Uncertainties of global moderate Uncertainties of global moderate resolution Leaf Area Index (LAI) resolution Leaf Area Index (LAI)

products derived from satellite dataproducts derived from satellite data

Hongliang FangHongliang Fangaa, Shanshan Wei, Shanshan Weia,ba,b, Shunlin Liang, Shunlin Liangcc

aaLREIS, Institute of Geographic Sciences and Natural Resources LREIS, Institute of Geographic Sciences and Natural Resources Research,Research,

Chinese Academy of Sciences, Beijing, 100101, China.Chinese Academy of Sciences, Beijing, 100101, China. bbDepartment of Geography, School of Urban and Environmental Department of Geography, School of Urban and Environmental

Sciences, Northeast Normal University, Changchun, Jilin Province, Sciences, Northeast Normal University, Changchun, Jilin Province, 130024, China. 130024, China.

ccDepartment of Geography, University of Maryland, College Park, Department of Geography, University of Maryland, College Park, Maryland, 20742, USA. Maryland, 20742, USA.

IGARSS’01, Vancouver, Canada, Jul 24-27, 2011IGARSS’01, Vancouver, Canada, Jul 24-27, 2011

OutlineOutline

I.I. IntroductionIntroduction

II.II. Validation methodValidation method

III.III. ResultsResults

IV.IV. ConclusionsConclusions

BackgroundBackground

Leaf Area Index (LAI): the one-sided green leaf Leaf Area Index (LAI): the one-sided green leaf area per unit of ground area in broadleaf area per unit of ground area in broadleaf canopies and the projected needle leaf area in canopies and the projected needle leaf area in coniferous canopies coniferous canopies (Myneni et al., 2002; Chen and Cihlar, 1996)(Myneni et al., 2002; Chen and Cihlar, 1996)

An Essential Climate Variable (ECV) necessary An Essential Climate Variable (ECV) necessary fo many process modelsfo many process models

Observational requirement by the Global Observational requirement by the Global Climate Observation System (GCOS): Climate Observation System (GCOS): ±0.5±0.5 (GCOS, (GCOS, 2006)2006)

Project EOSCYCLOPES

GLOBCARBON

ECOCLIMAP

POLDER

Spatial1km, 4km, 0.25°

1/112D1km, 10km, 0.25D,0.5D

30” to 1D 1/9°(monthly)

Temporal

8-day 10-day Monthly Monthly10-day (L3) and monthly (HDF)

Time1999-present

1999-2007

1998-2007 [Sep 2006]

1996.11.5-1997.6.25; 2003.4.5-2003.10.25

InputRED, NIR

SZA, TOC ref in RED, NIR, & SWIR

VGT, ATSR, (MERIS) ref.

AVHRR NDVI

11 directional reflectance in G, R, NIR bands and angular config.

Alg.LUT (3D model)+VI

NN (PROSPECT+SAIL+5 TYPICAL SOIL)

SR method for forest and non-forest based on model

Linear regression of literature LAI and NDVI

NN (MCRM: PROSPECT+SAIL+PRICE/WALTHALL)

Ref.

Knyazikhin, 1998. JGR

Baret, 2007. RSE

Deng, 2006. TGRS

Masson, 2003. JOC

Lacaze, 2005. User Manual

Four stages of validation defined by the Committee on Four stages of validation defined by the Committee on

Earth Observation Satellites (CEOS)Earth Observation Satellites (CEOS) Stage Explanation Scale Support studies

1 Validation in a small number of selected locations, time periods and validation efforts

Local-regional

Fang and Liang (2005), Cohen et al. (2006), Hill et al. (2006), Pisek and Chen (2007), Sprintsin et al. (2009)

2 Validation over a widely distributed set of locations, and validation efforts;

Regional-continental

Verger et al. (2011; 2009), Luo et al. (2004)

3 Product accuracy assessed systematically and globally. Product uncertainties well established.

Global Weiss et al. (2007)Garrigues et al. (2008)Aim of our study

4 Validation results systematically updated with new releases and new data.

Systematic and global

Adapted From LPV/WGCV/CEOS (http://lpvs.gsfc.nasa.gov/)

ObjectivesObjectives

To extend the Stage 3 validation for both MODIS and To extend the Stage 3 validation for both MODIS and

CYCLOPES LAI products with a global field measurement CYCLOPES LAI products with a global field measurement

database.database.

