Infrared laser direct absorption spectroscopy for carbon isotope measurements from UAVs

Stable isotopologues of carbon dioxide and methane can be powerful tracers for identifying the sources of greenhouse gases. We propose to develop extremely lightweight infrared laser spectrometers for measurements of isotopologues of CO2 and CH4 to be usable for UAV airborne surveys with high precision and speed for studies of Arctic climate change and the terrestrial carbon cycle. The instrumentation will take advantage of the latest advances in continuous wave mid-infrared lasers, QCLs for CO2 and diode lasers for CH4, that operate close to ambient temperatures to minimize laser cooling requirements. The instrument design modifications to existing Aerodyne technology will allow absolute mixing ratios and isotopologue calibrations without reference gas tanks on the UAV aircraft. Advances in our existing multipass absorption cell technology will provide sufficient path length with lesser weight and greater stability to provide high precision measurements of isotopologues in a compact and lightweight instrument. Advances in our Tunable Infrared Laser Direct Absorption Spectroscopy (TILDAS) electronics and software will be incorporated to achieve the goals of low power consumption (50 Watts) and instrument weight (5 kg). Our performance goals are to achieve the same istopologue precisions of 0.05 per mil for 13CO2 and C18OO, 1 per mil for 13CH4, and 6 per mil for CH3D, that we are currently obtaining with our larger spectroscopic instruments used in laboratory and field studies. In Phase I we will focus on instrument design and demonstrate spectroscopic accuracy and precision. In Phase II we will design and construct a prototype instrument to be demonstrated in both laboratory and aircraft applications. Commercial applications and other benefits: The proposed work will lead to a new class of lightweight and low power precision instrumentation that will be useful for a wide variety of trace gases, in both land-based and airborne measurements. These instruments will compliment and lead to improvements in our existing commercially available trace gas instruments.