Road to CO2 DIAL Mission

1
Road to CO2 DIAL Mission

• Pierre H. Flamant1, Fabien Gibert1, Didier
  Bruneau2
• Institut Pierre Simon Laplace, France
• 1Laboratoire de Météorologie Dynamique, École
  Polytechnique, Palaiseau
• 2Service dAéronomie, Verrières-le-Buisson

2
Framework (1/2)

• Current situation for CO2 monitoring from space
• i) multipurpose passive sensor instruments are
  currently investigated and
• ii) two dedicated passive missions OCO and
  GOSAT, are under way. Their performances with
  respect to coverage, accuracy and bias (key
  issues) are under study by numerical simulation
  and an airborne demonstrator for GOSAT
• For decades, the atmospheric Differential-Absorpti
  on-Lidar (DIAL) technique has been successful in
  science and monitoring applications
• Can the DIAL technique be up to the job in terms
  of accuracy 1 to 2 ppm on total column content,
  and small bias? And if YES at what cost
• Our motivation is to contribute to the on-going
  effort on greenhouse gases monitoring and
  understanding of inexorable raise of atmospheric
  carbon dioxide (CO2) as seen from an experimenter
  point of view
• The Lidar community is cautious considering the
  requirements on accuracy
• Research funds are quite difficult to raise in
  France!

3
Framework (2/2)

• To draw a relevant itinerary from ground to
  space that addresses the science and technical
  issues
• The very basic idea in the last few years was to
  built meaningful puzzle based on the various
  contributions from different agencies in France
  and Europe
• In 2002, we began a new activity at IPSL on CO2
  Lidar monitoring.
• No dedicated funding for 2 years
• but a pulsed 2-µm Heterodyne wind Lidar in a
  bread-board stage
• In view of a feasibility demonstration we were
  lucky wrt i) the spectral domain i.e. 2 µm, and
  ii) a heterodyne detection
• Then we get some funding from IPSL in 2004 and
  2005, and we started an RD activity supported by
  CNES in 2006

4
Content

• Overview of basic DIAL techniques for atmospheric
  CO2 measurements
• IPSL ground-based 2-µm HDIAL work and preliminary
  validation activities
• RD activities for
• CNES to develop a ground-based transportable
  DIAL
• ESA to develop a high energy transmitter for
  DIAL applications in space
• FACTS a feasibility study conducted for ESA in
  2004-2005
• A-SCOPE a proposal selected (with 5 others) in
  response to the 2005 ESA call for ideas for the
  next Earth Explorer Missions
• A new study for ESA Observation techniques and
  mission concepts for analysis of the global
  carbon cycle, started in July 2007
• Two research proposals submitted in 2007 to the
  Agence Nationale de la Recherche (National
  Research Agency in France), decision expected mid
  July
• AIReS, an Airborne Integrated Remote Sensing
  platform for Regional Studies
• Sentinelle, as part of a full scale monitoring
  of a CO2 geological storage site

5
Basic DIAL (1/2) ? more than one single
technique but combination(s) of possibilities

• Spectral domain ? 1.57 µm or 2.06 µm (stronger
  line strengths at 2.06 µm)
• The CO2 line impacts the weighting function
• 2 or 3 transmitted wavelengths one or two On-
  and one Off-wavelengths
• 1.57 µm On-wavelength on CO2 absorption line or
  near line center
• 2.051 µm On-wavelength set in the wing of the
  CO2 absorption line
• One serious issue accurate spectroscopic
  parameters for the CO2 line of interest (S,
  width, dependence on temperature)
• On-going cooperation with the spectroscopic group
  of Reims University
• Transmitter
• i) pulsed, ii) Continuous Wave, iii) modulated or
  Pulse-random noise CW
• Great variety of laser technologies including
  non-linear optics conversion (optical parametric
  oscillator, )
• Detection Direct or heterodyne (driven by NEP
  and background radiometric signal)
• Direct detection for high/moderate pulse energy
  at low PRF
• Heterodyne detection for low energy per pulse at
  high PRF (CNR?1)
• Signal statistics are quite different
• Under optimal conditions the 2 detection schemes
  are similar and they result in same performance

6
Basic DIAL (2/2)

• Atmospheric measurements
• Range resolved CO2 measurements based on aerosols
  scattering in ABL
• Differential transmission by range gate ?
  differential local optical depth
• Slope technique i.e. DLOD plotted as a function
  of range
• If constant CO2 density along LOS ? straight line
  
