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Review of Previous Climate Calibration Workshop 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 Outline of Presentation Background, purpose, and organization of previous workshop Workshop findings Workshop recommendations Concluding remarks 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 centuryscale 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 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? 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 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 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 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 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 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 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 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 Traits: Accuracy, Precision and Uncertainty (After Stephens, 2003) Measured y precision, p Uncertainty, u = a2+p2 True y Traits: Stability & Bias (After Stephens, 2003) y(t2) p(t2) p(t1) y(t1) True y Desired Observing Characteristics (After G. Stephens, 2003) stability low uncertainty high high detecting change low understanding processes understanding change From Climate Signal to Satellite Instrument Requirements Decadal Climate Signal Data Set Requirements for Accuracy and Stability (1/5 of Signal) Satellite Instrument Requirements Required Accuracies and Stabilities: Solar Irradiance, Earth Radiation Budget, And Cloud Variables Variable Signal Accuracy Stability (per decade) Solar irradiance Forcing 1.5 W/m2 0.3 W/m2 Surface albedo Forcing 0.01 0.002 Downward longwave flux: Surface Feedback 1 W/m2 0.2 W/m2 Downward shortwave radiation: Surface Feedback 1 W/m2 0.3 W/m2 Net solar radiation: Top of atmosphere Feedback 1 W/m2 0.3 W/m2 Outgoing longwave radiation: Top of atmosphere Feedback 1 W/m2 0.2 W/m2 Cloud base height Feedback 0.5 km 0.1 km Cloud cover (Fraction of sky covered) Feedback 0.01 0.003 Cloud particle size distribution Feedback TBD TBD Forcing: Water Feedback: Ice Water: 10% Ice: 20% Water: 2% Ice: 4% Cloud ice water path Feedback 25% 5% Cloud liquid water path Feedback 0.025 mm 0.005 mm Cloud optical thickness Feedback 10% 2% Cloud top height Feedback 150 m 30 m Cloud top pressure Feedback 15 hPa 3 hPa Cloud top temperature Feedback 1 K/cloud emissivity 0.2 K/cloud emissivity Forcing/ Feedback 0.1 K 0.04 K Cloud effective particle size Spectrally resolved thermal radiance Required Accuracies and Stabilities: Atmospheric Variables Variable Signal Accuracy Stability per decade) Troposphere Climate change 0.5 K 0.04 K Stratosphere Climate change 0.5 K 0.08 K Climate change 5% 0.26% Total column Expected trend 3% 0.2% Stratosphere Expected trend 5% 0.6% Troposphere Expected trend 10% 1.0% Forcing 0.01/0.01 0.005/0.005 Forcing 0.03 0.015 Forcing greater of 0.1 or 10%/0.1 greater of 0.05 or 5%/0.05 Precipitation Climate change 0.125 mm/hr 0.003 mm/hr Carbon dioxide Forcing/ Sources-sinks 10 ppmv/10 ppmv 2.8 ppmv/1.0 ppmv Temperature Water vapor Ozone Aerosols Optical depth (troposphere/stratosphere) Single scatter albedo (troposphere) Effective radius (troposphere/stratosphere) Required Accuracies and Stabilities: Surface Variables Variable Signal Ocean color Accuracy Stability (per decade) 5% 1% Sea surface temperature Climate change 0.1 K 0.04 K Sea ice area Forcing 5% 4% Snow cover Forcing 5% 4% Vegetation Past trend 3% 1% Instrument Requirements: Solar Irradiance, Earth Radiation Budget, And Cloud Variables Variable Instrument Accuracy Solar irradiance Radiometer 