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 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
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
True y
accu
racy, a
Measured y
precision, p
Uncertainty, u = a2+p2
Traits: Accuracy, Precision and Uncertainty (After Stephens, 2003)
True y
a(t 1)a(
t 2)
p(t1)
p(t2)
y(t1)
y(t2)
Traits: Stability & Bias (After Stephens, 2003)
detecting change
understanding processes
understanding change
stability
unce
rtain
ty Attrib
utio
n
low
high low high
Desired Observing Characteristics (After G. Stephens, 2003)
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
Cloud effective particle size 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
Spectrally resolved thermal radiance Forcing/ Feedback 0.1 K 0.04 K
Required Accuracies and Stabilities: Atmospheric Variables
Variable Signal Accuracy Stability per decade)
Temperature
Troposphere Climate change 0.5 K 0.04 K
Stratosphere Climate change 0.5 K 0.08 K
Water vapor Climate change 5% 0.26%
Ozone
Total column Expected trend 3% 0.2%
Stratosphere Expected trend 5% 0.6%
Troposphere Expected trend 10% 1.0%
Aerosols
Optical depth (troposphere/stratosphere)
Forcing 0.01/0.01 0.005/0.005
Single scatter albedo (troposphere) Forcing 0.03 0.015
Effective radius (troposphere/stratosphere)
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
Required Accuracies and Stabilities: Surface Variables
Variable Signal Accuracy Stability (per decade)
Ocean color 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 Stability (decadal)
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
Net solar radiation: Top of atmosphere Broad band solar 1 W/m2 0.3 W/m2
Outgoing longwave radiation: Top of atmosphere
Broad band IR 1 W/m2 0.2 W/m2
Cloud base height Vis/IR radiometer 1 K 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 KVis/IR: see cloud optical thickness and cloud
top height
Microwave: 0.1 KVis/IR: see cloud optical thickness and
cloud top height
Cloud optical thickness Vis radiometer 5% 1%
Cloud top height IR radiometer 1 K 0.2 K
Cloud top pressure IR radiometer 1 K 0.2 K
Cloud top temperature IR radiometer 1 K 0.2 K
Spectrally resolved thermal radiance IR spectroradiometer 1 K 0.2 K
Instrument Requirements: Atmospheric Variables
Variable Instrument Accuracy Stability (decadal)
Temperature
Troposphere MW or IR radiometer 0.5 K 0.04 K
Stratosphere MW or IR radiometer 1 K 0.08 K
Water vapor MW radiometerIR radiometer
1.0 K1.0 K
0.08 K0.03 K
Ozone
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
Carbon dioxide IR radiometer 3% Forcing: 1%; Sources/sinks: 0.25%
Instrument Requirements: Surface Variables
Variable Instrument Accuracy Stability (decadal)
Ocean color VIS radiometer 5% 1%
Sea surface temperature
IR radiometerMW radiometer
0.1 K0.03 K
0.01 K0.01 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 LearnedImportance of Satellite Intercalibration
-0.60
-0.40
-0.20
0.00
0.20
0.40
0.60
1987 1989 1991 1993 1995 1997 1999 2001 2003
Year
Tb
An
om
aly
(K)
Blue Line: No SNO Intercalibration, Trend= 0.36 K Dec-1
Red Line: With SNO Intercalibration, Trend= 0.20 K Dec-1
By: Cheng-Zhi Zou
MSU Channel 2 Brightness Temperature Trend
NOAA -10NOAA -11
NOAA -12
NOAA -14
Lessons LearnedImportance of Multiple Independent Observations and Analyses
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)
Tropical Mean (20S-20N) TOA Radiative Flux AnomaliesTropical Mean (20S-20N) TOA Radiative Flux Anomalies
Examples of Global Time Series
Tropospheric Temp Anomaly (oC) (U. Alabama)
Global Cloud Amount Anomaly(%) (ISCCP) Global Precipitation (mm/day) (GPCP)
Snow Cover Anomaly (million sq. km) (Rutgers Univ.)
1979 2005
1983 2005
1967 2005
1979 2005
0.8
- 0.8
2.8
2.2
9
-6
-4
4
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: