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How can satellites help define the history of carbonaceous aerosols

in the industrial era.• Acknowledgements:

– Paris Workshop - September 2003 organized by Didier Tanré and Yoram Kaufman: Slides abstracted from the talks of M. Herman (POLDER), G. De Leeuw (ATSR), O. Torres (TOMS), C. Hsu (SeaWiFs), L. Remer (MODIS) and D. Diner (MISR), G. Myhre (comparison).

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How can satellites help define the history of carbonaceous aerosols in the industrial era

– Satellites do not measure optical depth (except for solar

occultation for stratospheric aerosols) they measure reflectance

– Assumptions are required about size, shape and refractive index

in retrievals

– More measurements reduces the number of assumptions

– More measurements are:

• More wavelengths

• More angles

• More elements in the Stokes vector (polarization)

• All of the above

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– VIS/NIR/SWIR single view measurements

• AVHRR on POESS, MODIS on Terra and Aqua, GLI and OCTS on

ADEOS, SeaWiFS, CZCS.

• Magnitude and spectral variation of radiances used to estimate size

and optical depth of aerosols.

• Easier over ocean where the surface has a fairly well defined

contribution

How can satellites help define the history of carbonaceous aerosols in the industrial era

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– VIS/NIR/SWIR single view measurements• Can estimate aerosol load over land

• Land surface variability is a problem particularly for bright surfaces since land

is generally brighter than the atmosphere but can be solved to some extent

How can satellites help define the history of carbonaceous aerosols in the industrial era

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– VIS/NIR/SWIR single view measurements

How can satellites help define the history of carbonaceous aerosols in the industrial era

MODIS burn scar Aug 23, 2000

MODIS AOT Aug 23, 2000

MODIS fire/smoke Aug. 23 2000

MODIS Fire Temp. Aug 23, 2000

MOPITT CO Aug 22-27

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Winter Spring

Summer Autumn

*Hsu et al. 2003, submitted

– VIS/NIR/SWIR single view measurements• Even over deserts blue/UV measurements can be used to estimate aerosol

optical depth and single scattering albedo.

How can satellites help define the history of carbonaceous aerosols in the industrial era

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– UV measurements (340/380 nm on TOMS)• TOMS, OMI on Aura, OMPS on NPOESS. Also possible using

measurements from the European GOME and SCHIAMACHY instruments.• Use effect of absorbing aerosols on the amount of molecular scattering that

occurs.• Land is less of a problem than VIS/NIR because surface is dark and

atmosphere is bright. Sensitive to vertical extent of aerosols.

How can satellites help define the history of carbonaceous aerosols in the industrial era

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Sept. 4/2002

SeaWIFS RGB

EP-TOMS TOMS-AERONET AOT comparison

ssa= 0.97`

(A. ChaikovskyMinsk, Earlinet)

How can satellites help define the history of carbonaceous aerosols in the industrial era

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– Multi-angle measurements• POLDER - up to 14 view angles with polarization in some bands

• MISR - high spatial resolution multi-angle and multi-spectral retrievals, spectral range 440-865 nm with nine view

angles

• ATSR, ATSR-2, AATSR on ERS satellites- broader spectral range with two view angles.

• Potential to identify non-spherical particles

How can satellites help define the history of carbonaceous aerosols in the industrial era

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– Multi-angle measurements

Nadir 70º

Stereo height Aerosol OD

How can satellites help define the history of carbonaceous aerosols in the industrial era

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– Multi-angle measurements

How can satellites help define the history of carbonaceous aerosols in the industrial era

– Spectral and Directional information of ATSR-2

– Shape of the BRDF independent of the wavelength

– Effects of aerosols small at 1.6 µm

– Bi-modal aerosol model

– Data available on TEMIS website (www.temis.nl)

– Implementation DV&SV algorithms at KNMI: AOD over Europe, end 1995-early 2001

Veefkind et al., GRL vol 25, no. 16, 3135-3138, 1998

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• False color images using measurements at 410, 865 and 2250 nm - left hand side is reflectance, right hand side is polarized reflectance.

• Strong spectral contrast and weak variation of reflectance with scattering geometry.

• Weak spectral contrast and large variation with scattering geometry of polarized reflectance

• Easier to separate surface contribution from atmospheric contribution using polarized reflectance.

– Polarization measurements• POLDER - polarization measurements at 440, 670 and 865 nm with 12-15 view angles

• RSP aircraft instrument, polarization measurements at from 410-2250 nm with 150 view angles.

• NASA’s Glory mission (2006/2007) and APS on NPOESS (2010?).