1.5 W/m2 0.3 W/m2 Surface albedo Vis radiometer 5% 1% Downward longwave flux: Surface IR spectrometer and Vis/IR radiometer See tropospheric temperature, water vapor, cloud base height, and cloud cover See tropospheric temperature, water vapor, cloud base height, and cloud cover Downward shortwave radiation: Surface Broad band solar and Vis/IR radiometer See net solar radiation: TOA, cloud particle effective size, cloud optical depth, cloud top height, and water vapor See net solar radiation: TOA, cloud particle effective size, cloud optical depth, cloud top height, and water vapor Broad band solar 1 W/m2 0.3 W/m2 Broad band IR 1 W/m2 0.2 W/m2 Cloud base height Vis/IR radiometer 1K 0.2 K Cloud cover (Fraction of sky covered) Vis/IR radiometer See cloud optical thickness and cloud to temperature See cloud optical thickness and cloud to temperature Cloud particle size distribution Vis/IR radiometer TBD TBD Cloud effective particle size Vis/IR radiometer 3.7 μm: Water, 5%; Ice, 10% 3.7 μm: Water, 1%; Ice, 2% Cloud ice water path Vis/IR radiometer TBD TBD Cloud liquid water path Microwave and Vis/IR radiometer Microwave: 0.3 K Vis/IR: see cloud optical thickness and cloud top height Microwave: 0.1 K Vis/IR: see cloud optical thickness and cloud top height Cloud optical thickness Vis radiometer 5% 1% Cloud top height IR radiometer 1K 0.2 K Cloud top pressure IR radiometer 1K 0.2 K Cloud top temperature IR radiometer 1K 0.2 K IR spectroradiometer 1K 0.2 K Net solar radiation: Top of atmosphere Outgoing longwave radiation: Top of atmosphere Spectrally resolved thermal radiance Stability (decadal) Instrument Requirements: Atmospheric Variables Variable Instrument Accuracy Stability (decadal) Troposphere MW or IR radiometer 0.5 K 0.04 K Stratosphere MW or IR radiometer 1K 0.08 K MW radiometer IR radiometer 1.0 K 1.0 K 0.08 K 0.03 K Total column UV/VIS spectrometer 2% (λ independent), 1% (λ dependent) 0.2% Stratosphere UV/VIS spectrometer 3% 0.6% Troposphere UV/VIS spectrometer 3% 0.1% Aerosols VIS polarimeter Radiometric: 3% Polarimetric: 0.5% Radiometric: 1.5% Polarimetric: 0.25% Precipitation MW radiometer 1.25 K 0.03 K IR radiometer 3% Forcing: 1%; Sources/sinks: 0.25% Temperature Water vapor Ozone Carbon dioxide Instrument Requirements: Surface Variables Variable Instrument Accuracy Stability (decadal) Ocean color VIS radiometer 5% 1% Sea surface temperature IR radiometer MW radiometer 0.1 K 0.03 K 0.01 K 0.01 K Sea ice area VIS radiometer 12% 10% Snow cover VIS radiometer 12% 10% Vegetation VIS radiometer 2% 0.80% 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 CDRs Constructed from Series of Overlapping Satellites Lessons Learned Importance of Satellite Intercalibration MSU Channel 2 Brightness Temperature Trend -1 Blue Line: No SNO Intercalibration, Trend= 0.36 K Dec Red Line: With SNO Intercalibration, Trend= 0.20 K Dec -1 0.60 By: Cheng-Zhi Zou Tb Anomaly (K) 0.40 0.20 0.00 -0.20 NOAA -14 -0.40 NOAA -12 NOAA -11 NOAA -10 -0.60 1987 1989 1991 1993 1995 Year 1997 1999 2001 2003 Lessons Learned Importance 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) Examples of Global Time Series Tropospheric Temp Anomaly (oC) (U. Alabama) 0.8 - 0.8 1979 9 2005 Global Cloud Amount Anomaly(%) (ISCCP) -6 1967 2005 Global Precipitation (mm/day) (GPCP) 2.8 4 -4 1983 Snow Cover Anomaly (million sq. km) (Rutgers Univ.) 2005 2.2 1979 2005 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 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 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 Workshop Publications 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: