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Project Progress

Design, construction and testing of a Cavity-Ring Down Spectrometer (CRDS) for determination of the concentration and isotopic composition of methane

During the past 12 months, we have measured in detail the absorption spectra for ¹²CH₄, ¹³CH₄, CH₃D and CO₂. We’ve designed a peak fitting routine to integrate the ¹²CH₄ and ¹³CH₄ peaks in the wavelength region of our CRDS. We’ve tested this software on a CH₄ gas standard of known isotopic composition and were able to reproduce the δ¹³C of the 2 ppm standard with an accuracy of ±5o/oo. Although this accuracy is twice that of the multipass instrument on MSL, it is 10 times less than the accuracy of the individual ring-down events. The inaccuracy is due to imprecision in the wavelength of the laser, which will be rectified by upgrading the instrument with a wavelength monitor. A manuscript describing the methodology, instrument and first measurement is being prepared for Optics Express. A proposal to take the current instrument to Technology Readiness Level 6 was submitted to the Mars Instrument Development Program in June ’07 with collaboration from Paul Mahaffy of Goddard Space Flight Center and has recently been awarded.

We also tested a Los Gatos CRDS at the McGill University arctic research station (MARS) on Axel Heiberg Island for two weeks in April ’08 where we measured CH₄ fluxes from the permafrost soil and hot springs. These results indicate that the CH₄ fluxes are sufficiently high that our current CRDS should be able to measure their isotopic composition and our current plan is to return to MARS next spring with the upgraded instrument. We are presently preparing the instrument for CH₄ activity measurements on permafrost methanogens while they are being exposed to simulated Martian conditions at the Techshot facility in Greenfield, Indiana.