Mapping vegetation photosynthesis from space
Jose F. Moreno
Depart. Earth Physics and Thermodynamics
Faculty of Physics
University of Valencia, Spain
JORNADA SOBRE NUEVAS ESTRATEGIAS DE OBSERVACION
DE LA TIERRA EN LA EVALUACION DE LOS SUMIDEROS DE CARBONO
Madrid, 17 diciembre 2007
FLEX PROPOSAL:
Submitted to ESA by August 2005
Call for Ideas - Earth Explorer Core Missions
78 authors, each one representing a full team
71 institutions from 14 countries
24 proposals in total received by ESA
FLEX was one of the 6 proposals selected
for Pre-Phase A studies
Outline:
- Scientific motivation
- Basic requirements
- Payload definition
- Feasibility considerations
- Data usage perspectives and science impacts
- Current status and perspectives
Evidence of the increase in CO2 concentration
and different possible future scenarios
from point data to
global modelling
CO2 vertical profile
CO2 (ppm)
Daily and seasonal
variations in CO2
vertical distribution
Strong
Convection
Summer
Low CO2
Concentration
Deep PBL
Mixing
Photosynthesis
Dilution of photosynthesis signal through deep mixing
Transport of low-CO2 air into upper troposphere
Weak Cumulus
Convection
Autumn
High CO2
Concentration
diurnal variation ∼ 5 × seasonal variation
vertical gradient ∼ 15 × pole-to-pole gradient
Shallow PBL
Mixing
Decomposition
Accumulation of respiration signal near the surface
Elevated CO2 in lower troposphere
PHOTOSYNTHESIS
Looking inside leaf
photochemical processes
absorption
An absorption spectrum (a)
shows a vibrational structure
characteristic of the upper state
Chlorophyll
fluorescence
spectral emission
A fluorescence spectrum (b) shows a
structure characteristic of the lower
state, displaced to lower energies
(mirror image of the absorption)
2-5 %
20-30 %
Effects of
fluorescence
on vegetation
reflectance
280
violaxanthin
zeaxanthin
260
240
220
absorption coefficient
200
180
160
140
120
100
80
60
40
Chemical conversions
20
0
400
450
500
550
600
650
wavelength (nm)
140
zeaxanthin-violaxanthin
120
100
absorption difference
80
60
40
20
0
-20
-40
-60
400
450
500
550
wavelength (nm)
600
650
Conformational changes
SEPARATION OF
SUNLIT AND SHADOWED
LEAVES
To solve the overestimation of
canopy fluxes (CO2 and water
vapour) for tropical rainforests
and underestimation for the
boreal conifer forests
TIME SCALES TO BE RESOLVED
3-5
years
3 - 10
days
Not covered
FLEX PAYLOAD
For core objectives but also for
appropriate data analysis (cloud
screening, atmospheric correction,
adequate signal interpretation)
A core instrument:
Fraunhofer and Atmospheric Lines Imaging Spectrometer (FALIS),
measuring individual line parameters between 480 nm and 760 nm.
and two secondary, dual-view angle instruments, consisting of:
Multi-Angle Vegetation Imaging Spectrometer (MAVIS),
with a spectral coverage from 400 to 2400 nm
Surface TIR Spectrometer (STIRS), operating in the thermal
infrared, with three channels in the 8.8 to 12 µm spectral range.
10
mW m-2 sr-1 nm -1
GSFC / ARS-USDA
LURE
1
0.1
0.01
400
450
500
550
600
650
emission wavelength (nm)
700
750
800
Deliverables and products from the FLEX mission
Data Level
Type of Product
Level 1 B
Calibrated radiances at original spatial reference for each sensor
Level 1 C
Co-located radiances from all on-board sensors, systemcorrected data. Geometrical correspondence between data from
different sensors
Level 2 A
Fluorescence products from multi-wavelength measurements
Geophysical products derived independently from each on-board
sensor
Level 2 B
Geophysical products derived from integration of multi-sensor
data (FALIS, MAVIS, STIRS) for a given geometrical frame
along each orbit with cloud screening mask
Level 3 A
Final geophysical products at global scale (weekly and monthly
products) generated by temporal and spatial compositing of
Level 2 products
Level 3 B
Data assimilated into global dynamical vegetation and climate
models
Preliminary design in favour of the grating spectrometer
concept for FALIS. Alternatives still under consideration.
entrance slit spectrometer
0.2 x 68 mm.
