Transcript TRUTHS T R U

TRUTHS
Traceable Radiometry Underpinning Terrestrial- & Helio- Studies
Nigel Fox
NPL
[email protected]
David Pollock
U of Alab.
Mike Sandford
RAL
James Aiken
Plym Mar Lab
Michael Schaepman U of Zur
Xavier Briottet
ONERA
Werner Schmutz
WRC/PMOD
John Barnett
Ox univ.
Keith Shine
Uni of Read
Steve Groom
Plym Mar Lab
Phil Teillet
CCRS
Claus Frohlich
WRC/PMOD
Theo Theocharous
NPL
Jo Haigh
Imp Coll
Kurtis Thome
U of Ariz
Olivier Hagolle
CNES
Terry Quinn
BIPM
Hugh Kieffer
USGS
Michel Verstraete
JRC(Italy)
Judith Lean
NRL
Emma Woolliams
NPL
John Martin
NPL
Ed Zalewski
U of Ariz
Need for improved Quality Assurance
Requirement
- baseline for climate studies
- global warming - Man or Nature?
Hugh
-From:
detection
of Keiffer
changeUSGS
- improve models
- prediction of weather systems
- monitoring the treaties
- auditing carbon sinks
- efficiency of carbon sinks
- identify crops from weeds
- automated farming
- QA of operational services (GMES)
& GEOSS
- instrument synergy
- compatible data sets (interoperability)
Difficulties
- Bias between sensors
MISR, MODIS, AVHRR …..
- Instruments change on launch and
0.1 %
degrade in-orbit (gain and spectral)
- On-board calibration systems
expensive! Reliable? Traceable?
- Inter-team / manufacturer /agency
debate
- Need for International agreement
0.1 %
- No consistent statements of uncertainty
or “degrees of confidence”.
Solar constant – 25 yr record
evidence of stability of the Sun
Reliable satellite data quality
Ideally Requires:
Pre-flight instrument design conformance
Traceable sub-system characterisation/calibration
“
End-to-end calibration
Maintenance/life-test of witness samples/sub-systems
Post-launch design/performance conformance
Traceable calibration/validation of all key characteristics
- on-board calibration system!
- comparison with physical parameter
-
“
with reference data/instrument
(comparison with existing similar instrument)
Infrastructure for innovation in measurement,
validation and QA of EO data
• Transfer standards
• Comparisons
Post-launch
airborne
• Measurement & test protocols
• International link
NPL
++
NPL+
Modelling & Data
processing
• Innovation on techniques
• Independence
NIST+
Calibration
QA
Traceability
Pre-flight
In-situ
Advice
Public
sector
Audit
Validation
Private
Industry
Academia
CCPR
RECOMMENDATION
Plaunch
1CEOS
(2005) requirements
……. Post
Resolution
adopted
by
Plenary 14include:
(Nov
2000)
(Committee
forSI
Earth
(a)
Vicarious
calibration
of ground
sites
with temporally
and spatiallyTO
stable
surface
ON THE
IMPORTANCE
OF
TRACEABLE
MEASUREMENTS
MONITOR
CLIMATE
characteristics
generally clear skies,
andCHANGE
where possible, observations of the Sun,
Observationand
Satellites)
Moon, and stars, are useful for characterizing calibration drifts of VIS and NIR
Options
The
CCPR, recalling
Resolution 4 calibrated
of the 21st General
Conference oninstruments
Weights and Measures
(1999)
instruments.
If appropriately
from benchmark
in space
these can
concerning
the
need
to
use
SI
units
in
studies
of
Earth
resources,
the
environment,
human
well–being
and
Provide
link to
SI via a sub-set of instruments flown to
be• used
as reference
standards.
related•issues,
1/
All EO measurement
systems
should
be verified
simultaneously
view
same
target
as
satellite
(b) Space-based benchmark observations, with the required accuracy, spectral coverage
Considering
increasing
importance
of optical
based measurements
from ground, air and space
traceable
to
SI
units
for radiation
all appropriate
measurands.
