A FIRST LOOK AT THE MODIS 8-DAY PSN A FIRST LOOK AT THE MODIS 8-DAY PSN DATA FOR 2001DATA FOR 2001

MODIS Science Team Mtg19 December 2001

Steven W. RunningNTSG, Univ. of Montana

MODIS PhotosynthesisMODIS Photosynthesis

GPP = Radiation

UseEfficiency

AbsorbedPhotosynthetically

ActiveRadiation

x

The Monteith equation….The Monteith equation….

APAR

(FPAR) (0.45Rnet )

0

20

40

60

80

100

120

0 5 10 15 20 25 30

Daily APAR (MJ m-2 day-1)

GP

P (

gC

m

-2 d

ay

-1)

Grass

Forest

Wheat

Photosynthesis Under Optimum Conditions

Epsilon is the slope of theline described by

GPP = APAR

MODIS PhotosynthesisMODIS Photosynthesis

Radiation Use EfficiencyRadiation Use Efficiency

= max [mtmin ][mvpd ]

MaximumRadiation Use Efficiency

under ideal conditionsfor each biome

Vapor Pressure DeficitCoefficient

Temperature Coefficient for each biome

The coefficients are calculated from daily minimum and maximum air temperature which are therefore necessary inputs to the model

0.0

0.2

0.4

0.6

0.8

1.0

1.2

-10 -5 0 5 10 15 20 25 30

Daily Minimum Temperature

mtm

in

Grassland Biome

Tmin_max & Tmin_minare Tabulated by biome

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

700 1200 1700 2200 2700 3200 3700 4200

Vapor Pressure Deficit (Pa )

mv

pd

All Biomes

Tmin_maxTmin_max

Tmin_minTmin_min

VPD Tmin

VPD & Tmin CoefficientsVPD & Tmin Coefficients

maxTm in, VPD fPAR, Rnet GPP

LAI SLA

fine rootm ass

allom etry

leaf m ass

Q10, Tavg MR

-

Daily"NPP"

=

MRindex

MOD-17Daily "NPP"

Photosynthesis

Maintenance Respiration

does not include growth respiration orlive wood maintenance respiration costs

leafm ass

D aily O utputs

ESTIMATION OF DAILY NPP IN MOD17 ALGORITHM

MODIS 8-day PSN Winter 2001

MODIS 8-DAY PSN SUMMER 2001

MODIS 8-day LAI Product

LAI of center pixel

Park Falls forest site17MAY2001 – 16OCT2001

Park Falls forest site17MAY2001 – 16OCT2001

The variability in LAI around the flux tower is shown by the scatter of blue (3x3 km) and green (5x5 km) dots.

The variability in LAI around the flux tower is shown by the scatter of blue (3x3 km) and green (5x5 km) dots.

Park Falls5x5 km

Land Cover

around towerDavis et al.

Land Cover around towerDavis et al.

LAI field data Co-KrigedAug 2000

Gower et al.

LAI field data Co-KrigedAug 2000

Gower et al.

MODIS Cutouts: fPAR for Park Falls

All pixels in5x5 cutoutGreen=rejectedBlue=accepted

Acceptedpixels

Day of Year

0 50 100 150 200 250 300 350

Ma

xim

um

Ca

no

py P

ho

tosyn

the

sis

a

nd

Eco

syste

m R

esp

ira

tio

n

( m

ol m-2

s-1)

-40

-30

-20

-10

0

10

Tallgrass Prairie in OklahomaWinter wheat in OklahomaGrassland in California

Photosynthesis

Respiration

FLUXNET GRASSLAND SITES

Day of Year

0 50 100 150 200 250 300 350

Ma

xim

um

ca

no

py p

ho

tosyn

the

sis

a

nd

Eco

syste

m R

esp

ira

tio

n

(

mo

l m-2

s-1)

-40

-30

-20

-10

0

10Respiration

Photosynthesis

Scots pine forest in FinlandMixed deciduous forest in TennesseeAspen forest in Canada

FLUXNET FOREST SITES

SUMMARY

3 Sources of variability of MODIS PSN

1. Radiometric – MODIS FPAR and LAI2. Meteorological – DAO IPAR and Temps3. Ecological – MOD 17 representation of plant physiology

Each require a different mode of validation