Resolving uncertainty in climate change data through Traceability to SI units. Nigel Fox Optical Radiation Measurement Tm Quality of Life Division

Transcription

1 1 Resolving uncertainty in climate change data through Traceability to SI units Nigel Fox Optical Radiation Measurement Tm Quality of Life Division

2 Earth Observation: certainty of data Pretty pictures Climate change Man made??? Good measurements in Space Not Rocket Science High London resolution at night image - digital of the camera M25 from galaxy space station Maybe a bit!! NPL Washington DC from 500 miles Photos: courtesy NASA

3 Monitoring and interpreting the Earth systems Solar Reflected Radiation Incoming Solar Radiation Atmosphere Drives all the processes of the Earth System and potentially damaging (UV) - clouds to Biosphere (Human health) Net primary production ~ 60 PgC/yr Water Land Anthropogenic contribution to atmosphere ~ 6 PgC/yr - Aerosol (size & distribution) - pollution (impact on health) - pollution (originator) - algae plumes - usage / condition - type/quantity of vegetation - minerals - Carbon & hydrological cycles Accuracy for LAI (leaf area index) <10 Governments % - treaties, tax, planning EO can indicate good areas to Accuracy in signal to detect ~< 0.5 % Spatial variability requires good stability fish (temp, and SNR phytoplankton, (signal noise ratio) algae) from a single sensor - but long term studies climate change Thermal Emitted Radiation need accuracy and consistency Atmosphere Atmospheric chemistry Effluent Engineering specification of SNR Water Temperature (AATSR) from Beach should equate to accuracy Land Fires, Volcanoes, Pollution, Sicily from ESA MERIS 2

4 Earth Observation and Climate Change SUN Energy source driving the climate Oceans, Atmosphere (Weather and Life) Is the Earth warming? What is the cause? Can we detect it? Can we stop it? Cause of climate change in the last 50 yrs is likely to be anthropogenic in nature (IPCC 2000) but its impact is far from clear likely = % probability

5 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 Difficulties - Bias between sensors MISR, MODIS, AVHRR.. - Instruments change on launch and degrade in-orbit (gain and spectral) - On-board calibration systems expensive! Reliable? Traceable? - Inter-team / manufacturer /agency debate - Need for International agreement - automated farming - QA of operational services (GMES) & GEOSS - instrument synergy - compatible data sets (interoperability) - No consistent statements of uncertainty or degrees of confidence.

6 Is the Sun getting hotter? Number of Sunspots Total Solar % % Irradiance (TSI) (solar constant) Longest climate Earth Surface Temp = - 2 C continuous T = -2 ºC climate change record from space Thames Frost Fair (1684) Sensitivity to detect 0.1% change in 11 yr Total cyclesolar Irradiance, TSI (Solar constant ) Sun-spot record goes back to This, combined with ice core and Total tree Solar ring data Irradiance allows historical (TSI) reconstruction (solar constant) Longest 0.1% variation climate over continuous 11 years climate change record from 0.1% space Sensitivity to detect 0.1% change in 11 yr cycle input data inconsistent in absolute level 11 yr cycle ~ 0.1 % variation Data gap lose record 0.3% increase since 17 th C. 0.02% mini-ice-age (~-0.3 C Source/TIM average, -2 C North Atlantic) 1361 W/m 2!! 0.15% increase since 1850

7 Non-linear aspect of Solar radiation on climate Variation of Solar Spectral Irradiance - Visible similar to TSI - UV 10 to 100 X greater UV drives atmospheric chemistry - middle and upper atmosphere Vis-NIR absorbed in Oceans - Sea temperature, Weather NIR absorbed in Atmos. H 2 O and CO 2 - Vis scattered by aerosols May trigger El Nino with ~ 18 mth time delay

