Atmospheric vertical profiles of O₃, N₂O, CH₄, CCl₂F₂, and H₂O retrieved from external-cavity quantum-cascade laser heterodyne radiometer measurements

Abstract

Atmospheric vertical profiles of ozone, nitrous oxide, methane, dichlorodifluoromethane, and water are retrieved from data collected with a widely tunable external-cavity quantum-cascade laser heterodyne radiometer (EC-QC-LHR) covering a spectral range between 1120 and 1238 cm(-1). The instrument was operated in solar occultation mode during a two-month measurement campaign at Rutherford Appleton Laboratory in Oxfordshire, UK, in winter 2010/2011, and ultrahigh-resolution (60 MHz or 0.002 cm(-1)) transmission spectra were recorded for multiple narrow spectral windows (~1 cm(-1) width) specific to each molecule. The ultrahigh spectral resolution of the EC-QC-LHR allows retrieving altitudinal profiles from transmission spectra that contain only few (1-3) significant absorption lines of a target molecule. Profiles are validated by comparing with European Centre for Medium-Range Weather Forecasts operational atmospheric profiles (ozone and water), with other data in the literature (nitrous oxide, methane, dichlorodifluoromethane), and with retrievals from a lower resolution (600 MHz or 0.02 cm(-1)) Fourier transform spectroscopy data that were also recorded during the measurement campaign.

High resolution heterodyne spectroscopy of the atmospheric methane NIR absorption

“…High resolution spectroscopy (λ/δλ~10 7 -10 8 ) allows for Doppler measurements of wind fields in the atmospheres of the Earth and other planets, implemented in the infrared spectral range in only a few instruments to date and resulted in seminal results on the dynamics of planetary atmospheres [3,4] and remote sensing of the Earth atmosphere [5,6]. High resolution laser spectroscopy has been proven to be a powerful method of in situ trace gas detection from various platforms, including aircraft and planetary rovers [7,8].…”

Evaluation of laser heterodyne radiometry for numerical weather prediction applications

“…The approach taken in this study is therefore consistent with OE information content studies for atmospheric chemistry (e.g. Tsai et al ., , for the LHR).…”

“…QCL‐based LHR technology has advanced rapidly in the last decade, initially for trace‐gas detection in Earth observation and planetary applications (Weidmann et al, ). Atmospheric science applications have included ozone profiling (Weidmann et al, ), multi‐constituent profiling (Weidmann et al, ; Tsai et al, ), and most recently atmospheric CO 2 measurements (Hoffmann et al, ). Developments are currently underway to miniaturize the LHRs using optical integration technologies (Weidmann et al, ) and make them suitable for small satellite applications (Weidmann et al, ).…”

Thermal infrared laser heterodyne spectroradiometry for solar occultation atmospheric CO<sub>2</sub> measurements

“…The wavenumber axis associated with a spectral scan is determined by an identical frequency calibration procedure as described by Tsai et al (2012). A high-order polynomial is fitted to the resulting data from the etalon optical arm, giving the relative laser frequency calibration by steps of half a free spectral range (between two consecutive extrema in the etalon trace).…”

“…With the objective to provide complementary instrumentation addressing these shortfalls, an alternative approach for generating high spectral resolution spectra of atmospheric transmittance is considered here. This paper reports on the technical development of a laband ground-based thermal infrared (TIR) laser heterodyne spectroradiometer (LHR) aiming at accurately characterizing total column and vertical profiles of CO 2 in solar occultation (solar absorption-atmospheric transmission) mode, building on past instruments successfully used for the passive remote sounding of a variety of trace gases in the atmosphere (Tsai et al, 2012;Weidmann et al, 2007aWeidmann et al, , b, 2011a. The prototype instrument has been installed at the Rutherford Appleton Laboratory near Chilton (Didcot), UK, and operated in fair weather conditions since May 2015.…”