TRUTHS: - Traceable Radiometry Underpinning Terrestrial- and Helio- Studies: A benchmark mission for Climate and GMES A “standards lab in space” Dr Nigel Fox 9 Dec 2010
Nov 26 th 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 objectives, and encourages ESA to investigate the potential for collaboration with NASA in instruments designed to be calibration standards in space, … .. ” Remains a significant 2 opportunity for the UK
Contributing Science team led by Dr Nigel Fox: Dr. Richard Allan Dr. Richard Bantges Prof. Michael Schaepman Dr. Xavier Briottet Prof. Werner K. Schmutz Dr. Helen Brindley Dr. Andy Shaw Mr. Steve Groom Prof. Keith Shine FRS Prof. Joanna Haigh Mr. Greg Stensaas Dr. Patrice Henry Dr. Thomas Stone Dr. Andrea Kaiser-Weiss Prof. Philippe M Teillet Dr. Steve Mackin Dr. Kurt Thome Prof. Jan-Peter Muller Dr. M Verstraete Dr. Gunnar Myhre, Dr. Bruce Wielicki Dr. Terry Quinn FRS CBE Dr. Jean-Luc Widlowski Dr. Jacqueline Russell Mr R Winkler Dr. Roger Saunders Dr Emma Woolliams 3
Industrial consortium (proposal) Implementation: many opportunities/possibilities 4
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 other 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 ) 5
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 TRUTHS IR full on-board SI primary standard SR full on-board SI primary Standard SR relative to another satellite GIFOV (40 m) Land : (200 m) Ocean SR GIFOV (500 m) Global nadir spectral radiances (275 channels resolution 1-10 nm) Global mean nadir averages Ref Caln & process studies (multi-angle) Ref calibration (multi-angle) Highly complimentary Polarimetric information partnership - aerosols 6
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) 7
Key Feedbacks Blue = Solar reflective - Temperature - Temperature (TRUTHS) Earth's Earth's - Water Vapor - Water Vapor Climate Climate Red = IR & GNSS - RO - Clouds - Clouds - Radiation - Radiation - Snow/Ice Cover - Snow/Ice Cover - Greenhouse Gases - Greenhouse Gases - Surface Albedo - Surface Albedo Cloud Feedback Cloud Feedback Water Vapor/Lapse Rate Feedback Water Vapor/Lapse Rate Feedback Snow/Ice Albedo Feedback Snow/Ice Albedo Feedback Roe and Baker, 2007 Roe and Baker, 2007 Also need to understand forcings and processes but largest uncertainty in model predictions due to feedbacks 8
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 9
Total Solar Irradiance (TSI) or “solar constant”: the driving force of the planet 30 yr record shows “regular” 11 yr cycle and No significant Variation Thames Frost Fair (1684) Thus No impact on climate 0.1 % 0.1 % 0.1 % 0.1 % 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 ??? Source data must be normalised to measurements to rule out solar remove unexplained biases: Allowing contribution to climate ? uncertainties to be reduced by ~100X!! 10
Solar Spectral variability may lead to surprises! J D Haigh et al Nature 467 p696 Oct 2010 Difference in Solar spectral irradiance (2004 - 2007) 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 O 3 (>45 km ~35 km ) T Cooler Sun - Warmer Earth! 11
Needs of ECV’s 12
All optical sensors drift from pre-flight calibrations – also biases between sensors? Sensor biases & drifts major issue: From: Hugh Keiffer “Celestial Reasonings ” / USGS From: Hugh Keiffer “Celestial Reasonings ” / USGS - 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? Only reliable (low risk) solution is to establish robust traceability Ratio of Band 1 to Band 2 should be to international agreed standards “SI units” in common with other terrestrial continuous straight line applications but must have traceability “in flight” 13
Providing Reference Calibrations 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…. 14
Operational calibration service through “CEOS standard” sites/methodologies Networks of test sites and Linked by TRUTHS methodologies can become operational calibration service (through ISIC?) - improved through use of reference standard SI traceable sensor e.g. TRUTHS Linked by TRUTHS Linked by TRUTHS 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 15
Summary of Mission Requirements Parameter: Mission Driving mission objective Required Desired requirement proposed value Spectral range: 320 nm – Nadir Reflectance Spectral 320 nm – 2450 nm Climate Change Benchmarks 2350 nm From 320 to “ Earth Radiation budget 2500 nm 380 nm – Plant optical traits and SI traceable “ Up to 2500 nm minerals 2450 nm measurement of the solar Accuracy: Trend estimation of cloud 0.3 % (2σ) reflected 0.3% (2σ) feedback spectrum Spectral Nadir Reflectance Spectral resolution: 1-10 nm Climate Change Benchmarks 1-10 nm 40 m (land) 200 m Cloud masking < 500 m <100 m (ocean) 0.2 to 35 m Spectral range: Solar variability and Earth SI traceable 0.2 to 35 m Radiation Budget measurement of total solar Accuracy: Solar variability and Earth irradiance 0.01% (2σ) Radiation Budget < 0.01% (2σ) Spectral range: SI traceable Solar variability and ozone 200-2500 nm 200-2500 nm measurement of spectral solar Accuracy: irradiance Solar variability 0.1% (2σ) 0.1% (2σ) 320 nm – Reference As for radiance Reference Intercalibration 16 calibrations above 2450 nm
~ 1 m 3 – Platform (SSTL 150) TRUTHS satellite 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 17
TRUTHS Payload: Solar & Earth view axis CSAR 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 18
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