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

We introduce a strategy for measuring the column‐averaged CO 2 dry air volume mixing ratio from space. It employs high resolution spectra of reflected sunlight taken simultaneously in near‐infrared (NIR) CO 2 (1.58‐μm and 2.06‐μm) and O 2 (0.76‐μm) bands. Simulation experiments, show that precisions of ∼0.3–2.5 ppmv for can be achieved from individual clear sky soundings for a range of atmospheric/surface conditions when the scattering optical depth τ s 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 measurements. We briefly discuss potential sources of systematic errors, and show that some of them may result in geographically varying biases in the measured . 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 measurements.