Dichroic
Red filter (656 nm.)
Mirror
Mirror
Cyl. mirror f_|_=240 mm.
(40 x 160 mm.)
Dichroic
Mirror
Blue filter
(434 or 486 nm.)
Relay
objective
Cyl. mirror f // =480 mm.
(30 x 100 mm.)
Ell. aperture 12 x 20 mm.
prism
FOV 0.024 x 16°
filter
grating
Ø=65°
red
1350 lines/mm.
m=2: 656 nm.
m=3: 434 nm.
blue
filter
or:
900 lines/mm.
m=3: 656 nm.
m=4: 486 nm.
Collimating objective
Grating spectrometer concept lay-out
IMAGING
SPECTROMETER
CHRIS concept
MULTIANGULAR
IMAGER
- High spectral stalibility (0.1 nm)
across field of view
- Large field of view
microbolometer spectrometer
THERMAL
RADIOMETER
(STIRS)
MERIS
multi-camera concept
AIRFLEX
Airborne FLEX Simulator
Standard FLD method
I (λ)
R (λ) I (λ) + f (λ)
f FLD
a ⋅ d − c ⋅b
=
a −b
Actual reflectance:
RFLD =
c−d
a−b
radiance
Emitted fluorescence:
wavelength
Sensitivity Analysis
CF signal detectable under usual satellite observation configuration
Sensitivity Analysis
Elevation
Aerosols
Surface
Reflectance
Topographic effects
Water vapor
µs
DEM
µil
14/07/03
14/07/04
3/06/05
90 km
MERIS
Barrax
14/07/03
FEASIBILITY STUDIES
Based on MERIS O2 absorption band
Vegetation
Bare Soil
SEN2FLEX Campaign
Barrax 3/06/05
MERIS FR
300 m/pixel
RGB
Fluorescence
(760 nm)
CASI
Barrax
2/6/05
(288 Bands, 13 m/pixel)
MERIS Spectral
Calibration Campaign
15 narrow bands
(covering the O2-A
absorption feature)
PAR 400-700 nm
1
80
0.8
60
0.6
40
0.4
20
0.2
0
400
500
600
Wavelength (nm)
700
Chlorophyll−a absorption/emission
Filter transmitance %
100
0
800
Fiber Optic
Filter
Leaf Clip
Dark Background
SEN2FLEX
Fs Measurements
W
W
BS
F
BS
C
Ivy
(Hedera helix)
helix)
Cabbage
(Brassica oleracea)
oleracea)
Tobacco
(Nicotiana tabaccum)
tabaccum)
Information content in steady state fluorescence:
transition in spring and autumn
Soukupová et al. Functional Plant Biology , submitted
On-going activities activities:
“Atmospheric Corrections for Fluorescence Signal Retrieval”
“Impact assessment of solar induced vegetation fluorescence observations
from space for improving dynamic vegetation models”
“CarboEurope, FLEx and Sentinel-2 (CEFLES2) campaign”
“FLEX Performance Analysis and Requirements Consolidation Study”
Two parallel industrial studies
All activities coordinated through the MAG
CERES-FLEX Campaign
Simultaneous measurements of vegetation fluorescence,
photosynthesis and carbon fluxes at different spatial scales
together with all necessary auxiliary information
vegetation
fluorescence
Coupling of energy, water and carbon exchanges
Fluorescence
Quantum
yield
Physiological
fluorescence
model
Leaf
fluorescence
Leaf
fluorescence
model
Development of an Integrated
Vegetation Canopy Fluorescence Model
Canopy
fluorescence
model
Leaf
illumination
Light level
Stress &
environ.
