Bridging the Gap in Scales between Flux Towers, Ecosystem Models and Remote Sensing

R.J. Olson1, R.B. Cook1, L.M. Olsen1, T. A. Boden1, J.T. Morisette2, and S.W. Running3

1Oak Ridge National Laboratory, Environmental Sciences Division, Oak Ridge, TN 37831-6038 United States*2Goddard Space Flight Center, NASA, Code 923, Greenbelt, MD 20771 United States

3University of Montana, School of Forestry, Missoula, MT 59812 United States

Abstract Combining ground-based studies, ecosystem models, and remote sensing data provides a broad basis for understanding the dynamics of ecosystem-atmosphere CO2 exchange. Data from a global network of flux tower sites (FLUXNET) are being compared to ecosystem model outputs and to remote sensing products, such as the photosynthesis product derived from the MODIS sensor on the Terra satellite. Comparison of information from multiple types of local and regional studies is needed prior to extrapolating site studies to larger-scale products derived from remote sensing or global-scale modeling.

This poster describes data being compiled by the ORNL DAAC to conduct the local and regional scale validation of remote sensing products. The FLUXNET database contains carbon, water vapor, sensible heat, momentum, and radiation flux measurements with associated ancillary and value-added data products for a wide range of ecosystems on five continents. The MODIS land products are 1-km resolution data in the immediate vicinity of the flux tower. Modeling groups are using the data to run terrestrial biosphere models for 17 flux tower sites to compare model outputs, flux measurements, field measurements, and MODIS products. AmeriFlux, the network of flux towers in the Americas, provides model initialization and driver data for this exercise.

Abstract Combining ground-based studies, ecosystem models, and remote sensing data provides a broad basis for understanding the dynamics of ecosystem-atmosphere CO2 exchange. Data from a global network of flux tower sites (FLUXNET) are being compared to ecosystem model outputs and to remote sensing products, such as the photosynthesis product derived from the MODIS sensor on the Terra satellite. Comparison of information from multiple types of local and regional studies is needed prior to extrapolating site studies to larger-scale products derived from remote sensing or global-scale modeling.

This poster describes data being compiled by the ORNL DAAC to conduct the local and regional scale validation of remote sensing products. The FLUXNET database contains carbon, water vapor, sensible heat, momentum, and radiation flux measurements with associated ancillary and value-added data products for a wide range of ecosystems on five continents. The MODIS land products are 1-km resolution data in the immediate vicinity of the flux tower. Modeling groups are using the data to run terrestrial biosphere models for 17 flux tower sites to compare model outputs, flux measurements, field measurements, and MODIS products. AmeriFlux, the network of flux towers in the Americas, provides model initialization and driver data for this exercise.

Data for a typical site - Walker Branch Watershed (WBW), Oak Ridge, TN

Photo of tower located at Walker BranchWatershed. Vegetation consists of mixedspecies of broad-leaved deciduous forest. IKONOS Image of

Walker Branch Watershed.

MOD09A1 - Surface Reflectance

ISIN or UTM? To reproject or not to reproject…?

Flux Tower location

ISIN

MOD12Q1- Quarterly Land Cover

Flux Tower location

MOD12Q1- Quarterly Land Cover

Flux TowerFlux Tower

MODISMODIS

B52A-02

Soil

CO2

N2

Fire

Biological N Fixation

P required

Decomposition

RubiscoStomata

Leaf

Wood

Denitrification

Leaching

N2O, N2

Soil water

Allocation

Model ofC,N,P and H2O in

terrestrial systems

Source: Bob Scholes, July 2001, Amsterdam

The Array of Scales Represented

in the Various Sources of Data

Source

Scale

Flux

Towers

In situ

Measure-ments

Remote Sensing (ETM,

IKONOS)

MODIS

Products

Models

Parameter NEE, respiration LAI, NPP, respiration

Land cover, NDVI, etc.

fPAR, Vi, LAI, PSN, NPP

NPP, NEP, LAI

Spatial Varying footprint

(~1 km2)

Points (<1 m2 )

30 m and finer 1x1 km Point

Temporal 0.5 hr Periodic, Annual

Periodic 8-day composite

Daily

FPAR -

FPAR

highlow

water

April 7

May 25

July 14

Sept 30

Fraction of PhotosyntheticallyActive Radiation (MOD15A2)

l

LAI

April 7

May 25

July 14

Sept 30

highlow

water

Leaf Area Index (MOD15A2)

Index (MOD13A2)low high

water

EVI

April 7

May 25

July 14

Sept 30

Enhanced VegetationIndex (MOD13A2)

low high

PSN

April 7

May 25

July 14

Sept 30

Daily Photosynthesis (MOD17A2)

MODIS Products8-day composites

Top panels show spatial pattern of 1x1-km pixels in 7x7-km subset centered on flux tower. EVI is a 16-daycomposite product.

Lower panels show temporal patterns of pixels with good QA flags, red line is pixel containing tower, dots are pixels near tower

ASCII Subsets available at://public.ornl.gov/fluxnet/modis.cfm

MODIS Products8-day composites

Top panels show spatial pattern of 1x1-km pixels in 7x7-km subset centered on flux tower. EVI is a 16-daycomposite product.

