Carbon dioxide column abundances at the Wisconsin Tall Tower site

We have developed an automated observatory for measuring atmospheric column abundances of CO2 and O2 using near-infrared spectra of the Sun obtained with a high spectral resolution Fourier Transform Spectrometer (FTS). This is the first dedicated laboratory in a new network of ground-based observatories named the Total Carbon Column Observing Network. This network will be used for carbon cycle studies and validation of spaceborne column measurements of greenhouse gases. The observatory was assembled in Pasadena, California, and then permanently deployed to northern Wisconsin during May 2004. It is located in the heavily forested Chequamegon National Forest at the WLEF Tall Tower site, 12 km east of Park Falls, Wisconsin. Under clear sky conditions, ~0.1% measurement precision is demonstrated for the retrieved column CO2 abundances. During the Intercontinental Chemical Transport Experiment–North America and CO2 Boundary Layer Regional Airborne Experiment campaigns in summer 2004, the DC-8 and King Air aircraft recorded eight in situ CO2 profiles over the WLEF site. Comparison of the integrated aircraft profiles and CO2 column abundances shows a small bias (~2%) but an excellent correlation.