Global NDVI Data for Climate Studies

Compton TuckerNASA/Goddard Space Fight Center

Greenbelt, Maryland 20771

NOAA AVHRR NDVI datasets• NDVI is Normalized Difference Vegetation Index

NDVI = (NIR – VIS) / (NIR + VIS)

• Global 8km data available daily since July 1981• Composites created at 15 day time step to create 27+

years of vegetation images with minimal clouds and artifacts.

• Drawbacks of AVHRR NDVI– Six (soon seven) different satellites used in series– Satellite orbit degrades over time, impacting the sun-

sensor-view angle and thus the reflectances and NDVI

• Models cannot be used to fix problems because of complexity of surface and number of physical parameters.

NOAA Advanced Very High Resolution NOAA Advanced Very High Resolution Radiometer NDVI Data Set ComparisonRadiometer NDVI Data Set Comparison

1.1. GSFC/DAAC PAthfinder Land (‘81-2000)GSFC/DAAC PAthfinder Land (‘81-2000)

2.2. NOAA’s GVI data set(1981-2009…)NOAA’s GVI data set(1981-2009…)

3.3. GIMMS precursor data sets (several)GIMMS precursor data sets (several)

4.4. GIMMS latest data set1981-2009…GIMMS latest data set1981-2009…

Same input data, different atmospheric Same input data, different atmospheric corrections, different calibrations, different post corrections, different calibrations, different post

processing normalization(s)processing normalization(s)

NDVI Data Sources

AVHRR instruments (1981 – 2012 at least)MODIS instruments (2000 – 2009)

SPOT Vegetation (1998 – 2009)SeaWiFS (1997 - 2009)

Data Set considerations

Must be quantitatively inter-comparable among sensorsMust be non stationary

Must be largely free of artifacts

NDVI Data Sets

•Direct linear relationship to FPAR•Thus direct relationship to photosynthetic

potential or capacity•No a priori knowledge of surface required (i.e.,

vegetation type, etc.)•Easily inter-calibrated among different remote

sensing instruments (unlike EVI)•Almost 28-year global record

NOAA-16

1982-20021992-2002

Decadal trends in Decadal trends in terrestrialterrestrial vegetation vegetation

NOAA AVHRR Channels 1 & 2

Ch 1 Ch 2

(Very broad or wide spectral

bands)

The NOAA The NOAA person(s) person(s)

responsible for responsible for these excellent these excellent

examples of examples of poor spectral poor spectral

resolution resolution should be should be

tarred and tarred and feathered.feathered.

LeafLeaf Reflectance & Absorption Reflectance & Absorption

Bean leaf x 3900Bean leaf x 3900

AVHRR NDVI analyses require Solar Zenith Angle correction

Use of Empirical Mode Decomposition to correct NDVI

Empirical Mode Decomposition can identify and separate the real vegetative signal from artifacts. Because the Empirical Mode Decomposition derives functions from the data and is adaptive, it is perfectly suited to identify the NDVI trends associated with the solar zenith angles, and to leave the vegetation dynamics intact.

Solar Zenith Angle Variations by Latitude

Empirical Mode Decomposition processing for solar zenith angle errors

African Tropical Forest(lat 1.4 N x long. 18 E)

0.3

0.35

0.4

0.45

0.5

0.55

1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

Year

NDVI

GIMMS

GIMMS-Corrected

EMD solar zenith angle correctionEMD solar zenith angle correction

Range w/o SZA Correction: 0.12 ndvi units

Range w/ SZA correction: 0.05 ndvi units

Empirical Mode Decomposition/reconstruction (EMD) technique Requires no land cover information a priori

Regions affected by solar zenith angle drift in AVHRR record

Stratospheric Aerosol correction also required

NOAA AVHRR 8-km NDVI Data Set

Mt. Pinatubo, Philippines

June 1991

0.00

0.05

0.10

0.15

0.20

0.25

0 100 200 300 400 500 600

1991

NDVI

1990

1991 corrected

1989

Max. NDVI Effect 0.1-0.15

1991 corrected

Stratospheric Aerosol correction also required

NOAA AVHRR 8-km NDVI Data Set

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

Time

Str

ato

sp

he

ric O

pti

ca

l D

ep

th(5

50

nm

)

Equator

40 N

60 N

30 SEl Chichon

Mt. Pinatubo

Space Shuttle Limb Photographs

Before Mt. Pinatubo Eruption

After Mt. Pinatubo Eruption

NOAA AVHRR 8-km NDVI Data Set

El Chichon (1982-1984) Mt. Pinatubo (1991-1994)

NOAA AVHRR 8-km NDVI Data Set Diffuse average daily PAR[W/m2/mic] (0.4-0.7 mic)

El Chichon (1982-1984) Mt. Pinatubo (1991-1994)

NDVI Data 1981 – 2007