The Atmospheric Infrared Sounder (AIRS) is a hyperspectral infrared instrument on the EOS Aqua Spacecraft, launched on May 4, 2002. AIRS has 2378 infrared channels ranging from 3.7 um to 15.4 um and a 13.5 km footprint. AIRS, in conjunction with the Advanced Microwave Sounding Unit (AMSU), produces temperature profiles with 1K/km accuracy on a global scale, as well as water vapor profiles, clouds, dust and trace gas amounts for CO2, CO, SO2, O3 and CH4. AIRS data are used for weather forecasting and studies of global climate change. The AIRS is a “facility” instrument developed by NASA as an experimental demonstration of advanced technology for remote sensing and the benefits of high resolution infrared spectra to science investigations.

The Orbiting Carbon Observatory (OCO) mission was selected by NASA's Office of Earth Science as the fifth mission in its Earth System Science Pathfinder (ESSP) Program. OCO will make global measurements of atmospheric CO2 with the precision, resolution, and coverage needed to characterize sources and sinks of this important greenhouse gas on regional scales. These measurements will improve our understanding of the processes that regulate CO2, enabling more reliable forecasts of climate change. During its 2-year mission, OCO will fly in a 1:15 PM sun-synchronous orbit, sharing its ground track with the Earth Observing System (EOS) Aqua platform. It will carry a single instrument that incorporates three high-resolution spectrometers to measure reflected sunlight in the molecular oxygen (O2) A-band at 0.76-microns and the CO2 bands at 1.61 and 2.06 microns. These data will be analyzed to retrieve the column-averaged CO2 dry air mole fraction with precisions of 0.3% (1ppm) on regional scales. A comprehensive validation and correlative measurement program has been incorporated into this mission to ensure the accuracy of the space-based XCO2 measurements. OCO is scheduled for launch in early 2009.

AIRS measures CO2 in the mid troposphere through emission of CO2 absorption lines, while OCO measures the total column of CO2 using reflective sunlight. Together these instruments can provide more information on contribution of CO2 near the boundary layer than either one individually. Both AIRS and OCO are grating spectrometers with high spectral resolution, precision and accuracy. Requirements and options for future instruments to measure CO2, CH4, H2O and other greenhouse and non-greenhouse gases based on the experience of AIRS and OCO will be presented and cover algorithms, instrument technology and orbital options for optimizing sensitivity, spatial and temporal resolution.