Use of Fabry-Perot annular summing spectroscopy to acquire geocoronal hydrogen Balmer-alpha line profile data

Susan M. Nossal; Fred L. Roesler; Monica M. Coakley; Ronald J. Reynolds

doi:10.1117/12.256139

31 October 1996 Use of Fabry-Perot annular summing spectroscopy to acquire geocoronal hydrogen Balmer-α line profile data

Susan M. Nossal, Fred L. Roesler, Monica M. Coakley, Ronald J. Reynolds

Author Affiliations +

Proceedings Volume 2830, Optical Spectroscopic Techniques and Instrumentation for Atmospheric and Space Research II; (1996) https://doi.org/10.1117/12.256139
Event: SPIE's 1996 International Symposium on Optical Science, Engineering, and Instrumentation, 1996, Denver, CO, United States

Abstract

A Fabry-Perot annular summing spectroscopy technique has been sued at the University of Wisconsin's Pine Bluff Observatory to acquire geocoronal Balmer-(alpha) line profile data with significantly improved precision and height resolution. The double-etalon Fabry-Perot interference pattern is imaged onto a photometrics PM512 CCD chip, thus enabling light to be gathered in multiple spectral bins simultaneously. In comparison with scanning systems we used earlier, the high quantum efficiency of the CCD and the multi-channel detection associated with the Fabry-Perot annular summing technique have enabled us to save a factor of about 10 in the integration time required for studies of the line profile. As a result, we are now able to both more precisely observe the line shape of the very faint Balmer- (alpha) emission and obtain data using shorter integration times. Our data illustrate the scientific potential for using this technique for the study of very faint extended emission line sources. The increase in the signal-to-noise of our data has enabled us to examine Balmer-(alpha) profile asymmetries which we have found to be compatible with predictions that on the order of 10 percent of the geocoronal Balmer-(alpha) excitation arises from cascades due to higher-member solar Lyman series excitation. This fine structure was overlooked in previous Balmer-(alpha) studies aimed at determining non-Maxwellian dynamical properties of exospheric hydrogen; we find that cascade excitation largely masks the expected very small dynamical perturbations to the line profile at low shadow heights, and must be more thoroughly studied before drawing conclusions about exospheric dynamics. Accounting for cascade laos leads to more realistic determinations of exospheric hydrogen temperatures near the exobase.

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Susan M. Nossal, Fred L. Roesler, Monica M. Coakley, and Ronald J. Reynolds "Use of Fabry-Perot annular summing spectroscopy to acquire geocoronal hydrogen Balmer-α line profile data", Proc. SPIE 2830, Optical Spectroscopic Techniques and Instrumentation for Atmospheric and Space Research II, (31 October 1996); https://doi.org/10.1117/12.256139

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KEYWORDS

Fabry–Perot interferometers

Hydrogen

Charge-coupled devices

Spectroscopy

Image processing

Calibration

Thorium

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