Improvement
Improvement ofof thethe GLI
GLI ocean
ocean color
color algorithm
algorithm andandmonitoring
monitoring ofof thethe trend
trend
inin thethe easteast Asian
Asian aerosol
aerosol characteristics
characteristics

H. Fukushima1), M. Toratani1), L.P. Li1,2), and H. Kobayashi3),
in collaboration with
R. Frouin4), H. Murakami5), and K. Hosoda5)1)Tokai University, 2)Ocean University of China,
3)Yamanashi University, 4) Scripps Institution of Oceanogr.
5)Japan Aerospace Exploration Agency

at GLI Workshop, Tsukuba, Japan
January 30, 2007
Fukushima - 1Works…
Works done
done soso far
far…
• worked on the GLI standard ocean color
atmospheric correction– Algorithm implementation/tuning• Iterative procedure for “turbid case 2 waters”• Absorptive aerosol correction: empirical algorithm for “V2GLI” processing• Refinement of QC flags incl. cloud screening• Sun-glitter masking/correction– Validation– Level-3 product evaluation

Fukushima - 2

WorksWorks this
this yearyear• FY’06: Further efforts towards “future”– Absorptive aerosol correction– Sun-glitter correction/evaluation• FY’06: Application studies– Atmospheric correction over coastal waters - use ofSWIR bands, and “red tide” observation– “Trend in East Asian aerosols”
A trial for “climate record”

Fukushima - 3

GLI
GLI atmosphericatmospheric correctioncorrection
ρT (λ ) = ρ M (λ ) + ρ A (λ ) + ρ MA (λ ) + T (λ )ρ G (λ ) + t (λ )ρWC (λ ) + t (λ )ρW (λ )ρT : Satellite observed reflectanceρM : Reflectance due to gas moleculesρA : Reflectance due to aerosol particles
ρMA : Reflectance due to molecule-aerosol interact.
ρG : Reflectance due to sunglint
ρWC : Reflectance due to whitcap
ρW : Reflectance of water body (our target!)t : Diffuse transmittance between sea-surface and satellite
T : Direct transmittance between sea-surface and satellite
Reflectance in atmospheric correctionπ⋅Lρ≡F0 ⋅ cos θ 0
Fukushima - 4

Features
Features andand difficulties
difficulties• Algorithm fairly established for “case 1” ocean waters• Difficulties– Over “turbid case 2” coastal waters• Needs to work with “in-water model”– Under “absorptive aerosol”

Important to SGLI

• Needs new aerosol models & schemes• Current V2 algorithm features…
– In-water optical models to estimate water reflectance ρW(λ)– Neural network to predict chl-a, SS, and CDOM
concentrations– Use of 380 nm band to estimate the aerosol “absorption”

Fukushima - 5

EmpiricalEmpirical absorptive
absorptive aerosol
aerosol correction
correction
forfor V2
V2 GLI
GLI data
data processing
processing• Normalized water-leaving radiance at 412nm band

Before correction

After correction
GLI 2003/4/17
Fukushima - 6EmpiricalEmpirical absorptive
absorptive aerosol
aerosol correction
correction
forfor V2
V2 GLI
GLI data
data processing
processing• Chlorophyll a concentration estimate

Before correction

After correction
GLI 2003/4/17
Current version algorithm to appear
in J. Oceanogr.Fukushima - 7

Radiative
RadiativeTransfer
TransferSimulation
Simulationon
on
Absorptive
AbsorptiveAerosol
Aerosol• Effect is larger in short wave
visible• Magnitude dependent– on Mixture ratio of absorptive
aerosol– on Path length– on Scan geometry– on Vertical distribution[FY’06] RTS ongoing withmodel-predicted aerosol
vertical profiles

Fukushima - 8

GLI
GLI Level
Level 22Sunglint
Sunglint Correction
Correction• SeaWinds-derived wind speed used for correction (25 km spatialresolution)• Based on Cox and Munk (1954) isotropic model for wave slope
probability distribution

Original
Originalimage
image

Predicted
Predictedsunglint
sunglintintensity
intensity

Corrected
Correctedimage
image
Fukushima - 9

Comparison-a imagery:
ComparisonofofChlorophyll
Chlorophyll-a
imagery:
versionversion11andand22sunglitter
sunglittermasking/correction
masking/correction

QuickTimeý Ç²TIFFÅiLZWÅj êLí£ÉvÉçÉOÉâÉÄ
Ç™Ç±ÇÃÉsÉNÉ`ÉÉÇ¾å©ÇÈÇžÇ½Ç…ÇÕïKóvÇ-Ç ÅB

Ver.1 algorithmwith JMA-OAQuickTimeý Ç²TIFFÅiLZWÅj êLí£ÉvÉçÉOÉâÉÄ
Ç™Ç±ÇÃÉsÉNÉ`ÉÉÇ¾å©ÇÈÇžÇ½Ç…ÇÕïKóvÇ-Ç ÅB

Ver.2 algorithmwith SeaWinds
Fukushima - 10

Sun-glitter evaluation:
Sun-glitterevaluation:
ongoing’06
ongoing refinement
refinement inin FY
FY’06• Paper submitted on “sun-glitter reflectance evaluation”
for wind-direction independent model– Based on the analysis of 750 GLI L1B FR scenes with
SeaWinds/SeaWiFS L3 data set• [FY’06] Re-analysis of the GLI L2AOA and SeaWinds
data set ongoing for wind-direction dependent model.
• Plan to complete the work to publish in FY’07

Fukushima - 11

Evaluation
Evaluation ofof AC
AC overover coastal
coastal waters
waters• Study area
– Bangpakong river estuary - “Turbid case 2”• The suspended matter is dominant.
• To evaluate AC with SWIR bands?

– Yellow Sea– Ise Bay
• Red tide
• To see possibility of identifying “dominant species”

Fukushima - 12

MODIS
MODIS specs
specs
Primary UseBand

BandwidthSpectral

RequiredRadiance

SNR

Land/Cloud/Aerosols

1620 - 670

21.8128

Boundaries

2841 - 876

24.7

201

Land/Cloud/Aerosols

3459 - 479

35.3

243

Properties

4545 - 565

29228

51230 - 1250

5.4

746

1628 - 1652

7.3

275

72105 - 2155

1110

Ocean Color/

8405 - 420

44.9

880

Phytoplankton/

9438 - 448

41.9

838

Biogeochemistry10483 - 493

32.1

802

11526 - 536

27.9

754

12546 - 556

21750

13662 - 672

9.5

910

14673 - 683

8.7

1087

15743 - 753

10.2

586

16862 - 877

6.2

516

Atmospheric

17890 - 920

10167

Water Vapor

18931 - 941

3.657

19915 - 965

15250

Fukushima - 13UpperUpper Gulf
Gulf ofof Thailand
Thailand

Bangpakong river

Fukushima - 14

InIn situ
situ observation
observation• May 23-27 in 2005
• Measured parameters– Chlorophyll-a concentration– Total suspended matter concentration– Water-leaving radiance by Radiometer (TriOSoptical sensors)

Fukushima - 15

33)
Total
Suspendedmatterconcentration(g/m
Total Suspended matter concentration (g/m )

362
316
36
7.19
3.77
3.28
1.94183

0.98

May 23-27 in 2005
Fukushima - 1633)
Shipobserved
totalsuspendedsolid(g/mShip-observed total suspended solid (g/m )Chl colud not
be estimated, 316
From MODIS,in May 26 2005.
1.94

36
7.19
3.77
3.28362183

0.98

Fukushima - 17

Comparison-leaving radiance
Comparison water
water-leaving
radiance
CHL
5.008mg/m3
TSS
36g/m3

Fukushima - 18

Comparison-leaving radiance
Comparison water
water-leaving
radiance
CHL
5.226mg/m3
TSS
3.28g/m3

Fukushima - 19

ACAC withwith SWIR
SWIR bandsbands• AC with SWIR band combination
useful over “highly turbid waters”
if high S/N achieved

Fukushima - 20

Concluding
Concluding Remarks
Remarks forfor ACAC partpart•

Towards further improvement on ocean color AC [FY’06 activities]
1. Absorptive aerosol correction•

RT simulations ongoing…

2. Sun glitter evaluation model•

Reanalysis on the global GLI L2AOA data with SeaWinds data

3. Atmospheric correction over “coastal waters”•Confirmed usefulness of SWIR bands over “Turbid Case II” waters•

Showed possibility of identifying “dominant Akashio species”

Future plans––••Fix the “absorptive aerosol correction” to evaluate the performance
Discuss/collaborate on “AC for coastal waters”

Suggestion/proposal–Need “precision” in-water optical model to predict ρW(λ)) spectrum
possibly using “Monte Carlo”?

Fukushima - 21

Increasing-micron aerosol
Increasing trends
trends ofof sub
sub-micronaerosol particles
particles
over-2004
over East
East Asian
Asian waters
waters observed
observed inin 1998
1998-2004
by-of View
by SeaSea Wide
Wide Field
Field-ofView Sensor
Sensor (SeaWiFS)(SeaWiFS)

Hajime Fukushima*a, Li-Ping Lia,b, Keisuke Takenoa
a School of High-tech., Tokai University, Japanb Department of Physics, Ocean University of China, China

January 30, 2007

Fukushima - 22

Motivation
Motivation ofof thethe Study
Study
1. Observation of aerosol characteristics and its spatial
variability is important••in terms of evaluating its effect on climate change
Even more important in East Asia

2. Can satellite observation measure the inter-annual
variability in characteristics of aerosol?
Candidate satellite sensors:••

