Review of Previous Climate Calibration Workshop

1. George Ohring, NOAA (Consultant) and Raju Datla (NIST) Bruce Wielicki (NASA) Roy Spencer (NASA) Bill Emery (CSU) Workshop on Achieving Satellite Instrument Calibration for Global Climate Change National Conference Center, Lansdowne, VA May 16-18, 2006 Review of Previous Climate Calibration Workshop

2. Outline of Presentation • Background, purpose, and organization of previous workshop • Workshop findings • Workshop recommendations • Concluding remarks

3. Background • At request of White House, National Research Council (NRC) recommends several research priorities for climate research (2001), including: • Ensure the existence of a long-term monitoring system that provides a more definitive observational basis to evaluate decadal-to century-scale changes • President Bush announces Climate Change Science Program (CCSP) to integrate Federal climate research (2002) • CCSP Strategic Plan (2003) • Optimize observations, monitoring, and data management systems of ‘climate quality” data

4. The Questions • Is the Earth’s climate changing? • If so, at what rate? • Are the causes natural or human-induced? • What will the climate be like in the future?

5. The Problem • Measuring long-term global climate change from space is a daunting task • Small signals - for example: • Atmospheric temperature trends as small as 0.10 C/decade • Ozone changes as little as 1%/decade • Variations in the sun’s output as tiny as 0.1%/decade or less • Satellite system problems • Sensors degrade in space • Time series produced by stitching together data from sequence of satellite instruments • Orbit drift

6. Purpose of Previous Workshop • Define absolute accuracies and long-term stabilities of global climate data sets that are needed to detect expected trends • Assess needed satellite instrument accuracies and stabilities • Evaluate ability of current observing systems to meet these requirements • Outline steps to improve state of the art

7. Previous Workshop Focus • Passive satellite sensors - ultraviolet to microwave • Climate variables • Solar irradiance, Earth radiation budget, and clouds • Total solar irradiance, spectral solar irradiance, outgoing longwave radiation, net incoming solar radiation, cloudiness • Atmospheric • Temperature, water vapor, ozone, aerosols, precipitation, and carbon dioxide • Surface • Vegetation, snow cover, sea ice, sea surface temperature, and ocean color

8. Organization of Previous Workshop • Organized by NIST, NPOESS-IPO, NOAA, and NASA • University of Maryland Inn and Conference Center, College Park, MD, November 12-14, 2002 • Organizing Committee • Raju Datla, Chair, NIST • Mike Weinreb, NOAA • George Ohring, Consultant to NOAA • Steve Mango, NPOESS-IPO • Jim Butler, NASA • Dave Pollock, UAH • 75 scientists (including 3 members of NAS) • Researchers who develop and analyze long-term data sets from satellites • Experts in the field of satellite instrument calibration • Physicists working on state of the art calibration sources and standards

9. Organization of Previous Workshop (Cont.) • Agenda • Invited presentations (posted on NIST web-site) • Breakout groups • Draft input for report • Breakout Groups • Solar irradiance, Earth radiation budget, and clouds • Chair: Bruce Wielicki, Scribe: Marty Mlynczak • Atmospheric variables • Chair: Roy Spencer, Scribe: Gerald Fraser • Surface variables • Chair: Bill Emery, Scribe: Dan Tarpley

10. Scales of Interest, Accuracy and Stability of Time Series • Scales of interest • Spatial: Global • Temporal: Decadal • Accuracy • Closeness to the truth • Measured by bias or systematic error • Stability • The extent to which the accuracy remains constant with time

11. Requirements for Accuracy and Stability : Basis • Climate changes or expected trends predicted by models • Significant changes in climate forcing or feedback variables (e.g., radiative effects comparable to that of increasing greenhouse gases) • Trends similar to those observed in past decades

12. Required Accuracies and Stabilities: Process • Specify anticipated signal in terms of expected change per decade • Accuracies versus stabilities • For measuring long-term trend: accuracy not critical - stability important • For understanding climate: accuracy critical • Stability appears to be less difficult to achieve in satellite instruments • Stability criterion • 1/5 of decadal climate signal (somewhat arbitrary) • Implies uncertainty range of 0.8 to 1.2, or factor of 1.5, for unit change • Climate model predictions differ by factor of 4 (temperature increase of 1.4 to 5.8 K by by 2100) • Stability of 1/5 of signal would lead to considerable narrowing of possible climate model scenarios • Presence of natural climate variability will increase uncertainty in detected signal and lengthen time required to detect signal