To investigate whether the current global LAI products could To investigate whether the current global LAI products could

meet the observational requirements proposed by GCOS. meet the observational requirements proposed by GCOS. • MODIS suite: Terra C4 (MOD15 C4), Terra C5 (MOD15 C5) and MODIS suite: Terra C4 (MOD15 C4), Terra C5 (MOD15 C5) and

Terra+Aqua C5 (MCD15 C5) Terra+Aqua C5 (MCD15 C5)

• SPOT/VEGETATION CYCLOPES V3.1 SPOT/VEGETATION CYCLOPES V3.1

• Consideration of the MODIS quality control (QC) layer and the CYCLOPES Consideration of the MODIS quality control (QC) layer and the CYCLOPES

status mask (SM)status mask (SM)

OutlineOutline

I.I. IntroductionIntroduction

II.II. Validation methodValidation method

III.III. ResultsResults

IV.IV. ConclusionsConclusions

Validation schemes Validation schemes

1.1. Direct comparisonDirect comparison with with in situin situ data data collected over validation sites (collected over validation sites (this this studystudy); );

2.2. Bridging methodBridging method: comparison with : comparison with products derived from high resolution products derived from high resolution airborne or spaceborne sensors (e.g., airborne or spaceborne sensors (e.g., Landsat TM/ETM+); Landsat TM/ETM+);

3.3. Cross-validationCross-validation with other independently with other independently obtained products; obtained products;

4.4. IntercomparisonIntercomparison and analysis with and analysis with process model simulations. process model simulations.

((http://lpvs.gsfc.nasa.gov/; Morisette et al, 2006; Justice et al., 2002) et al, 2006; Justice et al., 2002)

Direct field measurementDirect field measurement

Destructive sampling or collection of Destructive sampling or collection of total leaf litterfall. total leaf litterfall.

Calculation through the specific leaf area Calculation through the specific leaf area ((SLA: square centimeters of fresh leaf area per SLA: square centimeters of fresh leaf area per gram of dry foliage massgram of dry foliage mass) in the laboratory. ) in the laboratory. Multiplication of the SLA and total dry Multiplication of the SLA and total dry mass of each foliage age class to mass of each foliage age class to calculate the LAI. calculate the LAI.

Allometric method, based on the Allometric method, based on the relationship between leaf area and the relationship between leaf area and the diameter at breast height (DBH).diameter at breast height (DBH).

Indirect field measurementIndirect field measurement

Indirect contact methods, e.g, the Indirect contact methods, e.g, the point quadrats method. point quadrats method.

LAI 2000 and hemispherical LAI 2000 and hemispherical photography with no clumping photography with no clumping correction (Effective LAI).correction (Effective LAI).

LAI 2000, TRAC and hemispherical LAI 2000, TRAC and hemispherical photography with clumping photography with clumping correction (True LAI).correction (True LAI).

Direct validation campaignsDirect validation campaigns

BigFoot (Cohen & Justice, 1999)BigFoot (Cohen & Justice, 1999) CCRS (Fernandes et al., 2003)CCRS (Fernandes et al., 2003) MODLAND (Morisette et al., 2002)MODLAND (Morisette et al., 2002) VALERI (Baret et al., 2006)VALERI (Baret et al., 2006) CEOS LPV (Morisette et al., 2006)CEOS LPV (Morisette et al., 2006)

Share ground LAI data and maps Share ground LAI data and maps among the entire communityamong the entire community

Global field LAI measurement sitesGlobal field LAI measurement sites from from campaigns and literaturecampaigns and literature

219 observations over 129 sites

Fang et al., to be submitted.

