Page 1MERIS and (A)ATSR Workshop. ESA-ESRIN Frascati, September 26-30, 2005

THERMAL REMOTE SENSING GROUP

DEPARTMENT OF THERMODYNAMICS

Validation of Land Surface Temperatures derived from AATSR data at the Valencia

Test Site

César Coll, Vicente Caselles, Enric Valor, Raquel Niclòs, Juan M. Sánchez and Joan M. Galve

Thermal Remote Sensing Unit, Department of Thermodynamics, Faculty of Physics, University of Valencia

SPAINe-mail: cesar.coll@uv.es

Page 2MERIS and (A)ATSR Workshop. ESA-ESRIN Frascati, September 26-30, 2005

THERMAL REMOTE SENSING GROUP

DEPARTMENT OF THERMODYNAMICS

Objective• To collect a database of ground measurements of land surface temperature (LST) concurrent to AATSR (2002-2005)• To validate LST derived from AATSR split-window algorithms (2002-2004)

Plan of presentation• Test site • Experimental data• Validation of AATSR split-window algorithms • Conclusions

Page 3MERIS and (A)ATSR Workshop. ESA-ESRIN Frascati, September 26-30, 2005

THERMAL REMOTE SENSING GROUP

DEPARTMENT OF THERMODYNAMICS

The Valencia test site• AATSR LST product validation site. ASTER and MODIS cal/val site.• Flat, large and homogeneous area of rice fields (full cover in July and August)

AATSR Brightness temperature, 11 µm nadir

24.4 33.1 41.8

Brightness temperature (ºC)

Test site

N = 39 pixelsTmax = 27.71 ºCTmin = 26.84 ºCTaver = 27.19 ºC

σ = 0.20 ºC

0º

39º N

Valencia

Test site

Mediterranean Sea

AATSR RGB (11/07/03)

Page 4MERIS and (A)ATSR Workshop. ESA-ESRIN Frascati, September 26-30, 2005

THERMAL REMOTE SENSING GROUP

DEPARTMENT OF THERMODYNAMICS

0

30

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90

120

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210

25.5 26.5 27.5 28.5 29.5 30.5

temperature (ºC)

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N = 4400 pixelsTmax = 30.15 ºCTmin = 25.79 ºCTaver = 26.89 ºC

σ= 0.45 ºC

Terra/ASTER (03/08/04) Brightness temperature (ºC)ch. 13 – 10.66 µm (90 m)

RGB (15 m)

Page 5MERIS and (A)ATSR Workshop. ESA-ESRIN Frascati, September 26-30, 2005

THERMAL REMOTE SENSING GROUP

DEPARTMENT OF THERMODYNAMICS

Field campaigns in July and August2002-2004: 17 ground LST/AATSR

concurrent measurements2005: underway

July 20, 2002 August 12, 2004

Page 6MERIS and (A)ATSR Workshop. ESA-ESRIN Frascati, September 26-30, 2005

THERMAL REMOTE SENSING GROUP

DEPARTMENT OF THERMODYNAMICS

0.0

0.2

0.4

0.6

0.8

1.0

7 8 9 10 11 12 13 14wavelength (µm)

rela

tive

resp

onse

band 4

band 1

band 3

band 2

CE 312

Ground measurements of LST• Concurrent to cloud-free, morning AATSR overpasses (~10:30 UTC) • Thermal infrared radiometers:

2 CIMEL CE 312 radiometers (4 bands). Accuracy: ±0.1 ºC - ±0.2 ºC.

1 Everest 112.2L IR thermometer (8-13 µm). Accuracy: ±0.5 – ±0.7 ºC.

1 AGA 80 IR thermometer (8-13 µm). Accuracy: ±0.7 – ±0.9 ºC.

• Calibration and inter-comparison of radiometers in the field.