• ? mean extinction coefficient
• CO2 Total column content using diffuse targets
  i.e. surface, dense clouds
• Total differential transmission ? DOD
• But the Path length needs to be known accurately
  ? average extinction coefficient
• Geophysical quantities of interest
• Given the Optical depth (path length)
• knowing the CO2 absorption cross section
• Given the geophysical variables (p,T,q) ?
  weighting function
• CO2 dry mixing ratio

7
Laboratory breadboard
Injection seeded Ho,TmYLF ring cavity laser
pumped laser
The spectral drift of transmitter emission are
corrected by an a posteriori technique using
photo-acoustic cell (PAC) signals to cluster the
On- and Off-wavelength DIAL signals and eliminate
the outliers More to be presented by F. Gibert,
D. Edouart et al, oral paper, session 11
8
Field Deployment for Validation IPSL (LMD, LSCE)
Reims University 1st step accurate CO2
measurements in absolute value
In-situ Instruments Flasks Condor/Licor
(LSCE), Diode laser 2.8 µm SPC (GSMA-Reims)
Vertical sounding in ABL free troposphere
To the North Paris city Pollution plume
1.2 km
ONERA site
Horizontal slant LOS in ABL
2-µm HDIAL
SEBL
To the West
More to be presented by F. Gibert et al, oral
paper, session 5 2-µm Heterodyne DIAL for both
atmospheric CO2 and wind measurements validation
and geophysical application
Routine in situ measurements at IPSL/LSCE 5 km
away
École Polytechnique Campus
Radiosoundings twice a day at Met Station located
10 km away
9
2-µm HD2IAL performance in ABL Horizontal
LOS Range resolved measurements
Carrier-to-noise ratio (CNR) mean signal / mean
detection noise
mean for Mp 300 shots or 1 min
Signal-to-noise ratio (SNR)
Mt coherence cells i.e. independent samples, in
a range gate Mp independent realizations
-5dB
10
Pre-validation against in situ sensors
From Gibert et al., AO 2006
North
Lidar LOS
West

• LogPR2 or particle loading
• Radial wind velocity (m.s-1)
• CO2 mixing ratio measurements
• 300 shot pair averaging (o), 5 points smoothing
  (-) to be compared to LSCE in-situ measurements
  (- -)
• HDIAL statistical error 2
• ? Representativity error depends on wind
  direction and transport

11
Preliminary vertical measurements

• Observations
• Optical Depth to the cloud
• Range to the cloud
• Absorption coefficient in ABL
• Atmospheric variables from MM5 meso-scale model
• SWF in free trop and ABL

Free Troposphere CO2 mean mixing ratio
Airborne in situ 375 ppm
Weighting function
As cloud
1.9
Troposphere low aerosol loading
PBL aerosols
ABL
Range distributed aerosol target
Range resolution ?R75 m
1.2
The 2064 nm CO2 absorption line is well suited
for ABL measurements but not for long path
measurements in the troposphere
2-µm HD2IAL
12
On-going RD activities

• Development of a ground-based transportable DIAL
  based on
• 1st) Dual Resonant-OPO pumped by a NdYLF laser,
• 2nd) HoYAG pumped by a TmYLF laser (Shen 2004,
  Shelhorn 2003)
• Distributed feedback Laser diodes at 2064 and
  2051 nm for LO and spectroscopic studies
• Standard Photo-Acoustic Cells Resonant
  Helmholtz PAC
• Spectroscopic study of CO2 lines of interest
  (2051 nm) in collaboration with the spectroscopy
  group at Reims University
• Development of a high energy transmitter for DIAL
  applications in space (PULSNIR) investigation
  of a DR-OPO 2 OPA scheme pumped by a single
  mode NdYLF laser
• 2 entangled OPO cavities for the signal and idler
  emissions (no injection seeding)
• Activity Led by ONERA in Palaiseau
• IPSL/LMD is in charge of spectral characterization

13
Future Atmospheric Carbon Dioxide Testing From
Space (FACTS)

• Preliminary study on space borne application
  conducted for the European Space Agency (ESA)
  started in January 2004, final report December
  2005
• Driving science CO2 sink sources
• Objectives
• To derive the requirements for a mission aiming
  at the measurement of atmospheric carbon dioxide
  (CO2) by DIAL
• To establish the relevant strawman mission
  concept
• To define instrument concept for the mission
  implementation
• To define required technology developments