MODIS and CYCLOPES quality indicatorsMODIS and CYCLOPES quality indicators DN range Binary, Quality description

MODIS QC (DN range) and SCF_QC (binary, decimal values)

QC<32 000=0 Main (RT) method with the best possible results

32QC<64 001=1 Main (RT) method with saturation

64QC<96 010=2 Empirical method used (Main method failed due to geometry problems)

96QC<128 011=3 Empirical method used (Main method failed due to problems other than geometry)

128QC<255 100=4 Couldn't retrieve pixel

CYCLOPES SM SM<16 Bit 1 Land 0 / sea 1

Bit 2 Snow status: no 0 / snow 1

Bit 3 Cloud/shadow: no 0 / suspected 1

Bit 4 Aerosol status: pure 0 / mixed 1

Bit 5 Aerosol source: MODIS 0 / climatology 1

Bit 6 Parameter validity: ok 0 / no 1

Bit 7 B0 (blue) saturation: ok 0 / no 1

Bit 8 B2 (red) saturation: ok 0 / no 1

Bit 9 B3 (NIR) saturation: ok 0 / no 1

OutlineOutline

I.I. IntroductionIntroduction

II.II. Validation methodValidation method

III.III. ResultsResults

IV.IV. ConclusionsConclusions

Statistics of field measured LAIStatistics of field measured LAI

Biome type True Effective Overall

n Mean (SD) n Mean (SD) n Mean (SD)

1. Grasses and cereal crops

39 1.63 (1.09) 39 1.63 (1.09)

2. Shrubs 17 0.50 (0.58) 8 1.08 (0.79) 25 0.68 (0.70)

3. Broadleaf crops 4 2.36 (1.11) 4 2.36 (1.11)

4. Savanna 39 0.83 (0.84) 3 3.08 (2.53) 42 0.99 (1.14)

5. Broadleaf forest 31 3.31 (1.61) 20 3.64 (1.74) 51 3.44 (1.65)

6. Needleleaf forest 10 3.65 (1.88) 46 1.87 (1.10) 56 2.19 (1.43)

Overall 140 1.81 (1.61) 77 2.30 (1.57) 217 1.98 (1.61)

Fang et al., to be submitted.

MODIS/Terra C4(QC<128) Main: 85.8% R2=0.435RMSE=1.42

MODIS/Terra C5(QC<128)

Main: 92.5%R2=0.307

RMSE=1.53

MODIS/Terra+Aqua C5(QC<128)Main: 97.6%R2=0.526RMSE=1.09

VGT/CYCLYPES V3.1(LAI<6.0)R2=0.557

RMSE=0.97

Field true LAI

MODIS/Terra C4(QC<128) R2=0.234RMSE=2.08

MODIS/Terra C5(QC<128) R2=0.290

RMSE=1.74

MODIS/Terra+Aqua C5(QC<128) R2=0.186RMSE=1.63

VGT/CYCLYPES V3.1(LAI<6.0)R2=0.399

RMSE=1.34

Field effective LAI

Comparison of MODIS and CYCLOPES LAI with field LAI

Herbaceous Woody All biomes

n R2 RMSE n R2 RMSE n R2 RMSE

MOD15 C4 55 0.137 1.29 79 0.481 1.50 134 0.436 1.42

QC<64 52 (94.5%

)

0.061 1.25 63 (79.7%

)

0.718 1.13 115(85.8%

)

0.559 1.19

MOD15 C5 54 0.171 1.18 52 0.140 1.82 106 0.307 1.53

QC<64 52 (96.3%

)

0.221 1.09 46 (88.5%

)

0.382 1.27 98 (92.5%

)

0.465 1.17

MCD15 C5 24 0.042 1.16 59 0.593 1.06 83 0.526 1.09

QC<64 24 0.042 1.16 57 (96.6%

)

0.599 1.05 81 (97.6%

)

0.528 1.09

CYCLOPES(true)

53 0.449 0.87 58 0.629 1.05 111 0.557 0.97

CYCLOPES(effective)

7 0.005 0.82 56 0.348 1.39 63 0.399 1.34

Herbaceous Woody All biomes

n R2 RMSE n R2 RMSE n R2 RMSE

MOD15 C4 23 0.087 0.914 25 0.513 1.249 48 0.534 1.101MOD15 C5 46 0.270 0.994 32 0.509 1.012 78 0.478 1.001MCD15 C5 12 0.083 1.053 21 0.674 0.797 33 0.542 0.898CYCLOPES(True)

