langley research center / atmospheric sciences directorate climate calibration observatory...

Langley Research Center / Atmospheric Sciences Directorate

Climate Calibration Observatory Roadmap/Decadal Survey Mission Concept

Bruce Wielicki, NASA LaRC (CERES)Kory Priestley, NASA LaRC (CERES)

Peter Pilewskie, Colorado Univ. (SORCE)Tom Stone (USGS Lunar ROLO project)

Dave Siegel UCSB (SeaWIFS, ocean color)Chuck McClain, NASA GSFC (ocean color)Warren Wiscombe, NASA GSFC (Leonardo)

Joe Rice, NIST (Discover)Francesco Valero (Discover)

John Harries, Imperial College UK (GERB)Marty Mlynczak, NASA LaRC (Far-IR Interferometry)

Jim Anderson, Harvard (Climate Interferometry)Kevin Trenberth, NCAR (climate goals advisory)


Climate Calibration Observatory Mission

• Why a Satellite Calibration Observatory?– Anthropogenic forcing is 0.6 Wm-2/decade– Tropical 20S to 20N AMIP annual mean climate noise is 0.3 Wm-2

– Global net radiation annual mean sigma is 0.4 Wm-2 (ERBS)– 50% uncertainty in cloud feedback is change in cloud net radiative

forcing of 0.3 Wm-2/decade. 25% uncertainty is 0.15 Wm-2/decade. – Suggests threshold of 0.3 Wm-2 global net cloud forcing and goal of

0.15 Wm-2 for stability per decade. • 0.15 Wm-2 SW cloud forcing is 0.15/50 = 0.3% of global mean• 0.15 Wm-2 LW cloud forcing is 0.15/30 = 0.5% of global mean• 0.15 Wm-2 in clear-sky LW flux is ~0.1C temperature change/decade

– Converting to cloud optical depth/height/temperature for imagers:• equivalent visible channel stability is 0.5% stability per decade• equivalent cloud height/temperature is 15m or 0.1K stability per decade

– Temperature/Water Vapor Sounding: 0.04 to 0.08K per decade.– Vegetation and Ocean Color: 1% reflectance stability per decade.


Tropical (20S - 20N) TOA Radiation Anomalies:Observations vs. Climate Models

- Model "noise" 0.3 WmModel "noise" 0.3 Wm-2-2

- Climate Signals ~ 2 WmClimate Signals ~ 2 Wm-2-2

- Net tropical heating in 90sNet tropical heating in 90s- Opposite sign of "Iris" Opposite sign of "Iris" - Climate Forcing:Climate Forcing: 0.6 Wm0.6 Wm-2 -2 / decade/ decade- 50% Cloud Feedback:50% Cloud Feedback: 0.3 Wm0.3 Wm-2 -2 / decade/ decade 0.5% of TOA LW CRF 0.5% of TOA LW CRF 0.3% of TOA SW CRF0.3% of TOA SW CRF 0.3% of TOA Net CRF0.3% of TOA Net CRF- 0.3 Wm0.3 Wm-2 -2 climate reqmtclimate reqmt (BAMS, Sept 2005) (BAMS, Sept 2005)

High Accuracy Multi-Decadal Records Critical: High Accuracy Multi-Decadal Records Critical: Variability vs AnthropogenicVariability vs Anthropogenic


Tropical (20S - 20N) TOA Radiation Anomalies:ERBE/ScaRaB/CERES Comparisons

Best absolute accuracy of 0.5 to 2% insufficient for climate anomaliesBest absolute accuracy of 0.5 to 2% insufficient for climate anomaliesOverlap is Critical: stability capability exceeds absolute accuracyOverlap is Critical: stability capability exceeds absolute accuracy

Wong et al., J. Climate, in pressWong et al., J. Climate, in press


What do current instruments Provide?

• Goal of 0.3% SW and 0.5% LW stability very tough to achieve– CERES nominal stability design is 0.5% per 6 year mission life– Correction of RAP data transmission loss is ~ 1% SW in 4 years and was possible

only because of independent crosstrack/RAP data– AVHRR and geostationary imager visible channels: several % per year change.

Constrained to 3-5% using clear sky desert, ice.– MODIS/MISR differ by 3% in absolute calibration and estimate stability at 2% per 6

years or better (using diffuser plates) – SeaWIFS ocean color using monthly lunar views estimates stability constrained to

0.1% for annual mean, but only for dark targets (lunar reflectivity 5 to 10%).– For dark lunar targets: need linearity of ~0.1% to transfer to much brighter scenes

including clouds, snow, and desert.

