DEDICATED CLIMATE MISSION

1. DEDICATED CLIMATE MISSION ASIC3 Achieving Satellite Instrument Calibration for Climate Change Lansdowne, VA May 17, 2006 Jim Anderson, John Dykema, Jon Gero, Stephen Leroy, Eddie Harm, and Richard Goody Harvard University Cambridge, MA 617-495-5922 anderson@huarp.harvard.edu

2. VISION A healthy, secure, prosperous and sustainable society for all people on Earth “Understanding the complex, changing planet on which we live, how it supports life, and how human activities affect its ability to do so in the future is one of the greatest intellectual challenges facing humanity. It is also one of the most important for society as it seeks to achieve prosperity and sustainability.” NRC (2005)

3. Interim Report Issued Apr 27, 2005 “Today, this system of environmental satellites is at risk of collapse.”

4. Human health Water resources Climate Weather and severe storms Solid Earth hazards Land use, Ecosystems, Biodiv Airborne and water borne toxicity Rainfall, river flow, ground water, snow pack Regional temperatures, hurricane intensity, optical properties of atmosphere Earthquakes, volcanoes, tsunamis Strategic Choices Driven by Society’s Need for Decision Structures Critical Observations to Specifically Test Forecast Credibility Decision Structures in Service to Society for: Required Forecasts: • Nitrate, sulfate, organics, heavy metal effluents globally • Run-off rates, precipitation, soil moisture • Index of refraction, absolute spectrally resolved radiance, solar irradiance • Surface deformation

5. What would a Climate Program “Board of Inquiry” place at the top of the priority list? • We have a fundamental responsibility to future generations to put in place a climate record that is accurate in perpetuity, testable by scientists from any nation at any time in the future, and is global in coverage. • Long-term climate forecasts that are tested, trusted and systematically improved. • By what metric are differences in model performance most clearly revealed? How specifically does the Hamburg forecast differ from the GFDL forecast? The Hadley from the NCAR?

13. Congressional Hearings: Board of Inquiry • Stability and credibility underpin economic decisions and business forecasts that play out over the next decades, credibility of the forecasts thus takes on great importance – particularly the rate of change and the regional impacts. These depend upon irrefutable global climate records and climate forecasts of increasing credibility. • By what criteria are those observations selected? By what strategies are climate forecasts tested against observations?

14. SI traceable standards Technology and strategy for establishing absolute scales Innovation for detection of systematic errors Atomic clocks, phase transition cells, frequency stabilized lasers Accuracy, precision and bias on-orbit Blackbodies, frequency standards, temperature cells Quantum cascade lasers, linear detectors, polarization of optical systems in space Targets for calibration: Moon, stars, etc. Important Sub-fields Related to High Accuracy Long-term Climate Records Optical Systems for High Accuracy Observations from Space Metrology Climate Community and Climate Records • Ground-based observations • Sondes, GEOS • Use of weather data for climate • Intercomparison wethods between satellites • In-situ intercomparisons NIST CALCON Conference IPCC, GEOSS

15. What Fundamental Principles Emerge From the Metrology Community?

16. NIST

17. SI units SI 1 Counts Achieving SI traceability • The SI traceability requires two SI traceable standards : Pollock, D. B., T. L. Murdock, R. U. Datla, and A. Thompson, Data uncertainty traced to SI units. Results reported in the International System of Units, International Journal of Remote Sensing, 24(2), 225-235, 2003. Traceability established Gain SI 2

18. Accuracy, Precision, and Bias Accuracy is the measure of the non-random, systematic error, or bias, that defines the offset between the measured value and the true value that constitutes the SI absolute standard Precision, in sharp contrast, is the measure of reproducibility or repeatability of the measurement without reference to an international standard so that precision is a measure of the random and not the systematic error. Suitable averaging of the random error can improve the precision of the measurement but does not establish the systematic error of the observation. Stabilityis a term often invoked with respect to long-term records when no absolute standard is available to quantitatively establish the systematic error - the bias defining the time-dependent (or instrument-dependent) difference between the observed quantity and the true value.

