Workshop presentation

The impact of sun glint on the retrieval of water
parameters and possibilities for the correction of
MERIS scenes
ESA MERIS AATSR Workshop, 20080923
Roland Doerffer(1), Helmut Schiller(1), Jürgen Fischer(2), Rene Preusker(2) and Marc Bouvet(3)
(1) GKSS Research Center, Max-Planck-Str. 1, 21502 Geesthacht, Germany
(2) Institute for Space Research, Free University, Berlin, Germany
(3) ESA, ESTEC, Noordwijk, Netherlands
doerffer@gkss.de
Hawai 20030705
Cross section Hawai scene
radiance_9 [mW/(m^2*sr*nm)]
200
180
160
140
120
radiance_9 [mW/(m^2*sr*nm)]
100
80
60
40
20
-160
-158
-156
-154
-152
longitude (deg)
-150
-148
0
-146
Sun glint mask for medium and high glint
Sunglint MERIS RR 2.8.2002 band 8
- glint not homogeneously distributed over scene: strongly depends on local wind
- glint reaches into left half of scene
Sund glint and wind
TOA reflectance spectra at pins
120
p1
p2
p3
p4
p5
Ltoa Wm -2 sr-1 µm-1
100
80
60
40
20
0
400
Wind p1: 5.7,
p2: 4.8,
p3: 8.5
450
500
p4: 7.7,
550
600
650
700
wavelength nm
p5: 3.9
750
800
850
900
Goals of the glint project (supported by ESA)
•
(1) Investigate and quantify the impact of sunglint on ocean colour
remote sensing under various conditions of angles, wind speeds
and types of water.
•
(2) Develop a procedure to correct for this influence and integrate
this procedure into the BEAM software and
•
(3) Validate the procedure for various conditions and types of waters
and, based on this validation and the analysis of step (1), define the
scope of the algorithm and provide the user with a measure of the
accuracy of the sun glint correction.
•
Since the sun glint is closely related to the atmospheric correction,
we will treat both issues together.
•
2 approaches:
– Without SWIR and TIR bands (based on C2R processor)
– With SWIR and TIR bands (s. presentation by J. Fischer)
Sun glint radiance reflectance, sun zenith 20 deg
Monte Carlo photon tracing model
Sun glint radiance reflectance
MERIS band 1 (412 nm), wind 3 m/s, sun zenith 20 deg
0.05
90
2
60
120
0.045
1.5
0.04
150
30
1
0.035
0.5
0.03
180
0
0.025
0.02
0.015
210
330
0.01
Red circle 42 deg
Yellow lines:
possible MERIS swath planes
240
300
270
azimuth angle [deg] / nadir angle [rad]
0.005
0
RLglint [sr-1]
Sun glint radiance reflectance, principle plane
0.06
0.05
MERIS band 1 (412 nm)
Sun zenith 20 deg
Wind 3 m/s
RLglint [sr-1]
0.04
0.03
nadir
0.02
0.01
0
-100
-80
-60
-40
-20
0
20
zenith angle [deg]
40
60
80
100
Influence of wind
90
90
2
120
0.16
60
0.09
2
120
60
1.5
0.08
1.5
0.14
1
150
1
150
30
0.07
30
0.12
0.5
0.06
0.5
0.1
180
0
0.05
180
0
0.08
0.04
0.06
210
330
240
300
270
Sun 45 deg, wind 3 m/s
0.04
0.02
0
0.03
210
330
0.02
240
300
270
Sun 45 deg, wind 7 m/s
0.01
0
Spectral properties of sunglint, max toa sun glint
reflectance
Sun glint
Photons from the sun, which are specularly reflected at the
surface into the detector and which are not scattered in the
atmosphere
2x transmittance of Ed_toa -> max sunglint reflectance
1
transmittance
0.95
0.9
0.85
0.8
0.75
400
450
500
550
600
650
700
wavelength nm
750
800
850
900
Simulated Rayleigh path radiance reflectance and sun glint
radiance reflectance
0.04
nadir view
0.035
sun zenith 20 deg
wind 3 m/s
Radiance refelctance [sr-1]
0.03
Rayleigh path radiance
0.025
0.02
sun glint
0.015
0.01
0.005
0
400
450
500
550
600
650
700
wavelength [nm]
750
800
850
900
The Atmosphere & Glint Correction Processor
•
•
Processing of MERIS L1 data
Based on Neural Network inversion of bi-directional radiance reflectances of
12 MERIS bands
•
Atmospheric correction procedure produces:
– water leaving radiance reflectances
– Path radiance reflectances
– Transmittance
– Aerosol optical thickness tau550
•
Water properties:
– absorption and scattering a_total and b_total
– Absorption of particles, phytoplankton pigments and yellow substance
– Scattering of total suspended matter and whit scatterer
Glint Ratio
TOA reflectance spectra at pins
140
p1
p2
120
Ltoa Wm-2 sr-1 µm-1
100
80
GL = (RLpath_ng+RLglint ) / RLpath
60
For MERIS band 13 (865 nm)
40
20
0
400
450
500
550
600
650
700
wavelength nm
750
800
850
900
NN for atmospheric correction – 3rd new version
Output
Input
RLtosa
12 bands
Tau_aerosol 412, 550, 778, 865
Sun_glint ratio
sun zenith
view zenith
azimuth diff
Opt. wind
a_tot, b_tot
Neural Network
MERIS band 1-9
Trans tosa-surface
Path radiance reflectance
RLw
errcode
RLw(θ,φ) =Lw (θ,φ) /Ed
Model Atmosphere
direct calc.
