The authors are with the Laboratoire Interdisciplinaire des Sciences de l’Environnement, ELICO, Centre National de la Recherche Scientifique, Unité Propre de recherche et Enseignement Supérieur Associée 8051, Université du Littoral Côte d’Opale, Maison de la Recherche, 32 Avenue Foch, B. P. 59 62930 Wimereux, France.
Richard Santer and Catherine Schmechtig, "Adjacency effects on water surfaces: primary scattering approximation and sensitivity study," Appl. Opt. 39, 361-375 (2000)
The making of atmospheric corrections is a critical task in the
interpretation of ocean color imagery. In coastal areas, a fraction
of the light reflected by the land reaches a sensor. Modeling the
reduction of image contrast when the atmospheric turbidity increases,
the so-called adjacency effect, requires large amounts of computing
time. To model this effect we developed a simple approach based on
the primary scattering approximation for both nadir and off-nadir
views. A sensitivity study indicates that the decisive criterion
for measurement accuracy for aerosols is their vertical
distribution. As this distribution cannot generally be determined
from space, it is not possible to include a suitable correction of the
adjacency effects on satellite imagery. Conversely, we propose a
simple correction for molecular scattering based on the isotropic
approximation. We also address the problem of reduction of the
coupling between the Fresnel reflection and the atmosphere for
observations of coastal water. We study the influence of the
adjacency effects on determination of the abundance of chlorophyll in
water by combining use of the red and the infrared bands for aerosol
remote sensing and the blue/green-ratio technique for retrieval of
these data.
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Atmospheric Conditions To Simulate the Adjacency Effects
According to 5S Computationsa
V (km)
δa (unit)
s (unit)
T(μv) (unit)
Solar Zenith Angles
Θs = 30°
Θs = 60°
ρa (%)
T(μs) (unit)
ρa (%)
T(μs) (unit)
50
0.089
0.041
0.970
1.1
0.964
1.6
0.928
23
0.137
0.054
0.958
1.4
0.948
2.1
0.889
8
0.304
0.094
0.914
2.4
0.896
4.0
0.810
For the continental model and three
visibilities V, we give, for two solar zenith angles,
aerosol optical thickness δa, spherical albedo
s, total transmittance for a nadir view
T(μv), atmospheric reflectance
ρa, and total transmittance for the downward
path T(μs). Cases 1, 2, and 3
correspond to the three visibilities (50, 23, and 8 km,
respectively) for 30° solar zenith angle; cases 4, 5, and 6 the
same three visibilities and 60° solar zenith angle.
Table 2
Additional Reflectance (in percent) Owing to Adjacency
Effects Computed for the Cases of Fig. 2 for Disks of Radii
R = 5, 10, 20 km at the Center of the Disk (upper
value) and at the Edge (lower
value)a
R (km)
Atmospheric Cases
1
2
3
4
5
6
5
0.43
0.55
0.89
0.59
0.72
1.18
1.37
1.89
3.35
2.04
2.61
4.60
10
0.20
0.25
0.37
0.26
0.31
0.47
1.03
1.41
2.48
1.52
1.94
3.40
20
0.13
0.14
0.15
0.14
0.15
0.17
1.20
1.67
2.97
1.80
2.31
4.09
The six columns correspond to the two
solar zenith angles and to the three visibilities.
Table 3
Additional Reflectance (in percent) Owing to
Adjacency Effectsa
V (km)
D (km)
0
1
2
3
4
5
D
0
30°
50
1.14
0.39
0.27
0.21
0.17
0.13
6.2
23
1.59
0.52
0.35
0.27
0.21
0.17
7.2
8
2.84
0.88
0.58
0.43
0.34
0.27
9.2
60°
50
1.71
0.56
0.37
0.28
0.22
0.18
8.0
23
2.20
0.70
0.46
0.35
0.28
0.22
8.5
8
3.92
1.20
0.78
0.58
0.45
0.35
11.0
Δρ is given at various distances D
from the coast line for two solar zenith angles (30° and 60°)
and three visibilities V. D0 is the distance
for which Δρ becomes less than 0.1%.
Table 4
Contribution at 865 nm of Land to the Oceanic Signal for
Points at Distance d from the
Coasta
Case
d (km)
1
2
4
8
a
0.62
0.38
0.19
0.09
b
0.58
0.35
0.18
0.08
c
0.54
0.31
0.16
0.07
d
0.39
0.21
0.10
0.04
e
0.88
0.62
0.37
0.19
The solar angle is 30° for a visibility
of 23 km. For (a)–(c), slope ν is 4,
Ha = 2 km, and values of the refractive
index are, respectively, 1.55, 1.44, and 1.33. For (d) and
(e) we have the case a aerosol model but with
Ha equal to d, 1 km and e, 4 km.
