MODIS Aerosol Algorithm Validation, Updates and First Look at Aqua

Lorraine RemerYoram KaufmanDidier Tanré

Robert LevyRong-Rong LiCharles IchokuJ. Vanderlei MartinsAllen ChuShana MattooOleg DubovikZia AhmadRichard Kleidman

ValidationUpdates Implemented:

- extension over landUpdates to be Delivered :

- sediment mask- adjustments to cloud mask- dust replacement (over glint!)- new land models

On the horizon:- non-spherical dust models

First looks at Aqua

GRL special section

Ichoku et al. (2002)Martins et al. (2002)Chu et al. (2002)Remer et al. (2002)

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Effective Radius Validation

MODIS r_eff (

μ)m

_ (AERONET r eff μ )m

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Fine Mode Fraction Comparison

= 0.51 + 0.50 = 0.66 y x R

MODIS fine mode

τ

fraction

AERONET fine mode volume fraction

Fre

quen

cy (

%)

Absolute Variance

clouds

aerosols

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WestMed

EastMed

CoastAtl

Carrib

IslandAtl

IslandInd

y = 0.004 + 1.02x R= 0.94

MODIS

τ660

AERONETτ670

660 nm

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1

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= 0.031 + 0.94 = 0.95y x R

MODIS

τ870

AERONETτ870

870 nm

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WallopsCOVE

AERONET optical thickness (660 nm)

US_East Ocean

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Brazil

Abracos HillAlta FlorestaBalbina

AERONET optical thickness (660 nm)

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Aug Oct Dec Feb Apr Jun Aug Oct Nov

US_East Ocean

WallopsCOVE

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Aug Oct Dec Feb Apr Jun Aug Oct Nov

Brazil

Abracos HillAlta FlorestaBalbina

(MODIS - AERONET) / Error_Bars

2000 2001

N = 102

82% within error bars

N=86

77%within error bars

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All land validation

US centralUS eastN.Am_westMed_landFrance_landBrazilSAFARIAsiaEastEurope

(MODIS - AERONET) / Error_Bars

2000 2001

N withinerror

___________________________France_land 332 77%US east 282 56%NA_west 168 85%Med_land 139 60%Brazil 102 82%US central 100 72%SAFARI 89 72%East_Europe 58 84%Asia 45 64%

AERONET data from stations operated by the following PI’s:

B. Holben, C. McLain (SIMBIOS), D. Tanré

Analysis by R. Levy and L. Remer

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All ocean validation

US_AtlanticMediteraneanSaharan Atlantic

(MODIS - AERONET) / Error_Bars

2000 2001

N withinerror

___________________________Med_ocean 222 59%US_Atlantic 86 77%Saharan 63 37%

AERONET data from stations operated by the following PI’s:B. Holben, C. McLain (SIMBIOS), D. Tanré

Analysis by R. Levy and L. Remer

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Over land areas

AERONET AOT (660 nm)

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Over ocean areas

AERONET AOT (660 nm)

Land: N=119276% of retrievals within expected error

Ocean: N=37168% of retrievals within expected error

Validation of Aerosol Optical Thickness

Land algorithm: “dark targets”

But how dark is “dark” ?

Year 2000 Day 233 Time 0835Location: southern Africa, east coast

OLD

NEW

Following a suggestion by E. Vermote,we increase the 2.1 threshold from 0.25to 0.40 at nadir (and even higher at largerview angle). From the extended threshold,we derive in the blue and extrapolate to the red.

In this example the new version increases the number of retrievals over land from 7060 to 17,849. For the 285 granules collected over southern Africa during the SAFARI campaign, V3.1.0 increases the number of land retrievals by 130%.