Model Atmosphere
Ozone variable
Rayleigh variable
stratosphere
Ltoa
Ltosa
Eotoa
TOA
Eotosa TOSA
MC calculation
Cirrus
troposphere with
fixed continental
aerosol
planetary boundary layer
variable aerosol maritime, urban
water with scattering
particles
Lboa
Edboa
BOA
Vertical distribution of components of the atmosphere
50
50
ozone
mixed g as
45
45
40
40
35
35
30
30
25
25
20 e [km]
20 e [km]
15
15
10
10
5
5
0
0
0.002
0. 004
0.006
0.008
0.01
0. 012
0.014
0.016
0. 018
0. 02
0
-6
10
urban
maritime
contine ntal
s trato
cirrus
-5
10
10
-4
10
-3
10
-2
10
-1
Training of a neural network for atmospheric correction
Atmosphere-optical model
1
Bio-optical model
7
NNforward water
(based on Hydrolight simulations)
RLw
9
12
Transmittance
L_up
5
MC code
2
RLpath_noglint
RLpath_glint
Ed_boa
Tau_aerosole
RLpath
Ed_boa
Tau_aerosole
4
6
Optional
Polarisation
correction
8
Selection
Max sunglint
Max tau_aerosol
Min. Rlw(560)
Etc.
10
RLtosa
RLpath
Ed_boa
RLw
Tau_aerosole
11
Training &
Test data set
13
Glint processor in BEAM
MERIS
L1 da ta
TOA L + Ed
s urfa ce pre s s ure
ozone
s ola r ze nith
vie w ze nith
a zimuth diff
corre ction a tm. pre s s +ozone
diff. to s ta nda rd
Top of S ta nda rd Atmos phe re
TOS A
ra dia nce re fle cta nce s
che ck out of
tra ining ra nge
NN
a tmos phe ric corre ction
pa th ra dia nce re fle cta nce
tra ns mitta nce
Wa te r le a ving ra dia nce re fle cta nce s
RLw
a ngula r de pe nde nt
che ck out of
tra ining ra nge
Validation using MERMAID MOBY data
Case
MOBY MERIS L1
MERIS L2
All data
239
2151
1666
m_glint & h_glint off
103
925
921
m_glint & h_glint on
95
860
392
m_glint on, h_glint off
39
353
353
Hi stogram m RL_toa M ERIS band 865 nm al l cases
Hi stogram m RL_toa M ERIS band 865 no_gl i nt cases
40
60
35
50
30
40
frequency
frequency
25
20
30
15
20
10
10
5
0
0.00
0.02
0.04
0.06
0.08
0.10
RL_toa [sr-1]
0.12
0.14
0.16
0.18
0.20
0
0.0 0
0.02
0.04
0.06
0.08
0.10
RL_toa [sr-1]
0.12
0.14
0.16
0.18
0.20
Frequency distribution of medium and high glint
Hi stogram m RL _to a M ERIS band 8 65 nm m _gl in t case s
Hi stogram m RL_toa M ERIS band 865 n m h_ gli nt cases
140
30
120
25
100
80
frequen cy
freque ncy
20
15
60
10
40
5
20
0
0.000
0.005
0.010
0.015
0 .0 20
0.02 5
RL_ to a [sr-1]
0.0 30
0.03 5
0.040
0.045
0.050
0
0.00
0.01
0.02
0.03
0.04
RL_ to a [sr-1]
0.05
0 .0 6
0.07
No glint and high glint TOA reflectance spectra
M ERIS spectra for sun glint with RL_toa band 865 > 0.06
M ERIS spectra for no sun glint with RL_toa band 865 < 0.004
0.085
0.08
0.07
0.080
0.06
0.075
RL_toa [sr-1]
RL_toa [sr-1]
0.05
0.04
0.070
0.03
0.065
0.02
0.060
0.01
0.00
400
450
500
550
600
650
700
wavelength [nm ]
750
800
850
900
0.055
400
450
500
550
600
650
700
wavelength [nm ]
750
800
850
900
Comparison with MOBY data
M OBY - C2R com pari son of Rw newt
M OBY - C2R com pari son of Rw newt
20020720
20021213
0.05
0.040
0.035
0.04
0.030
0.03
0.025
rhow
rhow
0.020
0.02
0.015
0.01
0.010
0.005
0.00
0.000
-0.01
400
450
500
550
600
650
700
750
wavel ength
Red:
MOBY data
Green:
MERIS standard L2 data
