Vertically constrained CO_2 retrievals from TCCON measurements

Partial column-averaged carbon dioxide (CO_2) mixing ratio in three tropospheric layers has been retrieved from Total Carbon Column Observing Network (TCCON) spectra in the 1.6 μm CO_2 absorption band. Information analysis suggests that a measurement with ∼60 absorption lines provides three or more pieces of independent information, depending on the signal-to-noise ratio and solar zenith angle. This has been confirmed by retrievals based on synthetic data. Realistic retrievals for both total and partial column-averaged CO_2 over Park Falls, Wisconsin on July 12, 15, and August 14, 2004, agree with aircraft measurements. Furthermore, the retrieved total column averages are always underestimated by less than 1%. The results above provide a basis for CO_2 profile retrievals using ground-based observations in the near-infrared region.