Download Inter-Satellite Calibration of Microwave Sounders for - IEEE-GRSS

Lower-Tropospheric Temperature (TLT)
Climate Data Record Using NOAA/NESDIS/STAR
Recalibrated MSU Observations
Wenhui Wang1 & Cheng-Zhi Zou2
1IMSG
at NOAA/NESDIS/STAR
2NOAA/NESDIS/Center for Satellite Applications and Research
IGARSS
Vancouver, Canada
July 25-29, 2011
Outline
• Background
• Methods for Developing TLT Product Using
NOAA/NESDIS/STAR Recalibrated MSU Radiances
• Results and Discussion
• Summary and Future Works
Background
• Microwave Sounding Unit (MSU, 1978/11-2006/9)
• 9 instruments (NOAA TIROS-N – NOAA-14)
• 4 channels
Channel 2- mid-troposphere (TMT)
Channel 3 - upper-troposphere
Channel 4 - lower-stratosphere
25
• 11 scan angles: 0 – 47.35°
• Widely used in long-term atmospheric Tb trends studies
– TMT Affected by stratosphere cooling effect
– TLT: weighted average of TMT Tb
at different view angles
Scan Pos 5
20
Scan Pos 4
Scan Pos 2
(Spencer and Christy, 1992,2003; Mears and Wentz, 2009)
TLT=T3+T4+T8+T9-0.75(T1+T2+T10+T11)
NADIR
Scan Pos 3
Height (km)
• MSU Lower Tropospheric Temperature (TLT)
Weighting Function
(Ocean)
i=1-4, 8-10 scan positions
Reduce stratosphere cooling effect
Scan Pos 1
15
TLT
10
5
0
0
0.05
0.1
0.15
Background
• Two MSU TLT products available
Using NOAA pre-launch calibrated observations
– University of Alabama group (UAH)
– Remote Sensing Systems group (RSS)
• Major Issues need to addressed
– Calibration Errors (Warm Target Contamination)
– Orbital Decay Effect
– Diurnal Drift Effect
• TLT trends have important policy making implications
• Purpose of this study
– Generate STAR TLT product using NOAA/NESDIS/STAR recalibrated MSU
radiances
– Comparing STAR TLT with other two research groups
Methods for STAR TLT Product
1. Using NOAA/NESDIS/STAR Recalibrated MSU Radiances (v1.2)
(Zou et al. 2006, 2009, 2010)
– Simultaneous Nadir Overpass (SNO) Method to generate
consistent climate data records (CDR)
http://www.star.nesdis.noaa.gov/smcd/emb/mscat/mscatmain.htm
– Remove Warm Target (WT) Contamination at root level
– Can reduce inter-satellite bias by an order of magnitude
compared to NOAA pre-launch calibration
Methods for STAR TLT Product
1. Using NOAA/NESDIS/STAR Recalibrated MSU Radiances
NOAA 10 -14 averaged σ of intersatellite biases
SNO calibration (curve)
SNO + Christy Bias Correction
(straight line)
Christy Bias Correction is used to
removes residual WT contamination
after SNO calibration
Noises in TLT are 2 times as large as those in MSU
channel 2 (TMT)
Methods for STAR TLT Product
2. Satellite Altitude & Orbital Decay Effect Correction
870
860
• Satellite altitudes are different (morning
versus noon satellites)
Altitude (km)
850
• Satellite altitude trends to decay over time
840
• Cause view zenith angle changes, effects
vary with different limb positions
830
820
810
800
790
1978
NTN
N6
N7
N8
N9
N10
N11
N12
N14
1983
1988
1993
1998
2003
Methods for STAR TLT Product
2. Satellite Altitude & Orbital Decay Effect Correction
Simulated altitude effect climatology
– Community Radiative Transfer Model (CRTM)
– NASA MERRA reanalysis
– All observations adjusted to 850 km altitude
Rate of Tb change with satellite altitude (K/km)
Methods for STAR TLT Product
3.
Diurnal Drift Effect Correction
same as STAR TMT products (Zou and Wang 2009)
Using RSS monthly averaged diurnal anomaly climatology
Before Diurnal Correction
NOAA 11 - NOAA 10
Adjust the scene radiances at different
observation time to the local noon time
After Diurnal Correction
Results
5-day averaged MSU global mean TLT & TMT time series
Temporal Coverage: 1978/11-2006/9
Spatial Coverage: -82.5° – +82.5 °
Results: Spatial Trend Patterns (1978-2006)
TLT After Orbital Drift Effect Correction
TLT Without Orbital Decay Effect Corr.
TMT (channel 2)
Comparing STAR, UAH (v5.3), RSS (v3.2)
MSU TLT Products (1979 - 2003)
Summary and Future Works
• Generated MSU TLT product using NOAA/NESDIS/STAR recalibrated
channel 2 radiances
• STAR TLT shows a global warming trend of 0.145 K/dec (1978-2006),
• STAR TLT has the smallest warming trends compared to UAH and
RSS TLT products
– Larger differences exist during 1979 – 1986
• Next Step
– Generate TLT product using recalibrated Advanced Microwave
Sounding Unit A (AMSU-A) observations (1998 – present)
– Generate MSU/AMSU-A TLT merged Product
Results
TLT show similar trend stability as TMT (Zou and Wang, 2010)
Christy bias correction (almost horizontal lines)
Constant bias correction