for the GOCI Jae Hyun Ahn JooHyung Ryu Young Jae Park YuHwan Ahn Im Sang Oh Korea Ocean Research amp Development Institute Seoul National University I n d e x Introduction ID: 542351
Download Presentation The PPT/PDF document "Atmospheric Correction Algorithm" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
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 UniversitySlide2
I n d e x _
Introduction
_
Atmospheric CorrectionAtmospheric Algorithms of the GOCI> Standard NASA Algorithm
> SGCA
> SSMM
Process of Atmospheric Correction _Standard NASA AlgorithmSGCASSMMResult & Validation _ResultValidationConclusion _
Ocean ColorSlide3
1. Introduction _
Atmospheric
Correction
M(λ)
*L
TOA
(λ)*Rrs(λ)
Chl
SSCDOM
…
Radiometric Calibration
Atmospheric
Correction
L2 algorithms
L
TOA
(555
nm
)
Rrs
(555
nm
)
AtmosphericCorrection
*L : radiance
*
Rrs
: remote sensing reflectanceSlide4
1. Introduction
_
Atmospheric
Correction
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 LTOASlide5
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
GOCI
equatorSlide6
Introduction
_
3 atmospheric
Algorithms of the GOCIStandard NASA algorithmA classical standard atmospheric correction algorithm
Developed by
M.Wang
& H.R.GordonAerosol selection, turbid-water iterative method, diffuse transmittance models are updated by J.H.AhnSSMM (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
)Slide7
2. Process of Atmospheric Correction _
Geometric Corrected TOA Radiance Image
L
TOA(λ)
Raw Image
Reflectance of TOA Image
ρ(λ)=ρ‘ (λ) + ρR (
λ)
Reflectance of Ocean + Aerosol Image
ρ
‘
(
λ
) =
T
d
(λ
)ρW(λ) + ρA(λ)
+ ρRA(λ)
Reflectance of Ocean Image
ρW(λ)
Level 2 ProductChl, SS, CDOM, Kd490, …
Radiometric Calibration & Geometric Correction
Downward Solar Irradiance Normalization
Longitude, Latitude, Time, SZA, VZA, AZA
Remove Rayleigh & Sun-glint Reflectance & Mask
Radiative
Transfer Equation,
Cox&Munk
Model
Remove Aerosol Reflectance
Radiative
Transfer Equation, Aerosol Model
Underwater Algorithm
Reflectance of Ocean Image
Rrs
(
λ
)
Atmospheric Correction
Standard
NASA
Algorithm
SSMM
SGCASlide8
2. Process of Atmospheric Correction _
Step 1. Downward Solar Irradiance Normalization
Downward Solar Irradiance
Normalization
L
TOA
(
λ
)
cos
(
θ
S
)
*
θ
S : solar zenith angleF0(
λ) : Extraterrestrial spectral irradianceρTOA
(λ)Slide9
0
1
2
3
4
5
7
6
9
8
12
13
14
15
11
10
2. Process of Atmospheric Correction _
Slot Correction of Solar Irradiance Normalization
cos
(
θ
S
)
Step 1. Downward Solar Irradiance NormalizationSlide10
2. Process of Atmospheric Correction _
Step
2.
Remove Rayleigh Signal
ρ
TOA
(443
nm
)
ρ
R
(443
nm
)
ρ
‘
(443
nm)Slide11
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
Scattering off a rough sea surface
Molecular scatteringSlide12
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
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
MSlide13
2. Process of Atmospheric Correction _
Step 4. Remove Aerosol
Signal
ρ
‘
(555
nm
)
ρ
A
(555
nm
)+
ρ
RA
(555
nm
)ρW (555nm
)Slide14
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 Correction
Select
2 Aerosol Type
Multiple Scattering to Single Scattering
for all Aerosol Types
Get Two Aerosol Models (model1/model2)
ε
model1
(
B7, B8
)
<
ε
ave(B7, B8
) < εmodel2(B7, B8)
Look-up Table
from
RTE (6S)
Calculate Multiple Scattering of Specific Aerosol type
Get
ε
(λ, B8) for all band
Calculate Single Scattering of 2 Specific Aerosol type
Calculate Single Scattering Reflectance
for all Band
ρ
as
model
(
λ
)
2 Aerosol Models
sza
/
vza
/
aza
ρ
as
model1
(
λ
)
ρ
as
model2
(
λ
)
Get
ρ
a
(
λ
) +
ρ
ra
(
λ
)
and t(
λ
)
of 2 models
Interpolate
ρ
a
(
λ
) +
ρ
ra
(
λ
)and t(λ)
of 2 models
Calculate Rayleigh ScatteringSlide15
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)
ε
model1
(
B7, B8
)
<
ε
ave
(B7, B8) < ε
model2(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 modelsSlide16
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 :
ρ
w
(443))
East sea
East sea
East sea
East seaSlide17
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 Correction
LUT
Reflectance of Specific Aerosol type
2 Aerosol Models
sza
/
vza
/
aza
ρ
a
(
λ
) + ρra
(λ)and t(λ)
Calculate Rayleigh Scattering
Reference site
Get Aerosol reflectance
Get Two Aerosol Models & mixing ratio from LUTSlide18
ρ
TOA
(NIR)=
ρ
r
(NIR) + ρa(NIR) + ρra(NIR) + t(NIR) ρf(NIR) + t(NIR) ρw(NIR)
ρr (λ
) calculated by RTEρa
(
λ
) +
ρ
ra
(
λ
) calculated by LUTt(NIR)
calculated by LUT + RTEρf(NIR) calculated by Cox&Munk’s
Eqρ
w (λ) chl
, ss
Atmospheric Correction
Underwater Algorithm
CHL, TSM
ρw (NIR)
Ocean Color Model
ρ
w
(
λ
),
chl
corrected
ρ
w
(
λ
)
BRDF
2. Process of Atmospheric Correction _
Step 4. Remove Aerosol Reflectance
Iterative Method of NASA Standard Algorithm & SSMM
Turbid water :
ρ
W
(NIR) ≠0Slide19
2. Process of Atmospheric Correction _
Step 4. Remove Aerosol
Signal Iterative Method of NASA Standard Algorithm & SSMM
Rrs(NIR) = f/Q*bb(NIR)/(a(NIR)+bb(NIR)) Bb(NIR) = b
b
w
(NIR)+bbchl(NIR) + bbnc(NIR) a(NIR) = aw(NIR)+ achl(NIR) + anc(NIR
ρW
(865nm)
ρ
W
(865
nm
)Slide20
2. Process of Atmospheric Correction _
Step 4. Remove Aerosol
Signal
ρ‘ (λ)
Td(λ)
ρ
WMOD(λ) + ρA(λ)+ρRA(λ)+ error(λ)ρWMOD parameters
(λ
, chl,
Bb
S
)
ρ
Aerosol
MOD
parameters
(C
0
, C1
, C2)
Min-error
(λ)
Final value
(chl, C0, C1, C2)
ρW(λ)
SGCA (Sun-glint Correction Algorithm) Basic Assumption :
ρ
W
MOD
(
λ
) is valid
Polynomial fitting :
ρ
W
MOD
(
λ
) &
ρ
Aerosol
MOD
(
λ
)
ρ
W
MOD
(
λ
) : Using Biogenic optical model (by
A.Morel
)
ρ
Aerosol
MOD
(
λ
) : C
0
+ C
1
λ
-2
+
C
2
λ
-4Slide21
B1
2. Process of Atmospheric Correction _
Step 5. Apply Diffuse Transmittance
Extract Rayleigh diffuse transmittance Generic Rayleigh diffuse transmittance model
τ
r(λ) : use H.R.Gordon’s model
B3
B4
B8
Td
r
cos
(
Ф
)
Model’s
Td
r
RTE’s
Td
rSlide22
2. Process of Atmospheric Correction _
Step 5. Apply Diffuse Transmittance
Extract Rayleigh diffuse transmittance
A simple Rayleigh diffuse transmittance model
C
6
C
5
C4
C
3
C
2
C
1
C
0
412nm
2.446662E+00
-8.426278E+00
1.091486E+01
-5.986775E+003.424127E-011.212632E+00
3.582148E-01443nm
2.439042E-016.214171E-02-2.343571E+00
4.741604E+00
-4.368938E+002.218751E+00
3.401276E-01
490nm
-3.409564E+00
1.368336E+01
-2.270315E+01
2.024385E+01
-1.059768E+01
3.364536E+00
3.456215E-01
555nm
-6.190158E+00
2.375412E+01
-3.712744E+01
3.049661E+01
-1.420755E+01
3.801402E+00
4.276636E-01
660nm
-6.027454E+00
2.276901E+01
-3.481947E+01
2.770477E+01
-1.228477E+01
3.025252E+00
6.094426E-01
680nm
-5.722233E+00
2.158916E+01
-3.295611E+01
2.615090E+01
-1.154451E+01
2.820577E+00
6.416646E-01
745nm
-4.680227E+00
1.760824E+01
-2.677182E+01
2.111729E+01
-9.234431E+00
2.219140E+00
7.273351E-01
865nm
-3.040593E+00
1.140555E+01
-1.727012E+01
1.354123E+01
-5.866066E+00
1.386646E+00
8.353374E-01Slide23
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 methodSlide24
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)Slide25
3.
Result & Validation
_ Result
Comparison spectrums of GOCI & MODIS (with NASA Standard Algorithm)
B1 : 412nm
B2 : 443nm
B3 : 490nm (MODIS : 488nm)B4 : 555nm (MODIS : 551nm)B5 : 660nm (MODIS : 667nm)B6 : 680nm (MODIS : 678nm)
GOCI
MODIS
GOCI
MODISSlide26
SSMM
Rrs
(412
nm
)
SSMM
Rrs
(443nm
)
SSMM
Rrs
(490
nm
)
SSMM
Rrs
(555
nm)
MODIS Rrs(412
nm)
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
_
Result
Comparison images of SSMM & MODIS (NASA Standard Algorithm)Slide27
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)
3.
Result & Validation
_
Validation
SSMM
SGCA
NASA Standard (MODIS)Slide28
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 tuningSlide29
THANK YOU