Date post: | 26-May-2015 |
Category: |
Technology |
Upload: | grssieee |
View: | 434 times |
Download: | 0 times |
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
• Background
• Methods for Developing TLT Product Using NOAA/NESDIS/STAR Recalibrated MSU Radiances
• Results and Discussion
• Summary and Future Works
Outline
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
• 11 scan angles: 0 – 47.35° • Widely used in long-term atmospheric Tb trends studies
• MSU Lower Tropospheric Temperature (TLT) – TMT Affected by stratosphere cooling effect
– TLT: weighted average of TMT Tb
at different view angles (Spencer and Christy, 1992,2003; Mears and Wentz, 2009)
TLT=T3+T4+T8+T9-0.75(T1+T2+T10+T11) i=1-4, 8-10 scan positions
Reduce stratosphere cooling effect
0
5
10
15
20
25
0 0.05 0.1 0.15
He
igh
t (k
m)
Weighting Function (Ocean)
NADIR
Scan Pos 5
Scan Pos 4
Scan Pos 3
Scan Pos 2
Scan Pos 1
TLT
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
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
SNO calibration (curve)
SNO + Christy Bias Correction (straight line)
Christy Bias Correction is used to removes residual WT contamination after SNO calibration
Methods for STAR TLT Product
NOAA 10 -14 averaged σ of intersatellite biases
Noises in TLT are 2 times as large as those in MSU
channel 2 (TMT)
1. Using NOAA/NESDIS/STAR Recalibrated MSU Radiances
2. Satellite Altitude & Orbital Decay Effect Correction
Methods for STAR TLT Product
790
800
810
820
830
840
850
860
870
1978 1983 1988 1993 1998 2003
Alt
itu
de
(km
)
NTN N6 N7
N8 N9 N10
N11 N12 N14
• Satellite altitudes are different (morning
versus noon satellites)
• Satellite altitude trends to decay over time
• Cause view zenith angle changes, effects
vary with different limb positions
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
After Diurnal Correction
NOAA 11 - NOAA 10
Methods for STAR TLT Product
Adjust the scene radiances at different
observation time to the local noon time
Results
5-day averaged MSU global mean TLT & TMT time series Temporal Coverage: 1978/11-2006/9
Spatial Coverage: -82.5° – +82.5 °
TLT Without Orbital Drift Effect Correction
TLT After Orbital Drift Effect Correction
Results: Spatial Trend Patterns (1978-2006)
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
TLT show similar trend stability as TMT (Zou and Wang, 2010)
Christy bias correction (almost horizontal lines)
Constant bias correction
Results