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Special Sensor Microwave Imager (SSM/I) Intersensor Calibration and Impact on
Precipitation Trend
Song Yang, Fuzhong Weng, Banghai Yan, and Ninghai Sun
NOAA/NESDIS/STARCamp Springs, MD 20746
4th Workshop of International Precipitation Working Group (IPWG), Beijing, Oct 13-17, 2008
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Outline
• Why need SSM/I TDR Calibration• SCO Calibration Technique• Impacts on TDRs/EDRs/CDRs• Impacts on Rainfall Climate Trend• Conclusions
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Ascending Descending
Overall
SSM/I Oceanic Rain-free Ta Difference against Scan Central Pixel before Calibration (60°S-60°N)
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SSM/I Monthly Oceanic Rain-free TDR Time Series
before Calibration
SSM/I Intersensor Bias of Oceanic Rain-Free Monthly Mean Ta
Ta (
K)
37V
Ta B
ias
(K)
Oceanic Rain-Free Monthly Mean Ta
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F13 provides the stable and longest time series for inter-sensor calibration
SSM/I Orbit Draft
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Analysis of SCO Pixels Ta - Water t 30 sec & d 3 Km)
19H
22V
F11
F14
F14
F11
Std 5
F11
Std 2
F11
Std 2|Ta| 20
100 140 180 220 260 300 100 140 180 220 260 300 100 140 180 220 260 300 100 140 180 220 260 300
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85 H
Bia
s °K
Std 2|Ta|
20
F13-F11 SCO Pixels Ta Bias (Water - with scan angle adjustment)
F13-F14 SCO Pixels Ta Bias - Water (t 30 sec & d 3 Km, with scan angle adj.)
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19V 19H 22V 37V 37H 85V 85H Satellite
Surface Type Bias Bias Bias Bias Bias Bias Bias
W 0 0 0 0 0 0 0 0 0 0 0 0 0 0
L 0 0 0 0 0 0 0 0 0 0 0 0 0 0
I 0 0 0 0 0 0 0 0 0 0 0 0 0 0 F08
C 0 0 0 0 0 0 0 0 0 0 0 0 0 0
W -0.16 2.66 -0.12 2.19 -0.20 2.27 -0.16 1.42 -0.09 2.65 -0.30 1.61 -0.29 2.81
L 0.54 1.19 0.33 1.32 0.53 1.32 0.44 1.36 0.49 1.49 0.11 2.31 0.12 2.39
I -0.05 1.23 -0.03 2.01 -0.04 1.10 -0.04 0.91 0 2.13 -0.07 1.19 -0.09 3.96 F10
C 0.11 0.57 0.23 1.13 0.09 0.46 0.08 0.62 0.23 1.22 -0.02 1.20 0.10 1.28
W -0.56 0.55 0.09 1.07 -0.88 1.03 -0.34 0.55 0.39 1.58 -0.92 1.46 -0.17 1.10
L 0.02 1.01 0.21 1.05 -0.17 1.08 -0.19 0.96 0.01 1.04 -0.56 1.69 -0.62 1.56
I 0.23 0.90 0.35 0.98 -0.05 0.92 0.03 0.87 0.28 1.11 -0.26 2.01 -0.24 1.99 F11
C -0.10 1.83 0.21 2.50 -0.42 1.90 -0.07 1.82 0.19 2.58 -0.03 3.32 -0.03 3.49
W -0.43 0.64 0.32 0.54 -0.32 0.85 -0.81 0.45 0.21 0.63 -0.32 0.89 0.32 1.29
L 0 0.85 0.11 0.75 0.10 0.97 -0.42 0.67 -0.06 0.98 -0.01 1.54 0.23 1.30
I 0.06 0.76 0.25 0.87 0.13 0.91 -0.32 0.88 -0.05 0.83 0.23 1.32 0.43 1.33 F14
C 0.20 1.25 0.38 1.85 0.30 1.28 -0.08 1.16 0.25 1.73 0.39 2.67 0.74 2.86
W 0.42 0.65 -0.23 0.55 0.03 0.87 -0.17 0.51 -0.04 0.67 -0.05 0.87 -0.02 1.32
L 0.15 0.85 0.06 0.71 0.02 0.75 -0.02 0.59 -0.04 0.56 -0.02 0.81 -0.09 0.74
I 0.83 0.81 0.23 0.85 0.43 0.83 0.50 0.63 0.30 0.72 0.71 1.19 0.35 1.65 F15
C 0.16 1.10 -0.13 1.55 -0.07 1.08 0.12 1.10 0.09 1.64 0.33 1.91 0.41 2.30
Criteria: | t| 0.5 min; d 3 km; 2 K;Ta| 20 K; : Standard deviation (K) Surface Type Category: W Š Water; L Š Land; I Š Ice; C Š Coast
