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Information Content of Space Based CO2 Measurements

David Crisp(1)

(1) Jet Propulsion Laboratory/Caltech, MS 183-501, 91109 Pasadena, California, United States


Despite the recent expansion of the ground based CO2 monitoring network, large regions of the globe such as the ocean basins and tropical continents remain so sparsely observed that we cannot determine whether they are sources or sinks of CO2. Recent advances in space based measurements of CO2 and other greenhouse gases provide opportunities to address these needs. However, a more complete understanding of the information content these space-based measurements is needed to fully exploit their potential. For example, operational thermal infrared sounders such as the Atmospheric Infrared Sounder (AIRS) on the Earth Observing System (EOS) Aqua platform and the European Space Agency (ESA) Infrared Atmospheric Sounding Interferometer (IASI) on MetOp can make CO2 measurements with accuracies of ~1% (3 - 4 ppm) at altitudes between 5 and 15 km. While these measurements contribute to our understanding of the CO2 distribution at these altitudes, they have very limited sensitivity near the surface, where the CO2 sources and sinks are located. Other instruments that measure the absorption of reflected sunlight, such as the TANSO-FTS on the Japanese Greenhouse Gases Observing Satellite (GOSAT, nicknamed IBUKI), can make spatially resolved global measurements of the column averaged CO2 dry air mole fraction that have their greatest sensitivities near the surface. However, because these measurements are made in reflected sunlight, they can only be made over the sunlit hemisphere. Combining these solar and thermal measurements of CO2 can potentially yield insight into both day-night variations and the vertical distribution of CO2, providing a preview of the capabilities promised by future LIDAR-based systems. Even with these current and future space based CO2 monitoring capabilities, near-surface and airborne in situ measurements will continue to play vital roles, both as ground truth for the space based measurements as the primary means to identify and characterize the processes governing variations and trends in carbon exchanges. The space and ground based capabilities must therefore must be integrated into a coordinated system for monitoring greenhouse gas sources and sinks.


Workshop presentation