A unique, multi-frequency, single-beam, laser absorption spectrometer (LAS) that operates at 1.57 μm has been developed for a future space-based mission to determine the global distribution of sources and sinks of atmospheric carbon dioxide (CO₂). A prototype of the space-based LAS system was developed by ITT, and it has been successfully flight tested in five airborne campaigns conducted in different geographic regions over the last three years.

Flight tests were conducted over Oklahoma, Michigan, New Hampshire, and Virginia under a wide range of atmospheric conditions. Remote LAS measurements were compared to high-quality in situ measurements obtained from instrumentation on the same aircraft on spirals under the ground track of the LAS.

LAS flights were conducted over a wide range of land and water reflectances and in the presence of scattered clouds. An extensive data set of CO₂ measurements has been obtained for evaluating the LAS performance. LAS CO₂ measurements with a signal-to-noise in excess of 250 were obtained for a 1-s average over land and for a 10-s average over water. Absolute comparisons of CO₂ remote and in situ measurements showed agreement over a range of altitudes to better than 2 percent. Details of flight test campaigns and measured versus modeled results are presented.

LAS oxygen (O₂) measurements, which are needed to convert LAS CO₂ density measurements to CO₂ mixing ratios (XCO₂), have been made in the 1.26-μm region in horizontal ground-based experiments and in initial flight tests. Recent results from these experiments are also discussed in this paper.