• Emissivity correction of radiometric temperatures (emissivity and downwelling sky radiance measurements)

Page 7MERIS and (A)ATSR Workshop. ESA-ESRIN Frascati, September 26-30, 2005

THERMAL REMOTE SENSING GROUP

DEPARTMENT OF THERMODYNAMICS

25

26

27

28

29

30

10:25 10:30 10:35 10:40 10:45 10:50

Time (UTC)

Tem

pera

ture

(ºC

)CE 312EverestAGA

Methodology• Temperatures measured along transects in the 1 km2

square.Test site 1 (2002-03): 0º17’50” W, 39º14’27” NTest site 2 (2004): 0º17’43” W, 39º15’01” N

• Average temperatures for each transect/radiometer (±1.5 minutes around satellite overpass).

• Standard deviation of temperatures, σ(var): natural variability.• Estimation of error budget:

σ(T) = [σ(var)2 + σ(cal)2 + σ(em)2]1/2

calibration error emissivitycorrection error

• Average temperatures for all transects(Everest and AGA discarded when σ(T)>1.0 ºC or |T-TCE|>1.0 ºC)

Page 8MERIS and (A)ATSR Workshop. ESA-ESRIN Frascati, September 26-30, 2005

THERMAL REMOTE SENSING GROUP

DEPARTMENT OF THERMODYNAMICS

Ground LST database (± uncertainties) coincident with AATSR overpasses.LST ± σ(T) (ºC)

Year Date(day/month)

Overpass time

(UTC) CE1 CE2 Everest AGA Average10/07 10:30 28.4±0.6 – 29.1±1.0 – 28.6±0.613/07 10:37 27.2±0.8 – 28.2±0.8 27.9±1.0 27.6±0.929/07 10:34 28.1±0.5 – 27.2±0.8 28.1±1.0 27.9±0.708/08 10:19 26.4±0.6 – – 26.7±1.0 26.5±0.714/08 10:31 28.4±0.5 – 28.6±0.8 – 28.5±0.508/07 10:23 28.4±0.8 28.4±0.7 28.6±0.9 27.8±0.9 28.3±0.711/07 10:28 29.2±0.8 29.1±0.5 28.9±0.8 – 29.1±0.714/07 10:34 28.7±0.8 28.6±0.4 28.4±0.8 – 28.6±0.624/07 10:20 28.5±0.6 29.1±0.4 28.9±0.9 – 28.8±0.630/07 10:30 29.2±0.3 29.4±0.4 28.4±0.5 – 28.9±0.612/08 10:23 31.6±0.5 31.0±0.5 31.1±0.8 – 31.3±0.628/06 10:34 29.1±0.6 29.3±0.6 – – 29.2±0.608/07 10:20 25.7±0.6 – 25.8±0.7 – 25.7±0.614/07 10:31 27.4±0.5 26.9±0.6 27.6±0.9 – 27.2±0.727/07 10:23 27.6±0.5 27.8±0.4 – – 27.7±0.430/07 10:28 27.5±0.5 28.0±0.5 – – 27.8±0.412/08 10:20 28.6±0.6 28.1±0.5 28.6±0.7 – 28.4±0.6

2004

2003

2002

|TCE1 – TCE2| ≤ 0.6 ºC∆T ≤ 1.0 ºC

LST: 25.7 – 31.3 ºCσ(T): ±0.4 – ±0.9 ºC

Page 9MERIS and (A)ATSR Workshop. ESA-ESRIN Frascati, September 26-30, 2005

THERMAL REMOTE SENSING GROUP

DEPARTMENT OF THERMODYNAMICS

AATSR brightness temperatures T11 and T12, nadir (L1b data, 3×3 pixels average and σ)

Year Date (day/month)

Viewing angle (º) T11 (ºC) σ(T11) (ºC) T12 (ºC) σ(T12) (ºC)

