1. MAG: F.M. Breon, H. Dolman, G. Ehret, P. Flamant, N. Gruber, S. Houweling, M. Scholze, R.T. Menzies and P. Ingmann (ESA) A-Scope Measuring CO 2 Using a space-based Lidar A-SCOPE: F. M. Breon, H. Dolman, G. Ehret, P. Flamant, N. Gruber, S. Houweling, M. Scholze, R.T. Menzies and P. Ingmann (MAG) ASCENDS: P. Rayner

2. Outline Introduction: Active remote sensing A-SCOPE ASCENDS Instrument Requirements Prospects for launch

3. Measurement methods: 1. Passive: Thermal IR e.g. AIRS, IASI Information on vertical profile But, low sensitivity to the surface Application: T retrieval (ECMWF) AIRS CO2, July - August 2003 Tiwari et al, JGR, 2006

4. Measurement methods: 2. Passive: Short Wave IR e.g. Sciamachy, OCO, GOSAT Sensitive to the PBL Aim: Estimation of CO 2 sources & sinks Critical: Aerosols, thin clouds SCIAMACHY CO2, July - October ppm Buchwitz et al, ACP, 2007

5. Measurement methods: 3. Active: Diff. Absorption Lidar Carries own light source (laser) Day + night time measurements Always nadir (glint, high lats) Detects aerosols, thin clouds DIAL

6. Wavelength selection H2OH2O CO 2 on off Low T sensitivity Low contribution H 2 O Line wing = High surface sensitivity

7. Aerosol correction 1; Passive Problem: Optical path Solution: measure CO 2 & O 2, wide wavelength range Determine CO 2 /O 2 + aerosol parameters Sciamachy CO 2 Houweling et al., ACP, 2005

8. Aerosol correction 2; Active Solution: pulsed laser Select surface echo from pulse delay time Potentially: use aerosol echo for CO 2 vertical profile

9. A-SCOPE Pulsed Laser CO 2 (1.6 or 2.0 micron) Altimeter: Vegetation vertical distribution Aerosols & clouds Among the 6 ESA Earth explorer missions (Phase 0) Launch (if succesful): ~2015 Proposed instrument: Note: ECMWF(H 2 O, T, p) needed for conversion to XCO 2

10. Canopy Lidar Harding & Carabajal (GRL, 2005) Canopy height distribution

11. ASCENDS CO 2 (1.6 micron), O 2 (0.76 micron) CW laser (not pulsed) Proposed instrument: Status: No call yet but: US Decadal Survey: 2013 - 2016

12. A-SCOPE: Accuracy requirements Target requirement on surface flux estimation (level 3): 0.02 PgC/yr over 10 6 km 2 (or ~ 50% of the annual flux)

13. Translation to XCO2 (level 2) Inverse modelling simulations Required precision: 0.5 - 1.5 ppm Systematic error: 10% of precision

14. Performance estimation OCO: DIAL (no pressure broadening): Chevallier et al., 2007 Rayner, pers. comm.

15. Performance estimation DIAL, no pressure broadening: DIAL, + pressure broadening: Rayner, pers. comm.

16. Summary DIAL: Promising technique for measuring CO 2 Technological challenge Will A-Scope fly? => ESA User Consultation Mtg Granada, Oct. 2008