Comparison of Multiyear Time Series Observations Over Land from AMSR-E and Windsat

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Comparison of Multiyear Time Series Observations
Over Land from AMSR-E and Windsat Narendra N.
Das1, Steven Chan1, Eni Njoku1, and Li
Li2 1JPL/Caltech 2Naval Research Lab AMSR-E
Science Team Meeting June 25-26, 2009 Arlington,
VA
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Metrics for Comparison between AMSR-E and Windsat
Rationale of comparison is similarity in
microwave channels and instrument
characteristics, and overlap of long time series
that will help to cross-calibrate the instruments
AMSR-E Freq. (GHz) 6.92 10.65 18.7 23.8 36.5 89
  Bandwidth 350 100 200 400 1000 3000
  polarization V,H V,H V,H V,H V,H V,H
  Incidence angle 54.8 54.8 54.8 54.8 54.8 54.8
  IFOV (km x km) 76x44 49x28 26x16 31x18 14x8 6x4
               
Windsat Freq. (GHz) 6.8 10.7 18.7 23.8 37  
  Bandwidth 125 300 750 500 2000  
  polarization V,H V,H,U,4 V,H,U,4 V,H V,H,U,4  
  Incidence angle 53.5 49.9 55.3 53 53  
  IFOV (km x km) 71x39 38x25 27x16 20x12 13x8  

• Primary focus is in land observations
• Only descending passes are considered (AMSR-E
  1.30 A.M. and Windsat 5.59 A.M.)
• B. Compatible channels relevant for soil
  moisture and vegetation water content are
  considered (i.e., 6, 10, 18, and 36 GHz)
• C. Homogenous sites like Dome-C (stable),
  Amazon forest, and Sahara desert are chosen to
  evaluate the apparent difference/similarity among
  compatible channels observations
• RMSE, Annual Mean Difference and Polarization
  Ratio are discussed
• For comparison Tb data are binned in Ease Grid
  (25 km) using drop in the bucket technique

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DomeC
High Plateau Region in Antarctica
6 GHz
10 GHz
18 GHz
36 GHz
Scatter plot of H-pol Mean Tb June, 2005 to May
2006 (Lat -74 to -75, Lon 123 to 124)
Distinct biases of 4 K and 2 K are observed at
10 and 36 GHz (H-pol) channels, respectively.
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DomeC Comparison of Monthly mean
High Plateau Region in Antarctica
H-pol
V-pol
June, 2005 to May 2006 (Lat -74 to -75, Lon 123
to 124)
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Amazon Region
Tropical Forest
6 GHz
10 GHz
18 GHz
36 GHz
Scatter plot of H-pol Mean Tb June, 2005 to May
2006 (Lat -6.5 to -7.5, Lon -65 to -66)
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Amazon Region Comparison of Monthly mean
Tropical Forest
H-pol
V-pol
June, 2005 to May 2006 (Lat -6.5 to -7.5, Lon
-65 to -66)
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Sahara Region
Desert
6 GHz
10 GHz
18 GHz
36 GHz
Scatter plot of H-pol Mean Tb June, 2005 to May
2006 (Lat 19 to 20, Lon -6 to -7)
Distinct biases of 5 K and 2 K are observed at
10 and 36 GHz (H-pol) channels, respectively.
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Sahara Region Comparison of Monthly mean
Desert
H-pol
V-pol
June, 2005 to May 2006 (Lat 19 to 20, Lon -6 to
-7)
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Difference of Annual Mean between AMSR-E and
Windsat for Descending Pass
6 GHz
H-pol
V-pol
Tb K
Beside RFI hotspots, globally good agreement
within /- 1 K is observed
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Difference of Annual Mean between AMSR-E and
Windsat for Descending Pass
10 GHz
H-pol
V-pol
Tb K
Large difference in tune of 4-5 K is observed
over arid regions and 2-4 K for permanent ice
sheet for H-pol
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Difference of Annual Mean between AMSR-E and
Windsat for Descending Pass
18 GHz
H-pol
V-pol
Tb K
Good agreement is observed at a global scale for
both H- and V-pol channels
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Difference of Annual Mean between AMSR-E and
Windsat for Descending Pass
36 GHz
H-pol
V-pol
Tb K
Reasonably good agreement is observed at a global
scale for both H- and V-pol channels
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RMSE between AMSR-E and Windsat for Descending
Pass
Tb K
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Comparison of Polarization Ratio
AMSR-E
Windsat
10.7 GHz
lt
gt
Mean
For June05 to May06
Globally similar pattern is observed, however,
AMSR-E shows higher values over arid regions
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AMSR-E
Windsat
Std
lt
gt
For June05 to May06
Globally similar pattern is observed, however,
AMSR-E shows higher temporal variability in
surface emissivity caused primarily by change
in surface soil moisture
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Conclusion
Based on these preliminary analysis of overland
AMSR-E and Windsat data

• Among the eight channels, 18.7 GHz H- and V-pol
  channels have the best
• agreement
• Distinct bias of 3-5 K and 2-3 k are observed at
  10.7 GHz H-pol especially over
• bare soil (arid regions) and permanent ice
  sheet, respectively
• AMSR-E polarization ratio mean and standard
  deviation shows higher dynamic
• range as compared to Windsat
• These results show inconsistencies and
  similarities and guides us to take future
• course of action for more thorough analysis
  for cross-calibration.