estimation of vegetation photochemical processes from...

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:


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.


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


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



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



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)



Test of the Photochemical Reflectance Indexcorrelation with light-use efficiency and NPQ across time and species



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



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



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



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



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

estimation of vegetation photochemical processes from...

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