10/07 3.7 25.04 0.09 22.99 0.1413/07 13.8 22.28 0.08 19.26 0.0829/07 8.8 22.96 0.08 21.08 0.0708/08 16.2 20.29 0.08 17.31 0.0914/08 3.9 23.69 0.12 21.52 0.0708/07 11.1 25.30 0.12 23.03 0.1011/07 1.2 27.03 0.13 25.50 0.1214/07 8.7 24.73 0.15 22.39 0.1324/07 16.3 24.68 0.15 22.36 0.1130/07 3.7 23.44 0.11 20.63 0.0612/08 11.1 28.10 0.10 26.51 0.1128/06 8.7 26.41 0.10 24.36 0.1008/07 16.3 23.15 0.41 21.60 0.3714/07 3.7 22.45 0.12 19.78 0.1827/07 11.1 25.02 0.11 23.35 0.0930/07 1.2 23.37 0.12 20.58 0.0812/08 16.3 25.50 0.12 23.98 0.15

2004

2003

2002

σ: 0.08 – 0.15 ºC(except for 08/07/04)

σ: 0.06 – 0.18 ºC(except for 08/07/04)

Page 10MERIS and (A)ATSR Workshop. ESA-ESRIN Frascati, September 26-30, 2005

THERMAL REMOTE SENSING GROUP

DEPARTMENT OF THERMODYNAMICS

Validation of AATSR split-window algorithmsAATSR LST operational product - Prata (2000) (ATBD)

Coefficients depend on:

• i : land cover type. 13 classes or biomes (i=1 – 13). • f : fractional vegetation cover (0 ≤ f ≤ 1).

For each class, separate coefficients for the vegetated (subscript v) and for the bare surface (subscript s).

• pw : precipitable water (in cm).

LST = af,i,pw + bf,i(T11-T12)n + (bf,i + cf,i)T12

af,i,pw = 0.4[sec(θ)-1]pw + f av,i + (1-f) as,i

bf,i = f bv,i + (1-f) bs,i cf,i = f cv,i + (1-f) cs,i n = cos(θ/5)

• RAL processor →f, i : global classification and fractional vegetation cover maps (0.5º × 0.5º).pw: climatologyCoefficients from Prata (2002)

Page 11MERIS and (A)ATSR Workshop. ESA-ESRIN Frascati, September 26-30, 2005

THERMAL REMOTE SENSING GROUP

DEPARTMENT OF THERMODYNAMICS

i = 6 (broadleaf trees with groundcover)f = 0.404 pw = 2.795 cm (July)f = 0.473 pw = 2.884 cm (August)

LST validation RAL processor

Year Date (dd/mm)

Ground LST (ºC)

AATSR LST (ºC)

Ground – AATSR LST (ºC)

10/07 28.6 32.1 -3.5 13/07 27.6 31.8 -4.2 29/07 27.9 29.5 -1.6 08/08 26.5 29.4 -2.9

2002

14/08 28.5 30.8 -2.3 08/07 28.3 33.1 -4.8 11/07 29.1 33.0 -3.9 14/07 28.6 32.7 -4.1 24/07 28.8 – – 30/07 28.9 32.5 -3.6

2003

12/08 31.3 33.9 -2.6 28/06 29.2 34.0 -4.8 08/07 25.7 28.8 -3.1 14/07 27.2 31.1 -3.9 27/07 27.7 31.2 -3.5 30/07 27.8 32.1 -4.3

2004

12/08 28.4 31.0 -2.6 Average difference (ºC) -3.5 Standard deviation (ºC) 0.9

Range of differences (ºC): [–4.8 ; –1.6]

With i = 6 and f =1 (full cover)Average Diff. = –1.3 ºCStand. Dev. = 0.7 ºC

Range of Diff. = [– 2.4 ; 0.4] ºC

Page 12MERIS and (A)ATSR Workshop. ESA-ESRIN Frascati, September 26-30, 2005

THERMAL REMOTE SENSING GROUP

DEPARTMENT OF THERMODYNAMICS

• AATSR LST algorithm optimised for the test site →i = 8 (broadleaf shrubs with groundcover) f = 1 (full cover) T11, T12: L1b data

