Experimental validation of the MODTRAN 5.3 sea surface ...Experimental validation of the MODTRAN 5.3...
Transcript of Experimental validation of the MODTRAN 5.3 sea surface ...Experimental validation of the MODTRAN 5.3...
Experimental validation of the MODTRAN 5.3 sea surface radiance model
Denis Dion, Vincent Ross* andDaniel St-Germain
33rd Review of Atmospheric Transmission Models Meeting
June 2011
* With AEREX Avionic Inc
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Contents
• Introduction
• The sea surface BRDF model
• Complementary models
• The MIRAMER campaign
• Experimental and modeling uncertainties
• Experimental Results
• Conclusions
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Introduction
Complexity of sea surface radiance– Background
• Thermal emissions• Direct solar reflections• Indirect solar reflections
– Foreground• Contributes to atmospheric radiance
Radiative coupling
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Introduction
A sea surface BRDF for greater radiance accuracy
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Situation with MODTRAN
• No full BRDF coupling up to MODTRAN 4• No sea surface BRDF up to MODTRAN 5 v2• Basic aerosol models, limited user inputs• Shortcomings in refracted path at horizon ranges in
MODTRAN 4
• MODTRAN 5 v3– Fully coupled analytical sea surface BRDF– SAP (Spectral Aerosol Profile) input– Refracted path input
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The sea surface BRDF
( ) ( )[ ]3
, ( ) ( , ) ( , ),
4 ( ) 1 ( ) ( ) cos coss r r r
s rn n r r s r s
r p W Hf
z v vζπ
θ θ=
⋅ + Λ + Λψ ψ ζ ζ Ψ ζ Ψ
ψ ψU U
Ross, V., D. Dion, and G. Potvin, “Detailed analytical approach to the Gaussian surface bidirectional reflectance distribution function specular component applied to the sea surface,” J. Opt. Soc. Am. A Opt. Image Sci., 22, 2442– 2453 (2005).
Fresnel reflectance
Probability of specular reflection
Wave facet angle weighing
Wave facet hiding
Bistatic wave shadowing
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Coupling to MODTRAN
• BRDF is coded in FORTRAN in MODTRAN 5
• Fourier moments are computed– Input in DISORT
• DISORT multiple scattering uses BRDF as a lower boundary condition
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Other modeling considerations
• Marine aerosols are computed using MEDEX– Well suited for the Mediterranean– Input in MODTRAN using the SAP input
• MBL (marine boundary layer) thermodynamic profiles are computed using the DRDC modules– Monin-Obukhov similarity theory
• Refracted optical paths are used as input
• Sea surface statistical properties: Elfouhaily et al.– Fetch, atmospheric stability
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The MIRAMER campaign (May 2008)• Cedip Jade (Flir ATS) cameras on board
the Atalante ship– 3.4 – 5.5 mm (3.93 – 4.14 mm filter for glint)– 8.19 – 8.96 mm
• Environmental characterization– Radiosondes (2-3 day)– Local meteorological measurements
• Air and sea temperature• Wind speed/direction• Relative humidity
– Visibility meter (aerosols)– Aeronet station nearby (Toulon)– Solar pyranometer (solar irradiance)
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• Experimental– Image calibration and limited dynamic range
• Can reach 20% but probably lower (4-5%)– Horizontal variations (temperature, etc.) not measured
• Temperature +/- 1o
– Wind gusts– Bulk vs. skin temperature
• +/- 1o
• Modeling– Slope statistics values
• 80% between models– Aerosol modeling– Multiple reflections– Cirrus clouds
Experimental and modeling uncertainties