14
Considering various DIAL techniques

• The various combinations have been analyzed for a
  400 km orbit and an observation over 50 km
• 1.57 and 2.06 µm (spectroscopic parameters from
  HITRAN or GEISA data bases) 3 lines
• On-wavelength at line center or off line center
  edge or wing
• One On- or two-On-wavelength
• Pulsed, CW, PRN-CW
• Direct (NEP) Heterodyne detection
• Total column Range resolved
• Performances derived from analytical models and
  given in CO2 mixing ratio
• Standard deviation
• Bias
• Bruneau, 2005 (FACTS report) provide theory for
  heterodyne detection with PRN-CW
• Bruneau et al, 2006 complementary study of
  differential absorption Lidar optimization in
  direct and heterodyne detection

15
CO2 Weighting function
3 km
This function is independent of the pressure
profile. It dependents on humidity profile and on
temperature profile through the absorption
cross-sections. Average mixing ratio calculation
requires the knowledge surface pressure The
weighting function is dependent on the laser
spectral positioning with respect to the line
centre
16
FACTS the Preferred Concept

• Total Column Content using surface or dense cloud
  returns (LOS few degrees off nadir)
• Pulsed 2-µm DIAL tuned on 2051 nm CO2 absorption
  line
• Direct detection with improved detector NEP ?
  5.10-14 W Hz-0.5
• High spectral purity transmitter (99.95)
• Accurate spectroscopic parameters of the 2051 nm
  CO2 line
• One Off- and two On-laser emissions in double
  Wing symmetrical position wrt to CO2 absorption
  line center
• Either a high energy low PRF or a low energy high
  PRF transmitter for same resources provided by
  the platform
• In optimal conditions SNR scales as the square
  root of PRF

Surface reflectance
A sounding at 2-µm in the wing of 2051 nm line
results in 18 of the total WF in the ABL (1 km)
while a constant pressure WF corresponds to 11
17
Advanced Space Carbon and Climate
Observation of Planet Earth (A-SCOPE)

• Schedule
• Proposal submitted to ESA in August 2005, in
  response to a call for ideas for the next Earth
  Explorer Mission
• Selected in June 2006 with 5 other potential
  missions
• A Mission Assessment Group has been formed by ESA
  
• Two parallel Assessment studies of the 6 missions
  by Industry ASTRIUM, Thalès-Alénia
• To be presented to the Scientific Community
  (Users consultation meeting) in Granada, Spain
  in October 2008
• Mission and Payload
• Main objective CO2 total column content, one
  observation over 50 km, CO2 dry mixing ratio,
  1-2 ppm statistical error, regional bias lt 0.2
  ppm
• Additional objective Canopy height (depending on
  PRF and pulse length)
• Spin-off products aerosols clouds
• Core instrument a CO2 Pulsed DIAL in Direct
  detection preferably at 2 µm
• Auxiliary instrument a WFC, 3 bands, for
  contextual information

18
Advanced Space Carbon and Climate
Observation of Planet Earth (A-SCOPE)

• Mission Assessment Group (MAG) 8 members
• P. H. Flamant, France (Chair), F.-M. Breon,
  France, H. Dolman, Nederland, G. Ehret, Germany,
  N. Gruber, Switzerland, S. Houweling, Nederland,
  R. T. Menzies, USA, M. Scholze, UK
• Duty responsibility
• Mission Requirement Document for mission
  implementation
• Report for Assessment in view of the Users
  consultation Meeting
• Science studies Field campaigns for MRD and RfA
  
• Lidar reflectivities at 1.6 and 2.0 µm using
  existing data sets MODIS, POLDER,
• ? DIAL wavelength
• CO2 diurnal cycle and variation of total column
  content with latitude
• ? equator crossing time
• Optimal DIAL footprint wrt cloud cover,
  topography variability fluctuations
• Outline of new studies addressing data
  assimilation for the biosphere
• ? to assess the benefit A-SCOPE for reducing
  uncertainties in current and future terrestrial
  carbon uptake

