Abstract
Atmospheric methane concentration levels were detected using a custom built laser dispersion spectrometer in a long open-path beam configuration. The instrument is driven by a chirped distributed feedback mid-infrared quantum cascade laser centered at ~1283.46 cm-1 and covers intense rotational-vibrational transitions from the fundamental ν4 band of methane. A full forward model simulating molecular absorption and dispersion profiles, as well as instrumental noise, is demonstrated. The instrument's analytical model is validated and used for quantitative instrumental optimization. The temporal evolution of atmospheric methane mixing ratios is retrieved using a fitting algorithm based on the model. Full error propagation analysis on precision gives a normalized sensitivity of ~3 ppm.m.Hz-0.5 for atmospheric methane.
Highlights
Chirped Laser Dispersion Spectroscopy (CLaDS) has recently been established as a promising alternative method for high spectral resolution molecular gas sensing
With CLaDS, unlike sensing that relies on molecular absorption, dispersion profiles in the vicinity of a resonance are used to infer molecular density
CLaDS signals stem from the phase alteration of electromagnetic fields, making the method more immune to laser intensity variations when compared with absorption spectrometers
Summary
Chirped Laser Dispersion Spectroscopy (CLaDS) has recently been established as a promising alternative method for high spectral resolution molecular gas sensing. Whilst in situ monitoring provides valuable insights on methane concentrations and emissions [8, 9], most applications would benefit from sensors able to monitor over large distances, and/or large areas In this respect, open-path sensing systems offer the advantage of measuring the integrated molecular mixing ratios over long lines of sight if needed. 2. Experimental implementation The CLaDS spectrometer was set up in the laboratory with two purposes: 1) to carry out measurements on low pressure gas mixtures contained in a short path gas cell. Experimental implementation The CLaDS spectrometer was set up in the laboratory with two purposes: 1) to carry out measurements on low pressure gas mixtures contained in a short path gas cell This simple and well-controlled configuration was believed to be ideal for the validation of the instrument’s theoretical model.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
