1. CO 2 Science and Sounder Overviews Jim Abshire

1. 1. CO2 Science and Sounder Overviews Jim Abshire Laser Sounder for Remotely Measuring Atmospheric CO2 Concentrations

2. 1. The Global Carbon Cycle ATMOSPHERE ~90 Pg /yr ~120 Pg /yr + 3 Pg /yr OCEANS LAND 7 Pg /yr 1Pg C = 1015g C • Only about 50% of the CO2 emitted each year shows up in the atmosphere. The rest is absorbed by ocean or terrestrial “sinks”. • A detailed understanding of these sinks is needed to predict future atmospheric CO2 levels. Laser Sounder for Remotely Measuring Atmospheric CO2 Concentrations

3. Possible consequences of inaccurate or too late predictions: Laser Sounder for Remotely Measuring Atmospheric CO2 Concentrations

4. CO2 Sounder Concept Laser Sounder for Remotely Measuring Atmospheric CO2 Concentrations

5. Why measure CO2 with Lidar from orbit ? Current capability for measuring CO2 is primarily the NOAA/CMDL surface air sampling network: Lidar on satellites can give the needed global coverage and the needed dawn-dusk measurement times. Sun-synchronous Orbit – 1 month 600 km 550 km Significant limitations: • Flask samples are obtained only biweekly at most sites. • Samples are infrequent • Too coarse in spatial coverage to capture the CO2 signal Laser Sounder for Remotely Measuring Atmospheric CO2 Concentrations

6. CO2 1570nm Absorption Band CO2 1570nm Absorption Band Single CO2 Absorption Line & Background Laser Sounder for Remotely Measuring Atmospheric CO2 Concentrations

7. 60 50 LINE CENTER 90% 40 75% Pressure Altitude (km) 50% 25% 30 COLUMN 20 10 0 0.0 0.05 0.10 0.15 Relative Absorptivity Using Pressure broadening permits weighting to troposphere The absorption lines are pressure broadened Measuring on side of absorption line permits weighting of tropospheric CO2 1.0 0.8 0.6 Transmittance 0.4 0.2 0.0 -1.0 -0.5 0.0 0.5 1.0 Relative Frequency (wavenumbers) Sounder technique permits selecting the on-line locking point to optimize the weighting function Laser Sounder for Remotely Measuring Atmospheric CO2 Concentrations

8. ICESat & GLAS provide needed data and Heritage ICESat/GLAS Measurements • Surface Altimetry: • Range to ice, land, water, clouds • Time of flight: 1064 nm laser pulse • Digitizes transmitted & received 1064-nm pulse waveforms • Laser-beam attitude from star-trackers, laser camera & gyro • Atmospheric Lidar: • Laser backscatter profiles from clouds & aerosols • 1064 nm & 532 nm laser pulses • Profiles; 75 m vertical resolution • Analog; photon counting detection • Simultaneous, co-located measurements with altimeter Laser Sounder for Remotely Measuring Atmospheric CO2 Concentrations

9. 400 390 CO2 (ppmv) 380 370 104.5 105.0 105.5 106.0 106.5 Day of 2003 Licor In-Situ Co2 Sampler - Update • Licor now operating continuously, 24 hours per day with automatic calibrations. • Repaired Building 33 weather station—provides meteorological context • (e.g., wind speed, direction) needed to compare Licor data with laser sounder. Morning Rush Hour: 6-9am Evening Rush Hour: 4-7pm Laser Sounder for Remotely Measuring Atmospheric CO2 Concentrations

10. 2. GLAS Instrument on the ICESat mission • GLAS is now in space & operational • Our CO2 Sounder team had leadership roles in it • In terms of the CO2 Sounder, GLAS has: • Demonstrated some key measurements • Demonstrated some key lidar technologies • Shown complexity of the real atmosphere & the actual CO2 measurement environment • Our CO2 measurement approach is best suited to leverage from GLAS & measure in actual atmospheric conditions ICESat I Laser Sounder for Remotely Measuring Atmospheric CO2 Concentrations

11. GLAs Instrument during Testing Primary involvements: Science measurement approach & specification, technology trades, laser technology tradeoffs, detector and filter development, pre-& post- launch testing, calibration GLAS during integration with ICESat in June 2002 at Ball Aerospace in Boulder, Colorado Laser Sounder for Remotely Measuring Atmospheric CO2 Concentrations

12. IST and LRS Altimeter Detectors (2) Lasers (3) Lidar Detectors (8) Main Mirror (1m) Secondary Mirror Reflected Laser Pulse (532 nm) Telescope Sun Shade Graphics courtesy of GLAS Instrument Team (not to same scale) Emitted Laser Pulse (532 nm) GLAS Instrument Laser Sounder for Remotely Measuring Atmospheric CO2 Concentrations

13. New Space Lidar Technology developed by GLAS Team for ICESat a) d) GLAS instrument components now available for use on future lidar missions: 100 cm diameter telescope; laser flight unit which delivers 75 mJ at 1064 nm & 35 mJ at 532 nm; thermally tuned solid etalon with 42% peak transmission and a 26 pm bandwidth; (d) Perkin Elmer SPCM photon counting detector with 70% counting efficiency at 770 nm. Laser Sounder for Remotely Measuring Atmospheric CO2 Concentrations

14. Glas Surface Topography Measurements GLAS Science Team Laser Sounder for Remotely Measuring Atmospheric CO2 Concentrations

15. Glas Surface Topography Measurements GLAS Science Team Laser Sounder for Remotely Measuring Atmospheric CO2 Concentrations

16. Open Path CO2 measurements - test range Test Range (laser path highlighted) Laser Sounder for Remotely Measuring Atmospheric CO2 Concentrations

17. Measurement validationComparison of CO2 Sounder Prototype with Licor • Comparison Approach: • Sounder raw data offset & scaled • Sounder referenced to Licor at single point • Best results were Excellent: • Agreement (correlation) was ±1 ppm over 6 hours. • Measurement precision < 1 ppm Laser Sounder for Remotely Measuring Atmospheric CO2 Concentrations