Preprints
https://doi.org/10.5194/amt-2021-133
https://doi.org/10.5194/amt-2021-133

  10 Aug 2021

10 Aug 2021

Review status: a revised version of this preprint is currently under review for the journal AMT.

Mobile and high spectral resolution Fabry Pérot interferometer spectrographs for atmospheric remote sensing

Jonas Kuhn1,2, Nicole Bobrowski1,2, Thomas Wagner2, and Ulrich Platt1,2 Jonas Kuhn et al.
  • 1Institute of Environmental Physics, University of Heidelberg, Heidelberg, Germany
  • 2Max Planck Insitute for Chemistry, Mainz, Germany

Abstract. Grating spectrographs (GS) are presently widely in use for atmospheric trace gas remote sensing in the ultraviolet (UV) and visible spectral range (e.g. differential optical absorption spectroscopy, DOAS). For typical DOAS applications, GSs have a spectral resolution of about half a nm corresponding to a resolving power R (ratio of operating wavelength to spectral resolution) in the range of 1000. This is sufficient to quantify the vibro-electronic spectral structure of the absorption of many trace gases with good accuracy and further allows for mobile (i.e. compact and stable) instrumentation.

However, a much higher resolving power (R ≈ 105, i.e. a spectral resolution of about the width of an individual rotational absorption line) would facilitate the measurement of further trace gases (e.g. OH radicals), significantly reduce cross interferences due to other absorption and scattering processes, and provide enhanced sensitivity. Despite of these major advantages, only very few atmospheric studies with high resolution GSs are reported, mostly because increasing the resolving power of a GS leads to largely reduced light throughput and mobility. However, for many environmental studies, light throughput and mobility of measurement equipment are central limiting factors, for instance when absorption spectroscopy is applied to quantify reactive trace gases in remote areas (e.g. volcanoes) or from air borne or space borne platforms.

Since more than a century, Fabry Pérot interferometers (FPIs) have been successfully used for high resolution spectroscopy in many scientific fields where they are known for their superior light throughput. However, except for a few studies, FPIs received hardly any attention in atmospheric trace gas remote sensing, despite their advantages. We propose different high resolution FPI spectrograph implementations and compare their light throughput and mobility to GSs with the same resolving power. We find that nowadays mobile high resolution FPI spectrographs can have a more than two orders of magnitude higher light throughput than their immobile high resolution GS counterparts. Compared to moderate resolution GSs (as routinely used for DOAS), a FPI spectrograph reaches a 250 times higher spectral resolution while the signal to noise ratio (SNR) is reduced by only a factor of 10. With a first compact prototype of a high resolution FPI spectrograph (R ≈ 148000, < 8 litres, < 5 kg) we demonstrate that these expectations are realistic.

Using mobile and high resolution FPI spectrographs could have a large impact on atmospheric near UV to near IR remote sensing. Applications include the enhancement of sensitivity and selectivity of absorption measurements of many atmospheric trace gases and their isotopes, the direct quantification of OH radicals in the troposphere, high resolution O2 measurements for radiative transfer and aerosol studies and solar induced chlorophyll fluorescence quantification using Fraunhofer lines.

Jonas Kuhn et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2021-133', Anonymous Referee #3, 01 Sep 2021
    • AC1: 'Reply on RC1', Jonas Kuhn, 27 Sep 2021
  • RC2: 'Comment on amt-2021-133', Anonymous Referee #2, 07 Sep 2021
    • AC2: 'Reply on RC2', Jonas Kuhn, 27 Sep 2021

Jonas Kuhn et al.

Jonas Kuhn et al.

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Short summary
We describe an alternative spectrograph implementation (using a Fabry Pérot interferometer) for atmospheric trace gas remote sensing. Compared to widely used grating spectrographs we find substantial light throughput and mobility advantages for high spectral resolution. Besides lowering detection limits and increasing the spatial and temporal resolution of many atmospheric trace gas measurements, this might enable the simple detection of furhter important gases like tropospheric OH radicals.