1. Combining Multiple References
GSICS Web Meeting

2. Advantages of multiple references
Robustness
In case of failure of one reference
Allows transition between references – e.g. MetopA->B
Greater coverage of diurnal cycle
Both scene and instrument calibration variability
Important for 3-axis stabilized spacecraft
Political

3. Disadvantages of multiple references
Segal's law:
"A man with a watch knows what time it is. A man with two watches is never sure." [Bloch, Arthur (2003). Murphy's Law. Perigee. p. 36.]
It refers to the potential pitfalls of having too much conflicting information when making a decision.
User confusion
Metrological Traceability Problems
as the references can never be perfectly consistent
“There can be only be one” [Highlander, 1986]

4. Solution to using multiple references
Define only one as the calibration reference
All others are regarded as calibration transfer standards
For example:
Time series of homogenised HIRS data? – Covered later
Use AIRS is used as a transfer standard to complement the inter-calibration against IASI as the calibration reference.
Allows collocations with GEO imagers over the diurnal cycle
because of different orbits of Aqua and Metop satellites carrying these instruments
MODIS + Desert BRDFs characterised by other instruments?
Discuss!

5. GSICS Correction using Reference 1
GSICS Correction for Monitored Instrument
Based on Reference 1
Function with uncertainty

6. GSICS Correction using Reference 2
GSICS Correction for Monitored Instrument
Based on Reference 2
Different function with different uncertainty

7. Delta Correction Reference 2->1
GSICS Correction for Reference 2
Based on Reference 1
Function with uncertainty

8. Delta Correction Reference 2->1
Delta GSICS Correction for Reference 2
Based on Reference 1
Function with uncertainty

9. GSICS Correction using Reference 2->1
Add Delta Correction to Reference 2
Maps GSICS Correction based on Reference 2 to Reference 1
Consistent function, but larger uncertainty

10. Implementation GSICS Correction Correction using Reference 1
Delta Correction Reference 2-1

11. From Draft Minutes of GRWG06
Handling Multiple References:
T. Hewison reminded the group that the traceability concept needs a single reference – so in case where the GSICS product is done for more than one reference (AIRS and IASI being one example), one reference should be traceable to the other one. Current GSICS IR products, based on AIRS and IASI must account for the difference between IASI and AIRS. NOAA and CMA base their GSICS correction only on IASI. JMA shows the AIRS and IASI results separately and in a combined version. KMA also does a separate reference to AIRS and IASI. Any combination of product must account for the additional uncertainty that this combination produces…
No.
Title
Actionee(s)
Due Date
Action GRWG06_17
Find out time overlaps between geostationary satellites (commissioning and operational periods), find out about the availability of such data and publish this information on the GSICIS Wiki
All GPRCs
End of 2011

12. From Draft Minutes of GRWG06 cont.
Strategy for Migrating References:
An example of the migrating reference will be the upcoming availability of IASI on Metop-B (launch date is 02 April 2012). To ensure traceability, the differences between the two IASIs, together with its uncertainty, must be recorded as a delta-correction to be applied to the GSICS correction. The following actions were agreed:
No.
Title
Actionee(s)
Due Date
Action GRWG06_18
Document the difference between IASI on Metop-A and IASI on Metop-B
EUMETSAT and CNES
After first year of IASI operations on Metop-B
Action GRWG06_19
Update GPPA to reflect the need of a delta correction due to a migrating reference
B. Iacovazzi

13. But what about Current Products?
Need to develop Delta Correction
To remap GSICS Corrections based on AIRS->IASI
In GEOs’ radiance-space (for each GEO)
Can double-differencing (GEO-IASI)-(GEO-AIRS)
But only if they are comparable – e.g. night-time?
Need a stable GEO as transfer reference – assumption?
Can also do SNO comparison of AIRS-IASI
Convolved with GEO SRFs
After gap-filling

14. Work Plan Which approach is better?
One-off delta correction or continuous?
Who will do it?
What is needed?
When by?
Do we hold off migration to pre-operational status until we can include this into products using multiple references?