atmospheric correction algorithm for the goci

29
Atmospheric Correction Algorithm for the GOCI Jae Hyun Ahn* Joo-Hyung Ryu* Young Jae Park* Yu-Hwan Ahn* Im Sang Oh** Korea Ocean Research & Development Institute Seoul National University

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Atmospheric Correction Algorithm for the GOCI. Jae Hyun Ahn * Joo-Hyung Ryu * Young Jae Park* Yu-Hwan Ahn * Im Sang Oh** Korea Ocean Research & Development Institute Seoul National University. I n d e x _. Introduction _ Atmospheric Correction Atmospheric Algorithms of the GOCI - PowerPoint PPT Presentation

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Page 1: Atmospheric Correction Algorithm for the GOCI

Atmospheric Correction Algo-rithm

for the GOCIJae Hyun Ahn*Joo-Hyung Ryu*Young Jae Park*

Yu-Hwan Ahn*Im Sang Oh**

Korea Ocean Research & Development InstituteSeoul National University

Page 2: Atmospheric Correction Algorithm for the GOCI

I n d e x _

1. Introduction _- Atmospheric Correction- Atmospheric Algorithms of the GOCI

> Standard NASA Algorithm> SGCA> SSMM

2. Process of Atmospheric Correction _- Standard NASA Algorithm- SGCA- SSMM

3. Result & Validation _- Result- Validation

4. Conclusion _Ocean Color

Page 3: Atmospheric Correction Algorithm for the GOCI

1. Introduction _ Atmospheric Correction

M(λ) *LTOA(λ)

*Rrs(λ)

ChlSS

CDOM…

Radiometric Calibration

AtmosphericCorrection

L2 algo-rithms

LTOA(555nm) Rrs(555nm)

Atmo-spheric

Correction

*L : radiance*Rrs : remote sensing reflectance

Page 4: Atmospheric Correction Algorithm for the GOCI

1. Introduction _ Atmospheric Correction

B1 B2 B3 B4 B5 B6 B7 B80

10

20

30

40

50

60

70

80

B1 B2 B3 B4 B5 B6 B7 B80

10

20

30

40

50

60

70

80

LrLaLw

Clear water / thin aerosol case

*Lr: Radiance of molecular scattering La : Radiance of aerosol scattring*Lw : Radiance of Ocean

Case 1 water : LW is 1~7% of LTOA

Page 5: Atmospheric Correction Algorithm for the GOCI

1. Introduction _ Atmospheric Correction

Issue : GOCI has longer optical path than the polar orbit satellite

(MODIS : 0˚ < Satellite zenith angle < 40˚)26˚ < Satellite zenith angle < 55˚

Observation area

Earth GOCIequator

Page 6: Atmospheric Correction Algorithm for the GOCI

1. Introduction _3 atmospheric Algorithms of the GOCI

Standard NASA algorithmA classical standard atmospheric correction algorithmDeveloped by M.Wang & H.R.GordonAerosol selection, turbid-water iterative method, diffuse transmittance models are updated by J.H.Ahn

SSMM (Spectral Shape Matching Method)Developed by Y.H.Ahn & P.ShanmugamUsing reference siteAerosol models updated by J.H.Ahn

SGCA (Sun-Glint Correction Algorithm)Developed by HYGEOSRemoving sun-glint & atmospheric signalPolynomial fitting algorithm (ocean color & atmospheric model)

Page 7: Atmospheric Correction Algorithm for the GOCI

2. Process of Atmospheric Correction _

Geometric Corrected TOA Radiance Im-age

LTOA(λ)

Raw Image

Reflectance of TOA Imageρ(λ)=ρ‘ (λ) + ρR (λ)

Reflectance of Ocean + Aerosol Imageρ‘ (λ) = Td(λ)ρW(λ) + ρA(λ) + ρRA(λ)

Reflectance of Ocean Image ρW(λ)

Level 2 ProductChl, SS, CDOM, Kd490, …

Radiometric Calibration & Geometric Cor-rection

Downward Solar Irradiance Normalization Longitude, Latitude, Time, SZA, VZA, AZA

Remove Rayleigh & Sun-glint Reflectance & Mask Radiative Transfer Equation, Cox&Munk Model

Remove Aerosol ReflectanceRadiative Transfer Equation, Aerosol Model

Underwater Algorithm

Reflectance of Ocean Image Rrs(λ)At

mos

pher

ic C

orre

ctio

n

Stan-dardNASAAlgo-rithm

SSMM SGCA

Page 8: Atmospheric Correction Algorithm for the GOCI

2. Process of Atmospheric Correction _ Step 1. Downward Solar Irradiance Normalization

Downward Solar IrradianceNormalization

LTOA(λ)

cos(θS )*

•θS : solar zenith angle•F0(λ) : Extraterrestrial spectral irradiance

ρTOA (λ)

