COMPARING RADIANCES MEASURED BY HIGH SPECTRAL RESOLUTION POLAR ORBITING
AIRS AND BROADBAND GEOSTATIONARY IMAGERS
Mathew M. Gunshor*
1
1,
David
1
Tobin ,
Timothy J. Schmit
2,
3
and W. Paul Menzel
Cooperative Institute for Meteorological Satellite Studies - University of Wisconsin
2 NOAA/NESDIS/ORA/ASPT
3 NOAA/NESDIS/ORA
Madison, Wisconsin
* Mat.Gunshor@ssec.wisc.edu
INTRODUCTION
METHODS
SUMMARY
Purpose
Intercalibration Equation
IRW Results
WV Results
• Global applications of weather satellites require a comparison
of the various operational instruments.
• Geo minus Leo
Routine comparisons of NOAA-14 (top) and
NOAA-15 (bottom) to 5 operational geostationary
instruments.
Routine comparisons of NOAA-14 (top) and
NOAA-15 (bottom) to 5 operational geostationary
instruments.
• Radiance validation of new instruments during post-launch
checkout provides confidence in instrument performance or
could provide an indication of a problem.
• Forward model calculated radiances
are subtracted from measured mean
radiances.
Number of
Comparisons
GOES-10 Imager IRW Band
• LEO = Low Earth Orbiting Instrument (HIRS or AVHRR)
Data Collection
• GEO = Geostationary Orbiting Instrument
• Mean = Measured Mean Radiance in Intercalibration Area
• Geo/Leo within +/- 30 Minutes
ΔR
 R GEO  R GEO   R LEO  R LEO 
Cal  Mean
Clear   Mean
Clear 
• Clear = Forward Model Calculated Clear Sky Radiance
Convert to Brightness
Temperatures
• R = Radiance (mW/m2/ster/cm-1)
• Leo within +/- 10 degrees Lat/Lon of geo nadir
• T = Temperature (K)
• TCAL = Brightness Temperature Difference
• B-1 = Inverse Planck Function Conversion From Radiance to
Temperature
GEO
GEO  
LEO
LEO 

ΔT
 B  1Mean  B  1Clear   B  1Mean  B  1Clear 
CAL 
 

Spatial Averaging
Intercalibration Equation Applied to AIRS
• Geo and Leo data smoothed to 100 km (effective
resolution) using a moving average.
• AIRS radiances are convolved with GEO spectral response functions.
• Smoothing and averaging reduces the effects of possible
navigation errors and the differences between instrument
resolutions.
• Spectrally convolved AIRS radiances are compared with measured GEO
radiances.
• T  B
-1GEO
Mean
GOES-8
IRW
42
42
-0.6 K
-0.3 K
0.8 K
0.3 K
N-14 Delta (geo – leo)
Mean
AIRS Convolved w/GOES-10 IRW SRF
Standard
Deviation
THIRS
TAVHRR
THIRS
TAVHRR
THIRS
TAVHRR
N-15 Delta (geo – leo)
Should Differences with AIRS be expected?
Number of
Comparisons
• When AIRS radiances are convolved with GEO spectral response
functions, any substantial gaps in the AIRS spectra creates some
“convolution error.” The magnitude of this error increases as the
gaps in the AIRS spectral coverage increase.
Mean
Standard
Deviation
• Convolution error is small in the IRW, but large in the water vapor
channel.
• In addition to convolution error, other contributions can come
from temporal, field of view size and shape, and navigation
differences as well as GEO spectral response function uncertainty.
-1AIRS
Mean
-B
THIRS
TAVHRR
THIRS
TAVHRR
THIRS
TAVHRR
GOES-10
IRW
353
353
-0.6 K
-0.1 K
1.2 K
0.3 K
GOES-8
IRW
39
39
-0.1 K
0.1 K
0.9 K
0.4 K
GOES-10
IRW
168
168
-0.1 K
-0.2 K
1.4 K
0.4 K
MET-5
IRW
352
352
-0.8 K
-0.4 K
1.1 K
0.6 K
MET-7
IRW
424
424
-1.1 K
-0.7 K
1.1 K
0.7 K
MET-5
IRW
175
175
-0.5 K
-0.6 K
1.8 K
1.4 K
MET-7
IRW
198
198
-1.2 K
-1.0 K
1.1 K
0.7 K
GMS-5
IRW
137
137
-0.9 K
-0.6 K
1.0 K
0.6 K
GMS-5
IRW
40
40
-0.6 K
-0.7 K
1.3 K
0.4 K
N-14 Delta (geo – leo)
GOES-8
WV
GOES-10
WV
MET-5
WV
MET-7
WV
GMS-5
WV
Number of
Comparisons
THIRS
237
488
458
327
252
Mean
THIRS
1.5 K
2.2 K
3.9 K
3.9 K
1.2 K
Standard
Deviation
THIRS
0.7 K
0.8 K
1.3 K
0.8 K
1.0 K
GOES-8
WV
GOES-10
WV
MET-5
WV
MET-7
WV
GMS-5
WV
N-15 Delta (geo – leo)
Number of
Comparisons
THIRS
119
219
200
0
78
Mean
THIRS
0.6 K
1.8 K
3.2 K
na
-0.1 K
Standard
Deviation
THIRS
1.1 K
1.5 K
1.8 K
na
1.7 K
• All GEO IRW agree within 1.0 K of LEO IRW on
NOAA-14 and NOAA-15 (HIRS and AVHRR).
• All GEO WV agree within 4 K of LEO WV on
NOAA-14 and NOAA-15 (HIRS).
• GOES-10 Imager and AIRS show preliminary
differences between 0.1 and 0.3 K.
• GOES-10 Imager and AIRS show preliminary
differences between 1 and 2 K.
• “Convolution Error” between GOES and AIRS is
approximately 0.1 K.
• “Convolution Error” between GOES and AIRS is
between 2 and 3K.
• The Mean Radiance inside the Intercalibration Area is
calculated from the spatially averaged data.
GOES-8
Imager
GOES-10
Imager
GOES-12
Imager
Meteosat-7
• Better intercalibration is possible when operational high spectral resolution instruments cover the entire spectral
response function of the broadband instruments. Such comparisons will be vital for validation and monitoring sensor
degradation.
Meteosat Second
Generation
FUTURE WORK
IR
Window
IRW Bands
Satellite
WV Bands
TBB (K)
TBB from
GOES-8 (K)
TBB (K)
TBB From
GOES-8 (K)
GOES-8
289.5
N/A
248.7
N/A
GOES-10
289.5
0.0
248.9
0.2
GOES-12
289.5
0.0
262.2
13.5
Meteosat-7
288.4
-1.1
257.7
9.0
MSG
289.4
0.1
253.7
5.0
AIRS
• More cases will be studied with all operational
geostationary instruments.
• Convolution error correction methods will be
explored.
• Additional comparisons will be made with
MODIS on Aqua.
Routine Intercalibration
Water Vapor
Channel
Sample AIRS spectrum convolved with various
GEO IRW and WV bands. Note the gaps in the
WV coverage.
• New instruments to be added include NOAA-17,
MSG, and GOES-12.
Acknowledgements
• Kevin Baggett, Jim Nelson, and Geary Callan for their
programming assistance. Tony Schreiner for providing the
background images.