-thehigh
aircraft,
Balloon,
Rocket,
Shuttle,
ISS
and resolution
andaltitude
traceable
to international
standards
as “gold”
standards for validation
which support research into the understanding of the causes and impacts of climate change;
- degradation/outgassing,
and inter-calibration
of other satellite sensors.multiple targets, range of parameters
 2/thePre-launch
calibration
shouldreference
be performed
Considering
cooperation
between
the
World
Meteorological
Organisation,
the
BIPMusing
and the CCPR,
•
Vicarious
calibration
via
calibrated
targets
(c)
Permanent
reference
sites
and
dedicated
campaigns
to
collect
in
situ
measurements
relating to equipment
the metrological needs
of
the
WMO;
and
can beused
demonstrably
Desserts,
Moon,
Stars, SnowAllthat
fields
of the state- of
the surface
andtechniques
atmosphere.
instruments
for in-situ
Considering
the difficulty
of
demonstrating
and
traceability
the SIaccuracy
in theof
space
environment
measurements
should
be
calibrated
andmaintaining
traceable
tothe
SI standards.
- Maintenance/establishment
of
radiometric
traceable
to
and
consistent
with
SItosystem
units,
and because the levels of accuracy needed are often more demanding than those needed to satisfy current
•) Satellite
Designation
of onefrom
or simultaneous
group
instruments
as
“reference
(d
and collocated
observations:
andinter-calibration
traceability
should
be of
maintained
throughout
the
industrial
requirements;
- Relyobservations
onofmission
overlap
for traceability
continuity
-Considering
Simultaneous
from
collocations
between
a LEOtoand
all GEO
lifetime
the
mission.
the particular need for space-based experiments to be traceable
SI units
and thesensors
difficulty of
Which
one
?
Improved
calibration/reliability
?
Degradation
have
also
been
demonstrated
and
can
be
used
as
a
means
to
inter-calibrate
GEO
obtaining a calibration during the operational phase of a mission ;
satellites.
Conversely,
an instrument Calibration
with high accuracy,
precision
and stability
in GEO
•
Dedicated
International
mission
–
“Std
Lab
in-orbit”
Traceability
–
Property
of
the
result
of
a
measurement
or
the
value
Strongly
recommends
relevant
bodiestotointer-calibrate
take steps to ensure
all sensors;
measurements used to make of a
orbit can
be used as
a means
all that
LEO
observations
may be used
for climate
studies are
made fully
traceable
to SIusually
units; long-term
standard
whereby
it can
be related
to international
stated
references,
through an
-which
Optimised
calibration
system,
agreement,
-Collocatedunbroken
high spectral
resolutions
observations
are important
for
validating and
chain
of
comparisons
all
having
stated
uncertainties
reliability,
mimic
terrestrial
systems,
(could
additionally
do science!!)
And
further recommends
fundingradiometers.
bodies to support the development of techniques
which can
vicariously
calibratingappropriate
broader band
make possible a set of
radiometric
standards
and
instruments
to allow
such traceability to be
- SI-traceable
Cost,
Degradation?
Traceability?
Accuracy?
“Vocabulary
for International
Metrology
(VIM)
ISO”
established in space.
-From CEOS strategy
document for
(2005)
- Transference
to GEOSS
other missions
Radiometric traceability
Cryogenic
Radiometry
SI
~0.01 %
Spectral
Responsivity
~0.1 %
Spectral
radiometry
Appearance
Solar
~0.5 %
Pyrometry
Photometry
Remote Sensing
Lighting
Transport
Aerospace
Medicine
Industry
Environment
Traceability for Optical
radiation measurements
Fundamental constants (SI)
Primary standard
cryogenic radiometer
Spectral Radiance/Irradiance
calibrations
LAND
OCEAN
ATMOSPHERE
Electrical Substitution Radiometry a 100 yr old technology
When thermometer
temperature T=To=TE then
Po=PE
Optical power
=Po
Absorbing black
coating
Electrical Heater Power = PE
Copper disk
Thermal shroud
Optical power
=Po
When T =To=TE then
Po=PE
Mechanical cryogenic cooler
“Fridge” (T = 20 K)
Shutter
Cooling improves sensitivity
by 1000 X
Absorbing cavity (~ 0.99999)
Electrical Heater Power = PE
Principle of Cryogenic radiometry
Cryogenic Radiometry – international
agreement and consistency
~300 K
1.0
Terrestrial solar
<20 K
Space solar
SORCE / TIM
0.1
•
Nat Met Inst
High diffusivity
0.01
- potential of large cavity,
(high absorbtance)
Cryogenic rad
1950
1970
1990
- rapid isothermal conditions
- controlled heat flow paths
• Superconductive leads
- no joule heating loss
High sensitivity thermometry
• Stable thermal environment
- low external load (background)
- low cavity radiative loss
Accuracy to SI <~0.01 %
2010
Fundamental constants (SI)
GERB
Detector
Satellite Pre-flight
Primary standard
cryogenic radiometer
Calibration
Laser
Cal interval ~100nm
Traceability ??
Satellite In-flight
Calibration
Photodiode
(spectral responsivity
or SIRCUS
Laser
Cal interval ~0.1 nm
Filter Radiometer
Radiance Temperature
Ultra High Temperature
Black Body (3500 K)
Radiance continuum
(Planck)
Spectroradiometer
(multi-band filter radiometer
Spectral Radiance/Irradiance
calibrations
Lamp
Solar
illuminated
Diffuser
Geostationary Earth Radiation Budget
(GERB)
Vicarious
Spectral radiance using filter radiometer
with plancks
allows Meteosat
determination
(in-flightlaw
on-board
SG) of
T of Ultra high temp blackbody (~3200 K)
Atmosphere/
Spectral Responsivity calibrations
- Plancks
lawofthen
spectral
Model
Spectral
response
filterpredicts
radiometer
determined
- Transference
of reference detector calibration
radiance
for
all
over full bandwidth using tuneable lasers
to each GERB Pixel
Comparing response of reference detector to that
- Detector array (256 elements ~ 50 m Sq) each
of filter radiometer
pixel cal from 300 nm to 20 m at NPLData products
– uncertainty in spectral radiance ~ 0.02%
LAND
OCEAN
ATMOSPHERE
TRUTHS: Traceable Radiometry Underpinning
Terrestrial- and Helio- Studies
Satellite based mission to:
• make SI traceable high accuracy
measurements of solar radiation
incident on, and reflected from,
the Earth
• transfer its unprecedented
calibration accuracy to other
satellite-based EO instruments
through the calibration of
reference targets such as the
Sun, Moon and the Earth’s
deserts
• Supporting measurements of
land processes, ocean colour,
Earth radiation budget,
atmospheric chemistry and
aerosol distribution
- Wide spectrum (380 to 2500 nm)
baseline
- Spatial resolution ~ 25 m (multi-angle)
- Spectral radiance uncertainty <0.5% (using novel
in-flight calibration system)
Geophysical parameters measured by
TRUTHS (baseline)
Measurand
Spectral resolution
Total Solar Irradiance
Solar Spectral Irradiance
Lunar Spectral Irradiance
and Radiance
Earth Spectral Radiance
(Polarised and Non-pol)
multi-angle
nm
Total
Spatial resolution Accuracy
m
-
%
0.01
200 – 2500
(0.5 - 1)
-
0.1
380 – 2500
(10)
-
<0.5
380 – 2500
(10)
~ 25
(20 x 20 km)
<0.5
via filter rads
TBD
20 km (TBD)
for Aerosols / E Rad Bud
Optional orbit for consideration
Observing conditions (near polar 700 km)
Oblique angle away from pole:
Solar viewing
- fewer repeats- ~ 10 mins per orbit
<0.5
- more satellite
coincidences
Earth viewing
~ 10 sites
(20 * 20 km) at 5 angles per orbit
Filter radiometers used to transfer calibration from
CSAR to the Earth Imager
TRUTHS Traceability
Fundamental Constants (SI)
Cryogenic Solar Absolute RTerrestrial
adiometer
Traceability
Filter transmittance
0.9
0.98
Potential degradation
0.8
0.96
0.7
0.94
0.6
0.92
Glass filters
Interference filters
0.5
0.9
0.4
0.88
0.3
0.86
0.2
0.84
0.1
0.82
0
0.001 %
CSAR
cooling fromCryogenic
Astrium
20 K cooler
Most optical
Cryogenic
Radiometer
Solar Absolute
1
Spectralon
Spectralon reflectance
1
Total Solar
Irradiance
0.8
2500
2250
2000
1750
1500
1250
1000
750
500
250
Wavelength
Earth Imager calibrated in-flight using reflected solar
radiation from a deployable diffuser plate.
