metrology principles for earth observation: the nmi view
TRANSCRIPT
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Metrology Principles for Earth Observation:
the NMI view
Emma Woolliams
17th October 2017
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Interoperability
Decadal Stability
Radiometric Accuracy
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• Identical worldwide
• Century-long stability
• Absolute accuracy
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Organisation of World Metrology
The Convention of the Metre
(Convention du Mètre)
International System of Units (SI)
(Système International d'Unités)
Mutual Recognition Arrangement
(CIPM-MRA)
1875
1960
1999
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This presentation
1. How world metrology achieves
interoperability, stability and accuracy
2. How these principles can be applied
to Earth Observation
3. Resources to help
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This presentation
1. How world metrology achieves
interoperability, stability and accuracy
2. How these principles can be applied
to Earth Observation
3. Resources to help
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• How do we make sure a wing
built in one country fits a
fuselage built in another?
• How do we make sure the SI
units are stable over
centuries?
• How do we improve SI over
time without losing
interoperability and stability?
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History of the metre
1 ten millionth of the
distance from the
North Pole to the
Equator through
Paris
1795 1799Metre des Archives
1889International
Prototype
1960
1 650 763.73
wavelengths of a
krypton-86
transition
1983
Distance light
travels in
1/299 792 458th of
a second
2018
Distance that makes
the speed of light
299 792 458 m s-1
• Stable
• Improves over time
• Reference to physical process
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Three principles
Traceability
Uncertainty Analysis
Comparison
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SI
Primary standard
Secondary standard
Laboratory calibration
Industrial / field measurement
Traceability
Unit definition
At BIPM and NMIs
Users
Incre
asin
g u
ncert
ain
ty
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Traceability:
An unbroken chain
SI
Documented
procedures
Rigorous
uncertainty
analysis
Audits
Transfer
standards
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Rigorous Uncertainty Analysis
The Guide to the expression of Uncertainty in Measurement (GUM)
• The foremost authority and guide to the expression and calculation of uncertainty in measurement science
• Written by the BIPM, ISO, etc.
• Covers a wide number of applications
• Also a set of supplements
http://www.bipm.org/en/publications/guides/gum.html
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X1
X2
X3
Y
Error effects Input quantities
Measurement model
Output quantity
Principle of Uncertainty Analysis
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Y
Error effects Input quantities
Measurement model
Output quantity
Monte Carlo Approach
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X1
X2
X3
Y
Error effects Input quantities
Locally linearised model
Output quantity
1u X
2,au X
2,bu X
2,cu X
3u X
u Y
Law of Propagation of
Uncertainty
1 2y
n
f f f
x x x
C
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Comparisons
Scientific
comparisons:
Immature field –
learning what we don’t
know
Formal MRA
comparisons:
Mature field – to check
world metrology still
works!
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Lab-to-lab
(results of a scientific comparison)
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MRA Formal comparison
Luminous Intensity key comparison
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CMC Database
https://kcdb.bipm.org/
Evidence: Formal peer review or audit of procedures,
participation in a relevant key comparison (within 10
years) with declared uncertainties defended, review
within region and between regions
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Protocol
Measurements
Pre-Draft A
Draft A
Draft B
Final report
• Written by working group
• Approved by participants
• Reviewed then approved by CCPR
• Results sent to pilot only
• Often star-form
• Relative results (intra-lab consistency)
• Review of uncertainty statements
• No results shown
• Discussion on dealing with outliers (blind)
• First time participants see results
• Review by participants
• Review by experts
• Approval by CCPR
• Published
Used to:
• Validate CMCs
• Inform customers
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Ongoing research: Outliers
-2.0%
-1.5%
-1.0%
-0.5%
0.0%
0.5%
1.0%
1.5%
2.0%
0 2 4 6 8 10
Participants
De
via
tio
n f
rom
KC
RV
(all)
KCRV(subset) - KCRV(all) X_i - KCRV(all) X_i(excluded) - KCRV(all)
c2obs 20.5
c20.05(n) 15.507
Error bars: expanded unc.(k = 2)
If you exclude 5 or 7 the others
(including 7 or 5) become consistent
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Accredited Calibration
Laboratories
auditingprocedures
transfer
standards
calibration
INDUSTRY
EURAMET
Regional
comparisons
CONVENTION OF THE METRE
Key comparison of primary unit
National Metrology InstitutesSIM APMP
Mutual Recognition Arrangement
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• Identical worldwide
• Century-long stability
• Absolute accuracy
Achieved through:
• Traceability
• Uncertainty Analysis
• Comparison
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This presentation
1. How world metrology achieves
interoperability, stability and accuracy
2. How these principles can be applied
to Earth Observation
3. Resources to help
![Page 25: Metrology Principles for Earth Observation: the NMI view](https://reader030.vdocuments.mx/reader030/viewer/2022012720/61b2f6228dc53034d06e2778/html5/thumbnails/25.jpg)
The traceability
chain is broken
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No repeat
measurements
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No reference in
space …
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Three principles
Traceability
Uncertainty Analysis
Comparison
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Traceability
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Traceability: Using reference sites
Drift of MVIRI Vis band since launch as determined from desert (red) and ocean (blue) test sites.Figure from: https://scienceblog.eumetsat.int/2016/11/improving-climate-data-records-with-fiduceo/
FastOpt
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Reference radiance, or
sensor-to-sensor
Many (150 million +)
Correlated
Sensor to
sensor
Reference
to sensors
Traceability
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Traceability: Using matchups
22T T
E E E
T
1 20 2
0L Ca a
aL CC
a C
Time (years)
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Uncertainty Analysis
S2 Radiometric Uncertainty Tool
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Error correlation
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Error correlation between
measured values
Earth view Calibration target view Space view
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Error correlation between
measured values
Earth view Calibration target view Space view
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Error correlation between
measured values
Earth view Calibration target view Space view
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Comparison
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This presentation
1. How world metrology achieves
interoperability, stability and accuracy
2. How these principles can be applied
to Earth Observation
3. Resources to help
![Page 42: Metrology Principles for Earth Observation: the NMI view](https://reader030.vdocuments.mx/reader030/viewer/2022012720/61b2f6228dc53034d06e2778/html5/thumbnails/42.jpg)
Training materials
www.meteoc.org/outreach-training.html
• Text book “uncertainty analysis for
EO instrument calibration”
• Videos of lectures (30-60 minutes
each)
www.npl.co.uk/e-learning
• Sign up for NPL’s e-learning courses
• Includes free “introduction to metrology” and
“introduction to uncertainty”
• And (currently free) “Uncertainty Analysis for Earth
Observation”
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Screen shots from e-Course
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New material under development
Question and answer based “shorts” (2
minute videos/single page texts)
Focus on satellite Level 1 products
Examples:• What do I need to know about an effect
to propagate uncertainties?
• Can noise ever be correlated?
• How do we calculate the error
correlation between measured values in
different spectral bands?
• How do I know whether my uncertainties
are right?
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Resources to help…
• NPL
• MetEOC
• FIDUCEO
• FRM programme
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The National Physical Laboratory is operated by
NPL Management Ltd, a wholly-owned company
of the Department for Business, Energy and
Industrial Strategy (BEIS).
Thank youMetEOC and MetEOC-2 were funded by EMRPMetEOC-3 is funded under EMPIR
FIDUCEO has received funding from the European
Union’s Horizon 2020 Programme for Research and
Innovation, under Grant Agreement no. 638822