opens up a new window into understanding our environment in unprecedented detail.
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Article Information
Advanced mesospheric temperature mapper for high-latitude airglow studies
P.-D. Pautet, M. J. Taylor, W. R. Pendleton, Y. Zhao, T. Yuan, R. Esplin, and D. McLain
Appl. Opt. 53(26) 5934-5943 (2014) View: Abstract | HTML | PDF