Download Satellite Instrument Calibration for Measuring Global

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
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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: