inter-comparisons of aatsr, meris and atsr-2 calibrations using desert targets

AATSR Calibration Using Deserts ENVISAT Validation Review 9-13 December 2002

Inter-Comparisons of AATSR, MERIS and ATSR-2 Calibrations using Desert Targets

Dave Smith - Rutherford Appleton Laboratory


Objectives

• Use remote desert sites to verify calibrations of AATSR and MERIS by comparison with other instruments (in particular ATSR-2), and in-situ radiometer measurements.

• Long-term stability of sites will enable temporal calibration drifts to be determined.

• Results can be extended to improve the calibrations of other instruments such as SCIAMACHY and AVHRR.

• Crucial to blending of records of geophysical parameters derived from different sensors.


Desert Calibration Targets

Sonora - Mexico

Sudan - Egypt


Orbit 2136 comparison (MERIS/AATSR)


ATSR-MERIS Comparisons

AATSR

MERIS

AATSR

MERIS

AATSR

MERIS

870 nm


Orbit 2136 comparison (AATSR/ATSR-2)

ATSR-2870nm

AATSR 870nm


AATSR Data Processed to Date

Products Downloaded

Valid Scenes

Algeria 1 5 3 Algeria 3 8 5 Algeria 5 2 1 Amburla 2 - Arabia 1 1 1

Dunhuang 6 0 Hay 1 -

Libya 1 10 6 Libya 2 6 2 Sonora 14 2 Sudan 1 5 2

Total 60 22

NOTE: Data before October 1st not used for validation


Example ‘cloud’ test result

No clouds 1.6um reflectances out of range 12um variance threshold exceeded 11um variance threshold exceeded 11 and 12um variance threshold exceeded 1.6um threshold exceeded 1.6um + 12um threshold exceeded 1.6um + 11um threshold exceeded 1.6um + 11um +12µm threshold exceeded BT distribution Test failed

Sonora, Mexico


METRIC Extractions

• METRIC tar files downloaded from MERIS Calibration Site (370 files to date)

• No METRIC outputs for SONORA, Dunhuang, Hay, Amburla and Thangoo

• HDF Files extracted from tar files and read by IDL routine

• TOA reflectances extracted and stored in file for each site

• Coincident MERIS and AATSR observations compared (11 match-ups so far)

• How do METRIC cloud test results compare with AATSR?


MERIS/AATSR Comparison

AATSR Vs. MERIS Comparisons

y = 1.0417x

20

25

30

35

40

20 22 24 26 28 30 32 34 36 38 40

MERIS 560nm Reflectance (%)

AA

TS

R 5

55n

m

Ref

lect

ance

(%

)

AATSR Vs. MERIS Comparisons

y = 1.0051x

35

40

45

50

55

35 37 39 41 43 45 47 49 51 53 55


AA

TS

R 6

70n

m

Ref

lect

ance

(%

)

AATSR vs. MERIS Comparisons

y = 1.0371x

50

55

60

65

70

50 52 54 56 58 60 62 64 66 68 70


AA

TS

R 8

65n

m

Ref

lect

ance

(%

)

560nm

RAATSR/RMERIS = 1.041

660nm


870nm



ATSR-2 Desert Reflectances

Coefficients for ATSR-2 BRDF for site SUDAN1 (R = a0 + a1 + a2

2) Nadir Along Track a0 a1 a2 a0 a1 a2 1.6µm 78.2736053 -0.2023685 0.0009938 106.6791382 -0.6175243 0.0024774 0.87µm 65.2568512 -0.2483396 0.0010956 85.1799927 -0.5492774 0.0022903 0.67µm 56.3275871 -0.2425693 0.0010161 77.0637436 -0.5996294 0.0025522 0.56µm 34.4137306 -0.1228843 0.0005610 60.6836205 -0.5556419 0.0023956

Use archive of ATSR-2TOA Reflectances from 1995 to 2000


AATSR/ATSR-2 Indirect comparisons

1600nm

y = 0.837x + 5.0372

303540

45505560

6570

30 40 50 60 70

ATSR-2 Normalised TOA Radiances

AA

TS

R N

orm

alis

ed T

OA

R

adia

nce

s

870nm

y = 0.9968x + 3.0079

202530

35404550

5560

20 30 40 50 60


AA

TS

R N

orm

alis

ed T

OA

R

adia

nce

s

660nm

y = 0.9582x + 3.7356

15

20

25

30

35

40

45

15 20 25 30 35 40 45


AA

TS

R N

orm

alis

ed T

OA

R

adia

nce

s

560nm

y = 1.045x + 1.5986

10

15

20

25

30

10 15 20 25 30


AA

TS

R N

orm

alis

ed T

OA

R

adia

nce

s

RAATSR/RATSR-2 =1.088

RAATSR/RATSR-2 = 1.081RAATSR/RATSR-2 = 0.945

RAATSR/RATSR-2 =1.132


AATSR vs. ATSR-2 Coincident Data


Summary of Previous ATSR-2 Intercomparisons

-15.0%

-10.0%

-5.0%

0.0%

5.0%

10.0%

15.0%

0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9

Wavelength µm

(RA

TS

R-2

- R

ob

s )/R

ob

s

Pre-Launch vs. In-Flight Data (Smith)

Amburla (Rondeax and Prata 1997)

Hay (Rondeax and Prata 1997)

POLDER (Haggolle et al)

GOME (Koelemeijer)

GOME (Stevens)

SWIFS (Govaerts 2002)

MISR (Govaerts 2002)

Desert Models (Govaerts 2002)

Average

AATSR


Summary of results obtained so far

• First TOA reflectance extractions performed for selection of Desert targets for October 2002.

• AATSR agrees well with MERIS RAATSR/RMERIS =

1.041 (560nm), 1.001 (660nm), 1.037 (870nm)

• Significant differences observed between AATSR/MERIS and ATSR-2 RAATSR/RATSR-2

1.132 (560nm), 1.088 (660nm), 1.081 (870nm), 0.945 (1600nm)

• Results consistent with other investigations (Haggolle, Govaerts)


Remaining activities

• Process remaining sites and coincident ATSR-2 data

• MERIS/METRIC products for Sonora, Hay, Amburla, Thangoo and Dunhuang

• Greenland Data – need data for period between May and August.

• Atmospheric corrections

• Walk through from raw data to calibrated radiances – identify possible processing errors

• Long Term analysis – – Requires data products delivered on a regular (monthly) basis – preferably

on CD-ROM rather than FTP site

inter-comparisons of aatsr, meris and atsr-2 calibrations using desert targets

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