Atmospheric Correction Algorithm for the GOCI
description
Transcript of 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
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
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
1. Introduction _ Atmospheric Correction
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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
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
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)
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
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
Target Area
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110.00 115.00 120.00 125.00 130.00 135.00 140.00 145.00 150.00Longitude (deg)
Lat
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(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
2. Process of Atmospheric Correction _ Step 2. Remove Rayleigh Signal
)()()( RTOA' ρTOA(443nm) ρR(443nm)
ρ‘ (443nm)
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
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
2. Process of Atmospheric Correction _ Step 4. Remove Aerosol Signal
)()()()()(
Td' RAA
w
ρ‘ (555nm) ρA(555nm)+ρRA (555nm) ρW (555nm)
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
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
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
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
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
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)
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
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
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Tdr
cos(Ф)
)00013.0()0113.0(0.1008569.0)( 424 r
Model’s TdrRTE’s Tdr
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
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
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)
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
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)
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
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3. Result & Validation _ Validation
SSMMSGCANASA Standard (MODIS)
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
THANK YOU