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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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doi:10.5194/amt-2017-36
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
22 Mar 2017
Review status
This discussion paper is under review for the journal Atmospheric Measurement Techniques (AMT).
Optimising hydroxyl airglow retrievals from long-slit astronomical spectroscopic observations
Christoph Franzen1,2, Robert Edward Hibbins1,2, Patrick Joseph Espy1,2, and Anlaug Amanda Djupvik3 1Norwegian University of Science and Technology (NT NU), Trondheim, 7491, Norway
2Birkeland Centre for Space Science (BCSS), Norway
3Nordic Optical Telescope, E-38700 Santa Cruz De La Palma, Spain
Abstract. Astronomical spectroscopic observations from ground-based telescopes contain background emission lines from the terrestrial atmosphere’s airglow. In the near infrared, this background is composed mainly of emission from Meinel bands of hydroxyl (OH), which is produced in highly excited vibrational states by reduction of ozone near 90 km. This emission contains a wealth of information on the chemical and dynamical state of the Earth's atmosphere. However, observation strategies and data reduction processes are usually optimised to minimise the influence of these features on the astronomical spectrum. Here we discuss a measurement technique to optimise the extraction of the OH airglow signal itself from routine J-, H- and K-band, long-slit, astronomical spectroscopic observations. As an example, we use data recorded from a point source observation by the Nordic Optical Telescope’s intermediate-resolution spectrometer, which has a spatial resolution of approximately 100 m at the airglow layer. Emission spectra from the OH vibrational manifold from v' = 9 down to v' = 3, with signal-to-noise ratios up to 280, have been extracted from 10.8 s integrations. Rotational temperatures representative of the background atmospheric temperature near 90 km, the mesosphere and lower thermosphere region, can be fitted to the OH rotational lines with an accuracy of around 0.5 K. Using this measurement and analysis technique, we derive a rotational temperature distribution with v’ that agrees with atmospheric model conditions and the preponderance of previous work. We discuss the derived rotational temperatures from the different vibrational bands and highlight the potential for both the archived and future observations, which are at unprecedented spatial and temporal resolutions, to contribute toward the resolution of long-standing problems in atmospheric physics.

Citation: Franzen, C., Hibbins, R. E., Espy, P. J., and Djupvik, A. A.: Optimising hydroxyl airglow retrievals from long-slit astronomical spectroscopic observations, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2017-36, in review, 2017.
Christoph Franzen et al.
Christoph Franzen et al.
Christoph Franzen et al.

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Short summary
We discuss a technique to extract the hydroxyl (OH) airglow signal from routine astronomical spectroscopic observations from the Nordic Optical Telescope. Emission spectra from the vibrational manifold from v' = 9 down to v' = 3. The fitted rotational temperature distribution with v’ agrees with model conditions and the preponderance of previous work. We highlight the potential for archived and future observations with unprecedented spatial and temporal resolutions.
We discuss a technique to extract the hydroxyl (OH) airglow signal from routine astronomical...
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