Light blue: C2R from path radiance
Dark blue: C2R RLw from NN
-0.005
400
450
500
550
600
wavel ength
650
700
750
Comparison with MOBY and L2 data
M OBY - AG C com parison of Rwn
20021020
M OBY - AG C com parison of Rwn
20061111
-1
0.040
10
0.035
-2
0.030
10
rhow
rhow
0.025
0.020
-3
10
0.015
-4
0.010
10
0.005
0.000
400
-5
450
500
550
600
650
700
750
wavel ength
Red: MOBY,
10 400
450
500
550
600
wavel ength
green: L2, blue: AGC
650
700
750
Scatter plots: no glint
Log10 scale
Com pari son M O BY data wi th ACG processor
1
1
0
0
-1
-1
-2
-2
rhown_meris
Rw
Com pari son M O BY data wi th ACG processor
-3
-3
-4
-4
-5
-5
-6
-6
-7
-7
-5
-4
-3
-2
-1
0
rhow_m oby
Comparison MOBY with AGC
processor 73 no-glint MOBY cases
1
-5
-4
-3
-2
-1
0
rhown_m oby
Comparison MOBY with L2
processor 73 no-glint MOBY cases
1
Scatter plots: medium glint
Log10 scale
Com parison M OBY data with ACG processor
Com parison M OBY data with ACG processor
1
1
0
0
-1
-1
rhown_meris
Rw
-2
-3
-2
-3
-4
-4
-5
-5
-6
-7
-6
-6
-5
-4
-3
-2
-1
0
rhow_m oby
Comparison MOBY with AGC
processor 21 medium-glint MOBY
cases
1
-6
-5
-4
-3
-2
-1
0
rhown_m oby
Comparison MOBY with L2
processor 21 medium-glint MOBY
cases
1
Scatter plot: high glint AGC
Log10 scale
Com pari son M OBY data with ACG processor
1
0
-1
Rw
-2
-3
-4
-5
-6
-7
-5
-4
-3
-2
rhow_m oby
-1
0
1
MERIS 20070429 LTOA RGB
C2R AGC Path radiance reflectance band 5
Water leaving radiance reflectance band 5
MERIS water reflectance band 5 (standard product)
All water pixel flagged
Water leaving radiance reflectance band 12
Water reflectance band 12 (standard product)
MERIS full resolution: Baltic and North Sea, 20080606
Stockhom
Sun glint
Oslo
Baltic Sea
North Sea
Sun glint
Copenhagen
Spatial resolution: 300 m
Hamburg
Swath: 1200 km, 4800 pixel
Water leaving radiance reflectance
Path radiance reflectance incl. Sun glint band 5 (560 nm)
Water leaving radiance reflectance band 5 (560 nm)
MERIS FR, Area of Gotland, TOA RLw RGB
Stockholm
Estonia
sunglint
Lettland
Ca. 100 km
Gotland
Baltic Sea
Water leaving radiance reflectance RGB
Gotland
Ca. 100 km
MERIS FR, TOA RLw, May 7 2008
•
•
North Sea
Reduced to 13%
Full swath:
– 1200 km
– 4290 pixel
– 300 m pixel
TOA
Radiance reflectance
RLw RGB
Shetland
Aerosol optical thickness at 550 nm
Shetland
C2R Chlorophyll (MERIS FR)
100 km
Shetland
Black Sea MERIS RR May 12 2007
Azovskoe
More
Dnipro
Krim
Danube
Sun glint
Full swath
RR 1200 m
RL_toa
Istanbul
MERIS RR 20070512 water leaving radiance reflectance
Azovskoe
More
Dnipro
Danube
Istanbul
Krim
Path radiance reflectance band 5 (560 nm)
Total Suspended Matter
Summary and Conclusion
• Glint can be corrected to some extend even for high glint
correction by using visible and near infrared bands only
• MOBY data with high glint conditions (GR > 6) can be
corrected, however results show higher scatter than
without glint
• Further validation with turbid case 2 water necessary
• Further improvement is expected when using also SWIR
and TIR bands
• (s. presentation by J. Fischer, Thursday 17:30)