The SPIRIT airborne infrared absorption spectrometer for the measurements of trace gases was mounted onboard the Falcon-20. A complete description of the instrument principle can be found in Catoire et al. (2017). In brief, it uses continuous-wave distributed-feedback room-temperature Quantum Cascade Lasers (QCLs), allowing rapid scanning (each 1.6 s) of strong fundamental molecular ro-vibrational lines lying in the mid-infrared, with ultra-high spectral resolution (10‑3 cm‑1). The QCL infrared beams are absorbed by constituents of the ambient air sampled in a multipass cell (with 83.88 m of pathlength) at reduced pressure (33 hPa), and detected using a cooled HgCdTe photodetector. In the present campaign, measurements were carried out at the wavenumber 2179.772 cm‑1 for 12C16O. Total molecule abundance is deduced from a home-made software using the HITRAN 2012 database (Rothman et al., 2013) with a precision of 0.3 ppbv for CO at 1.6 s time resolution. Dry volume mixing ratios (vmr) are deduced using the measured pressure and temperature of the optical cell, and using the water vapour mixing ratios measured by a laser absorption spectroscopy hygrometer (WVSS-II from SpectraSensors). Total uncertainties for CO were estimated to be 4.7 ppb using comparisons performed during previous flights with high altitude instrumented surface stations (Pic du Midi de Bigorre and Puy de Dôme, France) belonging to the World Meteorological Organization/Global Atmosphere Watch (WMO/GAW) network and with a NOAA standard cylinder on-board the aircraft (Catoire et al. 2017).
HISTORY / USE
Three instruments were built between mid-2007 and early 2011.
1: SPIRIT SOL: in operation since 2009; modified in 2012 for isotopic measurements
2 lasers installed
N2O and CH4 measurement: ISTO, INRA, ICARE collaborations
Measurements of the isotopic ratio of carbon to CO2
2: SPIRIT INRA (CNRS-INRA contract): in operation since 2011
2 lasers installed
Measurement of N2O, H2O and CH4
3: SPIRIT AVION (European SHIVA project: Instrument on aircraft (FALCON) 11-2011
3 lasers installed
Measurement of N2O, CH4, H2O,CO, NO2, NH3
Flying on DLR and SAFIRE FALCON aircraft and on ATR42
Last campaign on the DLR Falcon in TOGO in July 2016 (European project DACCIWA)