8 Where is the Missing Sunlight? Emitted IR radiation Reflected by clouds, atmosphere (~23%) Input solar radiation (100 %) Natural greenhouse heating Greenhouse gases (2.5 Wm -2 ) Absorbed by atmosphere (20%) ~60 Wm -2 Measured absorption (25%) ~80 Wm -2?? Reflected from surface (~8%) Absorbed by ground (~49%) Heating effect of missing radiation = 10X that of sum of all greenhouse gases

9 Microwave measurements of Temperature SNO Derived Climate Trend from MSU Trend=0.32 K Dec -1 Combined Linear (Combined) Trends for linear calibration algorithm 0.32 K Decade Trend = K Decade Combined Linear (Combined) Trends for NESDIS operational calibration algorithm 0.22 K Decade -1 (Vinnikov and Grody, 2003) Trend = 0.17 K Dec C om bined Linear (C ombined) Trends for nonlinear calibration algorithm using SNO cross calibration 0.17 K Decade Courtesy of C. Zou

10 Quality Assurance fit for purpose 5 Reliability Benefits - reproducibility Specification of performance Likelihood of meeting performance/expectations Confidence in use Improved efficiency in production Consumers rightly assume the QA Manufacturers often request the evidence of sub-contractors e.g. ISO 9002/17025 EO products consumers often assume QA is the same as per terrestrial products

11 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)

12 NPL leads a study for ESA to review existing, and identify new, QA procedures required to meet USER requirements in the context of GMES Validated data products require all processing steps and data to be QA Accredited? Consider development of a quality reporting system quality index to be associated with all data products Pre-flight - all sensor technology types User specification - complete Instrument data build processing compliance chain Calibration? (commissioning, validation, processing, delivery, archive) Post-launch Leading toin-flight checks - ability Ground to realistically Truth comparison combine data from different sources Inter-sensor cross calibration - confidence to users Processed data released - efficiency validated for data providers - increased Uncertainty uptake statement? of EO data Independence and international reputation of NPL considered essential to ESA. Rare for all these activities to have been independently reviewed and/or audited 7

13 Infrastructure for innovation in measurement, validation and QA of EO data 8 Transfer standards Comparisons Post-launch Modelling & Data processing NPL ++ airborne Innovation on techniques Measurement & test protocols International link Independence QA GEOTRUST NPL+ Calibration In-situ Pre-flight Traceability Advice Public sector Audit Validation Private Industry Academia

14 Radiometric traceability SI Cryogenic Radiometry ~0.01 % Spectral Responsivity ~0.1 % Spectral radiometry ~0.5 % Pyrometry Appearance Photometry Solar Remote Sensing Lighting Transport Aerospace Medicine Industry Environment

15 Traceability for Optical radiation measurements Fundamental constants (SI) Primary standard cryogenic radiometer Spectral Radiance/Irradiance calibrations LAND OCEAN ATMOSPHERE

16 Electrical Substitution Radiometry - a 100 yr old technology Optical power =P o When thermometer temperature T=T o =T E then P o =P E Absorbing black coating Copper disk Electrical Heater Power = P E Optical power =P o Thermal shroud When T =T o =T E then P o =P E Mechanical cryogenic cooler Fridge (T = 20 K) Shutter Absorbing cavity (~ ) Cooling improves sensitivity by 1000 X Electrical Heater Power = P E Principle of Cryogenic radiometry

17 Cryogenic Radiometry international agreement and consistency 1.0 Terrestrial solar ~300 K <20 K Space solar High diffusivity - potential of large cavity, (high absorbtance) - 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 / % 0.1 SORCE / TIM Nat Met Inst 0.01 Cryogenic rad Accuracy to SI <~0.01 %

