ESTO Advanced Component Technology 11/17/03 Laser Sounder for Remotely Measuring Atmospheric CO 2 Concentrations GSFC CO 2 Science and Sounder Overviews Jim Abshire

ESTO Advanced Component Technology 11/17/03 Laser Sounder for Remotely Measuring Atmospheric CO 2 Concentrations GSFC 1- 2 OCEANS LAND ATMOSPHERE + 3 Pg /yr 7 Pg /yr ~120 Pg /yr ~90 Pg /yr 1. The Global Carbon Cycle 1Pg C = g C  Only about 50% of the CO 2 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 CO 2 levels.

ESTO Advanced Component Technology 11/17/03 Laser Sounder for Remotely Measuring Atmospheric CO 2 Concentrations GSFC 1- 3 Possible consequences of inaccurate or too late predictions:

ESTO Advanced Component Technology 11/17/03 Laser Sounder for Remotely Measuring Atmospheric CO 2 Concentrations GSFC 1- 4 CO 2 Sounder Concept

ESTO Advanced Component Technology 11/17/03 Laser Sounder for Remotely Measuring Atmospheric CO 2 Concentrations GSFC 1- 5 Current capability for measuring CO 2 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. Significant limitations:  Flask samples are obtained only biweekly at most sites.  Samples are infrequent  Too coarse in spatial coverage to capture the CO2 signal Sun-synchronous Orbit – 1 month 600 km 550 km Why measure CO 2 with Lidar from orbit ?

ESTO Advanced Component Technology 11/17/03 Laser Sounder for Remotely Measuring Atmospheric CO 2 Concentrations GSFC 1- 6 CO2 1570nm Absorption Band Single CO2 Absorption Line & Background CO2 1570nm Absorption Band

ESTO Advanced Component Technology 11/17/03 Laser Sounder for Remotely Measuring Atmospheric CO 2 Concentrations GSFC 1- 7 Relative Absorptivity Pressure Altitude (km) LINE CENTER 90% 75% 50% 25% COLUMN Relative Frequency (wavenumbers) Transmittance The absorption lines are pressure broadened Measuring on side of absorption line permits weighting of tropospheric CO 2 Sounder technique permits selecting the on-line locking point to optimize the weighting function Using Pressure broadening permits weighting to troposphere

ESTO Advanced Component Technology 11/17/03 Laser Sounder for Remotely Measuring Atmospheric CO 2 Concentrations GSFC 1- 8 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 ICESat & GLAS provide needed data and Heritage

ESTO Advanced Component Technology 11/17/03 Laser Sounder for Remotely Measuring Atmospheric CO 2 Concentrations GSFC 1- 9 Day of 2003 CO 2 (ppmv) 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

ESTO Advanced Component Technology 11/17/03 Laser Sounder for Remotely Measuring Atmospheric CO 2 Concentrations GSFC ICESat I GLAS is now in space & operational Our CO 2 Sounder team had leadership roles in it In terms of the CO 2 Sounder, GLAS has: Demonstrated some key measurements Demonstrated some key lidar technologies Shown complexity of the real atmosphere & the actual CO 2 measurement environment Our CO 2 measurement approach is best suited to leverage from GLAS & measure in actual atmospheric conditions 2. GLAS Instrument on the ICESat mission

ESTO Advanced Component Technology 11/17/03 Laser Sounder for Remotely Measuring Atmospheric CO 2 Concentrations GSFC GLAS during integration with ICESat in June 2002 at Ball Aerospace in Boulder, Colorado GLAs Instrument during Testing Primary involvements: Science measurement approach & specification, technology trades, laser technology tradeoffs, detector and filter development, pre-& post- launch testing, calibration

ESTO Advanced Component Technology 11/17/03 Laser Sounder for Remotely Measuring Atmospheric CO 2 Concentrations GSFC GLAS Instrument Graphics courtesy of GLAS Instrument Team (not to same scale) Emitted Laser Pulse (532 nm) Reflected Laser Pulse (532 nm) Altimeter Detectors (2) Lidar Detectors (8) Lasers (3) Telescope Sun Shade Main Mirror (1m) Secondary Mirror IST and LRS

ESTO Advanced Component Technology 11/17/03 Laser Sounder for Remotely Measuring Atmospheric CO 2 Concentrations GSFC New Space Lidar Technology developed by GLAS Team for ICESat 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. a) d)

ESTO Advanced Component Technology 11/17/03 Laser Sounder for Remotely Measuring Atmospheric CO 2 Concentrations GSFC Glas Surface Topography Measurements GLAS Science Team

ESTO Advanced Component Technology 11/17/03 Laser Sounder for Remotely Measuring Atmospheric CO 2 Concentrations GSFC Glas Surface Topography Measurements GLAS Science Team

ESTO Advanced Component Technology 11/17/03 Laser Sounder for Remotely Measuring Atmospheric CO 2 Concentrations GSFC Open Path CO2 measurements - test range Test Range (laser path highlighted)

ESTO Advanced Component Technology 11/17/03 Laser Sounder for Remotely Measuring Atmospheric CO 2 Concentrations GSFC Measurement validation Comparison 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