Development of AMSU Fundamental CDR
Development of AMSU Fundamental CDR
AMSU-A Scan Bias Correction and Verification
Two-point (2P) correction vs. three-point (3P) correction Verification using brightness temperature (FCDR) Verification using L2 products (TCDR)
Background
Goals General methods
Further Studies
Possible source of scan bias Characterization over three reference ranges Asymmetry as a function of observed brightness temperature
AMSU-A Scan Bias Characterization
Attempt to improve 50.3 and 89 GHz results
Goals
Develop Advance Microwave Sounding Unit-A and -B (AMSU-A/-B), and Microwave Humidity Sounder (MHS) FCDR’s for window and water vapor channels AMSU-A: 23.8, 31.4, 50.3 and 89.0 GHz, i.e. Channel 1-3 and 15 AMSU-B/MHS: 89, 150/157; 183.3±1, 183.3±3, 183.3±7/190.3 GHz, i. e. all channels
Develop TCDR’s for hydrological products, i. e., Rain Rate, TPW, CLW, IWP, Snow Cover, SWE, SIC
Presently in Stage One to develop FCDR’s including NOAA-15, 16, 17,18, 19 & MetOp-A L1B data from launch to 2010 (NOAA-15 AMSU-B from 2000 to 2010, due to RFI)
General Methods
AMSU 1b raw count
Ta
Tb
Clear sky AMSU-A/-B/MHS FOV Over tropical/subtropical oceans
ERA interim T, q, O3 profiles; ERA interim SST, 10m U & V;
Geo corrected AMSU LZA, scan angle
Tb
Compare collocated Tb’s with same atmospheric condition for each beam position
CRTM
General Result of Scan Bias Characterization
Explanation and Characterization
AMSU-A scan bias may due to sensor problem including
1. Cross polarization, η 2. Reflector normal angle error, θ 3. Mis-alignment of polarization angle, ψ 4. Sensor scan angle error, φ
Three reference ranges to characterize the scan bias
1. Vicarious cold reference (VCR) 2. Most probable values (MPV) of environmental variables 3. Vicarious hot reference (VHR)
Sensitivity Test of The Sensor Problems
Mean Brightness Temperature over Ocean
Mean Scan Bias over Ocean
Possible Combination of Sensor Error to Explain The Scan Bias
Deeper Survey into VCR Assumption
TELSEM for VHR over Amazon Rain Forest
Observation and Scan Bias of VHR
Correction and Verification
Correction after characterization
1. Asymmetry as a function of observed brightness temperature 2. Two-point (2P) correction vs. three-point (3P) correction
Verification
1. Using brightness temperature (FCDR) 2. Using L2 products (TCDR)
Scan Bias (ASYM) as a Function of Observed Brightness Temperature (TBO)
Verification Using Brightness Temperature for 2P Correction Approach
Verification Using Brightness Temperature for 3P Correction Approach
Verification Using L2 Products
Statistic Angular Comaprison
Attempt to Improve Scan Bias Characterization of 50.3 GHz and 89 GHz Channels
1. Lowest brightness temperature of these two channels appear on Antarctica in southern winter
2. The lowest brightness temperature can be 60 K below VCR results
3. Serious sampling bias due to cross scan in Polar region
4. Plan to exclude some limb beam positions
Location of Extreme BT for 89 GHz Channel, Antarctica
Reference Coldest Brightness Temperature for NOAA-15, 2008
MPV�
VCR�
Lowest Observation�
OBS vs. SIM Brightness Temperature for NOAA-15, 2004
Sampling Bias in Polar Region, Red – Nadir, Blue – Beam Position 30
Conclusion
1. The correction approaches are promising
2. The two channels with lower frequency have better correction results
3. Correction results may improve with radiative transfer model regarding to more accurate angular representation
4. The assumption that lower brightness contains higher degree of polarization may have some exceptions
5. The asymmetry pattern is stable through years, but quite different among on-board satellites
6. Currently working on inter-satellite calibration