SSM/I TDR Bias Correction CoefficientsF13 as Reference Satellite
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SSM/I Monthly Oceanic Rain-free TDR Time Series after Calibration (F13 as Reference Satellite)
SSM/I Intersensor Bias of Oceanic Rain-Free Monthly Mean Ta
Ta (
K)
37V
Ta B
ias
(K)
Bef
ore
Cal
ibra
tion
Oceanic Rain-Free Monthly Mean Ta
Ta B
ias
(K)
37V
Ta (
K)
Oceanic Rain-Free Monthly Mean Ta
Aft
er C
alib
rati
on
SSM/I Intersensor Bias of Oceanic Rain-Free Monthly Mean Ta
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Before Calibration After CalibrationSSM/I Intersensor Bias of Oceanic Rain-Free Monthly Ta
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19V 19H 22V 37V 37H 85V 85H
Ta_Raw (K)
0.59 0.31 0.65 0.59 0.33 0.77 0.85
Ta_Cal
(K) 0.30 0.38 0.48 0.21 0.19 0.40 0.39
Chg (%)
-49 22 -26 -64 -42 -43 -54
Mean SSM/I TDR Absolute BiasF13 as Reference Satellite
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SSM/I Monthly Oceanic Rain-free TDR Trend (F13 as Reference Satellite)
Before C
alibration
After C
alibration
19V 19H 22V 37V 37H 85V 85H
S S S S S S S
Before 188.5 -0.92 125.2 -0.11 212.2 -0.74 208.3 -0.62 151.5 -0.18 251.8 -0.72 219.6 -0.46
After 188.2 -0.54 124.9 -0.23 211.9 -0.54 208.0 -0.58 151.4 -0.30 251.5 -0.36 219.3 -0.38
Comparison of SSM/I Monthly Oceanic Rain-free TDR before and after Calibration [(K), S (K/10yr)]
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F14 SSM/I Monthly Mean Surface Rainrate for December 2006 from NOAA Heritage Rain Algorithm and Matched TRMM 3B42
BeforeCalib.
AfterCalib.
Matched3B42
0.5°x0.5°grid scale
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F14 SSM/I Monthly Mean Surface Rainrates for December 2006 from NOAA Heritage Rain Algorithm
BeforeCalib.
AfterCalib.
Difference(aft - bef)
0.5°x0.5°grid scale
29% bias deduction with calibrated TDR against matched TRMM 3B42 Rain products
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F14 SSM/I Monthly Mean Total Precipitable Water (TPW) for December 2006 from NOAA Heritage Rain Algorithm
BeforeCalib.
AfterCalib.
Difference(aft - bef)
11% bias deduction with calibrated TDR against radiosonde measurement
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F14 SSM/I Monthly Mean Sea Ice Concentration (%) Near North Pole
Region for December 2006 from NOAA Heritage Algorithm
Before Calib. After Calib. Difference (aft - bef)
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Climate Trend of Oceanic Total Precipitable Water Path
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The importance of SSM/I intersensor calibration is presented.
NOAA/NESDIS SCO-based calibration scheme can dramatically reduce the intersensor biases of SSM/I TDRs.
Test results indicate that the SSM/I TDR calibration scheme shows significant impacts on EDRs/CDRs.
Although the bias correction of SSM/I TDRs is small, the calibration has a significant impact on TDR’s trend.
The very small decreasing trend of precipitation is evident, however, this trend could not be treated as the “truth” because of uncertainties associated with the calibrations and SSM/I sampling issue.
Conclusions
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