Spaceborne measurements of atmospheric CO2 by high-resolution NIR spectrometry of reflected sunlight:: An introductory study -: art. no. 1716

[1] We introduce a strategy for measuring the column- averaged CO2 dry air volume mixing ratio X-CO2 from space. It employs high resolution spectra of reflected sunlight taken simultaneously in near- infrared (NIR) CO2 (1.58-mum and 2.06-mum) and O-2 (0.76-mum) bands. Simulation experiments, show that precisions of similar to0.3-2.5 ppmv for X-CO2 can be achieved from individual clear sky soundings for a range of atmospheric/ surface conditions when the scattering optical depth tau(s) is less than similar to0.3. When averaged over many clear sky soundings, random errors become negligible. This high precision facilitates the identification and correction of systematic errors, which are recognized as the most serious impediment for the satellite X-CO2 measurements. We briefly discuss potential sources of systematic errors, and show that some of them may result in geographically varying biases in the measured X-CO2. This highlights the importance of careful calibration and validation measurements, designed to identify and eliminate sources of these biases. We conclude that the 3- band, spectrometric approach using NIR reflected sunlight has the potential for highly accurate X-CO2 measurements.