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: