TRUTHS: - Traceable Radiometry Underpinning Terrestrial- and Helio- - - PowerPoint PPT Presentation

TRUTHS: - Traceable Radiometry Underpinning Terrestrial- and Helio- Studies: A benchmark mission for Climate and GMES

Dr Nigel Fox 9 Dec 2010

A “standards lab in space”

2

Nov 26th Not selected as EE8 mission candidate But - “ESAC stresses the scientific importance of the TRUTHS mission ….. ….ESAC notes the likely launch of the NASA CLARREO mission, which has closely related

• bjectives, and encourages

ESA to investigate the potential for collaboration with NASA in instruments designed to be calibration standards in space, …..” Remains a significant

• pportunity for the UK

3

• Dr. Richard Allan
• Dr. Richard Bantges
• Dr. Xavier Briottet
• Dr. Helen Brindley
• Mr. Steve Groom
• Prof. Joanna Haigh
• Dr. Patrice Henry
• Dr. Andrea Kaiser-Weiss
• Dr. Steve Mackin
• Prof. Jan-Peter Muller
• Dr. Gunnar Myhre,
• Dr. Terry Quinn FRS CBE
• Dr. Jacqueline Russell
• Dr. Roger Saunders
• Prof. Michael Schaepman
• Prof. Werner K. Schmutz
• Dr. Andy Shaw
• Prof. Keith Shine FRS
• Mr. Greg Stensaas
• Dr. Thomas Stone
• Prof. Philippe M Teillet
• Dr. Kurt Thome
• Dr. M Verstraete
• Dr. Bruce Wielicki
• Dr. Jean-Luc Widlowski

Mr R Winkler Dr Emma Woolliams Contributing Science team led by Dr Nigel Fox:

4

Industrial consortium (proposal)

Implementation: many opportunities/possibilities

5

What is TRUTHS? (& CLARREO)

Mission to establish benchmark measurements of SI traceable high accuracy spectrally resolved; incident & reflected solar and emitted thermal radiation as well as atmospheric refractivity through GNSS-RO. To allow observation of decadal climate radiative: forcings, responses and feedbacks from a background of natural variability from:

• its own measurements
• through upgrading of performance of
• ther observing systems: sensors and

in-situ by in-flight reference calibration underpinning, CEOS, GMES and GEOSS

UNCERTAINTY DRIVERS (Climate) Total Solar Irradiance - 0.02 % (2) Spec solar Irradiance - 0.2 % (2) Reflected Solar Radiance - 0.3% (2) IR and GNSS-RO - 0.1 K (3)

6

Climate Absolute Radiance and Refractivity Observatory

4 small satellites: 2 off IR + GNSS RO & 2 off Solar Reflective (SR) Orbits in pairs 90 deg polar and 90 deg separation at 609 km Global averages - Nadir spectrally resolved 0.32-2.3 m <10 nm & 5-50 m 0.5 cm-1 Expect to Start Phase A 2011 with Launch 2018 – 2020

CLARREO

IR full on-board SI primary standard SR relative to another satellite SR GIFOV (500 m) Global mean nadir averages Ref calibration (multi-angle)

TRUTHS

SR full on-board SI primary Standard GIFOV (40 m) Land : (200 m) Ocean Global nadir spectral radiances (275 channels resolution 1-10 nm) Ref Caln & process studies (multi-angle) Polarimetric information

• aerosols

Highly complimentary partnership

7

Reducing uncertainty in impact by constraining the models

All climate models reliably predict the past (nearly) but provide wide variances in their prediction of the future. Uncertainty in data/feedbacks limits ability to discriminate to ~ 30 yrs!! Need to test and constrain models with data more accurate than natural variability. IPCC estimate f (feedback factor = 0.62 ± 0.26)

8

Key Feedbacks

Roe and Baker, 2007

• Temperature
• Water Vapor
• Clouds
• Radiation
• Snow/Ice Cover
• Greenhouse Gases
• Surface Albedo

Cloud Feedback Water Vapor/Lapse Rate Feedback Snow/Ice Albedo Feedback

Earth's Climate

Roe and Baker, 2007

• Temperature
• Water Vapor
• Clouds
• Radiation
• Snow/Ice Cover
• Greenhouse Gases
• Surface Albedo

Cloud Feedback Water Vapor/Lapse Rate Feedback Snow/Ice Albedo Feedback

Earth's Climate Blue = Solar reflective (TRUTHS) Red = IR & GNSS - RO

Also need to understand forcings and processes but largest uncertainty in model predictions due to feedbacks

9

Time to detect Cloud Radiative Forcing (CRF) from natural variability

TRUTHS accuracy (0.3% k=2) near optimum to the perfect observing system for 100% cloud feedback TRUTHS ~ 12 yrs CERES ~ 25 yrs MODIS ~ 40 yrs For 50% difference > 20 yrs Other parameters e.g. Albedo have similar curves

10

Total Solar Irradiance (TSI) or “solar constant”: the driving force of the planet

0.1 % 0.1 %

30 yr record shows “regular” 11 yr cycle and No significant Variation Thus No impact on climate

0.1 % 0.1 %

Source data must be normalised to remove unexplained biases: Allowing uncertainties to be reduced by ~100X!! Thames Frost Fair (1684) Mini-Ice age caused by ~ 0.3 % reduction in solar output.

• No sunspots for 50 yrs
• 2008 to 2010 (unusually low

sunspot activity!!!) Can we rely on 30 yrs of ??? measurements to rule out solar contribution to climate ?

11

Solar Spectral variability may lead to surprises! J D Haigh et al Nature 467 p696 Oct 2010

TOA measurements of Solar Spec irrad by NASA SIM indicate significant variance in expected spectral content at end of solar cycle 23.  surprises when used in and compared to models: 2007 - 2004 TSI UV   Vis O3 (>45 km  ~35 km ) T 

Cooler Sun - Warmer Earth!

Difference in Solar spectral irradiance (2004 - 2007)

12

Needs

• f

ECV’s

13

All optical sensors drift from pre-flight calibrations – also biases between sensors?

Sensor biases & drifts major issue:

• philosophy of establishing climate

record through overlapping data sets extremely high risk

• potential of error propagation,
• cannot have any data-gap
• Operational data
• Existing Post-launch

calibration strategies (on-board and vicarious) limited in accuracy and traceability

• Harmonised, combined data

sets GEOSS, GMES (QA4EO) how?

From: Hugh Keiffer “Celestial Reasonings” / USGS From: Hugh Keiffer “Celestial Reasonings” / USGS

Ratio of Band 1 to Band 2 should be continuous straight line Only reliable (low risk) solution is to establish robust traceability to international agreed standards “SI units” in common with other terrestrial applications but must have traceability “in flight”

14

Near Simultaneous Nadir Observation (SNO) sensor Caln

TRUTHS 90 deg polar orbit

• allows many overpasses with other sensors
• different cross-over times/locations
• ToA reflectances/radiances ± 5 mins
• Platform pointing to co-align view angles
• relatively low (609 km) orbit increase dwell time
• high spectral and spatial resolution to match

sensor under calibration

• Can upgrade performance to facilitate “climate

quality” data

Surface sites (BoA) & (ToA)

• Polarimetry improves atmospheric correction
• Calibrate Aeronet
• High accuracy leads to improved retrieval algorithms
• Multi-angle, hyper-spectral, 40 m spatial, - supports:

albedo, canopy structure, FLUXNET….

Providing Reference Calibrations

15

CEOS endorsed test sites for Land and Ocean can be used as standards to cross-compare between sensors and to ground data providing each site is compared to each other Networks of test sites and methodologies can become

• perational calibration service

(through ISIC?) - improved through use of reference standard SI traceable sensor e.g. TRUTHS

Operational calibration service through “CEOS standard” sites/methodologies

Linked by TRUTHS Linked by TRUTHS Linked by TRUTHS

16

Mission requirement Parameter: proposed value Driving mission objective Required Desired Spectral range: 320 nm – 2450 nm Nadir Reflectance Spectral Climate Change Benchmarks 320 nm – 2350 nm “ Earth Radiation budget From 320 to 2500 nm “ Plant optical traits and minerals 380 nm – 2450 nm Up to 2500 nm Accuracy: 0.3% (2σ) Trend estimation of cloud feedback 0.3 % (2σ) Spectral resolution: 1-10 nm Nadir Reflectance Spectral Climate Change Benchmarks 1-10 nm SI traceable measurement of the solar reflected spectrum 40 m (land) 200 m (ocean) Cloud masking < 500 m <100 m Spectral range: 0.2 to 35 m Solar variability and Earth Radiation Budget 0.2 to 35 m SI traceable measurement of total solar irradiance Accuracy: 0.01% (2σ) Solar variability and Earth Radiation Budget < 0.01% (2σ) Spectral range: 200-2500 nm Solar variability and ozone 200-2500 nm SI traceable measurement of spectral solar irradiance Accuracy: 0.1% (2σ) Solar variability 0.1% (2σ) Reference calibrations As for radiance above Reference Intercalibration 320 nm – 2450 nm

Summary of Mission Requirements

17

TRUTHS satellite

~ 1 m3 – Platform (SSTL 150) Orbit: 90 deg – 609 km Agile platform >2° /s slew rate Payload mass – 165 kg including (2 off coolers for redundancy) Payload peak power – 185 W Daily data download – 4500 Gbits per day

18

TRUTHS Payload: Solar & Earth view axis

On-Board SI Traceability (calibration/performance)

*Cryogenic Solar Absolute Radiometer (CSAR)*

• Primary SI reference standard

Spectral Calibration Monochromator (SCM)

• Spectrally dispersed monochromatic radiation from Sun for calibration system

*Polarising Transfer Radiometer (PTR)* (2 OFF)

• ~13 spectral bands to link calibration from CSAR to Earth Imager

CSAR

19

TRUTHS Payload: Solar & Earth view axis

Observation instruments (science)

*Cryogenic Solar Absolute Radiometer (CSAR)*

• Total Solar Irradiance

Earth Imager

• 320 to 2450 nm (275 channels inc polarisation analysis)
• 40 m at nadir - 40 km swath

Solar Spectral Irradiance Monitor (SSIM)

• 200 to 2500 nm (0.5 to 1 nm bandwidth)

*Polarising Transfer Radiometer (PTR)* (2 OFF)

• off-nadir polarised radiance for aerosols (atmospheric correction)

Baseline imager: APEX

• Many potential options

e.g. CHRIS-2

20

Cryogenic Solar Absolute Radiometer (CSAR): Primary standard & TSI

CSAR is an electrical substitution radiometer

• perating at ~ 20 K.

Technology is same as used for primary standards at national standards labs for 25 yrs (at ambient temps 100 yrs - also in space: 1970’s for TSI) An “engineering model” designed and built currently operating in a vacuum can at Davos for terrestrial TSI In space, cooled by Astrium 10 K cooler (dual for redundancy). 4 – TSI cavities (exposure varied) 2 – High sensitivity cavities (W) 6 – primary Apertures on wheel at ambient temps Cavity absorptance only potential source

• f optical degradation (>0.99998)

If Topt = TElec then Popt = PElec

0.35 m

21

Primary standard lamp Working standard lamp Cal Lab Primary lamp Cal Lab working std Lamp User Cal Lamp User Instrument Spectroradiometer Spectroradiometer Spectroradiometer Spectroradiometer LAND OCEAN ATMOSPHERE Satellite Pre-flight Calibration Traceability ?? Satellite In-flight Calibration Data products Atmosphere/ Model Vicarious Lamp Solar illuminated Diffuser

22

Traceability Strategy:

• mimic that used on ground at

standards labs

• Primary reference standard is

cryogenic radiometer compares heating effect of monochromatic optical power to electrical power

• Tuneable monochromatic

Optical beam (monochromator dispersed solar) calibrates

• ther TRUTHS instruments
• Earth imager aperture

illuminated by diffuse solar from deployable diffuser (or Moon, or Earth)

• Radiance measured by multi-

channel Polarised Transfer Radiometer (PTR) calibrated traceable to CSAR as above.

23

SI Traceability

CSAR is SI primary standard

• only source of optical degradation is

cavity (100 X to impact accuracy of Earth radiance (at 0.1% level)

• measures power of monochromatic

radiation (dispersed solar from Spectral Calibration Monochromator (SCM))

• optical radiation from SCM via a fibre

bundle controlled movement to minimise bending losses (“one-system”) degradation in fibre calibrated out by CSAR

• Fibre moves radiation between

CSAR and PTR (multi-channel filter radiometers and photodiodes “transfer standard”) calibration of spectral response.

• Fibre transfers calibration from

PTR to solar spectral irradiance monitor (SSIM)

24

PTR links solar axis to Earth axis

25

Traceability for Earth Radiances

Calibrated PTR moved to view Earth target or Moon simultaneous with Earth Imager. Traceability established/monitored at ~13 bands across spectrum SSIM can also view Moon to link both instruments and evaluate traceability chains Solar illuminated lambertian diffuser deployed to fill Earth Imager FOV also viewed by PTR (same angles)

26

Traceability for Total Solar Irradiance Gold boxes = SI traceability

27

Traceability for Solar Spectral Irradiance

28

SI Traceability for Earth Radiance

29

Summary

• TRUTHS highly complementary to CLARREO
• Climate science requirements and key operational characteristics as CLARREO
• Methodology for SI Traceability based upon use of on-board primary standard

CLARREO (solar reflected) relies on relative measurements using Sun as transfer calibrated by instrument on another platform, needs V large 105 dynamic range

• Measures input solar irradiances (total and spectral resolved) on same platform
• Together can provide international benchmark climate and calibration constellation
• TRUTHS payload based on existing technologies
• (baseline) imager upgrade of ESA- APEX aircraft spectrometer (other EU options)
• CSAR only new technology – Engineering model now built and under test
• All could be built in 3 yrs
• Low cost agile platform capable of increased payload both mass and power
• Could add CLARREO instruments or other IR Imager
• Opportunities
• Small mission < 100M Euro
• Potential to partner with NASA (platform/payload/launch)
• Could all be built and operated in UK as headline for UKSA and ISIC
• Opportunity for Re-build as operational cal system (e.g. EUMETSAT) CEOS
• Underpins downstream data services enabling confidence, interoperability & growth.

30

Conclusion

• International community have identified traceability, accuracy and data quality

as key drivers for GEOSS / GMES and in particular for climate studies

US utilising NIST as partner, UK & NPL in lead position for Europe / ESA facility in UK (TRUTHS could be flagship for this) NCEO, EUMETSAT, CEOS all supporters

• All aspects/steps of producing EO data products needs validation and

traceability (instrument calibration and algorithms/models) QA4EO

UK well placed to establish infrastructure for Europe

• Traceability (benchmark measurements) from space seen as only plausible

solution for decadal climate

TRUTHS only mission proposed for UV/VIS/SWIR fully traceable to SI NASA and CLARREO collaboration/momentum timely and support from NASA

• Opportunity for “grand challenge project” to demonstrate UK innovation and

provide leadership/traceability for all EO measurements (particularly climate)

• Collaboration with US and Swiss could make mission relatively low cost, yet establish

significant kudos with all EO optical missions traceable to the UK (also demonstrator of Astrium 10 K cooler)

• SSTL not only hardware and data provider but could also provide calibration

reference to all EO sensors and opportunity to open markets in USA

• ISIC could be used to facilitate: full mission design, build, test, operations

Title of Presentation

Name of Speaker Date

The National Measurement System is the UK’s national infrastructure of measurement Laboratories, which deliver world-class measurement science and technology through four National Measurement Institutes (NMIs): LGC, NPL the National Physical Laboratory, TUV NEL The former National Engineering Laboratory, and the National Measurement Office (NMO).

The National Measurement System delivers world-class measurement science & technology through these organisations

Thankyou

Nigel.Fox@npl.co.uk For more details: www.npl.co.uk/TRUTHS http://www.youtube.com/npldigital#p/a/u/0/aQAREkaZjfI