LST = 0.4[sec(θ)-1]pw + 1.5662 + 3.1384(T11-T12)n + 0.8965T12 (Eq. 1)(pw=2.5 cm)

• Quadratic, emissivity-dependent algorithm (Coll and Caselles, 1997) →

LST = T11 + a0 + a1(T11-T12) + a2(T11-T12)2 + α(1-ε) – β∆ε ε=(ε11+ε12)/2; ∆ε=ε11-ε12

Coefficients calculated for AATSR and taking ε=0.985; ∆ε=0 for the test site:

LST = T11 + 0.72 + 0.94(T11-T12) + 0.25(T11-T12)2 (Eq. 2)

Page 13MERIS and (A)ATSR Workshop. ESA-ESRIN Frascati, September 26-30, 2005

THERMAL REMOTE SENSING GROUP

DEPARTMENT OF THERMODYNAMICS

LST validationAATSR LST (ºC) Ground – AATSR

LST (ºC) Year Date (dd/mm)

Ground LST (ºC) Eq. (1) Eq. (2) Eq. (1) Eq. (2)

10/07 28.6 28.6 28.7 0.0 -0.1 13/07 27.6 28.3 28.1 -0.7 -0.5 29/07 27.9 26.4 26.3 1.5 1.6 08/08 26.5 26.5 26.0 0.0 0.5

2002

14/08 28.5 27.7 27.6 0.8 0.9 08/07 28.3 29.4 29.4 -1.1 -1.1 11/07 29.1 29.2 29.8 -0.1 -0.7 14/07 28.6 29.0 29.0 -0.4 -0.4 24/07 28.8 28.9 28.9 -0.1 -0.1 30/07 28.9 28.9 28.8 0.0 0.1

2003

12/08 31.3 30.3 30.9 1.0 0.4 28/06 29.2 29.8 30.1 -0.6 -0.9 08/07 25.7 25.8 25.9 -0.1 -0.2 14/07 27.2 27.7 27.5 -0.5 -0.3 27/07 27.7 27.8 28.0 -0.1 -0.3 30/07 27.8 28.8 28.7 -1.0 -0.9

2004

12/08 28.4 27.9 28.2 0.5 0.2 Average difference (ºC) 0.0 -0.1 Standard deviation (ºC) 0.7 0.7

Range of differences (ºC): [–1.0 ; 1.5] [–1.1 ; 1.6]

Page 14MERIS and (A)ATSR Workshop. ESA-ESRIN Frascati, September 26-30, 2005

THERMAL REMOTE SENSING GROUP

DEPARTMENT OF THERMODYNAMICS

LST validation

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groundRALEq. (1)Eq. (2)

2002

Date (dd/mm/yy)

Page 15MERIS and (A)ATSR Workshop. ESA-ESRIN Frascati, September 26-30, 2005

THERMAL REMOTE SENSING GROUP

DEPARTMENT OF THERMODYNAMICS

Conclusions• Database of ground LSTs for the validation of AATSR derived LSTs in the Valencia test site. Field campaigns in the summers of 2002-04 (17 matchups) and 2005 (underway).

• Thermal homogeneity of the site analysed with satellite brightness temperatures at different scales (AATSR – 1 km: σ < 0.2 ºC; ASTER – 90 m: σ < 0.5 ºC).

• LST validation: The RAL processor overestimates the ground LSTs by 3.5 ºC. Optimised algorithms yield differences in the range between –1.0 and 1.5 ºC.

• High sensitivity of split-window LSTs to land cover (i) and vegetation fraction (f).

• The 0.5º × 0.5º resolution of land cover/vegetation fraction classification used by the operational AATSR algorithm is too coarse in order to account for the heterogeneity of land surfaces.

• 1 km resolution is recommended for i and f.