Lower panels show temporal patterns of pixels with good QA flags, red line is pixel containing tower, dots are pixels near tower

ASCII Subsets available at://public.ornl.gov/fluxnet/modis.cfm

Remote SensingRemote Sensing

EcosystemModelsEcosystemModels

EOS Core Validation SitesEOS Core Validation Sites

Participating ModelersLotec: ORNL – King

Biome BGC: UMT – RunningPnET: UNH - Aber

Participating ModelersLotec: ORNL – King

Biome BGC: UMT – RunningPnET: UNH - Aber

Many Scales: Need a Scientific Strategy and

Information ManagementStrategy to Bridge Scales

Many Scales: Need a Scientific Strategy and

Information ManagementStrategy to Bridge Scales

Email Contact Information: R. J. Olson <olsonrj@ornl.gov>*Managed by the University of Tennessee-Battelle LLC under contract DE-AC05-00OR22725 with the U.S. Department of Energy

Email Contact Information: R. J. Olson <olsonrj@ornl.gov>*Managed by the University of Tennessee-Battelle LLC under contract DE-AC05-00OR22725 with the U.S. Department of Energy

Making MODIS Products Available: 7x7-km ASCII Subsets Centered on Towers

UTM

Difficult to collocatefield measurements within

remote sensing pixels

Difficult to collocatefield measurements within

remote sensing pixels

In situMeasurementsIn situMeasurements

Measuring soil Respirationon Walker Branch Watershed

Summary• Strategies for supporting validation have been designed and reviewed -

tested and refinements are ongoing• Distribution systems are in place and working• Validation data are available and more data are being added• Plans are in place to hold workshops and communicate validation results

via special journal issues

Summary• Strategies for supporting validation have been designed and reviewed -

tested and refinements are ongoing• Distribution systems are in place and working• Validation data are available and more data are being added• Plans are in place to hold workshops and communicate validation results

via special journal issues

Strategies for Bridging Scales to Compare Diverse Observations

Data Resources for Many Applications Available for EOS Core Sites

Ongoing Concerns• Testing and refining of the

comparison strategies are needed

• Spatial differences - scaling of points to cells, comparing one pixel vs. subsets

• Temporal differences – satellite 8-day vs. field observation on a specific day

• Data inconsistencies - methods, variables, formats

• Sites - 26 core and ~170 towers site; need for a wider variety of ecosystem types

Ongoing Concerns• Testing and refining of the

comparison strategies are needed

• Spatial differences - scaling of points to cells, comparing one pixel vs. subsets

• Temporal differences – satellite 8-day vs. field observation on a specific day

• Data inconsistencies - methods, variables, formats

• Sites - 26 core and ~170 towers site; need for a wider variety of ecosystem types

Data Collection and Flux-Model-MODIS Comparisons are Ongoing

EOS Core Site in situ data activities ARM

/CART

Barto

n Ben

dish

Bondvi

lle

BOREAS_NSA

BOREAS_SSA

Casca

des

Harva

rd F

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Howla

nd

Ji-P

aran

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Jorn

ada

Konza

Pra

rie

Krasn

oyar

sk

Man

dalg

obi

Mar

icopa

Ag. C

ente

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Mon

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SALSA

Sevill

eta

Skuku

za

Tapa

jos

Uardr

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USDA BARC

Virgin

ia C

oast

Res

erve

Wal

ker B

ranc

h

Park

Falls

Barro

w

Lake

Tah

oe

EOS Val

AERONET P

FLUXNET 3 1 1 1 3 1 3 3 1 1 P 3 1 1 1 3 2

LAI Net

BIGFOOT

Networks / Field Studies A B B G

H, E L

E, H, P

E, F, H H S E

E, G S L C

E, G E E

Model Runs

Field studies - A-ARM, B-BOREAS, C-CIGNS, F-FIFE, E-LTER, G-GTNET, H-Landcover helicopter, L-LBA, P-PROVE, S-SAVE/S2K

EOS Val - sites with study funded by the EOS Validation NRA

FLUXNET - number indicates multiple towers in 200x200 km EOS Core Site area

Real-Time Validation - inter-comparison of MODIS, eddy covariance data, field data, and model outputs

MODIS PSN for 2001 (red) and NEE for 1996-1998

MODIS PSN for 2001 (red) and NEE for 1996-1998

MODIS PSN for 2001 and Biome BGC Model NEP

Outputs for 2000 and 2001

MODIS PSN for 2001 and Biome BGC Model NEP

Outputs for 2000 and 2001

Gap-filled Flux Tower NEE for 1996-1998

Gap-filled Flux Tower NEE for 1996-1998

Years differ, MODIS 8-day composite (best day in period) multiplied

by 8

Years differ, MODIS 8-day composite (best day in period) multiplied

by 8

½ hr NEE data gap-filled and summed to 8-day periods

½ hr NEE data gap-filled and summed to 8-day periods

Biome BGC Model NEP for 2000 and 2001 and NEE

for 1996-1998

Biome BGC Model NEP for 2000 and 2001 and NEE

for 1996-1998

Daily model outputs summed to

8-day periods

Daily model outputs summed to

8-day periods

Formal Comparisons• Ecosystem Model-Data

Intercomparison (EMDI 3)

