1. Joint GRWG and GDWG Meeting 09-11 February 2010, Toulouse, France
Monitoring of IR Clear-sky Radiances over Oceans for SST (MICROS) Towards Cross-Platform Radiance Consistency Between AVHRRs Onboard NOAA-16, -17, -18, -19 and MetOp-A
Alexander Ignatov and XingMing Liang
NOAA/NESDIS, Center for Satellite Applications and Research
and
Presented by: Andy Heidinger
NESDIS/STAR and U. Wisconsin
10 February 2010
Joint GRWG & GDWG Meeting Toulouse, France

2. Joint GRWG & GDWG Meeting Toulouse, France
MICROS
A web-based Near-Real Time tool
Monitoring global “model minus observation” bias
Model: Community Radiative Transfer Model (CRTM) used in conjunction with GFS upper air data and Reynolds SST
Observation*: AVHRR Ch3B (3.7μm), Ch4(11μm), and Ch5(12μm) onboard NOAA-16, -17, -18, -19 and MetOp-A
Implemented in July 2008
*Produced by the Advanced Clear-Sky Processor over Oceans (ACSPO)
10 February 2010
Joint GRWG & GDWG Meeting Toulouse, France

3. Joint GRWG & GDWG Meeting Toulouse, France
Objectives
MICROS Objectives
Monitor and test improvements in ACSPO main product Clear-Sky Radiances over Oceans
Validate and improve Community Radiative Transfer Model (CRTM)
Monitor AVHRR radiances over clear-sky global ocean in NRT for stability, self- and cross-platform consistency
This presentation:
Present examples of nighttime analysis in Ch3b (3.7 μm)
Discuss potential factors affecting cross-platform consistency
CRTM v1 performance during daytime suboptimal & being improved
10 February 2010
Joint GRWG & GDWG Meeting Toulouse, France

4. Joint GRWG & GDWG Meeting Toulouse, France
Methodology
Use robust statistics to monitor brightness temperatures (BT)
More informative of sensor calibration performance
(Minimizes effects of possible outliers)
Employ Double-differencing (DD) technique to rectify cross-platform biases from “noise” in M-O bias
NOAA-17 = Reference satellite (Stable; EXT close to MetOp-A)
CRTM used as a ‘transfer standard’
DD minimizes artifacts in M-O biases arising from e.g.
Errors in Reynolds SST and GFS upper air data
Missing aerosol in current implementation
Possible systematic biases in CRTM
Changing versions of ACSPO algorithm
Note that DD do take into account differences in spectral responses between different sensors (unless those are in error)
10 February 2010
Joint GRWG & GDWG Meeting Toulouse, France

5. Nighttime M-O bias in Ch3b: Maps
NOAA-19, 28 March 2009, UTC
Close to zero and uniformly distributed
10 February 2010
Joint GRWG & GDWG Meeting Toulouse, France

6. Nighttime M-O bias in Ch3b: Histograms
NOAA-16, -17, 18, 19, and MetOp-A 28 March 2009
Model is warmer than Obs by ~0.1 K due to
using bulk SST (instead of skin)
using diurnal-mean Reynolds SST at night
missing aerosol in CRTM implementation
possible residual cloud in AVHRR BTs
Stat: million clear-sky pixels per day
Shape of histograms: Close to Gaussian
Cross-platform consistency: within ~0.1 K
(Note: Overpass time is from 9:30pm-5am)
10 February 2010
Joint GRWG & GDWG Meeting Toulouse, France

7. Nighttime M-O bias in Ch3b: Angular Dependencies
NOAA-16, -17, 18, 19, and MetOp-A 28 March 2009
Angular dependencies: within <0.2 K
Cross-platform consistency: within < 0.1 K
10 February 2010
Joint GRWG & GDWG Meeting Toulouse, France

8. Joint GRWG & GDWG Meeting Toulouse, France
Stability of biases
in Ch3b BT and SST
V1.02
V1.10
V1.00
BT Biases in Ch3b
ACSPO version: No effect on M-O biases
SST Biases (Retrieved – Reynolds)
BT and SST biases change in time by several tenths of a Kelvin.
BT bias change in anti-phase with SST biases.
This suggests that Reynolds SST (input to CRTM) is unstable within several tenths of a Kelvin.
10 February 2010
Joint GRWG & GDWG Meeting Toulouse, France

9. Double Differences (DD) in Ch3b:
Cancel out most errors in BT/SST biases
Mean Ch3b biases relative to N17:
MetOp-A: K
NOAA-18: K
NOAA-19: K
NOAA-16: Unstable
V1.00
V1.02
V1.10
Cross-platform inconsistencies are due to
Sensor calibration systematic biases
Spectral response function deviations from those used in CRTM
Local time differences (affect SST and BTs through diurnal cycle)
Work is underway to attribute the causes and reconcile different platforms
10 February 2010
Joint GRWG & GDWG Meeting Toulouse, France

10. Double-Differences in Ch4 and Ch5
V1.00
V1.02
V1.10
V1.00
V1.02
V1.10
Mean Ch4 biases relative to N17:
MetOp-A: K
NOAA-18: K
NOAA-19: K
NOAA-16: Unstable
Mean Ch5 biases relative to N17:
MetOp-A: K
NOAA-18: K
NOAA-19: K
NOAA-16: Unstable
10 February 2010
Joint GRWG & GDWG Meeting Toulouse, France

11. Joint GRWG & GDWG Meeting Toulouse, France
Conclusion
Nighttime global BT biases in AVHRR IR bands on N17, -18, -19, and MetOp-A, show artificial variations up to several tenths of a Kelvin. NOAA-16 is out-of-family and unstable
This variability likely arises from instabilities in Reynolds SST (used as input to CRTM). It largely cancels out when Double-Differences are calculated
The DDs show that BTs are cross-platform consistent to within several hundredths of a degree Kelvin in all three IR bands
Improved sensor calibration and response functions and accounting for diurnal variability is needed
10 February 2010
Joint GRWG & GDWG Meeting Toulouse, France

12. Ongoing and Future Work
Work with NESDIS CAL experts (Changyong Cao, Fred Wu, Andy Harris, Jon Mittaz) to explore improving sensor radiances: calibration, response functions
Work with CRTM Team (Yong Han) to improve daytime CRTM performance
Work with Chelle Gentemann (RSS) to explore diurnal and skin-to-bulk corrections to Reynolds SST as input to CRTM in MICROS
Check sensitivity of DDs to
SST (Reynolds vs. RTG vs. OSTIA)
upper air fields (GFS vs. ECMWF)
ACSPO cloud mask
10 February 2010
Joint GRWG & GDWG Meeting Toulouse, France

13. Joint GRWG & GDWG Meeting Toulouse, France
Back-Up slide
M-O Biases in AVHRR Ch4 and Ch5
10 February 2010
Joint GRWG & GDWG Meeting Toulouse, France

14. Joint GRWG & GDWG Meeting Toulouse, France
M-O biases in Ch4 and Ch5
M-O Biases in Ch4
M-O Biases in Ch5
V1.00
V1.02
V1.00
V1.10
V1.02
V1.10
Similar to Ch3B, warm M-O biases observed at all times for Ch4 and Ch5
The excursions of M-O biases in Ch4 and Ch5 are also observed
However, they are smaller than in Ch3B due to more oblique atmosphere in Ch4 and Ch5
10 February 2010
Joint GRWG & GDWG Meeting Toulouse, France