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