13. Measured y accuracy, a precision, p Uncertainty, u = a2+p2 True y Traits: Accuracy, Precision and Uncertainty (After Stephens, 2003)

14. y(t2) p(t2) a(t2) p(t1) a(t1) y(t1) True y Traits: Stability & Bias (After Stephens, 2003)

15. stability low high high detecting change uncertainty Attribution understanding processes understanding change low Desired Observing Characteristics (After G. Stephens, 2003)

16. From Climate Signal to Satellite Instrument Requirements Decadal Climate Signal Data Set Requirements for Accuracy and Stability (1/5 of Signal) Satellite Instrument Requirements

17. Required Accuracies and Stabilities: Solar Irradiance, Earth Radiation Budget, And Cloud Variables

18. Required Accuracies and Stabilities: Atmospheric Variables

19. Required Accuracies and Stabilities: Surface Variables

20. Instrument Requirements: Solar Irradiance, Earth Radiation Budget, And Cloud Variables

21. Instrument Requirements: Atmospheric Variables

22. Instrument Requirements: Surface Variables

23. Standards for Achieving Satellite Instrument Requirements • Transfer standards from National Measurement Institutes (e.g., NIST in USA) should have accuracies and stabilities far more stringent than satellite instrument requirements • The stability of extra-terrestrial sources should be established for on-board stability monitoring of satellite instruments • Techniques for self-calibrating satellite instruments should be developed

24. CDRs Constructed from Series of Overlapping Satellites

25. Lessons LearnedImportance of Satellite Intercalibration MSU Channel 2 Brightness Temperature Trend NOAA -14 NOAA -12 NOAA -11 NOAA -10

26. Lessons LearnedImportance of Multiple Independent Observations and Analyses Tropical Mean (20S-20N) TOA Radiative Flux Anomalies • Anthropogenic Radiative Forcing is 0.6 Wm-2 per decade • Observation goal for TOA fluxes is <0.3 Wm-2 per decade • Climate record discrepancies range from 1 to 10 Wm-2 • Confidence in resolving climate signals requires independent climate quality data sets • Red: ERBS Active Cavity • Blue: ISCCP + Rad. Model • Green: AVHRR Pathfinder • Purple: HIRS Pathfinder (Wong et al., J. Climate, In press)

27. Examples of Global Time Series Tropospheric Temp Anomaly (oC) (U. Alabama) Snow Cover Anomaly (million sq. km) (Rutgers Univ.) 0.8 9 - 0.8 -6 1979 2005 1967 2005 Global Cloud Amount Anomaly(%) (ISCCP) Global Precipitation (mm/day) (GPCP) 2.8 4 -4 2.2 1983 2005 1979 2005

28. Overarching Principles: Satellite Systems • Establish clear agency responsibilities for the U.S. space - based climate observing system • Acquire multiple independent space-based measurements of key climate variables • Ensure that launch schedules reduce risk of a gap in the time series to less than 10% probability for each climate variable • Add highly accurate measurements of spectrally resolved reflected solar and thermal infrared radiation to NPOESS Environmental Data Record (EDR) list • Increase U.S. multi-agency and international cooperation to achieve a rigorous climate observing system

29. Overarching Principles: Calibration • Elevate climate calibration requirements to critical importance in NPOESS • Develop characterization requirements for all instruments and insure that these are met • Conduct and verify pre-launch calibration of NPOESS and GOES-R instruments using NIST transfer radiometers • Simplify the design of climate monitoring instruments • Implement redundant calibration systems • Establish means to monitor the stability of the satellite sensors

30. Overarching Principles: Climate Data Records (CDRs) • Define measurement requirements for CDRs • Establish clear responsibility and accountability for generation of climate data records • Arrange for production and analysis of each CDR independently by at least two sources • Organize CDR science teams • Develop archive requirements for NPOESS CDRs

31. Workshop Publications

32. Concluding Remarks • Perhaps first time that a large group of climate data set producers/users and instrument experts assembled • Attempt at end-to end process: data set requirements satellite instrument requirements current capabilities recommendations • Included detailed tables of measurement requirements, overarching principles, and specific recommendations • Valuable guidance for the US (NPOESS and GOES-R) and international agencies (GCOS Implementation Plan for Systematic Observation Requirements for Satellite-Based Products for Climate) responsible for monitoring global climate change • Recommended follow-up workshop to discuss implementation: