Spaceborne measurements of atmospheric CO2 by high-resolution NIR spectrometry of reflected sunlight: An introductory study

[1] We introduce a strategy for measuring the column-averaged CO2 dry air volume mixing ratio XCO2 from space. It employs high resolution spectra of reflected sunlight taken simultaneously in near-infrared (NIR) CO2 (1.58-mm and 2.06-mm) and O2 (0.76-mm) bands. Simulation experiments, show that precisions of 0.3–2.5 ppmv for XCO2 can be achieved from individual clear sky soundings for a range of atmospheric/surface conditions when the scattering optical depth ts is less than 0.3. 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 XCO2 measurements. We briefly discuss potential sources of systematic errors, and show that some of them may result in geographically varying biases in the measured XCO2 . 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 XCO2 measurements.