19. Accuracy, Precision, and Bias (cont.) The difference between accuracy and stability: • is that in accuracy the biases are independently determined through strategic design of the instrument providing on-orbit diagnostics of experimental factors that dictate bias with respect to international standards; SI traceability/NIST • Whereas in stability the biases are unknown and, often, assumed to be constant in time. The latter assumption is un-provable on-orbit without reference to SI traceable units.

20. Accuracy, Precision, and Bias (cont.) Thus, a climate monitoring system based on stability is subject to risk for two reasons: • Breaks or gaps in the data record or inadequacy of overlaps between data sets that are needed to remove relative biases that are assumed to be constant in time, and/or • The ability to quantify, against an international standard, time dependent biases that result from instrument differences, orbit changes, subsystem aging, etc., are needed to prove the assumption of stability.

21. Climate Benchmarks: What are They? • Observations that are absolute, with an accuracy traceable to SI standards on-orbit that provide a record in perpetuity of absolute values of key climate observables • Observations, the accuracy (absolute) of which are not compromised by interruption

22. GPS Occultation: The Time Standard • GPS occultation is tied to ground-based atomic clock standards by double-differencing technique. • NIST F1 measures time with fractional error of 1.7•10-15 (as of 1999). Benchmark Observations: A Critical Category of Climate Observables • GPS occultation measurements • Absolute spectrally resolved radiance in the thermal infrared • Absolute spectrally resolved radiance in the visible • Solar irradiance

23. Signal Source EM Signals Signal Source LEO Sensor Signal Source LEO Transmitted Signals Received Signals Global Climate Benchmark MeasurementsOccultation methods: How they work Occultation methods • Exploit extinction and/or refraction of electromagnetic signals along limb paths • Providing self-calibrated measurements of transmission and/or Doppler shift profiles • Leading via opt. thickness or column density, bending angle, and (complex) refractivity • To key atmospheric and climate parameters such as temperature, humidity, ozone, and geopotential height (among others) [Basic figures from D. Feng, Univ. of Arizona, private communications, 2001 (modified)]

24. GPS Occultation: Processing

25. “Dry” T from two independent COSMIC satellites 00:07 GMT 20.4°S 95.4°W 5 s and 1.5 km apart

26. SI Traceability to NIST Time Standard for Index or Refraction

27. Critical Advantages of GPS • Absolute calibration: GPS occultation is based on a timing measurement using atomic clocks • Diurnal cycle coverage with compelling cost effectiveness • Unambiguous retrieval of temperature, from mid-troposphere up, with ~ 100 m resolution, meaning capability to observe tropopause temperature globally • All-weather capability: Insensitive to clouds • Insensitive to instrument generation: absolute record in perpetuity

28. Why is spectrally resolved absolute radiance so fundamental to climate diagnostics?

29. degK Wavenumber GFDL Zonal Average Centered around 11S Clear Sky Radiance Changes

31. Priority for Climate Radiance Measurements: Blackbodies Blackbody

32. Priority for Climate Radiance Measurements: Blackbodies On-Orbit Blackbody

33. TNIST On-orbit On-orbit On-orbit SI Traceability to NIST Temperature Standards for Radiance

34. SI Traceability Locking TNIST, Radiance, Doppler Shift

35. SI units SI 1 Counts Achieving SI traceability • The SI traceability requires two SI traceable standards : Pollock, D. B., T. L. Murdock, R. U. Datla, and A. Thompson, Data uncertainty traced to SI units. Results reported in the International System of Units, International Journal of Remote Sensing, 24(2), 225-235, 2003. Traceability established Gain SI 2

