An OpenPath Tunable Diode Laser Sensor for Simultaneous

An Open-Path Tunable Diode Laser Sensor for Simultaneous Measurement of Methane and Carbon Dioxide D. Michelle Bailey, Erin M. Adkins, Emily L. Wilson†, J. Houston Miller The George Washington University, Department of Chemistry, Washington, DC 20052 † NASA Goddard Space Flight Center, Laser Remote Sensing Lab, Code 694, Greenbelt, MD 20771 Abstract Thawing arctic permafrost is a large carbon source which releases key greenhouse gasses (GHG) into the atmosphere. In collaboration between NASA Goddard Space Flight Center, the University of Alaska-Fairbanks, and the George Washington University a study of the feedbacks to climate change caused by thawing permafrost has been initiated. An array of ground experiments at three unique permafrost sites will record permafrost depth, structure, meteorological data, and emissions of key greenhouse gases during a springtime permafrost thaw. Ground data will be linked to climate models and landscape structure from satellite imagery to gauge the magnitude of the feedbacks. Tunable Diode Lasers Show wavelength calibration curve and explain about current injection Noise Reduction Techniques Wavelength Modulation Spectroscopy -Theory and application GWU will perform high-sensitivity ground-level measurements of carbon dioxide and methane. Currently, we are developing a low-power and portable open-path instrument which builds on our laboratory’s previous experience with deployment of multi-laser, multi species sensors. Spectral simulations suggest that at ambient levels of CO 2 and CH 4 (390 and 2 ppm. V, respectively) we will observe extinction coefficients of ≈ 10 4 m-1 or ≈ 1% absorption over a 200 m path. Prior work in our laboratory suggests that a SNR in excess of 100 will be achievable at these absorption levels using wavelength-modulation techniques. Here we report on the progress of the sensor’s construction and exploration of wavelength modulation spectroscopy (WMS) and other noise reducing techniques. Permafrost as a Carbon Source Balanced Detection -Theory and application Direct Absorption Spectroscopy What is permafrost? Permafrost is ground that is frozen all year round. Field Sites -Discuss the replacement of certain electrical components with raspberry pi, etc. Placeholder On-Going Work Shown is a boreal peatland system with forests underlain by cold soils and permafrost, collapse scar thermokarst bogs resulting from permafrost thaw, and rich fens underlain by various unfrozen sediments and gravels and no near-surface permafrost. Blue arrows indicate groundwater movement and red arrows indicate atmospheric heating impacts, emissions of CH 4 and CO 2 are shown with green arrows. Credit R. Daanen Field Experiments Open Path Design Placeholder A: High spatial resolution remote-sensed data, B: NASA suborbital aircraft, C: covariance flux towers, D: ground penetrating radar, E: open path tunable diode laser absorption spectroscopy, F: Atmospheric column measurements, G: Earth System Modeling Acknowledgements Placeholder