How can satellites help define the history of carbonaceous aerosols in the industrial era

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How can satellites help define the history of carbonaceous aerosols in the industrial era

– Polarization measurements• Identification of non-spherical

particles more straightforward with polarization measurements,

• Sensitivity of polarization to refractive index of aerosols can be used to identify aerosol type, particularly differentiation of smoke from sulfates.

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• Over the oceans, product of optical thickness and Angstrom coefficient

• Over land, sensitive to « small aerosols » since large particles do not polarise

Biomassburning

Mai 1997Bréon, François-Marie, LSCE, France

How can satellites help define the history of carbonaceous aerosols in the industrial era

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• With more angles and spectral bands than POLDER retrieve a detailed aerosol model

• optical depth at 0.55µm of 0.102• a bimodal size distribution with modes of effective radius 0.35µm (water soluble)

and 1.01µm (sea salt). • The spectral optical depths measured by a MFRSR (right panel) indicate that the

retrieved optical depth and size distribution are realistic.

How can satellites help define the history of carbonaceous aerosols in the industrial era

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• Retrievals (and POLDERs index) work over land because the surface polarized reflectance is grey which allows the 2250 nm polarized reflectance to be used as a proxy for the surface even when the surface albedo is bright and/or variable (e.g. at 555 and 865 nm). Including over deserts and urban areas such as LA.

How can satellites help define the history of carbonaceous aerosols in the industrial era

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•What sort of differences do different species show in polarization?

•East coast summer time haze over the Dismal swamp shows polarized reflectance increasing with frequency indicating small particles with a refractive index consistent with a hydrated salt of some kind.

How can satellites help define the history of carbonaceous aerosols in the industrial era

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•West coast fires, 10-29-03. Size and refractive index of smoke aerosols are substantially different to the haze. Still small but appear to have very high real refractive index and single scattering albedo of order 0.9.

•Implication is that POLDER should have particularly good sensitivity to smoke in its aerosol index.

How can satellites help define the history of carbonaceous aerosols in the industrial era

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•LIDARs such as the GLAS will provide the best information on the vertical profile of aerosol opacity.

How can satellites help define the history of carbonaceous aerosols in the industrial era

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How can satellites help define the history of carbonaceous aerosols in the industrial era

•Retrievals use different approaches with different assumptions and biases.

•What does it all mean for a scientist interested in the aerosols?

•Following summary taken from Myhre et al. based on paper in press JAS 2003:

•Factor of two differences•Largest uncertainty over SH

high latitude ocean.•Upper limit on AOD

retrievals is a problem•Biased low compared to

AERONET at high optical depths

Global land and ocean

Global land

Global ocean

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How can satellites help define the history of carbonaceous aerosols in the industrial era

• History

– TOMS and AVHRR have the longest record allowing some evaluation of

inter-annual variability.

• A TOMS-like record will continue because of the need for ozone monitoring.

– SeaWiFS and ATSR are more recent and capable than AVHRR but

precede (AD) EOS satellites.

• ATSR data availability has been an issue but may be being resolved based on

de Leeuw presentation. SeaWiFs data and reprocessing to do aerosols over

bright surfaces is planned.

– GLI, OCTS and POLDER are all of interest for aerosols but failures of

ADEOS satellites limit temporal coverage.

• POLDER is only space-borne polarimeter to fly around our planet.

• GLI has highest spatial resolution 380 nm measurements made providing a

potential improvement over information available from TOMS.

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How can satellites help define the history of carbonaceous aerosols in the industrial era

– Presently MODIS, MISR, AATSR, Schiamachy, GOME, TOMS

and AVHRR are all providing aerosol products.

– In future

• NASA’s A-train with a POLDER sensor, OMI (TOMS+), A-band on

OCO, CALIPSO.

• VIIRS and OMPS on NPP.

• GOME2, other European spectrometers following on from

Schiamachy?

• NASA’s Glory with advanced polarization measurements

• EarthCARE with HSRL?

• Japanese SGLI with polarization measurements?

• Advanced MISR sensor with spectral range from 380-2150 nm and

polarization measurements under study.

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How can satellites help define the history of carbonaceous aerosols in the industrial era

• Summary– Current sensors provide capability to estimate not only optical

depth, but also size distribution and single scatter albedo (if

enough aerosol present) over ocean and land.

– Future sensors will provide speciation (in so far as an estimate of

an aerosols refractive index is a useful tool for this) from

polarization measurements and lidars will provide good

constraints on the vertical profile of aerosols.

– Primary difficulty in using products for the evaluation of aerosol

transport models is understanding how the assumptions that are

required in the estimate of aerosol properties interact with the

assumptions in transport models.