-12 Modeling Groups

-NPP, NEE flux, MODIS products-Kathy Hibbard, <kathyh@eos.sr.unh.edu>

-Santa Barbara, CA; April 21-24, 2002

• MODIS Vegetation Workshop

-Products: fPAR, LAI, VI, PSN-Steve Running, <swr@ntsg.umt.edu>

-Missoula, MT, July 16-18, 2002- http://www.forestry.umt.edu/ntsg/MODISMTG/

Formal Comparisons• Ecosystem Model-Data

Intercomparison (EMDI 3)

-12 Modeling Groups

-NPP, NEE flux, MODIS products-Kathy Hibbard, <kathyh@eos.sr.unh.edu>

-Santa Barbara, CA; April 21-24, 2002

• MODIS Vegetation Workshop

-Products: fPAR, LAI, VI, PSN-Steve Running, <swr@ntsg.umt.edu>

-Missoula, MT, July 16-18, 2002- http://www.forestry.umt.edu/ntsg/MODISMTG/

B52A-02

URLs for

Data

URLs for

Data

Data Type Data Center URL

Flux data FLUXNET www.daac.ornl.gov/FLUXNET/fluxnet.html

Model Driver and Initial Parameters

AmeriFlux public.ornl.gov/ameriflux/Analysis/Model_Evaluation/index.html

EOS Core Sites NASA GSFC modarch.gsfc.nasa.gov/MODIS/LAND/VAL/

MODIS Subsets ORNL DAAC public.ornl.gov/fluxnet/modis.cfm

MODIS Images EDC DAAC edcdaac.usgs.gov/modis/dataprod.html

In Situ data Mercury System mercury.ornl.gov/ornldaac/

EOS Core Site Imagery Data ARM

/CART

Barto

n Ben

dish

Bondvi

lle

BOREAS_NSA

BOREAS_SSA

Casca

des

Harva

rd F

ores

t

Howla

nd

Ji-P

aran

a

Jorn

ada

Konza

Pra

rie

Krasn

oyar

sk

Man

dalg

obi

Mar

icopa

Ag. C

ente

r

Mon

gu

SALSA

Sevill

eta

Skuku

za

Tapa

jos

Uardr

y

USDA BARC

Virgin

ia C

oast

Res

erve

Wal

ker B

ranc

h

Park

Falls

Barro

w

Lake

Tah

oe

MODISSeaWiFSETM+ 2 1 7 3 1 1 7 1 1 5 5 2 1 8 1 2 9 5 1 10 2 1 1 2 5IKONOS 1 3 1 5 5 1 2 4 4 1 1 1 2 3 5 2 2 1 3 1 1 3 5ASTER 1 7 4 4 3 12GLCTSTM 90's eraMQUALSAVRISCRESSGLCFEO-1MISR planned

ComparisonWorkshops

CDIAC/AmeriFlux• Model initialization parameters• Weekly micromet data• Initial 0. 5 hr flux data

DAAC/FLUXNET• MODIS products – 7x7 cutouts• FLUXNET gap-filled data• Links to field data via Mercury

MODIS• 25 sites• 8 products

Modeling Groups• Estimating NPP and NEP for flux towers

Individual Site Data

Additional validation data

Information ManagementStrategy: Collocate data at

central site or with Internet links

Information ManagementStrategy: Collocate data at

central site or with Internet links

First Steps to Bridge the Gap in Scales, Illustrated with Walker Branch Watershed Data

Validation “Assessing by

independent means the uncertainties of

data products”

Model Outputs (ensemble including Biome BGC) versus Measured NPP

Model Outputs (ensemble including Biome BGC) versus Measured NPP

MODIS LAI (2001) – red line - 8-day composites with high quality QA flags - average of 1x1 km pixels near flux towerField LAI measurements (1996 – 1999) - relative LAI with max LAI=1.0 - measured at a point near tower - Source: Paul Hanson, ORNLComparisons- MODIS LAI shows similar greening pattern in spring as field data; however, fall pattern shows earlier leaf-off - it is not clear why the MODIS LAI shows significant drop around day 151

Comparing MODIS LAI product to LAI field

measurements

WBW is a deciduous forest with annualleaf-on and leaf-off phenology

Models tended to be higher than data at

low NPP sites, lower at high NPP sites

Models tended to be higher than data at

low NPP sites, lower at high NPP sites

MODIS PSN is meanof 3x3-km subset, BGC

NEP is for tower site

MODIS PSN is meanof 3x3-km subset, BGC

NEP is for tower site

1. 26 Core Sites in 6 biomes, sites with active research programs

2. Flux towers using eddy covariance methods to sample large footprint

3. Gap-filling of flux data to create complete temporal record

4. BigFoot project to develop spatial scaling methods

5. Fine-scale remote sensing to scale-up point measurements

6. Models to estimate parameters that are difficult to measure and to bridge scales

Scientific Strategy:Collocate data in time

and space

Scientific Strategy:Collocate data in time

and space