Land Surface Temperature derived from the advanced IR sounders on METOP and NPOESS

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Land Surface Temperature derived from the
advanced IR sounders on METOP and NPOESS

• Robert Knuteson,
• Henry E. Revercomb, David C. Tobin
• University of Wisconsin-Madison
• Space Science and Engineering Center

ITWG 1st Land Surface Workshop, Paris, 21 June
2006
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Topics Advanced IR Sounder

• Temperature and IR Emissivity Separation -
  Example from Sahara
• Temperature IR Emissivity Validation-
  Continental U.S. ARM site (Oklahoma)
• Suggestion for NWP. (follow the approach outlined
  in Pequignot, LMD talk)

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Surface Temperature Emissivity
Brightness Temperature (K)
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(No Transcript)
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Infrared Radiative Transfer Equation (lambertian
surface)
SurfaceEmission
Surface Reflection
Skin Temperature Surface Emissivity
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Approximate Solutions
(spectral relative)
(atmospheric corrected spectral relative)
(formal solution - known atmosphere -
unknown skin temperature)
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IR Land Surface Signatures QUARTZ Mineral
JPL Spectral Library Laboratory Measurements
1.0
1-R
12 ?m
Alluvial Sand Sandy Loam Soil
9 ?m
4 ?m
0.5
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AIRS Observation 16 Nov 2002 11 UTC Red Sea
B.T.(K)
B.T.(K)

• Microwindows are used to look between
  absorption lines.

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NIGHT -- 9 ?m relative to 12 ?m
1.0
Thessaly Plain, Greece
Relative Emissivity
Libyan Desert Satellite Validation Target
Site (27.12N,26.10E)
0.7
16 November 2002 0000-0006 UTC (15-km FOV)
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NIGHT -- 4 ?m relative to 12 ?m
1.0
Thessaly Plain, Greece
Relative Emissivity
Libyan Desert Satellite Validation Target
Site (27.12N,26.10E)
0.7
16 November 2002 0000-0006 UTC (15-km FOV)
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DAY -- 9 ?m relative to 12 ?m
1.0
Relative Emissivity
Red Sea, Ocean
Libyan Desert Satellite Validation Target
Site (27.12N,26.10E)
0.7
16 November 2002 1100-1106 UTC (15-km FOV)
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AIRS Spectral Relative Emissivity Egypt One
16 November 2002 1103 UTC
Egypt One
OBS. B.T. (K)
B-1(Robs)
Red Sea
Robs B(T12?m)
Raw Relative Emissivity
9 ?m

• Relative emissivity is derived only from AIRS
  radiances.

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AIRS Spectral Relative Emissivity Egypt One
Need Ozone Fit
Raw Relative Emissivity
9 ?m

• Quartz reflectivity features are apparent in the
  desert case.

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AIRS Relative Emissivity and Temperaturewith
Atmospheric Correction

• 16 November 2002
• Focus Day

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ECMWF Analysis 16 Nov. 2002 12 UTC

• Square symbol marks Egypt One site in Libyan
  Desert

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ECMWF Analysis 16 Nov. 2002 12 UTC
Temperature
Water Vapor

• ECMWF profile over Egypt One site in Libyan
  Desert

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LBL Calculation Using ECMWF Model Profile
Up Down Radiance
Total Trans- mission

• LBLRTM calculations reduced to AIRS spectral
  resolution.

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AIRS Atmosphere Corrected Relative Emissivity
Need Ozone Fit
Atmos. Corrected Relative Emissivity
9 ?m

• Atmospheric Correction uses ECMWF model T WV
  profiles.

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AIRS Absolute EmissivityandSurface
Temperature(including Surface Reflection)

• 16 November 2002
• Focus Day

Technique follows that described in Knuteson, et
al., Adv. Space Res., 33 (2004) 1114-1119.
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IASI Simulated IR Reflected Radiance
Contribution to TOA Radiance. (Note
Reflection is independent of Ts!)
Reflected contribution can be large !
Radiance (mW/(m2 sr cm-1))
Bare Soil
60 Veg.
Vegetation
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Constraint Emissivity solution should be
smoothly varying across atmospheric absorption
lines!
E?
Std. Dev. E(Ts)
Minimum

• Minimum Std. Deviation is at the true skin
  temperature !!

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AIRS Absolute Emissivity
Preliminary!
Need Ozone Fit
AIRS Observ. JPL Spectral Library Alluvial Sand
UW Online- Offline Technique
9 ?m

• Reflection calculation uses ECMWF model T WV
  profiles.