Table 5
Reduction of the Fresnel Reflection (in percent)
According to Eq. (28) versus Distance D from the Coast
for Three Wavelengths, 440, 560, and 865
nma
V (km)
Wavelength (nm)
Solar Zenith Angle
D = 0 (km)
D = 1 (km)
D = 2 (km)
D = 3 (km)
D = 4 (km)
30°
60°
30°
60°
30°
60°
30°
60°
30°
60°
50
440
-0.80
-1.34
-0.41
-1.12
-0.23
-0.95
-0.15
-0.81
-0.10
-0.71
50
560
-0.50
-0.72
-0.24
-0.59
-0.12
-0.48
-0.07
-0.40
-0.04
-0.34
50
865
-0.24
-0.29
-0.10
-0.23
-0.05
-0.18
-0.02
-0.14
-0.01
-0.11
23
440
-1.13
-1.70
-0.55
-1.40
-0.29
-1.15
-0.17
-0.97
-0.11
-0.82
23
560
-0.72
-0.97
-0.33
-0.78
-0.16
-0.62
-0.09
-0.51
-0.05
-0.42
23
865
-0.36
-0.42
-0.15
-0.33
-0.07
-0.25
-0.03
-0.20
-0.02
-0.15
8
440
-2.26
-2.95
-1.02
-2.33
-0.49
-1.86
-0.25
-1.50
-0.15
-1.22
8
560
-1.51
-1.84
-0.66
-1.43
-0.30
-1.11
-0.14
-0.87
-0.08
-0.69
8
865
-0.77
-0.88
-0.33
-0.67
-0.14
-0.51
-0.06
-0.39
-0.03
-0.30
The Sun is over the land, and
computations correspond to the cases in Table 1.
Table 6
Reduction of Fresnel Reflection (in percent) According
to Eq. (30) versus Distance D from the Coast for Three
Wavelengths, 440, 560, and 865
nma
Ha (km)
Wavelength (nm)
Distance from the Coast
D = 0 (km)
D = 1 (km)
D = 2 (km)
D = 3 (km)
D = 4 (km)
30°
60°
30°
60°
30°
60°
30°
60°
30°
60°
1
440
-1.13
-1.70
-0.32
-1.20
-0.15
-0.90
-0.11
-0.72
-0.081
-0.60
1
560
-0.72
-0.97
-0.17
-0.64
-0.07
-0.45
-0.04
-0.33
-0.03
-0.26
1
865
-0.35
-0.42
-0.07
-0.25
-0.02
-0.16
-0.01
-0.10
-0.01
-0.07
2
440
-1.13
-1.70
-0.55
-1.40
-0.29
-1.16
-0.17
-0.97
-0.11
-0.82
2
560
-0.72
-0.97
-0.33
-0.78
-0.16
-0.62
-0.09
-0.51
-0.05
-0.42
2
865
-0.35
-0.42
-0.15
-0.33
-0.07
-0.25
-0.03
-0.20
-0.02
-0.15
4
440
-1.13
-1.70
-0.76
-1.51
-0.52
-1.35
-0.36
-1.21
-0.24
-0.11
4
560
-0.72
-0.97
-0.48
-0.86
-0.32
-0.76
-0.22
-0.67
-0.15
-0.59
4
865
-0.35
-0.42
-0.23
-0.37
-0.15
-0.32
-0.10
-0.28
-0.06
-0.25
The Sun is over the land, and
computations correspond to a visibility of 23 km and three aerosol
scale heights, 1, 2, and 4 km.
Tables (6)
Table 1
Atmospheric Conditions To Simulate the Adjacency Effects
According to 5S Computationsa
V (km)
δa (unit)
s (unit)
T(μv) (unit)
Solar Zenith Angles
Θs = 30°
Θs = 60°
ρa (%)
T(μs) (unit)
ρa (%)
T(μs) (unit)
50
0.089
0.041
0.970
1.1
0.964
1.6
0.928
23
0.137
0.054
0.958
1.4
0.948
2.1
0.889
8
0.304
0.094
0.914
2.4
0.896
4.0
0.810
For the continental model and three
visibilities V, we give, for two solar zenith angles,
aerosol optical thickness δa, spherical albedo
s, total transmittance for a nadir view
T(μv), atmospheric reflectance
ρa, and total transmittance for the downward
path T(μs). Cases 1, 2, and 3
correspond to the three visibilities (50, 23, and 8 km,
respectively) for 30° solar zenith angle; cases 4, 5, and 6 the
same three visibilities and 60° solar zenith angle.
Table 2
Additional Reflectance (in percent) Owing to Adjacency
Effects Computed for the Cases of Fig. 2 for Disks of Radii
R = 5, 10, 20 km at the Center of the Disk (upper
value) and at the Edge (lower
value)a
R (km)
Atmospheric Cases
1
2
3
4
5
6
5
0.43
0.55
0.89
0.59
0.72
1.18
1.37
1.89
3.35
2.04
2.61
4.60
10
0.20
0.25
0.37
0.26
0.31
0.47
1.03
1.41
2.48
1.52
1.94
3.40
20
0.13
0.14
0.15
0.14
0.15
0.17
1.20
1.67
2.97
1.80
2.31
4.09
The six columns correspond to the two
solar zenith angles and to the three visibilities.
