Infrared Laser Direct Absorption Spectroscopy for Carbon Isotope Measurements from UAVs

There is a need for extremely lightweight low power instrumentation for real-time measurement of isotopic variants of carbon dioxide (CO2) in ambient air, suitable for use on un-manned aerial vehicles, to allow better quantification of sources and sinks of this major greenhouse gas in remote areas such as the Arctic. The proposing company is developing such instrumentation using infrared laser spectroscopy, a technique which has been shown to provide the extremely high precision needed to measure the small changes in the proportions of CO2 isotopic variants (isotopologues) that are induced by biological and physical processes in the environment. To be useful great precision is needed in the measurement of the ratios of isotopologues of CO2, typically a fraction of a part in 1000 (written as per mil, & quot; & quot;, i.e. 1/1000). The measurement precision goal of this project is 0.2 (in 1s) for the ratios of two minor (i.e. rare) isotopic variants of CO2 to the major isotopic variant: [13CO2]/[ 12CO2] and [ 12C18O16O]/[12CO2]. The proposed general approach is laser absorption spectroscopy in the mid-infrared, with a & quot;quantum cascade & quot; laser which can access the specific absorption lines of the 3 isotopologues at the same time. The proposing small company has previously demonstrated, and indeed currently sells field-ready laser-based instruments with better than the precision goal stated above, i.e. with a precision for CO2 isotopic variants of approximately 0.05 with 1 second averaging, which is the best precision of any commercial laser instrument for CO2 isotopes. The challenge that the proposing company is addressing is how to greatly reduce the current instrument & apos;s mass and power consumption while maintaining excellent precision. Very good progress was made during Phase 1 of the project, in that a new optical module was designed that is approximately one half the size of the current instrument & apos;s. Furthermore, that optical module was integrated with a laser, detector and electronics so that it functioned as a complete instrument with a demonstrated precision of 0.09 with 1 second averaging for two isotopic variants of CO2 in ambient air, thus exceeding the target precision goals. In addition, significant progress was made in reducing instrument mass and power requirements, with an identified path toward eliminating a water chiller/circulator used for thermal management, and by using a much smaller air sampling pump. Key elements of an extremely lightweight calibration system also were demonstrated during Phase 1. During Phase 2 the various elements of the instrument will be integrated into a complete stand-alone instrument and the performance will be tested. The general approach of Phase 1 will be continued, with staged reductions in mass and power while precision is tested and maintained, so that a useful instrument result is nearly guaranteed. The methods to reduce size and power will be of benefit to the company & apos;s other trace gas instrumentation, and thus will be of benefit to the atmospheric research community.