19
Observation techniques and mission
concepts for analysis of the global carbon cycle

• The Team
• MPI-Jena and LSCE are two leading laboratories in
  Europe on Carbon cycle research
• IPSL/LMD-SA and DLR have expertise in DIAL
  technique and CO2 DIAL measurements. They have
  been leading two ESA-funded feasibility studies
  and are involved in A-Scope MAG
• The Team has expertise in passive remote sensing
  to retrieve CO2 mixing ratio SRON for
  Sciamachy, ECMWF for AIRS, Noveltis for IASI,
  LSCE for OCO
• ECMWF, MPI, SRON and LSCE are leading
  laboratories in Europe for atmospheric transport
  model
• MPI, SRON and LSCE are leading laboratories in
  Europe for inversion technique using atmospheric
  transport model for Carbon cycle research.
• Study led by F.-M. Bréon (IPSL/LSCE) and P.
  Prunet (Noveltis)
• The Lidar analysis to be conducted by D. Bruneau
  (IPSL/SA), G. Ehret (DLR),
• P. H. Flamant (IPSL/LMD)

20
Observation techniques and mission
concepts for analysis of the global carbon cycle

• Framework
• All satellite observations of CO2 concentration
  have an accuracy that is not as good as that of
  the surface network. In addition, the spaceborne
  observations provide a concentration that is
  averaged over the column (with various weighting
  functions)
• Depending on the vertical weighting function,
  this observation may be rather disconnected from
  the boundary layer and therefore difficult to
  relate to the surface fluxes. For instance,
  Chevallier et al 2005 has shown that the upper
  troposphere concentration provides little
  constrain on the surface fluxes
• As a consequence, the impact of a satellite
  mission measuring CO2 concentration may not
  provide a great deal of additional information,
  in particular in the context of a surface network
  growing in density
• Objectives
• Therefore, it appears necessary to evaluate
  quantitatively the benefit of a new satellite
  mission, dedicated to the monitoring of CO2
  concentrations, for an improved knowledge of the
  surface Carbon fluxes.
• This requires the knowledge of the sampling
  pattern provided by the various missions, the
  vertical weighting functions of each instrument,
  the measurement errors, the spatial and temporal
  correlations of these errors
• In addition, the surface fluxes inferred from the
  concentration observations may depend on the
  atmospheric transport model that is used, the
  selection procedure for the valid observations,
  the choice of the cost function to be minimized,
  and the method for the minimization. These
  choices constitute the so-called setup of the
  inversion.
• The study aims at an evaluation of the added
  value of an active CO2 remote sensing mission for
  the quantitative monitoring of CO2 surface fluxes
  in the context of an existing surface observation
  network and other (passive) CO2 monitoring
  missions

21
Observation techniques and mission
concepts for analysis of the global carbon cycle
Observation techniques and mission concepts for
analysis of the Global carbon Cycle
Task 1 Literature review
Task 2 Science Objective and Requirements for a
CO2 DIAL mission
Task 3 integrated observation system of CO2
spaceborne missions
Task 4 in depth analysis of surface retrieval
related errors for A-SCOPE
Task 5 Comparison of CO2 inverse modeling tools
Task 6 evaluation of CO2 mission scenarii using
inverse model runs
WP110 Carbon cycle research
WP 200 Potential benefit of an active mission
WP 310 Consistency and synthesis
WP 410 Surface pressure error in NWP
WP 510 Forward modeling tools
WP 610 Preparation
WP 620 Inversion runs
WP120 Inversion Tool for atmosphere
WP 320 Sciamachy
WP 420 Topography surface related error
WP 520 Forward model intercomparison of nature run
WP 630 Error analysis
WP 330 OCO GOSAT
WP 530 Validation of inverse modeling tools
WP 640 Implication for A-SCOPE
WP 340 IASI AIRS
WP leadership
NOVELTIS
IPSL/LSCE
WP 350 A-SCOPE
WP 650 Comparison with alternative inversion
schemes
SRON
IPSL/LMD
MPI
WP 360 Network and aircraft
Management NOVELTIS
Conclusion IPSL/LSCE
22
A look to the future
23
Conclusion

• We can say that we have been successful regarding
  our goal to draw a comprehensive and relevant
  itinerary from ground to space that addresses
  the science and (some) technical issues
• The coming year is crucial for A-SCOPE regarding
  the next Users Consultation Meeting in October
  2008
• It would be very beneficial to A-SCOPE if we can
  bring together the contributions of the various
  groups working on CO2 measurements using
  (various) DIAL techniques either ground- based or
  airborne
• I would be happy to help to set up a working
  group involving all experimenters active in the
  field of CO2 DIAL measurements