3rd ESA CHRIS PROBA WorkshopEsrin, 21-23 March 2005Frascati, Italy
Estimation of vegetation photochemical processes from CHRIS-PROBA data
An application of the Photochemical Reflectance Index at the San Rossore test site
Raddi Sabrina, University of Florence, ITALY
Cortes Solange, University of Basilicata, Potenza, ITALY
Pippi Ivan, CNR-IFAC, Firenze, ITALY
Magnani Federico, University of Bologna, ITALY
3rd ESA CHRIS PROBA WorkshopEsrin, 21-23 March 2005Frascati, Italy
Estimation of vegetation photochemical processes from CHRIS-PROBA data
An application of the Photochemical Reflectance Index at the San Rossore test site
Raddi Sabrina, University of Florence, ITALY
Cortes Solange, University of Basilicata, Potenza, ITALY
Pippi Ivan, CNR-IFAC, Firenze, ITALY
Magnani Federico, University of Bologna, ITALY
PAR Incident light (PAR = photosynthetically active radiation)
APAR Absorbed light (APAR = absorbed PAR)
GPP Gross Primary Production (GPP)
NPP Net Primary Production (NPP)
NEP Net Ecosystem Exchange (NEE)
Fractional inter-cepted PAR,
canopy closure(LAI)
Photosynthesis,light use efficiency (ε)
Plant respiration
Heterotrophic respiration
Estimation of vegetation photochemical processesmoving beyond LAI
3rd ESA CHRIS PROBA WorkshopEsrin, 21-23 March 2005
Although RS has
traditionally focused on the
first step (light interception),
photosynthetic light-use
efficiency cannot be assumed to be constant, but changes with species
and environmental
conditions.
from Demmig-Adams e Adams (2000)
Harvesting sunlight safelyphotochemistry, photoprotection and photodamage
Chl chlorophyll1Chl* excited singlet chlorophyll3Chl* excited triplet chlorophyllP photochemistry (green)D safe dissipation of
excess excitation energy as heat
F fluorescence;3T triplet pathway, leading to
the formation of singlet oxygen (1O2 *) and photo-oxidative damage
Fates of sunlight absorbed in the light-harvesting chlorophyll complexes:
3rd ESA CHRIS PROBA WorkshopEsrin, 21-23 March 2005
Harvesting sunlight safelymechanisms of excess light dissipation
from Horton et al. (1994)
Changes in PSII LHC associated with energy dissipation
Change from low light (top) to high light (bottom) results in increased proton concentration (red arrows) in the thylakoid lumen.
Protonation of the carboxyl residues on the minor LHCII (blue/green) and de-epoxidation of violaxanthin (yellow) to zeaxanthin (red) results.
Quenching, an increase in non-radiative dissipation of energy (shown as a decrease in brightness of the LHCII), is associated with a change in organization of LHCII (conformational change) and results from increased proximity of either Chls or xanthophyll and Chl.
3rd ESA CHRIS PROBA WorkshopEsrin, 21-23 March 2005
The xanthophyll cyclereversible de-epoxidation driven by ∆pH
Diurnal cycle of epoxidation state
A summary model for non-photochemical quenching (NPQ ; from Müller et al. 2001, modified).
Physiological changes in leaf spectroscopydeterminants of observed changes: role of ∆pH and xanthophyll EPS
A, in limiting light or darkness, no quenching occurs (black bar above). B, in high light (white bar) protons bind to the PSII protein PsbS and LHC. C, a quenching complex with different conformation, measurable as ∆R531 and PRI, is formed when zeaxanthin and protons are bound. Conversion of violaxanthin to zeaxanthin occurs more slowly than protonation. D, when the light stress has ended, the PSII proteins are de-protonated readily, whereas the epoxidation of zeaxanthin to violaxanthin is slower, reflecting in the dynamics of the ∆R525 signal.
The Photochemical Reflectance Index (PRI)a normalized index of xanthophyll de-epoxidation state and leaf ε
Penuelas et al., 1995 Gamon et al., 1997
However, the applicability of the index under drought conditions has been questioned
3rd ESA CHRIS PROBA WorkshopEsrin, 21-23 March 2005
570531
570531
RRRR
PRI+−
=
Detailed physiological studies led in 1992 to the development of a RS index, the Photochemical Reflectance Index (PRI):
Several studies have confirmed the correlation between PRI and light-use efficiency.
The Physiological Reflectance Index (PRI)correlation with light-use efficiency at the canopy level
narrow-band index broad-band index (10 nm)
PRI correlation with LUE at the canopy levelsensitivity analysis using the FLIGHT radiative transfer model
Simulation studies have
demonstrated that the correlation is
robust with respect to canopy
characteristics
PRI correlation with LUE at the canopy levelsensitivity analysis using the FLIGHT radiative transfer model
Potential
relevance of multi-
angular observations from
CHRIS-PROBA
Simulation studies have
demonstrated the sensitivity of the
index to solar geometry and viewing angle.