36. SI traceable standards Technology and strategy for establishing absolute scales Innovation for detection of systematic errors Atomic clocks, phase transition cells, frequency stabilized lasers Accuracy, precision and bias on-orbit Blackbodies, frequency standards, temperature cells Quantum cascade lasers, linear detectors, polarization of optical systems in space Targets for calibration: Moon, stars, etc. Important Sub-fields Related to High Accuracy Long-term Climate Records Optical Systems for High Accuracy Observations from Space Climate Community and Climate Records Metrology • Ground-based observations • Sondes, GEOS • Use of weather data for climate • Intercomparison wethods between satellites • In-situ intercomparisons NIST CALCON Conference IPCC, GEOSS

37. What Technology Developments are Emerging From the Optical/Mechanical Component of the Satellite Community?

38. SUMMARY:STRICT FOCUS ON CLIMATE MONITORING • Simplification in Instrument Design Eliminates: Cross-Track Scanning, High Horizontal Resolution, High Spectral Resolution/Vertical Resolution, High Instrument Throughput, High Gain Detectors, Sophisticated Pointing, Sophisticated Power Systems • Research Architecture That Executes the Same Calibration Experiments Using Identical Hardware in the Lab, Airborne, Satellite Environment • Redundant Tests for Systematic Errors On-Orbit • Extensive Cross-Calibration with National and International Standards • Orbit Selection Based on Demand for Climate Accuracy

39. PRIORITY: REDUNDANCY • Dual Interferometer • Error Breakdown • Orbit: 90° polar • Instrument mass: 13 kg • Power budget: 8W

40. Checking on-orbit emissivity with a quantum cascade laser

41. Locking the Temperature Scale: Phase Transition

42. Detector Design: Linearity, Stability, Simplicity, Stray Light Rejection • Linearity is first priority for high accuracy • Source of error for quantum detectors: • Carrier mobility decreased by high carrier concentration • Free-carrier effects alter surface reflectivity • Carrier lifetime reduced by higher recombination rates Stray light rejection: Pyroelectric detectors generate signal only in response to modulated radiation Pyroelectric coefficient Detector area

43. Amplitude of modulation from polarization Angular position of mirror Observed signal Polarized radiance relayed by pointing mirror Planck function at measured temperature of pointing mirror PRIORITY: Polarization Determination Rotation of scene selection mirror introduces polarization effect that modulates instrument gain

44. Intensity Stabilizer IR SIRCUS: Spectral Irradiance and Radiance Responsivity Calibrations with Uniform Sources Wavelengths (microns) 1.064 YAG (10 W) 1.4 - 4.9 OPO (continuous, 0.5 to 1 W) 9 – 11 CO2 (discrete 10 lines, W) 9-11 Isotopic CO2 (discrete 10 lines, W) 4.8 - >6 CO (discrete, lots of lines, W) 5-12 OPO difference (continuous, mW) 4-12 OPO pumped OPO (continuous 10-100 mW) 8-12 Quantum Cascade (continuous, several unit) Tunable Laser Chopper Reference Radiometer Radiometer Under Test Wavemeter Exit Port Reference Radiometers Electrically Substituted Bolometer (ESB) InGaAs (working standard) Extended InGaAs (working standard) Germanium, InSb, MCT (working standard) Computer Speckle-remover Lens Integrating Sphere Speckle-removers Wobbly Mirror (slow) Fiber or Waveguide in ultrasound Monitor Detector (output to stabilizer) Intensity Stabilizers Fresnel Attenuator (broadband, slow response) EOM (medium bandwidth, fast response, 1-5 mm) AOM (narrow bandwidth, fast response) Black: Existing Orange: Under development

46. PRIORITY: Orbit Choice Salby cloud imagery data at 11m

47. Comparison of 90º Polar Orbit, Sun-Sync Orbit, Low-Latitude Precessing Orbit

49. Upon what foundation must the long-term climate record for satellites be based?

50. Dissection of Instrument Bias Using Defined Target Area • Selection of optimal domain • Orbit crossing times • Diurnal and semi-diurnal phase and amplitude • Time overlap between intercalibrated instruments • Buoy array to provide SI traceable temperatures