• Current satellite instruments stress spatial/spectral resolution, not accuracy and stability of calibration. Detector linearity only ~ a few %.

• NPOESS VIIRS imager dropped lunar calibration (cost) • Ocean color community can’t use MODIS Terra: worried about VIIRS.• NPOESS weather priority cannot afford critical climate calibration

requirements: behind cost and schedule now.


Satellite Climate Calibration Observatory

• Major problem for climate is achieving both:– sufficient global sampling (large regional variability, small global signals)– sufficient calibration and especially stability– no designed climate observing system currently exists.

• Current instruments focus on sampling first, calibration second• Adding rigorous calibration sources and independence can double the

size/cost of instruments• Turn the problem around:

– don’t try to climate calibrate every satellite instrument– don’t try to sample the entire earth– instead design instruments to be highly calibrated and stable transfer

radiometers in orbit– essentially provide a NIST quality calibration standard laboratory in orbit.– design orbits, fields of view, pointing capabilities to optimize calibrating

other instruments: not sampling earth’s highly variable fields.– much larger fields of view (~50 to 100km) could be used leading to much

smaller optics size/mass/power.



• What would such an observatory look like?– Precessing 67 degree inclined orbit

• Changes local sampling time by 24 hours every 3 months• Allows under-flight of all other spacecraft orbits: leo, geo, etc• Orbit period varies with altitude: choose an altitude different than other satellites to

allow matched time/location calibrations with all satellites: for example 650 km.• Varying local time assures that inter-calibration locations will vary from the equator to

about 70 degrees latitude and will cover a complete range of climate conditions.

– Two satellite calibration observatories at any time in orbit: 6 hours of local sampling time apart, altitudes can differ (e.g. 650, 750km) to allow each to have different phasing of orbit synchronization with other satellites.

– Require +/-5 minute simultaneity in orbit crossing locations: same time/location/viewing angles. 10% of orbits (100 min period) will fill this criteria. Over long time periods this averages 1.4 calibrations per day with a low earth orbit spacecraft (e.g. sunsynch NPOESS) or more for geostationary.

– Can predict a week ahead when matched calibration orbit crossings will occur, what location, and what viewing angles.

– When one of the observatories or its instruments fail: launch a replacement within 3 months. Use small Pegasus launch vehicles (instruments are small) and have spare spacecraft ready.



• What types of instruments could be used for calibration standards?– must be highly linear detectors (0.1%): cavities, bolometers, etc– must be capable of handling most of the solar and thermal infrared

spectrum, including spectral resolution to match imagers and other spectrometers

– must be able to constrain total broadband energy– field of view must be large enough to allow very accurate integration

of other radiometers to match its fov: nominally 100km– field of view must be narrow enough to allow close matching of

viewing zenith and azimuth angles to within +/- 5 degrees/unbiased– instruments and/or spacecraft must be able to control pointing

accurately enough to achieve 98% fov matching: ~ 2 km of 100 km fov. CERES is ~ 1km, MODIS is ~ 100m.

– must have very accurate/stable independent calibration sources (e.g. deep cavity backbodies, lamps, solar viewing, lunar viewing)


Satellite Climate Calibration Observatory• Example instruments:

– ERBS active cavities have demonstrated 0.1% stability/decade, use solar constant checks every 2 weeks.

– SORCE active cavities for solar irradiance, and prism spectrometer for spectral solar irradiance. Modify for earth viewing capability? Large fov?

– Truths instrument design for spectral solar? – Anderson/Goody interferometer for 4 to 20m (bolometer detectors, 100km fov,

nadir only). Reach 50- 100m water vapor greenhouse? – Mlynczak FIRST Far-IR interferometer for 10 to 100um (balloon test)– Leonardo reflectivity spectrometer concept: modify for calibration instead of

angle/spatial sampling? 0.4 - 2.5m. – Lunar stability monitoring requires ~ 1km fov to scan the roughly 6km lunar diameter

(e.g. SeaWIFs). Also requires 0.1% linearity (dark target). – In calibration mode, there is more dwell time for intercalibration when compared to

normal scanning: 10 to 100 times longer light gathering. – Suggests:

• 2 cavities (SW, Total) 500km fov• IR spectrometer, 100km fov, dual deep cavity sources, 4 to 100m wavelengths• SW spectrometer, 100km fov, diffuser, solar views• SW spectrometer, 1km fov/150km swath, lunar views, check 100km fov instrument


Climate Calibration Observatory Summary

• Calibration first design: linear, stable, full solar/ir spectra• Intercalibration design for precessing orbit/large fov/pointing• Launch on demand to reduce gap risk to < 1%.• Two observatories allows independent calibration confirmation• Provide a few hundred intercalibration samples for other instruments

per year. 1 sigma noise in each sample ~ 1%. Annual mean <0.1%• Allows a way to deal with uncertain NPOESS future calibration• Allows calibration of geostationary imagers/sounders• Allows calibration checks of international and U.S. missions• CERES Rotating Azimuth plane scanner has demonstrated such

intercalibration campaigns for precessing vs. sunsynchronous vs. geo orbits for CERES and GERB. Matches in time/space/angle

• Turns around our normal space mission design to a different paradigm to support climate change.

