Airborne Mid-Infrared Cavity enhanced Absorption spectrometer (AMICA)

Abstract. We describe the Airborne Mid-Infrared Cavity enhanced Absorption spectrometer (AMICA) designed to measure trace gases in situ on research aircraft using Off-Axis Integrated Output Spectroscopy (OA-ICOS). AMICA contains two largely independent and exchangeable OA-ICOS arrangements, allowing for simultaneous measurement of multiple substances different infrared wavelength windows tailored scientific questions related a particular flight mission. Three setups have been implemented with aim OCS, CO2, CO, H2O at 2050 cm−1; O3, NH3, CO2 1034 HCN, C2H2, N2O 3331 cm−1. The cm−1 setup has characterized laboratory successfully used atmospheric measurements during campaigns M55 Geophysica one German HALO (High Altitude Long Range Research Aircraft). For OCS data use produced 5 % accuracy (15 CO below 60 ppb, due additional uncertainties introduced by dilution standard) typical mixing ratios laboratory-measured 1σ precision 30 ppt 3 ppb 0.5 Hz time resolution. high absorption leads saturation effects that limit sensitivity complicate spectral analysis, resulting too large use. H2O, is weak be measured 100 ppm. By further reducing electrical noise improving treatment baseline retrieval, we hope improve resolve issues inhibiting useful measurements, lower detection H2O. 1035 arrangements only partially are still development. Although both flown recorded spectra field campaigns, no yet unresolved deviations retrieved known standards (O3) or insufficient (NH3, N2O). ∼100 kg instrument in-flight power consumption about 500 VA dimensioned fit into 19 in. rack typically deployment inside cabin. Its rugged design pressurized temperature-stabilized compartment containing sensitive optical electronic hardware also allow payload bays outside cabin even altitudes 20 km. A sample flow system parallel proportional solenoid valves size orifices allows precise regulation cavity pressure over wide range inlet port pressures encountered between ground maximum altitudes. Sample order 1 SLM (standard litre per minute) maintained an exhaust-side pump limits resolution 2.5 s (corresponding average flush time), equivalent m distance speed 200 s−1.