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Spatial Scales
Land Surface Temperature Remote Sensing Issues
Bare Soil

• Example from the U.S. Wheat Belt
• ARM Southern Great Plains Site

Winter Wheat
Pasture (Grassland)
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Field of View Scale 15 km to 1 km
AIRS 15-km sub-pixel
SHIS (2 km)
MODIS IR (1 km)
Approximate Location
Aerial Photograph Source USGS Terraserver
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Field of View Scale 1 km to 50 m
MODIS IR (1 km)
MODIS vis (250 m)
ARM SGP CF
MAS (50 m)
100 yd by 100 yd
Aerial Photograph Source USGS Terraserver
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U.S. Southern Great Plains (DOE ARM site)
1.00
Vegetation
Emissivity
Bare Soil
12 ?m
8.5 ?m
0.80
850
1250
Wavenumber

• MODIS Airborne Simulator (MAS) Spectral Bands
  compared to measured Bare Soil Green Vegetation

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1.5 km x 1.5 km
MAS 50 meter data
12 ?m
8.5 ?m
8.5 ?m minus 12 ?m
Rel. Emiss.

• Scales comparable to MODIS and VIIRS are highly
  variable.

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10 km x 7.5 km
MAS 50 meter data
12 ?m
8.5 ?m
8.5 ?m minus 12 ?m
Rel. Emiss.

• Scales of AIRS, IASI, and CrIS provide inherent
  averaging.

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UW-Derived IR Emissivity from NASA AIRS

• AIRS emissivity a linear combination of pure
  scene types.

LSE from AIRS Radiance Using UW Research Algorith
m
1.00
UW Research Product
0.85
750
1250
Wavenumber (cm-1)
Wavenumber (cm-1)
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Ts (Absolute) from AIRS Vs. Truth (Downlooking
IRT)
Point Validation
outlier

• Surface Variability is Large.

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Ts (Absolute) from AIRS Vs. Ts (12 ?m) from AIRS
Point Validation

• 12 ?m estimate as good as Absolute!

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Surface temperature and Vegetation Fraction
Distributions Sept. 2002 March 2005 (Clear
only)
Ts Day
Ts Night
Note similarDay NightVegetationFraction
fromvery differentTs distributions
Veg. Frac. Night
Veg. Frac. Day
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Surface Emissivity and Land Use as Observed by
EOS AIRS
Emissivity (9 ?m)
Nov. 2003
Nov. 2004
Nov. 2002
Emissivity (4 ?m)
Vegetated
Exposed Soil !

• AIRS measures the infrared emissivity change due
  to land use (agricultural cycle of wheat
  farming planting and harvesting)

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Recommendation for NWP

• Suggestion for IASI (AIRS, or CrIS) is to
  estimate the skin Temperature from narrow
  micro-window at 12 microns (about 832 cm-1),
  using a guess for the surface emissivity. (See E.
  Pequignot-LMD talk).
• With this Ts, the emissivity can be retrieved at
  all surface sensitive channels after atmospheric
  correction.
• Use of the spectral variance constraint can
  further improve the results if RTE errors are
  small enough.
• However, fits to laboratory data (see E. Borbas
  UW talk) will still be needed to provide
  emissivity spectra that cover all the sounding
  channels.

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Backup Slides
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AIRS Temperature Validation MODIS Comparison
Comments Day/Night algorithm 5 km spatial
resolution MOD11C product
320
300
270
JULY 2003 MODIS (MOD11C) DAY-TIME
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AIRS Temperature Validation MODIS Comparison
Comments MODIS Good Data Flag Used. Reduced from
0.05 degree to 1 degree resolution Within Std
Dev. lt 1 K
320
300
270
JULY 2003 MODIS Averaged to 1 degree Grid
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AIRS Temperature Validation MODIS Comparison
MODIS (v. 4)
AIRS (v. 4)
Comments AIRS minus MODIS Mean 1.4 K Std
Dev 2.1 K
July 2003
AIRS - MODIS
-5 0 5
-6 0 6
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AIRS Temperature Validation MODIS Comparison
320
Comments North AmericanDay-TimeMean
TsurfaceBias within ?1 K except during Winter
K
250
AIRS minus MODIS
2
-2
1
12
MONTH of 2003
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Acknowledgements

• NASA EOS Validation Support
• AIRS Team (JPL team leader, M. Chahine)
• NPOESS program (S. Mango, IPO)
• CNES and EUMETSAT
• ECMWF and the UK Met Office
• U.S. Department of Energy ARM program