18 Fundamental constants (SI) Primary standard cryogenic radiometer Laser Cal interval ~100nm Photodiode (spectral responsivity GERB Detector Satellite Pre-flight Calibration Satellite In-flight Calibration Traceability?? Laser Cal interval ~0.1 nm Lamp Solar illuminated Diffuser Filter Radiometer Radiance Temperature Ultra High Temperature Black Body (3500 K) Radiance continuum (Planck) Spectroradiometer (multi-band filter radiometer Geostationary Spectral radiance Earth using Radiation filter Budget radiometer Vicarious (GERB) with plancks (in-flight law on-board allows Meteosat determination SG) of T of Ultra high temp blackbody (~3200 K) Spectral Responsivity calibrations Atmosphere/ - Plancks law then predicts spectral Model Spectral response of filter radiometer determined - Transference radiance over full for bandwidth all of λreference using detector tuneable calibration lasers to each GERB Pixel Comparing response of reference detector to that - Detector array of filter (256 radiometer elements ~ 50 μm Sq) each pixel cal from 300 nm to 20 μm at NPLData products uncertainty in spectral radiance ~ 0.02% Spectral Radiance/Irradiance calibrations LAND OCEAN ATMOSPHERE

19 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) - Spatial resolution ~ 25 m (multi-angle) baseline - Spectral radiance uncertainty <0.5% (using novel in-flight calibration system)

20 ilter radiometers used to transfer calibration from SAR TRUTHS to the Earth Imager Traceability Filter transmittance Cryogenic Solar Absolute Radiometer Terrestrial Traceability Glass filters Spectralon Potential degradation Interference filters 1500 Wavelength Earth Imager calibrated in-flight using reflected solar radiation from a deployable diffuser plate Spectralon reflectance Most optical components degrade in space particularly when exposed to the Sun. Cryogenic Radiometer % Fundamental Constants (SI) Cryogenic Solar Absolute Radiometer (CSAR) (TSI cavity) Sun 3 cavities Laser for TSI t ~ 15 s CSAR HS Cavity Cal. Interval ~100 nm Photodiode Reference Photodiode (Spectral Responsivity) 3 off 5 mm High precision sensitivity Solar apertures cavity Calibration Monochromator + 2 off 0.5 mm Laser Cal. Interval ~0.1 nm % Total Solar Irradiance CSAR cooling from Astrium 20 K cooler 0.01 % - operating range 10 mw to 100 nw Solar Calibration Monochromator Cal. Interval ~100 nm 2 Cryogenic cavities for spectral Solar Absolute response Radiometer t ~ s % - operating range 0.1 mw to 10 nw CSAR Degradation is usually spectrally 0.02 variant % but unlikely to have significant structure Cal. Interval ~1 nm Using Provides: monochromator dispersed 0.03 % 0.1 % solar Absolute spectral radiance of diffuser plate determined using in-flight calibrated filter radiometers. Solar Spectral Filter Radiometer Polarised Measure radn ~ of 10 Irradiance TSI nm Monitor bandwidth filter- rads Radiance Temperature beam power To calibrate Primary standard photodiode for (working maintenance std) Solar/Lunar Earth Spectral / 0.05 % 0.2 as % input to of SI traceability atmosphere Irradiance Ultra High Temperature Solar Diffuser Plate Use of electrical substitution makes Black Body (3500 K) As on ground solar spec Radiance Continuum traceability to SI through convenient Radiance Continuum irradiance n.b. photodiode never Imager exposed ~0.3 % to electrical units optical interface via correction monitor Earth Imager Calibration drift, spectral and gain, 0.1 Sun/Earth % Other EO Hyperspectral black cavity absorber, coated with Spectroradiometer removed by performing calibrations in Instruments (Multi-band Filter NPL super-black Solar weighted Radiometer) Earth/Lunar Radiance Option space directly against a primary absorbtance of broad > band Filter Only radiometers source of uncontrolled optical standard using terrestrial Spectral degradation Radiance/Irradiance is cavity absorbtance methodologies Earth Radiation adapted for budget space. UV to IRCalibrations TRUTHS Traceability can degrade by ~0.3 factor % of 100 and still TIR channels achieve < 0.2 % accuracy to SI units Filter Radiometer Use calibrated Radiance via 10 spectral channels

21 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.

22 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)

23 NPL