and cannot readily be compared with mole fraction measurements at other places and times.
Research efforts are under way, primarily within the National Aeronautics and Space Administration (NASA), to demonstrate airborne DIAL measurements of CO2 as a step toward eventual space-based measurements. Browell et al. (2008) and Abshire et al. (2009) have both reported on airborne measurements of CO2 optical thickness at 1.57 μm. To avoid the problem of having to convert a column absorption measurement of a trace gas to a mole fraction, one can deploy a second lidar that simultaneously measures the column amount of oxygen (O2), which is a very accurate indicator of the total amount of dry air in the column. The challenges in developing high-precision DIAL systems for column content measurements are associated primarily with instrumentation issues such as maintaining and monitoring long-term laser stability. However, given the resources currently being directed toward the problem in both the United States and Europe, there is a high likelihood that such challenges will be met.
Hardesty et al. (2008) described co-deployment of a Doppler wind lidar and water vapor DIAL instrument on a research aircraft to measure horizontal transport of moisture over the southern Great Plains. In this way, airborne lidar techniques can be used as improvements over application of models for observing wind characteristics within the plume. The accuracy of the lidar wind measurement is about 10 cm s–1. These combined techniques could thus be applied to obtain measurements of greenhouse gas emission without the need for application of models.
Abshire, J.B., H. Riris, G.R. Allan, C. Weaver, J. Mao, and W. Hasselbrack, 2009, Airborne lidar measurements of atmospheric CO2 column absorption and line shapes from 3-11 km altitudes, Geophysical Research Abstracts, 11, EGU2009-11507.
Browell, E.V., M.F. Dobbs, J. Dobler, S. Kooi, Y. Choi, F.W. Harrison, B. Moore III, and T.S. Zaccheo, 2008, Airborne demonstration of 1.57-micron laser absorption spectrometer for atmospheric CO2 measurements, in Proceedings of the 24th International Laser Radar Conference, Boulder, Colo., January 12-15, pp. 697.
Ehret, G., C. Kiemle, M. Wirth, A. Amediek, A. Fix, and S. Houweling, 2008, Space-borne remote sensing of CO2, CH4, and N2O by integrated path differential absorption lidar: A sensitivity analysis, Applied Physics B, 90, 593-608.
Hardesty, R.M., W.A. Brewer, C.J. Senff, B.J. McCarty, G. Ehret, A. Fix, C. Kiemle, and E.I. Tollerud, 2008, Structure of meridional moisture transport over the U.S. southern Great Plains observed by co-deployed airborne wind and water vapor lidars, in Symposium on Recent Developments in Atmospheric Applications of Radar and Lidar, American Meteorological Society, January 21-24.
Senff, C.J., R.J. Alvarez II, R.M. Hardesty, R.M. Banta, L.S. Darby, A.M. Weickmann, S.P. Sandberg, D.C. Law, R.D. Marchbanks, W.A. Brewer, D.A. Merritt, and J.L. Machol, 2008, Airborne lidar measurements of ozone flux and production downwind of Houston and Dallas, in Proceedings of the 24th International Laser Radar Conference, Boulder, Colo., June 23-27, pp. 659-662.