)(0)cos()()(

F

L

S

TOATOA

Page 9: Atmospheric Correction Algorithm for the GOCI

Target Area

20.00

25.00

30.00

35.00

40.00

45.00

50.00

110.00 115.00 120.00 125.00 130.00 135.00 140.00 145.00 150.00Longitude (deg)

Lat

itude

(deg

)

P1P2

P3P4

0 1 2 3

457 6

98

12131415

1110

2. Process of Atmospheric Correction _

- Slot Correction of Solar Irradiance Normalization

cos(θS )

Step 1. Downward Solar Irradiance Normalization

Page 10: Atmospheric Correction Algorithm for the GOCI

2. Process of Atmospheric Correction _ Step 2. Remove Rayleigh Signal

)()()( RTOA' ρTOA(443nm) ρR(443nm)

ρ‘ (443nm)

Page 11: Atmospheric Correction Algorithm for the GOCI

2. Process of Atmospheric Correction _

- Remove direct & sun-glinted Rayleigh reflectance Computed by radiative transfer equation Integrate with GOCI bands’ spectral response Using pre-computed LUT Wind speed : 0~16 m/s

Step 3. Remove Rayleigh & Sun-glint Reflectance

)()()( gmmR

Scattering off a rough sea surface

Molecular scattering

Page 12: Atmospheric Correction Algorithm for the GOCI

M

2. Process of Atmospheric Correction _ Step 3. Land & Cloud Masking

- Using threshold of Band8 (865nm)- Masking 5x5 around the above threshold pixel

M M MM M M M MM M M M MM M M M M

M M M

Page 13: Atmospheric Correction Algorithm for the GOCI

2. Process of Atmospheric Correction _ Step 4. Remove Aerosol Signal

)()()()()(

Td' RAA

w

ρ‘ (555nm) ρA(555nm)+ρRA (555nm) ρW (555nm)

Page 14: Atmospheric Correction Algorithm for the GOCI

2. Process of Atmospheric Correction _ Step 4. Remove Aerosol Signal

- Standard NASA algorithm Basic Assumption : ρW(NIR) = 0 (GOCI’s NIR Band : 745nm,

865nm)Atmospheric Correc-tion

Select 2 Aerosol Type

Multiple Scattering to Single Scattering

for all Aerosol Types

Get Two Aerosol Models (model1/model2)

εmodel1(B7, B8) < εave(B7, B8) < εmodel2(B7, B8)

Look-up Ta-ble

fromRTE (6S)

Calculate Multiple Scattering of Specific Aerosol type

Get ε (λ, B8) for all band

Calculate Single Scattering of 2 Specific Aerosol typeCalculate Single Scattering Re-

flectancefor all Band ρas

model(λ)

2 Aerosol Mod-els

sza/vza/azaρas

model1(λ)ρas

model2(λ)

Getρa(λ) + ρra(λ)

and t(λ)of 2 mod-

els

Interpolateρa(λ) + ρra(λ)

and t(λ)of 2 mod-

els

Calculate Rayleigh Scat-tering

Page 15: Atmospheric Correction Algorithm for the GOCI

2. Process of Atmospheric Correction _ Step 4. Remove Aerosol Signal

- Standard NASA algorithm Aerosol model selection (Modified)

Select 2 Aerosol Type

Multiple Scattering to Single Scattering

for all Aerosol Types

Get Two Aerosol Models (model1/model2)

εmodel1(B7, B8) < εave(B7, B8) < εmodel2(B7, B8)

Average all aerosol models’ ε(B7, B8)

Select 4 aerosol models

Average 4 aerosol models’ ε(B7, B8)

Select 2 aerosol models

Get weight of 2 aerosol models

Page 16: Atmospheric Correction Algorithm for the GOCI

2. Process of Atmospheric Correction _ Step 4. Remove Aerosol Signal

- Aerosol models Maritime (RH 50%, RH 80%, RH 99%) Urban (RH 50%, RH 80%, RH 99%) Continental (RH 50%, RH 80% RH 99%)

Band 8 signal(aerosol signal)

Aerosol model selection result Aerosol removed signal(pure ocean signal : ρw(443))

East sea East sea East seaEast sea

Page 17: Atmospheric Correction Algorithm for the GOCI

2. Process of Atmospheric Correction _ Step 4. Remove Aerosol Reflectance

- SSMM (Spectral Shape Matching Method) Assumption : ρW(NIR) = 0 (GOCI’s NIR Band : 745nm, 865nm) Assumption : ρaerosol_model_1(λ) + ρaerosol_model_2(λ) = 0 Use reference site’s spectrum shape

