The Total Carbon Column Observing Network is a global network of ground-based Fourier transform spectrometers designed to measure column abundances of CO2, CO, CH4, N2O and other molecules that absorb in the near infrared. With stringent requirements on the instrumentation, data processing and calibration, the network achieves an accuracy and precision that is unprecedented for remote sensing observations (better than 0.25%). This makes the TCCON a valuable tool for further understanding the carbon cycle, validating satellite measurements, and providing a link between satellite measurements and the extensive ground-based in situ network. INTRODUCTION The Total Carbon Column Observing Network (TCCON) was established in 2004 with a primary focus of measuring precise and accurate columns of CO2. Currently, there are 19 sites affiliated with TCCON, 15 of which are currently operational. INSTRUMENTATION The central instrument at each TCCON site is a high-quality, highspectral-resolution Fourier transform spectrometer (FTS), into which direct solar radiation is passed by a solar tracker. The FTS instruments observe the absorption of solar radiation in the near infrared (NIR) by CO2, O2, CH4, N2O, CO and other molecules in the atmosphere. INSTRUMENTATION • TCCON measures total column abundances of atmospheric gases. • Helps disentangle the effects of atmospheric mixing from the surface exchange. • Particularly useful are column-averaged dry-air mole fractions (denoted xG for gas G). Insensitive to variations in surface pressure and atmospheric water amount. • Because the column vertically integrates the concentration of CO2 above the surface, horizontal gradients in measured xCO2 are more directly related to the underlying regional-scale fluxes than is the case for the surface in situ measurements of CO2 (Yang et al., 2007). • The latitudinal gradients in xCO2 are small, and to improve upon our current knowledge of the carbon cycle requires measurements with precisions better than ~0.25% in xCO2 (Rayner and O’Brien, 2001; Miller et al., 2007). SATELLITE VALIDATION • TCCON provides the ideal data for satelColumn averaging kernels for lite validation. Measures column abundanTCCON ces, the same quantities as satellites. Measures same molecules in the same spectral regions. • Apply Rodgers and Connor (2003) methods to compare TCCON to satellite data. A priori profiles for TCCON