2001

2002

Eight day means.Same dates,Different years

Images cropped fromMODIS Atmospheres web siteCreated by P. Hubanks

Sediment Mask

Li et al., submitted to IEEE TGARS

Sediment Mask

Li et al. submitted to IEEE TGARS

Sediment Mask

operational new sediment mask

Updates: Cloud mask for aerosol retrievals

spatial variabilitybefore: 3x3 window advances as a blocknow: 3x3 window advances every pixel

high AOT cutoffbefore: fill value for AOT > 5.0now: threshold on 0.47, not AOT

regaining retrievals in dustbefore: lost high dust valuesnow: r0.47/r0.66 separates dust from clouds

dust over glintbefore: no retrievals over glintnow: r0.47/r0.66 < 0.95 we retrieve heavy dust over glint

J.V. Martins et al. in preparation

Retrieving heavy dust over glint

J.V. Martins et al., in preparation

In 1493 C.E., Pope Alexander VI divided the world with an arbitrary line.

PortugalSpain

In 1995, Yoram Kaufmandivided the world again,with many arbitrary lines.

100

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0.1 1 10radius

biomass burning100

1000

10000

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dV/dlnr (10

-9

cm3

/cm2)

radius (μ )m

/Urban Industrial

Operationalaerosolmodels(1995 knowledge)

o = 0.90

o = 0.96

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SAFARI2000 (470 nm)

MODIS aerosol optical thickness (470 nm)

AERONET aerosol optical thickness (440 nm)

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SAFARI2000 (470 nm)

MODIS aerosol optical thickness (470 nm)

AERONET aerosol optical thickness (440 nm)

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o = 0.90

o = 0.85

(470 )MODIS aerosol optical thickness nm

(440 )AERONET aerosol optical thickness nm

Ichoku et al. (in revision): SAFARI 2000 special issue

o=0.90

0.90

0.90

0.85/0.96

0.96

0.85/0.90

New Aerosol Models based on 2002 informationAERONET and Dubovik et al. (2002)

Analysis by L.Remer and D.A. Chu

Retrieving non-spherical dust aerosol

QuickTime™ and aGIF decompressor

are needed to see this picture.

M. Meier and J. Reid

N withinerror

___________________________US_Atlantic 86 77%Med_ocean 222 59%Saharan 63 37%

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660 nm

observedM2 r=0.15M8 r=1.5coarse 660 M8spheroids

Phase function

scattering angle

Terra: 16:10 UTC Aqua: 17:45 UTC

Prepared by R. Levy MODIS: June 25, 2002

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21-Jun-0223-Jun-0225-Jun-0227-Jun-0229-Jun-0201-Jul-0203-Jul-0205-Jul-0207-Jul-0209-Jul-0211-Jul-02

Date

MODIS Aerosol Optical Thickness

Aqua_mean_AOT0470

Aqua_mean_AOT0550

Aqua_mean_AOT0660

Terra_mean_AOT0470

Terra_mean_AOT0550

Terra_mean_AOT0660

GSFC

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0.5

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2.5

21-Jun-0223-Jun-0225-Jun-0227-Jun-0229-Jun-0201-Jul-0203-Jul-0205-Jul-0207-Jul-0209-Jul-0211-Jul-02

Date

MODIS Aerosol Optical Thickness

Aqua_mean_AOT0470

Aqua_mean_AOT0550

Aqua_mean_AOT0660

Terra_mean_AOT0470

Terra_mean_AOT0550

Terra_mean_AOT0660

Arabian Sea

MODISTerra & AquaAOT over land

MODISTerra & Aqua

AOT over ocean

By C. Ichoku (July 2002)

Summary (page 1)

The primary aerosol products are valid within pre-launch errorestimations.

First operational retrieval of aerosol over land. First ever.Improvement of aerosol over ocean retrieval from AVHRR.

(AVHRR=0.04 MODIS =0.02)

No. Not every retrieval is perfect.Yes. We are making updates.

Some of these changes are to ‘fix’ small issues: sedimentsSome of these changes are to ‘re-call’ retrievals: dust in glint,

extension over land.

Fine mode/Coarse mode is a significant step forward.

Non-spherical phase functions will be a major innovation, but not ready for collection 4.

Qualitatively, Aqua looks good.

Summary (page 2)