Atmospheric Correc-tion

LUT

Reflectance of Specific Aerosol type

2 Aerosol Modelssza/vza/aza

ρa(λ) + ρra(λ)

and t(λ)

Calculate Rayleigh Scat-tering

Reference siteGet

Aerosol re-

flectance

Get Two Aerosol Mod-els & mixing ratio

from LUT

Page 18: Atmospheric Correction Algorithm for the GOCI

ρTOA(NIR)=ρr (NIR) + ρa(NIR) + ρra(NIR) + t(NIR) ρf(NIR) + t(NIR) ρw(NIR)

ρr (λ) calculated by RTE

ρa(λ) + ρra(λ) calculated by LUTt(NIR) calculated by LUT + RTE

ρf(NIR) calculated by Cox&Munk’s Eq

ρw (λ) chl, ss

Atmospheric Correc-tion

Underwater Algo-rithm

CHL, TSM ρw (NIR)

Ocean Color Model

ρw (λ), chl corrected ρw

(λ)BRDF

2. Process of Atmospheric Correction _ Step 4. Remove Aerosol Reflectance

- Iterative Method of NASA Standard Algorithm & SSMM Turbid water : ρW(NIR) ≠0

Page 19: Atmospheric Correction Algorithm for the GOCI

2. Process of Atmospheric Correction _ Step 4. Remove Aerosol Signal

- Iterative Method of NASA Standard Algorithm & SSMMRrs(NIR) = f/Q*bb(NIR)/(a(NIR)+bb(NIR))

- Bb(NIR) = bbw(NIR)+bb

chl(NIR) + bbnc(NIR)

- a(NIR) = aw(NIR)+ achl(NIR) + anc(NIRρW (865nm) ρW (865nm)

Page 20: Atmospheric Correction Algorithm for the GOCI

2. Process of Atmospheric Correction _ Step 4. Remove Aerosol Signal

ρ‘ (λ) Td(λ) ρWMOD(λ) + ρA(λ)+ρRA(λ)+ error(λ)

ρWMOD parameters(λ, chl, BbS)

ρAerosolMOD parameters

(C0, C1, C2)

Min-error(λ) Final value(chl, C0, C1, C2) ρW(λ)

- SGCA (Sun-glint Correction Algorithm) Basic Assumption : ρW

MOD(λ) is valid Polynomial fitting : ρW

MOD(λ) & ρAerosolMOD(λ)

ρWMOD(λ) : Using Biogenic optical model (by A.Morel)

ρAerosolMOD(λ) : C0 + C1λ-2 + C2λ-4

Page 21: Atmospheric Correction Algorithm for the GOCI

B1

2. Process of Atmospheric Correction _ Step 5. Apply Diffuse Transmittance

- Extract Rayleigh diffuse transmittance Generic Rayleigh diffuse transmittance model

τr(λ) : use H.R.Gordon’s model

)cos(2)(

)(

r

eTdr

00.10.20.30.40.50.60.70.80.9

1

0.1 0.2 0.3 0.4 0.5

0.600

0000

0000

0001

0.700

0000

0000

0001 0.8 0.9 10.1 0.2 0.3 0.4 0.5

0.600

0000

0000

0001

0.700

0000

0000

0001 0.8 0.9 1 0.1 0.2 0.3 0.4 0.5

0.600

0000

0000

0001

0.700

0000

0000

0001 0.8 0.9 1

B3

B4

B8

Tdr

cos(Ф)

)00013.0()0113.0(0.1008569.0)( 424 r

Model’s TdrRTE’s Tdr

Page 22: Atmospheric Correction Algorithm for the GOCI

2. Process of Atmospheric Correction _ Step 5. Apply Diffuse Transmittance

- Extract Rayleigh diffuse transmittance A simple Rayleigh diffuse transmittance model

6

0

)cos()()(n

nnr CTd

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10.45

0.55

0.65

0.75

0.85

0.95R² = 0.999622923906889R² = 0.999711743846593R² = 0.999777627817142R² = 0.999803644797189R² = 0.99994416876825R² = 0.9999965424593R² = 0.999995863458695R² = 0.999990472073208 Band1

(412nm)Polynomial (Band1 (412nm))Polynomial (Band1 (412nm))Band2 (443nm)Polynomial (Band2 (443nm))

