The Faraday Filter-Based Spectrometer for Observing Sodium Nightglow and Studying Atomic and Molecular Oxygen Associated with the Sodium Chemistry in the Mesopause Region


Harrell, S. D., She, C. Y., Yuan, T., Krueger, D. A., Plane, J. M. C., & Slanger, T. (2010). The Faraday filter-based spectrometer for observing sodium nightglow and studying atomic and molecular oxygen associated with the sodium chemistry in the mesopause region. Journal of atmospheric and solar-terrestrial physics, 72(17), 1260-1269.


This paper describes the operational principles, design and field testing of a new, compact, Faraday filter-based spectrometer to measure the D2 (589.158 nm) to D1 (589.756 nm) intensity ratio of the sodium nightglow. This work was motivated by the observations of Slanger et al. (2005) who reported an annual variation in D2/D1 with values ranging from 1.2 to 1.8. Their proposed explanation, a modified Chapman mechanism, requires that the intensity ratio is related to the concentration ratio of atomic oxygen [O] to molecular oxygen [O2]. Our method of measuring D2/D1 utilizes narrowband Na vapor Faraday filters, which can yield observations on the fractional contributions of the two chemical pathways of the modified Chapman mechanism. Since delineation of the two chemical pathways requires a spectral resolution of 0.0002 nm, this is not possible with any other existing instrument.

Research highlights

▶ The design of the Faraday-filter based spectrometer for studying sodium nightglow is presented.

▶ Simultaneous spectrometer and lidar-determined Na densities are presented.

▶ Initial measurements support the theory of a modified Chapman mechanism for nightglow production.

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