Table 3
Additional Reflectance (in percent) Owing to
Adjacency Effectsa
V (km)
D (km)
0
1
2
3
4
5
D
0
30°
50
1.14
0.39
0.27
0.21
0.17
0.13
6.2
23
1.59
0.52
0.35
0.27
0.21
0.17
7.2
8
2.84
0.88
0.58
0.43
0.34
0.27
9.2
60°
50
1.71
0.56
0.37
0.28
0.22
0.18
8.0
23
2.20
0.70
0.46
0.35
0.28
0.22
8.5
8
3.92
1.20
0.78
0.58
0.45
0.35
11.0
Δρ is given at various distances D
from the coast line for two solar zenith angles (30° and 60°)
and three visibilities V. D0 is the distance
for which Δρ becomes less than 0.1%.
Table 4
Contribution at 865 nm of Land to the Oceanic Signal for
Points at Distance d from the
Coasta
Case
d (km)
1
2
4
8
a
0.62
0.38
0.19
0.09
b
0.58
0.35
0.18
0.08
c
0.54
0.31
0.16
0.07
d
0.39
0.21
0.10
0.04
e
0.88
0.62
0.37
0.19
The solar angle is 30° for a visibility
of 23 km. For (a)–(c), slope ν is 4,
Ha = 2 km, and values of the refractive
index are, respectively, 1.55, 1.44, and 1.33. For (d) and
(e) we have the case a aerosol model but with
Ha equal to d, 1 km and e, 4 km.
Table 5
Reduction of the Fresnel Reflection (in percent)
According to Eq. (28) versus Distance D from the Coast
for Three Wavelengths, 440, 560, and 865
nma
V (km)
Wavelength (nm)
Solar Zenith Angle
D = 0 (km)
D = 1 (km)
D = 2 (km)
D = 3 (km)
D = 4 (km)
30°
60°
30°
60°
30°
60°
30°
60°
30°
60°
50
440
-0.80
-1.34
-0.41
-1.12
-0.23
-0.95
-0.15
-0.81
-0.10
-0.71
50
560
-0.50
-0.72
-0.24
-0.59
-0.12
-0.48
-0.07
-0.40
-0.04
-0.34
50
865
-0.24
-0.29
-0.10
-0.23
-0.05
-0.18
-0.02
-0.14
-0.01
-0.11
23
440
-1.13
-1.70
-0.55
-1.40
-0.29
-1.15
-0.17
-0.97
-0.11
-0.82
23
560
-0.72
-0.97
-0.33
-0.78
-0.16
-0.62
-0.09
-0.51
-0.05
-0.42
23
865
-0.36
-0.42
-0.15
-0.33
-0.07
-0.25
-0.03
-0.20
-0.02
-0.15
8
440
-2.26
-2.95
-1.02
-2.33
-0.49
-1.86
-0.25
-1.50
-0.15
-1.22
8
560
-1.51
-1.84
-0.66
-1.43
-0.30
-1.11
-0.14
-0.87
-0.08
-0.69
8
865
-0.77
-0.88
-0.33
-0.67
-0.14
-0.51
-0.06
-0.39
-0.03
-0.30
The Sun is over the land, and
computations correspond to the cases in Table 1.
Table 6
Reduction of Fresnel Reflection (in percent) According
to Eq. (30) versus Distance D from the Coast for Three
Wavelengths, 440, 560, and 865
nma
Ha (km)
Wavelength (nm)
Distance from the Coast
D = 0 (km)
D = 1 (km)
D = 2 (km)
D = 3 (km)
D = 4 (km)
30°
60°
30°
60°
30°
60°
30°
60°
30°
60°
1
440
-1.13
-1.70
-0.32
-1.20
-0.15
-0.90
-0.11
-0.72
-0.081
-0.60
1
560
-0.72
-0.97
-0.17
-0.64
-0.07
-0.45
-0.04
-0.33
-0.03
-0.26
1
865
-0.35
-0.42
-0.07
-0.25
-0.02
-0.16
-0.01
-0.10
-0.01
-0.07
2
440
-1.13
-1.70
-0.55
-1.40
-0.29
-1.16
-0.17
-0.97
-0.11
-0.82
2
560
-0.72
-0.97
-0.33
-0.78
-0.16
-0.62
-0.09
-0.51
-0.05
-0.42
2
865
-0.35
-0.42
-0.15
-0.33
-0.07
-0.25
-0.03
-0.20
-0.02
-0.15
4
440
-1.13
-1.70
-0.76
-1.51
-0.52
-1.35
-0.36
-1.21
-0.24
-0.11
4
560
-0.72
-0.97
-0.48
-0.86
-0.32
-0.76
-0.22
-0.67
-0.15
-0.59
4
865
-0.35
-0.42
-0.23
-0.37
-0.15
-0.32
-0.10
-0.28
-0.06
-0.25
The Sun is over the land, and
computations correspond to a visibility of 23 km and three aerosol
scale heights, 1, 2, and 4 km.
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