1. GSICS Products’ Improvements and Developments
24 April 2019
GSICS Products’ Improvements and Developments
Tim Hewison1 and all GSICS Developers
EUMETSAT

2. Outline of Presentation
Introduction to Types of GSICS Products
GSICS Correction
Near Real-Time and Re-Analysis
Error Budget
GSICS Bias Monitoring
Example prototype web pages
Harmonisation
GSICS Reports & Guidelines
Current Status
GEO-LEO IR hyperspectral
LEO-LEO Solar

3. GSICS Product Portfolio
Currently in Demonstration Mode
For Operational Meteorological Satellites
− Geostationary – IR & Solar
− LEO – IR, Solar and Microwave – Conical & Cross-track Scanners
− Current Operational & Historic Instruments
− In near real-time and re-analysis modes
GSICS Bias Monitoring
− Routine comparisons of satellite radiances against reference
GSICS Correction
− Function to correct issued radiances
− For consistent calibration with reference
GSICS Reports & Guidelines
− Recommendations to modify practices
− Design and Operation of future satellite instruments

4. GEO-LEO IR: Basic Methodology
Comparison of level 1 data (radiances)
− issued operationally from the Monitored satellite instrument
− with those of a Reference instrument (or model)
Ensuring these are comparable
− Transformations (spectral, spatial, temporal)
− Including sampling/homogeneity checks
Typically ~1000 comparable samples/day for GEO-LEO
These are analysed to identify any significant sensitivities
− e.g. Incidence angle, latitude, radiance, time
and combined where possible
− defining the domain of validity and smoothing period

5. GSICS Products: Bias Monitoring
xMON ∆x
Comparing samples of xMON v xREF
− Over fixed domain,
− Period (e.g. 1 orbit/1 day)
Comparison by regression
Calc bias, ∆x=xMON-xREF
− at standard scene, xSTD
− with uncertainty
Plot time series of bias ∆x
− Compare recent results with long-term trend
− Valuable for instrument monitoring
xSTD
xREF ∆x t

6. GSICS Products: GSICS Correction
xREF
xMON
GSICS Correction function
Compare all xREF v xMON samples
− over smoothing period
Regression coefficients
with uncertainty (covariance)
Provide a function users can apply
to convert level 1 data, xMON
to be consistent with calibration of reference, xREF
Two versions:
Near Real-Time (asymmetric)
Re-Analysis (symmetric) ∆x t
Time series of bias estimated from:
– GSICS Near Real-Time Correction
– GSICS Re-Analysis Correction

7. GSICS Products: Guidelines
Underlying assumption of GSICS Correction:
Small errors (e.g. SRF errors, blackbody temperature, ...) introduce small departures from ‘true’ calibration
If these are linearly related a predictor (radiance, time, ...) we can apply empirical correction based on inter-calibration
Can analyse GSICS products
to diagnose root causes of calibration errors
Derive recommendations to modify
operating practices (e.g. adopt new SRF definition),
pre-launch characterisation, etc.
These GSICS Guidelines are distributed as written reports

8. Outline of Presentation
Introduction to Types of GSICS Products
GSICS Correction
Near Real-Time and Re-Analysis
Error Budget
GSICS Bias Monitoring
Example prototype web pages
Harmonisation
GSICS Reports & Guidelines
Current Status
GEO-LEO IR hyperspectral
LEO-LEO Solar

9. Comparison of Collocated Radiances
24 April 2019
Comparison of Collocated Radiances
Simultaneous near-Nadir Overpass
of GEO imager and LEO sounder
Collocation Criteria:
ΔLat<35° ΔLon<35°
Δt < 5 mins
Δsecθ < (Atmospheric path diff.)
Concentrated in tropics
~1000 collocations/orbit
~1 orbit/night

10. Data Transformations (Spectral and Spatial)
24 April 2019
Data Transformations (Spectral and Spatial)
Spectral Convolution:
Convolve LEO Radiance Spectra with GEO Spectral Response Functions
to synthesise radiance in GEO channels
Spatial Averaging:
Average GEO pixels in each LEO FoV
Estimate uncertainty
due to spatial variability
as Standard Deviation of GEO pixels
Use in weighted regression
LEO FoV~10km
~ 3x3 GEO pixels
The next step is to transform the collocated data to allow direct comparisons between the instruments.
Firstly, the IASI radiance spectra is convolved with the Spectral Response Functions of the Meteosat channels, to calculate the expected radiance in each Meteosat channel.
Then the Meteosat pixels within each IASI iFoV are averaged.
Their variance is also calculated to quantify the uncertainty due to spatial variability and
is used to weight each collocation in a linear regression …

11. GSICS Products for GEO IR
xREF
xMON
GSICS Correction function
GSICS Monitoring
GSICS Corrections
Near Real-Time & Re-Analysis
for Monitored instrument
IR channels of GEO imagers
against reference instrument
IASI and AIRS (hyperspectral)
by direct comparison
of collocated radiances
Typical Corrections ~1K
For GEO IR channels t ∆x
Time series of bias estimated from:
– GSICS Near Real-Time Correction
– GSICS Re-Analysis Correction