• For Climate Remote Sensing: Calibration is the 1st dimension. – The other 8 are: x, y, z, t, wavelength, s. zenith, v. zenith, v. azimuth angle.


Examples that we are getting close

• Global Net Radiation and Ocean Heat Storage (In-situ/altimeter)

Wong et al. 2006J.Climate, in press



Shows consistent calibration stability at < 0.3 WmShows consistent calibration stability at < 0.3 Wm-2 -2 per decade (95% conf)per decade (95% conf)Unfortunately only works for tropical mean ocean (nband vs bband issues)Unfortunately only works for tropical mean ocean (nband vs bband issues)

Regional trends differ by +2 to -5 WmRegional trends differ by +2 to -5 Wm-2-2/decade SeaWiFS vs CERES/decade SeaWiFS vs CERES

Loeb et al. 2006JGR, submitted

0.21 Wm-2


CERES Shortwave TOA Reflected Flux Changes: CERES Shortwave TOA Reflected Flux Changes: Ties to Changing Cloud FractionTies to Changing Cloud Fraction

Unscrambling climate signal cause and effect requires complete parameter Unscrambling climate signal cause and effect requires complete parameter set at climate accuracy. For e.g.set at climate accuracy. For e.g. for forcing/response energetics: radiation, for forcing/response energetics: radiation, aerosol, cloud, land, snow/ice, temperature, humidity, precipitation aerosol, cloud, land, snow/ice, temperature, humidity, precipitation



Given climate variability, 15 to 20 years is required to first detect climate trends at Given climate variability, 15 to 20 years is required to first detect climate trends at cloud feedback level with 90% confidencecloud feedback level with 90% confidence

Half ofHalf ofAnthropAnthropForcing of Forcing of 0.6 Wm0.6 Wm-2-2

/decade/decade

Earthshine, ISCCP, CERES: 2000 to 2004Earthshine, ISCCP, CERES: 2000 to 2004

Loeb et al., AGU 2005Loeb et al., AGU 2005

Climate accuracy requirements are poorly understood by the Climate accuracy requirements are poorly understood by the community: recent Earthshine 6% changes were published in Science, community: recent Earthshine 6% changes were published in Science, causing much confusioncausing much confusion

ISCCP FD versus CERES: 2000 to 2004ISCCP FD versus CERES: 2000 to 2004

Loeb et al., AGU 2005Loeb et al., AGU 2005

Tropical 30S-30N

Global 90S-90N

Meteorological satellite climate data is not accurate Meteorological satellite climate data is not accurate or stable enough to determine decadal trends, but or stable enough to determine decadal trends, but very useful for regional studies.very useful for regional studies.


Amount of change for a factor of 6 in climate model sensitivity (2K to 12K for doubling CO2)

Murphy et al. Nature, 2004

Weather = dynamics, Climate = energeticsWeather = dynamics, Climate = energeticsNeed Climate Change OSSEs, Climate Obs. ReqmtsNeed Climate Change OSSEs, Climate Obs. Reqmts

Dynamicsvariables notvery sensitive

Cloud, Radiation, Sea Ice variables

very sensitive


Conclusions• The high confidence needed to be effective for climate policy critically

needs calibration/stability/independent obs/independent analysis. • IPCC AR4 preliminary conclusions:

– aerosol indirect effect is forcing uncertainty,

– cloud feedback is dominant sensitivity uncertainty: especially low cloud

– both require critical accuracy in SW cloud radiative forcing

• Climate Calibration Observatory concept can meet many of the ASIC^3 requirements, but needs development and demonstration

• Near-term actions:– Keep SeaWiFS alive: current source of lunar stability transfer

– Put Landsat/SPOT/etc on lunar stability scale with calibration manuevers

– Fill broadband gap by putting CERES FM-5 copy back on NPP (2009)

– Improve 80s/90s ISCCP and SRB data using ERBS active cavities as the poor mans climate calibration observatory for cloud/radiation

– Climate Calibration Observatory: need phase A/B studies soon

langley research center / atmospheric sciences directorate climate calibration observatory...

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