CNES concepts for microsatellites for CO 2 observations

1. CNES concepts for microsatellites for CO2 observations Clémence Pierangelo on behalf of Microcarb team: CNES: C. Deniel, F. Bermudo, V. Pascal, P. Moro, D. Pradines, S. Gaugain LSCE: F.-M. Bréon

2. Microcarb, a CO2 mission onboard a microsatellite • 1- Science objective and context • Science objective • Mission and system high-level requirement • Context of CNES studies • The Myriade evolution satellite • 2- Instrument concepts and requirements • Instrument high-level requirements • Static Fourier transform concept and specific requirements • Dispersive concept and specific requirements

3. 1- Science objective and context • Science objective • Mission and system high-level requirement • Context of CNES studies • The Myriade evolution satellite

4. Microcarb Science Objectives • Natural sources and sinks of CO2 are badly quantified and localized at a global scale, especially over land. We do not know how they will evolve with a changing climate. • In order to better quantify the CO2 fluxes at the surface, very high quality CO2 concentration measurements are necessary. Weekly flux error reduction (ratio with OCO) Ocean regions Land regions LSCE/CEA-NOVELTIS-CNES

5. MicroCarb Science Objective • The mission requirements are given by the microcarb science group (PI: F-M Bréon, LSCE/CEA). • They are driven by the need to better constrain natural CO2 fluxes at the Earth surface through data assimilation (LMDz). • => Priority is given to precision on measurement (in ppm) rather than high spatial resolution or sampling. • OCO-2 (launch~2013) instrument will bring extremely valuable information for the error reduction on carbon sources and sinks; Microcarb shall thus reach (as close as possible) OCO-2 performances for CO2 (no regression). • However, as operational CO2 monitoring becomes a priority, a future CO2 instrument might be small/cheap enough for constellations or long-term series with several flight models. • Microcarb in a nutshell : “to reach (as close as possible) OCO-2 performances (accuracy, sampling) in a MicroSatellite system constraint”

6. MicroCarb Phase A High Level Mission Requirements • MicroCarb will measure vertically integrated CO2 concentration • to quantify CO2 surface fluxes at regional scales (carbon sources and sinks) through assimilation • The CO2 concentration will be retrieved by measurements of the absorption of reflected sunlight by CO2 in near infrared. The payload shall consist in a passive instrument. • Myriade Evolution platform with Myriade Flight Operation Center design shall be used. • Mission design shall be based on technology with moderate development schedule and risks: a compact and low cost concept mission. • Mission target launch date: 2017 with 3 years mission life time

7. MicroCarb System summary requirement

8. Context of CNES studies • 2009: CNES phase 0 for a CO2 passive mission onboard a microsatellite. • June 2010: CNES decided to start a Phase A to explore the feasibility of Microcarb mission based on new assumptions: • Two new instrument concepts • An evolution of the Myriade platform • October 2010: phase-A open competitive tender: • Selection of both Eads/Astrium and Thales Alenia Space. • February 2011: kick-off of Industry studies.

9. 2000 2002 2004 2006 2008 2010 2012 2014 2016 2018 2020 TARANIS PARASOL PICARD ELISA x 4 DEMETER MICROCARB MERLIN ESSAIM x 4 MICROSCOPE MYRIADE Line of Products • Initial CNES development then partnership between CNES and Prime Contractors Astrium and Thales Alenia Space. • 19 satellites ordered: • 10 in flight, 5 ready for flight, 4 under development. • Multi Mission:5 scientific, 10 defense,4 export. • Demonstrated performances: • >90% availability, >3 years lifetime (6 years reached on 6 satellites). • Generic system architecture with standard interface.

10. CNES decided in 2010 to start the “Myriade Evolution project” with the following main goals: Myriade in the future • to enhance performances (Mass, Power…) to address future missions (10 satellites in 2015-2025) • to deal with some components • obsolescence's (computer) • to comply with French Space Law: • debris mitigation regulation Mass and power of myriade payload Power (W) In 2011, the Myriade Evolution Phase A, in close coordination with new mission requirements (MicroCarb, Merlin …) will define the improved flight and performance perimeter Mass (kg) Current characteristicsFuture characteristics (TBC)130 kg Satellite200 kg Satellite 60 kg 60 W Payload90 kg 90 W Payload

11. 2- Instrument concepts and requirements • Instrument high-level requirements • Static Fourier transform concept and specific requirements • Dispersive concept and specific requirements

12. Instrument concepts and requirements • 2 concepts are specified by CNES and studied by the industry during phase A1: • A static fourier transform interferometer • A grating spectrometer • For both concepts, the level 1 requirements are such that: • The goal gives the same level 2 performance as OCO • The threshold is such that the level 2 performance is relaxed by 35%. • Spectral bands: • measurement in SWIR CO2 and O2 bands (aerosol, surface pressure) • An imaging function at 0.55-0.7 µm • spatial resolution ~100 m • to discriminate clouds-free acquisition in the field of view of the sounding sensor. • For both concept, an option with only 2,06 µm CO2 band will be also considered for the trade Off. Studies are in progress: • Impact on CO2 measurement in presence of aerosol/thin cloud • Use of forecast and digital elevation map for surface pressure estimate

13. MicroCarb instrument summary requirement

14. Fixed mirror beamsplitter Moving mirror Detection I(x) Dynamic interferometer temporal aquisition (e.g. IASI) Static interferometer Spatial aquisition Static Fourier Transform interferometer Stepped mirrors • This concept as a spectrometer has been studied and breadboarded in phase A for CNES instrument SIFTI, and for Microcarb phase 0. • For Microcarb phase A: optimization of the concept for CO2 measurement through irregular sampling and direct retrieval on the interferogram Incident wave beamsplitter (image of stepped mirrors on detection matrix) Filter Matrix detector

15. A posteriori error (linear estimate) Regular sampling Optimal sampling 1.29 ppm Number of samples Static interferometer concept • The interest relies on • selection of interferogram optical path difference samples with respect to their geophysical content (optimal estimation) • no Nyquist sampling rules to respect (=>optical filters less critical to make)

16. Static interferometer requirements • Sample selection of Optical Path Differences (OPD): • emphasizes CO2 sensitivity and has been performed through optimal estimation analyses. • + regular sampling of low OPD for low resolution spectrum (instrument transmission monitoring) • 14 « high steps » x 14 « low steps » = 392 samples (x2 through phase modulation) OPD selection 14 high steps Optical Path Difference (cm) 14 Low steps

17. Satellite speed Length of the slit (swath) Width of the slit Each column is a monochromatic image of the slit 2D spectrum Dispersive spectrometer principle Dispersion Nbin Spatial axis Spectral axis Entrance slit => IFOV Pushbroom aquisition => FOV

18. Satellite speed Length of the slit (swath) Width of the slit Dispersive spectrometer principle Each column is a monochromatic image of the slit 2D spectrum FOV 1 Nbin Dispersion FOV 2 Nbin Spatial axis FOV 3 Nbin Spectral axis

19. Dispersive spectrometer requirements • SNR, spectral resolution and bandwidth • They are the instrument driving parameter for CO2 retrieval accuracy • As very different combinations of these parameters might give similarly good level 2 performances, we want to give such a freedom to the industry => trade-off based on instrument considerations for an optimal configuration • Parametric relation (« virtue factor ») • Calculated through linear error estimates for a clear scene (no aerosol) • Search for the optimal values for α, β and γ on a set of ~50 instrument configurations • k is fixed so that p=required performance in ppm • Min and max values of BW, SNR, R are specified, together with inter-band variations Linear error estimate + possibility to include the number of FOV across track and along track

20. Example of instrument design • Echelle grating spectrometer • It has the advantage of spectral multiplexing (one grating for 3 (or 4) spectral bands) • Concept studied and breadboarded at CNES • An instrument based on an echelle grating spectrometer + a QMA telescope fits on a Myriade Evolution micro-satellite 435 mm 397 mm Patent Pending CNES : « High performances compact echelle grating spectrometer with double pass telescope » • Assumptions : • scan mirror: swath +/- 45° - rolling only. • 3 calibration views (lamp, sun, cold space)

21. Conclusion • MicroCarb has a challenging approach: high quality measurement of CO2 but with high constraints induced by MicroSatellite capabilities limitation. • A compact design approach associated with Myriade Evolution product line will allow CNES to offer a cost reduced solution to fulfill mission purposes. • This solution will open the possibility for CO2 operational long-term monitoring: • from a constellation of micro-satellites • or as a small size passenger onboard operational platforms (meteorological satellites…) • please visit http://smsc.cnes.fr/microcarb/ Thanks for your attention!