Articles | Volume 9, issue 5
Research article
25 May 2016
Research article |  | 25 May 2016

Addition of a channel for XCO observations to a portable FTIR spectrometer for greenhouse gas measurements

Frank Hase, Matthias Frey, Matthäus Kiel, Thomas Blumenstock, Roland Harig, Axel Keens, and Johannes Orphal

Abstract. The portable FTIR (Fourier transform infrared) spectrometer EM27/SUN, dedicated to the precise and accurate observation of column-averaged abundances of methane and carbon dioxide, has been equipped with a second detector channel, which allows the detection of additional species, especially carbon monoxide. This allows an improved characterisation of observed carbon dioxide enhancements and makes the extended spectrometer especially suitable as a validation tool of ESA's Sentinel 5 Precursor mission, as it now covers the same spectral region as used by the infrared channel of the TROPOMI (TROPOspheric Monitoring Instrument) sensor. The extension presented here does not rely on a dichroic, but instead a fraction of the solar beam is decoupled near the aperture stop of the spectrometer using a small plane mirror. This approach allows maintaining the camera-controlled solar tracker set-up, which is referenced to the field stop in front of the primary detector. Moreover, the upgrade of existing instruments can be performed without alterating the optical set-up of the primary channel and resulting changes of the instrumental characteristics of the original instrument.

Short summary
We describe an extension of a portable FTIR (Fourier transform infrafed) spectrometer dedicated to the measurement of column-averaged abundances of greenhouse gases in the atmosphere. The measurement principle is based on a spectrally resolved solar absorption observation (trace gas amounts are deduced from the strength of near-infrared absorption bands). The dual-channel set-up presented here allows co-observing CO while maintaining the highly favourable characteristics of the original device.