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Results• Non glint
– Midwave
– Longwave
-7 -6 -5 -4 -3 -2 -1 02.15
2.2
2.25
2.3
Rad
ianc
e (W
/m2 /s
ter)
ATAL 95 (1159) BII
-7 -6 -5 -4 -3 -2 -1 0-2
-1
0
1
Diff
eren
ce (%
)
Elevation (degrees)
12.5
13
13.5
14
14.5
15
App
aren
t tem
pera
ture
(o C)
Measurment
Simulation (-0.227 W/m2/ster)
σerr = 0.56%
-7 -6 -5 -4 -3 -2 -1 02.3
2.35
2.4
2.45
Rad
ianc
e (W
/m2 /s
ter)
ATAL 109 (1267) BII
-7 -6 -5 -4 -3 -2 -1 0-2
0
2
Diff
eren
ce (%
)
Elevation (degrees)
14.5
15
15.5
16
16.5
17
App
aren
t tem
pera
ture
(o C)
Measurment
Simulation (-0.099 W/m2/ster)
σerr = 0.76%
-7 -6 -5 -4 -3 -2 -1 04
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
Rad
ianc
e (W
/m2 /s
ter)
ATAL 89 (1116) BIII
-7 -6 -5 -4 -3 -2 -1 0-2
0
2
4
Diff
eren
ce (%
)
Elevation (degrees)
-10
-5
0
5
App
aren
t tem
pera
ture
(o C)
Measurment
Simulation (-1.39 W/m2/ster)
σerr = 1.76%
-7 -6 -5 -4 -3 -2 -1 05.5
5.6
5.7
5.8
5.9
6
6.1
Rad
ianc
e (W
/m2 /s
ter)
ATAL 107 (1255) BIII
-7 -6 -5 -4 -3 -2 -1 0-2
0
2
Diff
eren
ce (%
)
Elevation (degrees)
4
6
8
10
12
14
16
18
20
App
aren
t tem
pera
ture
(o C)
Measurment
Simulation (-0.133 W/m2/ster)
σerr = 1.14%
-7 -6 -5 -4 -3 -2 -1 05.9
6
6.1
6.2
6.3
6.4
Rad
ianc
e (W
/m2 /s
ter)
ATAL 109 (1267) BIII
-7 -6 -5 -4 -3 -2 -1 0-3-2-101
Diff
eren
ce (%
)Elevation (degrees)
10
12
14
16
18
20
App
aren
t tem
pera
ture
(o C)
Measurment
Simulation (+0.265 W/m2/ster)
σerr = 1.42%
-7 -6 -5 -4 -3 -2 -1 0
2.32
2.34
2.36
2.38
2.4
2.42
2.44
Rad
ianc
e (W
/m2 /s
ter)
ATAL 107 (1255) BII
-7 -6 -5 -4 -3 -2 -1 0-1
-0.5
0
0.5
Diff
eren
ce (%
)
Elevation (degrees)
14.5
15
15.5
16
16.5
17
App
aren
t tem
pera
ture
(o C)
Measurment
Simulation (-0.113 W/m2/ster)
σerr = 0.19%
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Results
• Glint
Relative azimuth (degrees)E
leva
tion
(deg
rees
)
ATAL 145 (1416) BII reference image
-4 -2 0 2 4 6
-7
-6
-5
-4
-3
-2
-1
0
Rad
ianc
e (W
/m2 /s
ter)
0
0.5
1
1.5
2
2.5
3
3.5
4A
B
B
A
-7 -6 -5 -4 -3 -2 -1 00
0.5
1
1.5
2ATAL 145 (1416) BII vertical
Rad
ianc
e (W
/m2
/ste
r)
-7 -6 -5 -4 -3 -2 -1 0-100
0
100
200
Elevation (degrees)
Diff
eren
ce (%
)
Measurment
Simulation (-0.05 W/m 2 /ster)
-4 -3 -2 -1 0 1 2 3 4 5 60
0.5
1
1.5ATAL 145 (1416) BII horizontal
Rad
ianc
e (W
/m2
/ste
r)
-4 -3 -2 -1 0 1 2 3 4 5 6
-20
0
20
Relative Azimuth (degrees)
Diff
eren
ce (%
)
Measurment
Simulation (-0.05 W/m 2/ster)
(Note: Cirrus cloud modeled using Aeronet AOD data)
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Results
• Glint
Relative Azimuth (degrees)E
leva
tion
(deg
rees
)
ATAL 64 (902) BII reference image
-6 -4 -2 0 2
-8
-7
-6
-5
-4
-3
-2
-1
Rad
ianc
e (W
/m2 /s
ter)
5
10
15
20AA
B
B
-9 -8 -7 -6 -5 -4 -3 -2 -1 01
2
3
4
5
6
7ATAL 64 (902) BII vertical
Elevation (degrees)
Rad
ianc
e (W
/m2 /s
ter)
MeasurementSimulation (+0.2 W/m2/ster)Horizon correction
-8 -6 -4 -2 0 2 40
1
2
3
4
5
6ATAL 64 (902) BII horizontal
Relative Azimuth (degrees)
Rad
ianc
e (W
/m2 /s
ter)
MeasurementSimulation (+0.2 W/m2/ster)Horizon correction
Ross, V., Dion, D., "Sea surface slope statistics derived from Sun glint radiance measurements and their apparent dependence on sensor elevation, J. Geophys. Res., 112, C09015, (2007)
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Conclusions
• A radiatively coupled sea surface BRDF is important in maritime environment radiative transfer
• MODTRAN 5 v3 will introduce a coupled sea surface BRDF
• Analysis of MIRAMER radiometric images supports the validation of the MODTRAN sea radiance implementation– Simulations and measurements agree well within experimental
uncertainties