Global observations of the carbon budget 1. Expected satellite capabilities for emission spectroscopy in the EOS and NPOESS eras

This paper investigates the expected capabilities of the new generation of infrared satellite sounders for detecting CO₂. A general circulation model is used to simulate realistic CO₂ fields and to define the needed accuracy of CO₂ observations in order to be useful in constraining surface sources and sinks of CO₂, which will be described in more detail in a future paper. Optimal estimation retrieval theory is then used to determine the possible accuracy of the satellite measurements and to define the retrieval characteristics. A discussion of several factors that affect the retrievals is also included. We conclude that tropospheric column retrievals of CO₂ are possible with an accuracy of better than 1 ppmv on a monthly mean basis. Several factors, like thin cirrus clouds and radiative transfer modeling errors, will degrade these results if not carefully accounted for. The possibility of extensive time and spatial averaging of the satellite observations will overcome some of these problems.