C6 C5 C4 C3 C2 C1 C0

412nm 2.446662E+00 -8.426278E+00 1.091486E+01 -

5.986775E+00 3.424127E-01 1.212632E+00

3.582148E-01

443nm 2.439042E-01 6.214171E-02 -2.343571E+00 4.741604E+00 -

4.368938E+002.218751E+0

03.401276E-

01490nm -

3.409564E+00 1.368336E+01 -2.270315E+01 2.024385E+01 -

1.059768E+013.364536E+0

03.456215E-

01555nm -

6.190158E+00 2.375412E+01 -3.712744E+01 3.049661E+01 -

1.420755E+013.801402E+0

04.276636E-

01660nm -

6.027454E+00 2.276901E+01 -3.481947E+01 2.770477E+01 -

1.228477E+013.025252E+0

06.094426E-

01680nm -

5.722233E+00 2.158916E+01 -3.295611E+01 2.615090E+01 -

1.154451E+012.820577E+0

06.416646E-

01745nm -

4.680227E+00 1.760824E+01 -2.677182E+01 2.111729E+01 -

9.234431E+002.219140E+0

07.273351E-

01865nm -

3.040593E+00 1.140555E+01 -1.727012E+01 1.354123E+01 -

5.866066E+001.386646E+0

08.353374E-

01

Page 23: Atmospheric Correction Algorithm for the GOCI

2. Process of Atmospheric Correction _ Step 5. Apply Diffuse Transmittance

- Get aerosol diffuse transmittance from AOT Aerosol model, single scattering reflectance, single scattering

albedo, phase function Get aerosol optical thickness

A simple aerosol diffuse transmittance model (Hajime Fukushima, 1998)

- Using Aerosol+Rayleigh LUT (Future work) A generic data driven method

)cos()()()(1 0

)(

aerosol

eTdaerosol

Page 24: Atmospheric Correction Algorithm for the GOCI

GOCI with NASA standard 2011/03/17 03:16 (UTC)

3. Result & Validation _ ResultComparison images of GOCI & MODIS (NASA Standard Algorithm)

MODIS with NASA standard 2011/03/17 05:05 (UTC)

Page 25: Atmospheric Correction Algorithm for the GOCI

3. Result & Validation _ ResultComparison spectrums of GOCI & MODIS (with NASA Standard Algorithm)

B1 : 412nmB2 : 443nmB3 : 490nm (MODIS : 488nm)B4 : 555nm (MODIS : 551nm)B5 : 660nm (MODIS : 667nm)B6 : 680nm (MODIS : 678nm)

GOCIMODIS

GOCIMODIS

B1 B2 B3 B4 B5 B6 B7 B80

0.00050.001

0.00150.002

0.00250.003

0.00350.004

0.0045

B1 B2 B3 B4 B5 B6 B7 B80

0.00050.001

0.00150.002

0.00250.003

0.00350.004

0.00450.005

Page 26: Atmospheric Correction Algorithm for the GOCI

SSMM Rrs(412nm) SSMM Rrs(443nm) SSMM Rrs(490nm) SSMM Rrs(555nm)

MODIS Rrs(412nm) MODIS Rrs(443nm) MODIS Rrs(490nm) MODIS Rrs(555nm)

GOCI : SSMM 2010/09/17 04:16 (UTC)

MODIS : NASA Standard Algorithm 2010/09/17 04:45 (UTC)

3. Result & Validation _ ResultComparison images of SSMM & MODIS (NASA Standard Algorithm)

Page 27: Atmospheric Correction Algorithm for the GOCI

SSMM nLw(555nm): 2010. 08. 20 04:16 (UTC)SGCA nLw(555nm): 2010. 08. 20 04:16 (UTC)MODIS nLw(555nm): 2010. 08. 20 04:25 (UTC)

Comparison nLw spectrums of SSMM & SGCA & MODIS (NASA Standard Algorithm)

412 443 490 555 660 680 745 8650

2

4

6

8

10

12

14

3. Result & Validation _ Validation

SSMMSGCANASA Standard (MODIS)

Page 28: Atmospheric Correction Algorithm for the GOCI

4. Conclusion _

- NASA Standard Algorithm for the GOCI- Basic schema is all implemented.- Need to improve the ocean color model- Add more good arrangement aerosol models- Need to consider the new aerosol model for the GOCI observation area- Change to the look up table based diffuse transmittance estimation- Aerosol model selection and weight method update

- SSMM- Looks reasonable but needs more tuning- Better result high turbidity water and blue absorption aerosol case- Also consider about horizontal aerosol type changes- Collect more reference site

- SGCA- Relatively good matching at the high optical thickness case- Improvement for turbid water- Needs more local tuning

Page 29: Atmospheric Correction Algorithm for the GOCI

THANK YOU