Absolute spectral radiance of diffuser plate determined using
in-flight calibrated filter radiometers.
components degrade
in space particularly
0.005 %
when exposed to the
Laser
Sun.
Cal. Interval ~100 nm
Radiometer (CSAR) (TSI cavity)
0.01 %
Sun
3 cavities for TSI – t ~ 15
s
CSAR HS Cavity
- operating range
10 mW to 100 nW
Solar Calibration Monochromator
Degradation
iscavities
usually
Solar Absolute
2Cryogenic
for spectral
response Radiometer
– t ~ 0.5
s %
0.05
spectrally 0.02
variant%but
unlikely to havePhotodiode
- operating rangeReference
0.1 mW to 10 nW
CSAR Photodiode
Responsivity)
significant (Spectral
structure
Calibration Monochromator
3 offLaser
5 mm precisionSolar
apertures
+ 2 off 0.5 mm
Cal. Interval ~100 nm
High sensitivity cavity
Provides:
0.1 %
0.03 %
Solar Spectral
Filter Radiometer
Polarised
Using
monochromator
dispersed
solar
Filter Radiometer
Irradiance
Monitor
Use
calibrated
• Measure of filterTSIrads
Radiance via 10
Radiance Temperature
spectral channels
radn
~
10
nm
bandwidth
beam
power
• Primary standard for maintenance
Cal. Interval ~1 nm
Cal. Interval ~0.1 nm
Earth
/
Solar/Lunar
Spectral
Irradiance
0.05
of SI traceability
atmosphere
To %calibrate
photodiode
Ultra High Temperature
as%input
0.2
to
(working
std)
Solar Diffuser
Plate
solar
spec
Black Body (3500 K)
Use of electrical substitution makes
Radiance Continuum
irradiance
Radiance
Continuum
As
on
ground
traceability to SI through convenient
Imager
~0.3 %
monitor
correction
Earth Imager
electrical units – optical interface via
0.1 %photodiode never exposed to
Calibration drift, spectral and gain,
n.b.
Other EO
Hyperspectral
Spectroradiometer
black cavity absorber, coated with
Instruments
removed by performing calibrations in Sun/Earth
(Multi-band Filter
Radiometer)
Earth/Lunar Radiance
‘NPL super-black’ Solar weighted
space
directly
against
a
primary
Option
of broad
band Filter
radiometers
Only
source ofSpectral
uncontrolled optical
absorbtance
>0.99998.
standard using terrestrial
Radiance/Irradiance
degradation
is cavity absorbtance
• Earth Radiation
budget
methodologies
adapted for
space. UV to IRCalibrations
TRUTHS Traceability
can degrade by
factor
of 100 and still
~0.3
%
•TIR channels
achieve < 0.2 % accuracy to SI units
Instrument integration on Truths satellite
(baseline, other than calibration system
all are TBD)
SSIM
RPs
TASS
CSAR
FRTW
CSAR
SCM
Instrument
mounting
plate
PMO
SCM
Payload:
SSIM
Mass = 130 kg
Power = 185 W
FRTW
1m
PMO
Cooler
EI
Diffuser
EI
0.8 m
Solar: Cryogenic Solar Absolute Radiometer CSAR
- TSI , Primary standard
WRC PMO ambient temperature radiometers PMO - TSI
Solar Spectral Irradiance Monitor SSIM
Earth: Earth Imager (spectrometer) EI
Polarised Filter Radiometers PFR
- SSI
- Spectral radiance
- Polarised spectral radiance
TRUTHS Earth Imager
Hyperspectral and high spatial to
simplify matching to other sensors
VNIR
VNIR
Primary mirror
SWIR
GI
SWIR
Artist’s impression of TRUTHS EI
TRUTHS Imaging Spectrometer
* Prism based spectrometer
100 mm
* 212 channels nominal 10 nm bandwidth (1 to 8 nm)
* 200 mm diameter primary mirror * 380 to 2400 nm
* 20 m ground resolution
* Data rate ~ 1 Gbyte/second
Design based on upgrade of planned ESA / APEX aircraft spectrometer
4 independent filter radiometers measure s and p polarisation for
atmospheric correction and to monitor TRUTHS EI.
Spectral Calibration Monochromator (SCM)
• Three separate double grating
monochromators stacked and driven
by a common drive shaft.
• Wavelength calibration via laser
diode at input
- Higher power for irradiance
calibration
Transmitted
Power/uW
40
30
20
* Use of 3 separate fibre delivery systems
allows throughput to be maximised.
10
0
0
1
2
Wavelength/um
3
* Transmitted power calculated using
realistic commercial fibre, mirror and
grating specifications, now lab tested.
Solar Spectral Irradiance Monitor (SSIM)
(could be SIM of SORCE)
Spectral range: 200 to 2500 nm
Spectral resolution: 0.5 nm 200 – 1000 nm
1.0 nm 1000 – 2500 nm
Dynamic range: 0.001 – 5 Wm-2 nm –1
Temporal resolution: Variable
Accuracy: 0.1 %
Two single grating spectrometers
- Each utilising two “orders” via a beam splitter and two linear arrays
Solar input via a common integrating sphere diffuser and precision aperture
Transfer of calibration to global EO
missions
• Establishment of reference data for Sun and Moon.
 In-orbit Comparison of solar viewing instruments e.g SORCE.
-Link to VIRGO of SOHO.
 Establishment of network of Earth based Reference test sites.
-E.g Railroad Valley, Libyan Desert, Antarctica etc
-Sites to be characterised by field studies
-Instrumented with remotely controllable/readable monitors
-Calibration coefficients updated regularly by TRUTHS satellite
-Data accessible over WWW to allow reprocessing to suit individual
satellite footprints and spectral characteristics
- Improve accuracy of all sensors but particularly those with no on-board
e.g. MSG, DCM … and a reference for NPOESS etc DATA GAPS!
 Archived data reprocessable to improve historical reference.
-Many in-flight sensors have the resolution, dynamic range and
stability to allow update of calibration and viewed same desert targets.
Targeted Science: Surface BRDF, Carbon cycle, atmosphere, coastal zones ….
Summary
TRUTHS “in-flight calibration laboratory” removes uncertainty due to storage,
launch and degradation and its mission provides this benefit, together with SI
traceability, to all other EO optical sensors.
•
Set of SI traceable reference targets: Sun, Moon, network of ground sites
•
•
Utilises terrestrially implemented techniques and technology
- In-flight calibration concept applicable to other missions
Order of magnitude improvement in measurement accuracy
•
Baseline for detection of climate change – reduce need for overlapping data sets
•
Quality Assure data used by ‘decision makers’ and improve synergy between sensors
• Tools to underpin GMES and GEOSS initiative
•
Identify the polluters
•
Improved algorithms to allow quantitative measurement of bio-physical products
•
Provide data to improve understanding of natural solar induced variation on climate
and compare with anthropogenic effects.
The step change reduction in uncertainty and spin-off benefits is analogous
to that obtained in NMIs when cryogenic radiometers were introduced in
1980s Fox et al Adv in Space Physics 32 p2253 (2003)
NIST
NPL
NPL
TRUTHS : - Status
•
Proposed to EEOP (2002) - Not selected although received significant
interest – reviewers conclusion:–
“If the aim is merely to provide accurate, calibrated measurements
of Earths spectral radiances and of solar and lunar irradiance, the
mission can be classified as a solution. To the best of the reviewers’
knowledge, there is presently no strong need for absolutely accurate
Earth spectral radiances since other errors dominate the radiometric
error budgets of planned missions.” ???
–
Models and atmospheric correction can only improve with better
data to constrain them and test improvements
-
Mission seeks to provide solutions to wide range of EO communities
Atmosphere
Solar
Land
Ocean
Should be benefit – seen as a weakness
Media interest
Broad support from UK govt departments (looking at funding
mechanisms!) International collaborations seen as essential
Status 2
Costs: Estimates by EU industrial team
5 yr mission operations, Satellite, Launch
- ~$40 M (SSTL)
In-flight calibration system including CSAR
and TSI measurements
- ~$12 M
Hyperspectral imager + solar spec irradiance
- ~$12 M
- Plan to start designing and building operational engineering model
of CSAR from Apr 2007 in collaboration with WRC PMOD (Swiss)
-Awaiting Decision by EU on New Metrology funding programme
- potential to fund flight Calibration system
Need study:
- to optimise observation / mission requirements
- identify operational instruments/suppliers/partners
FOR SUCCESS MISSION SHOULD BE INTERNATIONAL
Perhaps developed under CEOS? GEO?