12. Example of GSICS Bias Monitoring
From CMA: Time Series of FY2D-IASI Standard Biases [K]

13. Example of GSICS Bias Monitoring
From JMA: Time Series of MTSAT-1R-IASI/AIRS Standard Biases [K]

14. Example of GSICS Bias Monitoring
From EUMETSAT: Time Series of Meteosat9-IASI Standard Biases [K]

15. Example of GSICS Bias Monitoring
From NOAA: Time Series of GOES12-AIRS Standard Biases [K]

16. GCC GEO-LEO Baseline Algorithm Implementation
24 April 2019
GCC GEO-LEO Baseline Algorithm Implementation
GOES-11/-12, FY-2C, MET-7/-9, and MTSAT-1R with IASI and AIRS
The Baseline Tb bias results computed at the GCC and EUMETSAT for Meteosat-9 are comparable 
GCC uses AIRS and IASI to monitor performance of the two instruments and for diurnal corrections due to solar contamination prone to 3-axis stabilized systems
Baseline algorithm for all GEOs provides confidence of GPRC implementation
Reprocessing of GSICS corrections for all GEOS to 2003 (AIRS) is underway at NOAA.

17. GSICS Common Bias Monitoring
Purpose
Common bias monitoring web page enable us to easily compare the inter-calibration results with other GPRC’s
Design for the top page
A draft design was proposed in April 2010
Timeline
Complete a prototype of monitoring page ( -Dec )
Review to GDWG and GRWG ( -Mar )
Implement at each GPRC

18. Web Design for Bias Monitoring

19. Outline of Presentation
Introduction to Types of GSICS Products
GSICS Correction
Near Real-Time and Re-Analysis
Error Budget
GSICS Bias Monitoring
Example prototype web pages
Harmonisation
GSICS Reports & Guidelines
Current Status
GEO-LEO IR hyperspectral
LEO-LEO Solar

20. First GSICS Guideline document
Best Practice Guidelines for Pre-Launch Characterization and Calibration of Instruments for Passive Optical Remote Sensing
Report to GSICS Executive Panel
R.U. Datla, J.P. Rice, K. Lykke and B.C. Johnson (NIST)
J.J. Butler and X. Xiong (NASA)
September 2009

21. HIRS Channel 6 : Root Causes and Corrections
24 April 2019
HIRS Channel 6 : Root Causes and Corrections
Without SRF shift
With SRF shift 0.2 cm-1
Since the HIRS sounding channels are located at the slope region of the atmospheric spectra, a small shift of the SRF can cause biases in observed radiances.
… the second factor, the spectral shift, which explains for some of the remaining differences.
There are other things in ICVS that GSICS can use. This is just one example.
Details can be referred to Wang et al. (manuscript for JTECH, 2006)

22. Outline of Presentation
Introduction to Types of GSICS Products
GSICS Correction
Near Real-Time and Re-Analysis
Error Budget
GSICS Bias Monitoring
Example prototype web pages
Harmonisation
GSICS Reports & Guidelines
Current Status
GEO-LEO IR hyperspectral
LEO-LEO Solar

23. GEO-LEO IR Product Status 2010-09
GPRC
Monitored Instrument
Reference Instrument
GSICS NRT Correction
GSICS Re-Analysis Correction
GSICS Bias Monitoring
EUMETSAT
Meteosat-9
Meteosat-8
Meteosat-7
IASI
Demonstration
In development
Prototype
JMA
MTSAT-1R }
MTSAT-2 }
IASI/AIRS
NOAA
GOES-11 Imager
GOES-12 Imager
CMA
FY2C }
FY2D }
FY2E }
KMA
COMS

24. GEO-LEO IR Error Budget

25. PATMOS-x PATMOS-x provides calibrations for Ch 1 & 2 of all AVHRRs
from TIROS-N, onward.
Consistent across all AVHRRs
radiometrically tied to equivalent channels on MODIS
Derived from
simultaneous nadir overpasses (SNOs) between AVHRR and MODIS,
benchmark reflectances established with MODIS,
and time-dependent relationships between coeval AVHRRs
The calibration itself takes the form of fitted parameters in an equation that is a function of instrument count and time
PATMOS-x products are computed using this calibration
Submitted to GSICS Product Acceptance Procedure
To be certified as GSICS compliant

26. Outline of Presentation
Introduction to Types of GSICS Products
GSICS Correction
Near Real-Time and Re-Analysis
Error Budget
GSICS Bias Monitoring
Example prototype web pages
Harmonisation
GSICS Reports & Guidelines
Current Status
GEO-LEO IR hyperspectral
LEO-LEO Solar

27. Summary GSICS is Global Space-based Inter-Calibration System!
Focuses on Level 1 data => FCDR
GSICS does not (generally) issue re-calibrated archives of data
But provides products to correct calibration of real-time and archive data to be consistent with reference instruments
Also provides tools to monitor biases in near real-time
GSICS Product Types defined:
GSICS Correction – Near Real-Time and Re-Analysis
GSICS Bias Monitoring
GSICS Reports & Guidelines
Now have demonstration products
GSICS Correction of GEO imagers’ IR channels – beta testing
GSICS Calibration of AVHRR solar channels (PATMOS-X) – submitted to GPPA
Need to ensure consistency between products
For different instruments – contemporary and historic

28. 24 April 2019
Thank You
Any Questions?