Greenhouse gas measurements over a 144 km open path in the Canary Islands
- 1Department of Chemistry, University of York, York, YO10 5DD, UK
- 2Department of Chemistry & Biochemistry, Old Dominion University, Norfolk, VA 23529, USA
- 3Wegener Center for Climate and Global Change and IGAM/Inst. of Physics, University of Graz, Brandhofgasse 5, 8010 Graz, Austria
- 4School of Chemical Engineering and Analytical Science, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
- 5Biogeochemical Systems Department, MPI for Biogeochemistry, Hans-Knöll-Str. 10, 07745 Jena, Germany
- 6Earth Observation Future Mission (EOP-SFP), ESA/ESTEC, P.O. Box 299, 2200 AG, Noordwijk, The Netherlands
Abstract. A new technique for the satellite remote sensing of greenhouse gases in the atmosphere via the absorption of short-wave infrared laser signals transmitted between counter-rotating satellites in low Earth orbit has recently been proposed; this would enable the acquisition of a long-term, stable, global set of altitude-resolved concentration measurements. We present the first ground-based experimental demonstration of this new infrared-laser occultation method, in which the atmospheric absorption of CO2 near 2.1 μm was measured over a ~144 km path length between two peaks in the Canary Islands (at an altitude of ~2.4 km), using relatively low power diode lasers (~4 to 10 mW). The retrieved CO2 volume mixing ratio of 400 ppm (±15 ppm) is consistent within experimental uncertainty with simultaneously recorded in situ validation measurements. We conclude that the new method has a sound basis for monitoring CO2 in the free atmosphere; other greenhouse gases such as methane, nitrous oxide and water vapour can be monitored in the same way.