parameters
Canopy
fluorescence
pigments
content,
Leaf
structure,…
Incident light
LAI(z),
Leaf
orientation,…
Future end-to-end mission simulator
C3 leaf
C4 leaf
EcoFluormod – SIF assimilation in ecosystem C models
representing the link between SIF and photosynthesis
Porcar-Castell et al 2006
Magnani et al. in preparation
Agati et al. 1998
Louis et al. 2005
van der Tol et al., 2007
Q = fraction of absorbed PAR (Q)
P = photochemistry (photosynthesis)
F = chlorophyll fluorescence
D = heat dissipation
Ci = internal CO2 concentration
MODELLING ACTIVITIES:
Linking fluorescence emission
to photosynthesis
Photosynthesis and Conductance
Linkage of photosynthesis, stomatal function, transpiration
Stomatal conductance related to photosynthesis:
humidity deficit
at leaf surface
photosynthesis
gs = g0 + m
An
(Cs - Γ)[1 + Ds/D0]
stomatal
conductance
CO2 at leaf surface
many key photosynthesis
parameters can be
related to observables
derived from
spectral reflectance
Photosynthesis is controlled by three limitations
(The Farquhar-Berry model):
An = min [AC, AL, AS ] - Rd
Enzyme kinetics
(“rubisco”)
Light
Starch
max
Vc
max
, J
GPP =
εg × fPARcanopy × PAR
Light Use Efficiency (g C / mol PAR)
fPARcanopy = F(LAI) = F(NDVI)
εg = ε0 (constant)
Classical approach
Too empirical !
or f(Air Temp, Soil Moist., Water vapour
pressure deficit, Leaf Water content, etc.)
ΦP = 1 -
α ΦP σ
kF + kL
ΦF
kF
From empirical to
quantitative
formulations
Signal-to-Noise Ratio
Required SNR calculated from simulated TOA
radiance L assuming a given uncertainty in Fs:
2 L( Fs , λ )
SNR ( Fs , λ ) =
L ( Fs + δFs , λ ) − L( Fs − δFs , λ )
0.06
0.4
0.3
0.04
0.2
0.02
0.1
0
760
761.5
wavelength (nm)
9
0.12
6
0.09
0.06
3
0.03
0.00
763
Reference spectrum
0.5
0.15
Fluorescence and
Reflectance
0.6
0.08
0
758.5
Hibiscus (front)
0.7
L eaf radiance (a.u.)
0
685
687
O2-A
689
691
693
O2-B
nm
Hibiscus (back-side)
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
653
0.14
0.12
0.1
0.08
0.06
0.04
0.02
654
655
656 nm657
658
659
Ra tio a nd L ea f spectrum
New methods are being
developed to exploit the full
spectral information:
more stable and robust
retrievals than those
based on discrete channels
ratios
Reference spectrum
Fluorecence (a.u.)
0.1
0
660
Hα
α
CONCLUDING REMARKS
- Plant photosynthesis is a key component of the global
carbon cycle, and global vegetation monitoring continues
being a key issue in global Earth Observation. A remaining
topic to be covered is the measurement of the actual
(not just potential) photosynthetic function.
- Recent scientific and technological advances make now
possible to derive maps of vegetation photosynthesis
at global scale to constraint models linking
surface/atmosphere processes (CO2 assimilation)
- The FLEX mission in now in Pre-Phase A development,
with several on-going activities to consolidate the mission
concept, involving a large science community
FLEX – Mission Fact Sheet
Primary Objective:
To quantify the photosynthetic efficiency of terrestrial ecosystems at global scale
Contribution:
To the improvement of the understanding of the role of vegetation in the water cycle, and
To globally monitor vegetation stress conditions
Scientific Requirements:
Global observation of solar induced vegetation fluorescence.
Technical concept:
Duration:
3-5 seasonal cycles
Revisit/Obs Time: 7days / 10:00 LTDN
Spatial Res:
100-300 m
Spectral Coverage: O2-A: 750-770 nm, O2-B: 677-697 nm
Ha : 646-667 nm, Hb : 476-496 nm
VNIR: 450-1000 nm
SWIR: dedicated bands
TIR: at least two bands for LST
Optional:
50 deg off-nadir (1km spatial resolution)
aerosol instrument