Remote sensing of canopy gas-exchange through PRIapplicability of the CHRIS sensor for PRI determination
3rd ESA CHRIS PROBA Workshop
Esrin, 21-23 March 2005
CHRIS band position and
width make it particularly
suitable for the
measurement of
vegetation PRI
Estimation of vegetation photochemical processesobjectives of the study
1. test the ability of the Photochemical Reflectance
Index to track differences in photochemical efficiency
across species and over the season under
Mediterranean conditions:
2. apply the index to the monitoring of light-use
efficiency from CHRIS-PROBA images at the San
Rossore core site
• seasonal changes at the Pinus pinaster eddy-covariance
tower at the San Rossore core site (43°43’N, 10°20’E Italy,
JRC-IES contract)
• seasonal changes in a large-scale artificial drought
experiment (LASMEX site, EU-MIND project)
• species comparison under laboratory conditions
• species comparison in the field at the San Rossore test site
3rd ESA CHRIS PROBA Workshop
Esrin, 21-23 March 2005
Test of the Photochemical Reflectance Indexseasonal changes in a Pinus pinaster canopy at the San Rossore site
Test of the Photochemical Reflectance Indexseasonal changes in a Pinus pinaster canopy at the San Rossore site
Test of the Photochemical Reflectance Indexseasonal changes in a Pinus pinaster canopy at the San Rossore site
Test of the Photochemical Reflectance Indexseasonal changes in a Pinus pinaster canopy at the San Rossore site
San Rossore CHRIS Proba Campaigns08 september 2004
Image CHRIS_SR_040908_45BA_31_L3R_v1 Nadir view
RGB band 4,8,14; (552nm, 675nm, 782nm) RGB band 1,4,8; (442nm, 552nm, 675nm)
15 ground truth sampling areas
3rd ESA CHRIS PROBA Workshop
Esrin, 21-23 March 2005
San Rossore CHRIS-PROBA campaignsspecies comparison in the field
Herbs and shrubsPhragmites australis (1)Rubus fruticosus (1)Silybum marianum (1)Medicago sativa (2)Graminacee (1)
ConifersPinus pinaster (1)Pinus pinea (3)
Deciduos broadleavesPopulus euroamericana (1)Fraxinus angustifolia (2)Alnus glutinosa (1)
Evergreen broadleavesQuercus i lex (1)
3rd ESA CHRIS PROBA Workshop
Esrin, 21-23 March 2005
Test of the Photochemical Reflectance Indexcorrelation with light-use efficiency and NPQ across time and species
3rd ESA CHRIS PROBA Workshop
Esrin, 21-23 March 2005
The good correlation of PRI and leaf non-photochemical quenching (NPQ, a measure of excess
energy dissipation), as well as light-use efficiency (estimated from modulated fluorescence as
∆F/F’m), has been confirmed across species and in response to a wide range of stress
conditions (drought, cold stress).
Test of the Photochemical Reflectance Indexcorrelation with light-use efficiency, functional basis
photodamage
3rd ESA CHRIS PROBA Workshop
Esrin, 21-23 March 2005
The correlation between PRI
and ∆F/F’m is the result of the
functional link of both
parameters with leaf non-
photochemical quenching
(NPQ).
Under extreme drought
conditions, ∆F/F’m is known to
decline even in the absence of
any NPQ, because of long-
lasting photodamage.
This could explain the lack of
correlation with PRI under
drought reported in the
literature.
San Rossore CHRIS-PROBA campaignsevaluation of scene PRI and comparison with ground truth
The preliminary analysis of one
CHRIS image (8 September 2004,
nadir view, MZA ~ -12 deg)
demonstrates the possibility of PRI
measurement from space.
Despite the noise of such a small
signal, differences among and within
vegetation types are clearly visible
(compare with NIR false color
image).
A comparison with
concurrent ground
measurements at the leaf
level demonstrates a general
agreement, despite the
different spectral resolution
(8.6 vs 0.3 nm).
NDVIPRI
PRI
ND
VI
0.0
7
0.2
8
0
.50
0.7
1
0.9
2-0.09 -0.02 0.05 0.12 0.19
PRI
San Rossore CHRIS-PROBA campaignscomparison with complementary vegetation indexes
3rd ESA CHRIS PROBA Workshop
Esrin, 21-23 March 2005
The coherence of the PRI signal is also
demonstrated by a comparison with
other vegetation indexes, such as NDVI.
LAI (and hence NDVI) is known to be
generally correlated with fertility and
light-use efficiency, and this could
explain the relationship with PRI.
There is however a considerable scatter
in the relationship, making PRI not
redundant.
15 ground
truth areas
whole scene
Conclusionsestimation of vegetation photochemical processes from CHRIS data
3rd ESA CHRIS PROBA Workshop
Esrin, 21-23 March 2005
RS has so far focused on the determination of light absorption, but
photosynthetic light-use efficiency cannot be assumed to be constant
The Photochemical Reflectance Index (PRI) has been proposed for the
estimation of light-use efficiency. The index is based on a strong body of
experimental studies at the leaf level
Detailed studies have demonstrated the validity and generality of the
relationship across species and conditions, in the absence of extreme stress
and photodamage (which is unusual under field conditions)
CHRIS appears particularly suitable for the determination of vegetation PRI
from space, because of spectral characteristics and viewing geometry
A preliminary analysis has demonstrated the possibility of PRI measurements
from space. Although small, the signal is coherent and (partly) correlated to
other vegetation indexes
Future developmentsestimation of vegetation photochemical processes from CHRIS data
3rd ESA CHRIS PROBA Workshop
Esrin, 21-23 March 2005
Analysis of multi-temporal series of CHRIS images (nadir view, hemispherical
reflectance in collaboration with CTCD) for 2003-4, correlation with ground
measurements at the leaf (photosynthesis, reflectance) and canopy level
(GPP from eddy-covariance)
3-year extension of ground truth measurements at the San Rossore site
through the Carbo-Italy project
Development of automated spectrometer for continuous VIS-NIR
measurements from above the canopy
Request for 12 CHRIS images over 2005 (mode 3)
Analysis of eddy-covariance data through inversion of HYDRALL ecosystem
model, estimation of light-use efficiency and photosynthetic potentials,
correlation with PRI