39 0.508 0.84 37 0.655 1.12 76 0.557 0.99

CYCLOPES(Effective ）

1 — 1.00 19 0.004 1.774 20 0.043 1.74

Comparison of best MODIS (QC=0) and CYCLOPES (SM=0) with field LAI

MOD15 C5 (QC<64)MCD15 C5 (QC<64)SPOT/VGT CYCLOPES2000.1-2005.12

Global Monthly AverageGlobal Monthly Average MODIS, MODIS, CYCLOPES and GLOBCARBON LAICYCLOPES and GLOBCARBON LAI

OutlineOutline

I.I. IntroductionIntroduction

II.II. Validation methodValidation method

III.III. ResultsResults

IV.IV. ConclusionsConclusions

ConclusionsConclusions MODIS LAI has MODIS LAI has improvedimproved consistently over all consistently over all

releases MOD15 C4releases MOD15 C4↗↗MOD15 C5MOD15 C5↗↗MCD15 C5. RMSE MCD15 C5. RMSE decreased by decreased by ~0.1~0.1 for each new release. for each new release.

MODIS C5 retrieved with the main algorithm MODIS C5 retrieved with the main algorithm (QC<64) and CYCLOPES showed similar range of (QC<64) and CYCLOPES showed similar range of uncertainties (uncertainties (1.0~1.21.0~1.2). ).

Uncertainties for the best MODIS C5 (QC=0) and Uncertainties for the best MODIS C5 (QC=0) and CYCLOPES (SM=0) were around CYCLOPES (SM=0) were around 0.9-1.00.9-1.0..

The overall mean differences between the best The overall mean differences between the best MODIS C5 and CYCLOPES were within MODIS C5 and CYCLOPES were within 0.100.10. .

The uncertainties of current LAI products (within The uncertainties of current LAI products (within 1.0) are still 1.0) are still unableunable to meet the accuracy to meet the accuracy requirement by GCOS (requirement by GCOS (0.5). 0.5).

Future workFuture work

Broadleaf crops, broadleaf treesBroadleaf crops, broadleaf trees Complex background/understoryComplex background/understory Low LAI (<1.0) regions: arid and Low LAI (<1.0) regions: arid and

semi-arid, tundra, permafrostsemi-arid, tundra, permafrost Beginning and ending periods of Beginning and ending periods of

growing season growing season Points other than NA and Europe Points other than NA and Europe

Seeking collaboration

Thank you!Thank you!

Questions, comments?Questions, comments?

Hongliang Fang (Hongliang Fang ( 方红亮）方红亮）Institute of Geographical Sciences and Natural Resources Institute of Geographical Sciences and Natural Resources

Research (IGSNRR), Chinese Academy of Sciences (CAS)Research (IGSNRR), Chinese Academy of Sciences (CAS)Email: fanghl@lreis.ac.cnEmail: fanghl@lreis.ac.cn

MODIS LAIMODIS LAI

3D Radiative Transfer model (Myneni 1997)3D Radiative Transfer model (Myneni 1997)• Parameterization for each of 6 biomesParameterization for each of 6 biomes• 25 modeled soil reflectances (Jacquemoud 1992)25 modeled soil reflectances (Jacquemoud 1992)

Retrieval with Look-up Table methodRetrieval with Look-up Table method• From MODIS B1 (Red) and B2 (NIR) From MODIS B1 (Red) and B2 (NIR)

Backup algorithm based on empirical NDVI-Backup algorithm based on empirical NDVI-LAI relationship for each biomeLAI relationship for each biome

True LAITrue LAI

http://wist.echo.nasa.govhttp://wist.echo.nasa.gov

CYCLOPESCYCLOPES

SPOT/VGT bi-directional normalization SPOT/VGT bi-directional normalization SAIL + PROSPECT + empirical soil SAIL + PROSPECT + empirical soil

description description Neural network Neural network

• Nadir normalized reflectance B2 (Red), B3 Nadir normalized reflectance B2 (Red), B3 (NIR), MIR (NIR), MIR

• SZA 10:00 local time SZA 10:00 local time • Daily fAPAR Daily fAPAR

Effective LAIEffective LAI

http://postel.mediasfrance.org

GLOBCARBONGLOBCARBON

SPOT/VGT, ERS/ATSR, (ENDVISAT/MERIS)SPOT/VGT, ERS/ATSR, (ENDVISAT/MERIS) 2 algorithms to retrieve LAIe: 2 algorithms to retrieve LAIe:

• LAIe = f(RSR, fBRDF) for forest classes LAIe = f(RSR, fBRDF) for forest classes • LAIe = f(SR, fBRDF) for other vegetation LAIe = f(SR, fBRDF) for other vegetation

fBRDF from modified Roujean model fBRDF from modified Roujean model Empirical clumping indexEmpirical clumping index True LAI True LAI

http://geofront.vgt.vito.be/geosuccess/relay.do?dispatch=LAI_infohttp://geofront.vgt.vito.be/geosuccess/relay.do?dispatch=LAI_info

ClumpingClumping

MODIS: canopy clumping parameters for MODIS: canopy clumping parameters for each biomeeach biome

CYCLOPES: account for clumping at the CYCLOPES: account for clumping at the landscape scale, each pixel was supposed landscape scale, each pixel was supposed to be made of a fraction to be made of a fraction vCovervCover of pure of pure vegetation and (1-vegetation and (1-vCovervCover) of pure bare ) of pure bare soil. (SAIL does not describe clumping at soil. (SAIL does not describe clumping at canopy level) canopy level)

ECOCLIMAP LAI: (not obvious)ECOCLIMAP LAI: (not obvious)

Rice paddy with waterRice paddy with water

http://spl.bnu.edu.cn

Mature crop with yellow leavesMature crop with yellow leaves

Big reflectance changes but small LAI variation; photosynthesis?http://spl.bnu.edu.cn

Gray/dead leavesGray/dead leaves

http://spl.bnu.edu.cn

Snow backgroundSnow background

Comparison of MODIS (QC<64) and CYCLOPES LAI with common field observations for 6 biome types

BELMANIPBELMANIP

Global Partnership and a benchmark for Global Partnership and a benchmark for indirect validation (Baret et al., 2006)indirect validation (Baret et al., 2006)

Use of additional networksUse of additional networks• FLUXNET, AERONETFLUXNET, AERONET

Eliminating replicates and sites with water Eliminating replicates and sites with water >25% @ 8>25% @ 88 km²8 km²

Adding sites to improve Adding sites to improve representativenessrepresentativeness• Surface typesSurface types• Latitudinal distributionLatitudinal distribution• Longitudinal distributionLongitudinal distribution

http://lpvs.gsfc.nasa.gov/lai_intercomp.php

BELMANIPBELMANIP

D

D

D DDD D

D

D

D

D D

D

D

DD

D

D

DDD

D

D

D

D D

D

DD

D

D

DD

D

D

DD

D

D

DD

D

D DDDD

D

D

D

DD

D

D

DDD

D

D

DD

D

D

DD DD D DD

DDD

DD D

DDD DD D

D

D

D

D

DD

D

DD

DD

D

FFF

F

FF

F

FF

F

FFFF

F F

F

FFFF

FFF FFF

F FFFFFF

FFF

F

F

F

FF

FF

FF

FF

F

F

F

FFFFFF

FF

FFF

F

FFFFFFFFF

FFFFF

F

F

F

FFF

FFFFFF FF

FFF

F FFFFFF

F

FFF

F

FF

FFF F

F

FFF

F

F

FF

FFF

FFFFFF

FF

FFFFF

F FF F

FF

FFF FFFFFF

FF

F

FF FF F

F F

F

FF FF

FFF

AA

A

A

A

A

A

A

AA

AA

AAA

AA

A

A

A

A

A

A

A

AA

A

A

A

A

A

AA

A A

A

AA

CC C

CC C

C

C

C C CC

C

C C

CC

CCCC

CC

CC C C

C

C

CC C

C

C

CCCC

C

C

CC

C CC C

CC

C C

CCC

CC C

C CCC

C

C C

C

C

C

C

CC

C

C

C

C

C

C

C

-180 -150 -120 -90 -60 -30 0 30 60 90 120 150

90

60

30

0

-30

-60

100 DIRECT + 218 FLUXNET + 58 AERONET + 78 COMPLET= 377 BELMANIP

Baret et al., EGU, 2005