Combining Multiple References
GSICS Web Meeting
2011-04-27
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
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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
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– as the references can never be perfectly consistent
– “There can be only be one” [Highlander, 1986]
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 intercalibration 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!
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GSICS Correction using Reference 1
• GSICS Correction for
Monitored Instrument
• Based on Reference 1
• Function with
uncertainty
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GSICS Correction using Reference 2
• GSICS Correction for
Monitored Instrument
• Based on Reference 2
• Different function with
different uncertainty
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Delta Correction Reference 2->1
• GSICS Correction for
Reference 2
• Based on Reference 1
• Function with
uncertainty
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Delta Correction Reference 2->1
• Delta GSICS Correction
for Reference 2
• Based on Reference 1
• Function with
uncertainty
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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
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Implementation
Correction
using
Reference 2
Correction
using
Reference 1
Delta
Correction
Reference 2-1
GSICS
Correction
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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…
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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
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:
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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
Action
GRWG06_19
Update GPPA to reflect the need of a
delta correction due to a migrating
reference
B. Iacovazzi
After first year
of IASI
operations on
Metop-B
After first year
of IASI
operations on
Metop-B
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
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Actions of Web Meeting
• Action: Fred Wu (NOAA) to circulate article by Likun
Wang comparing AIRS and IASI in GOES channel-space by
double-differencing and SNO methods and consider
application to other GEO imagers by 2011-06-30.
• Action: Tim Hewison (EUMETSAT) to ask CNES for details
of plans to compare MetopA/IASI and MetopB/IASI and
consider development of delta-correction function by
2011-06-30.
• All GPRCs will then consider how delta corrections could
be applied to their products.
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