NOAA/AVHRRTERRA/MODIS and AQUA/MODIS

3. SeaWiFS data set may provide a view for a potentialchange in aerosol characteristics••

Over 1998-2004
With well-calibrated sensor
Fukushima - 23

Analysis
Analysis ofof SeaWiFS
SeaWiFS EastEast Asian
Asian datadata setset• About 7500 scenes of SeaWiFS
GAC L1A analyzed tocover Jan. 1998 - Dec. 2004.
• Over adjacent seas of Japan(22.4-51.9°N, 116.6-146.5°E)• SeaDAS (ver.4.8) used to produce– Aerosol Optical Thickness (AOT)τA(490nm)– Angstrom exponent α– derived from 765 and 865 nmband data• Cloud mask: Local variance in ρA(865)in add. to simple threshold(τA(490) = 2.5)
• Daily composites averaged monthly

Fukushima - 24

Study-areas
Study subsub-areas

1. Okhotsk①

2. Sea of Japan②⑤

3. East China Sea
4. South of Japan③④

5. East of Japan

Fukushima - 25

Variabilities
Variabilitiesin
inmonthly
monthlymeanmeanττAA(490nm)(490nm)and-2004 period(765nm,865nm)
865nm)overover1998
1998-2004
periodandαα(765nm,3. East China Sea

2. Sea of Japan

1.6

0.6
0.5

0.8

1.4

1.20.71

0.6
0.5

0.8

0.4
0.6
0.3
0.2
0.2

0.1

00.3

0.1

0.2

00.2

0.1

001998 1999 2000 2001 2002 2003 2004
Time series (Monthly)

5. East of Japan
1.6
1.4
0.7

0.5
0.4

0.6

AOT

0.6

0.9

0.8

1.4

1.2

0.7

1.2

0.7

10.6

1

0.6

0.8

0.5

0.8

0.4
0.6
0.4

0.2

0.1

0.2

000

1998 1999 2000 2001 2002 2003 2004
Time series (Monthly)

0.8

0.5
0.4

0.6
0.3

0.3
0.2

1
1.6

0.9

AOT

0.8

1.2

6. Marcus Island
1

0.9

1.4

1998 1999 2000 2001 2002 2003 2004
Time series (Monthly)

0.5

0.8
0.6

1998 1999 2000 2001 2002 2003 2004
Time series (Monthly)

10.4

0.6

0.2

04. South of Japan

0.8

1

0.4

0.2

01

0.7

0.3
0.4

1998 1999 2000 2001 2002 2003 2004
Time series (Monthly)

1.6

1.2

0.4

0.4
0.6

0.4

0.8

0.8

AOT

1AOT

0.7

0.9

0.9
1.4

0.8

1.2

1.6

1.6

0.9
1.4

11

AOT

1

AOT

1. Okhotsk

0.2

0.3
0.4

0.2

0.1

0.2

0.1

000

1998 1999 2000 2001 2002 2003 2004
Time series (Monthly)

Fukushima - 26

Results…
Results soso farfar…
• Trend over 98-04 period– No significant increase in AOT– Angstrom exponent increased by 0.1 in mostof the East Asian waters over the 7 years• Accessed as
4-5 % increase in sub-micron fraction (SMF)(by conversion formula in Anderson et al., 2005)

SMF = −0.0512α 2 + 0.5089α + 0.02

• Most likely due to increasing anthropogenic
activities?

Fukushima - 27

Discussion
Discussion• Calibration reliable?
– Lunar calibration maintained in addition to solar
and vicarious calibration• Can compare with ground observation?
• How does it compare with MODIS?

Fukushima - 28

SeaWiFS-derved AOT
SeaWiFS vs.
vs. MODISMODIS-derved
AOT (single(single scene)scene)

MODIS τΑ (550nm)

0.5

0.25

0.00.00.25

0.5

SeaWiFS τΑ (490nm)
Fukushima - 29

SeaWiFS-derved Ang
SeaWiFS vs.
vs. MODISMODIS-derved
Ang.. Exp.
Exp. (v.1)(v.1)

MODIS Fine Mode Fraction

1.0

0.5

0.0
0.0

0.5

1.0

1.5

2.0

SeaWiFS ατ (490, 865nm)
Fukushima - 30

SeaWiFS-derved Ang
SeaWiFS vs.
vs. MODISMODIS-derved
Ang.. Exp.
Exp. (v.2)(v.2)ααρρ<--<---ρρAA(765)/(765)/ρρAA(865)(865)

MODIS Fine Mode Fraction

1.0

0.5

0.0
0.0

0.5

1.0

1.5

2.0

SeaWiFS αρ (765, 865nm)
Fukushima - 31

CONCLUSIONaerosol” part
CONCLUSION forfor ““aerosol”
part• The time series analysis shows the possibility of
tracking a “trend” in aerosol characteristics• Lessons:– Calibration of the satellite sensor is essential/critical– Aerosol model determination scheme in ocean color AC should
be re-evaluated• Future works– Collaboration: comparison with model prediction/groundmeasurements– Absorptive aerosol distribution mapping planned• Based on some “in-water model”

Fukushima - 32