Evaluation of LTDR dataat

AERONET sites(For Year 1999)

Jyothy Nagol

TOA AVHRR(9 pixel matrix)

Atmosphericdata from

AERONET

Atmospheric correction

(6s)

REFERENCE DATA(At surface NDVI)

Comparison withLTDR, PAL and GIMMS

Reference Data

Reference Data: Comprehensive atmosphericcorrection of 9 pixels around AERONET sites.

Comparison of LTDR and other NDVI datasetswith reference data

Sites: 48 sites

Data points: 580

Comparison with Reference data

Daily data comparisons (all data)– TOA, PAL, LTDR-beta_release(Dec_06)

15 day composite comparison (site)– TOA, PAL, LTDR and GIMMS

Monthly composite comparison (site)– LTDR, TOA, GVI

NOTE: ALL data is constrained to View zenith angle < 42

Daily data comparisonsfor

LTDR, PAL, and TOA

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

Corrected Rho1

PA

L R

ho

1 a

nd

LT

DR

Rh

o1

1 to 1 line

PAL_rho1

LTDR_rho1

Linear (PAL_rho1)

Linear (LTDR_rho1)

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

Corrected Rho2

PA

L R

ho

1 a

nd

LT

DR

Rh

o2

1 to 1 linePAL_rho2

LTDR_rho2

Linear (PAL_rho2)

Linear (LTDR_rho2)

BAND 1

Under estimation

NDVI is more sensitive to Red.

Different Calibration: PAL: Stable desert target vicarious calibration (Rao and Chen, 1996)

LTDR: ocean-cloud vicarious calibration (Vermote and Kaufman, 1995)

BAND 2

PAL

and

LTD

R R

ho 2

PAL

and

LTD

R R

ho 1

NDVI

-0.2

0

0.2

0.4

0.6

0.8

1

-0.2 0 0.2 0.4 0.6 0.8 1

Reference Data

TO

A,

PA

L,

an

d L

TD

R d

ail

y d

ata

TOA_NDVI

PAL_NDVI

LTDR_NDVI

1 to 1 line

-0.2

0

0.2

0.4

0.6

0.8

1

-0.2 0 0.2 0.4 0.6 0.8 1

Reference Data

TO

A,

PA

L,

an

d L

TD

R d

ail

y d

ata

TOA_NDVI

PAL_NDVI

LTDR_NDVI

1 to 1 lineLinear (TOA_NDVI)

Linear (PAL_NDVI)

Linear (LTDR_NDVI)

0.09150.031210.0645LTDR0.10840.07070.0889PAL0.19740.08090.1432TOA

RMSE(> 0.3 NDVI)

RMSE(< 0.3 NDVI)RMSE

15 day compositefor

LTDR, PAL and GIMMS

0

0.1

0.2

0.3

0.4

0 50 100 150 200 250 300 350

Day of the Year

ND

VI

Da

ta

TOA

PAL

GIMMS

LTDR

Reference

NDVI

0

0.05

0.1

0.15

0.2

0 0.05 0.1 0.15 0.2

Reference Data

TO

A,

PA

L,

an

d L

TD

R d

aily

da

ta

TOA_NDVI

PAL_NDVI

LTDR_NDVIDesert site

Solar village, Saudi Arabia

0

0.1

0.2

0.3

0.4

0 50 100 150 200 250 300 350

Day of the Year

ND

VI D

ata

GIMMS

PAL

LTDR

Reference NDVI

Semiarid SiteSevilleta, USA

0

0.1

0.2

0.3

0 0.1 0.2 0.3

Reference Data

TO

A, P

AL

, an

d L

TD

R d

aily d

ata

toa_NDVI

PAL_NDVI

LTDR_NDVI

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100 150 200 250 300 350

Day of the Year

ND

VI D

ata

GIM M S

PAL

LTDR

Reference NDVI

1

Agricultural SiteBondville, USA

0

0.2

0.4

0.6

0.8

0 0.2 0.4 0.6 0.8

Reference Data

TO

A, P

AL, and L

TD

R d

aily d

ata

toa_NDVI

PAL_NDVI

LTDR_NDVI

Monthly Compositefor

LTDR and GVI

Desert siteSolar village, Saudi Arabia

0

0.1

0.2

0.3

0.4

0 50 100 150 200 250 300 350

Day of the Year

ND

VI

Da

ta

GVI

LTDR

Reference NDVI

Agricultural SiteBondville, USA

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100 150 200 250 300 350

Day of the Year

ND

VI D

ata

TOA

GVI

LTDR

Reference NDVI

Conclusions from Comparison withReference Data

LTDR dataset is closest to reference dataPAL underestimates both band1 and band2GIMMS data overestimates in high NDVI and

underestimates in low NDVI,– Possibly due to use of statistical orbital drift correction.

GIMMS shows abnormal flatness in desert sitesbecause it has been normalized to be flat there.

GVI reduces the amplitude of phenology– Possibly due to use of averaging in compositing system

This method of evaluation gives us a chance toisolate atmospheric issues.

LimitationsAssumes spherical aerosol modelThe sample is not representative of all biomesVery few operational AERONET sites in 1999.Only 580 points

– Few operational AERONET sites,– non-operational Instruments (data gaps),– Clouds.

Future plansExpand this analysis to other years and include

other sensors in LTDR product.

Thank you

Jyothy Nagol