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Transcript of A Remote Sensing Study of Coral Reefs; Kailua Bay, Oahu. Ebitari Isoun, Charles Fletcher, Neil...
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A Remote Sensing Study of A Remote Sensing Study of Coral Reefs; Coral Reefs;
Kailua Bay, Oahu.Kailua Bay, Oahu.
Ebitari Isoun, Ebitari Isoun,
Charles Fletcher,Charles Fletcher,
Neil Frazer, Neil Frazer,
Jonathan Gradie,Jonathan Gradie,
Scott RowlandScott Rowland
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AcknowledgementsAcknowledgements For shared data and field work: John Rooney,
Jodi Harney, Eric Grossman, Melanie Coyne and Zoe Norcross
Members of the Coastal Geology Team for moral support: Tara Miller, Dolan Eversole, Clark Sherman, Scott Calhoun, Matt Barbee, Mary Engels, Rob Mullane, Rikki Grober-Dunsmore, Chris Conger, Ole Kaven
For spectral band selection and use of field targets: Eric Hochberg and Marlin Atkinson
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Acknowledgements (continued)Acknowledgements (continued) The people at TerraSystems Inc. for friendly
assistance: Pamela Elwin, Kevin Jim, and Elbert Hwang
For funding and workspace: NASA, USGS-Coastal Geology Program, Sea Grant, Department of Geology and Geophysics, and SOEST
For unconditional love: My Family For mystery and blessings: God
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Topical OverviewTopical Overview
High-resolution multi-spectral imagery Map bathymetry and percent living coral
NN
Kailua Bay, OahuKailua Bay, Oahu
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Topical Overview (continued)Topical Overview (continued)
Passive remote sensing Radiative transfer model
• Atmosphere, ocean surface, water, and ocean substrate
“Differencing” of two spectral bands
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Topical Overview (continued)Topical Overview (continued) Error Assessment
• Depth: hydrographic survey• Percent living coral: diver-obtained ground truth
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Topical Overview (continued)Topical Overview (continued) Correlation of predictions to
environmental and human factors Geographic Information System (GIS)
space• Better reef management e.g. Maragos and
Grober-Dunsmore, 1998• Basemaps for scientific studies e.g. Harney et
al., 1999
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Introduction• Study Site• Data Collection
Methods• Data Processing• Radiative Transfer Theory• Depth and Bottom-type by Band Difference• Applying the Model
Results• Depth Predictions• Percent Living Coral Predictions
Conclusion
OutlineOutline
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Study SiteStudy Site
Oahu KailuaBay
0 10 km
21.5˚
158˚
21˚
158˚HawaiianIslands
OahuNN
0 100 km
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630500m E. 10 15 20 25 30 633500m E.
2369500m
N.
90
85
80
75
2369
500m
N.
90
85
80
75
2367
000m
N.
630500m E. 10 15 20 25 30 633500m E.
2367000m
N.
sand channel
spur andgroove
Sand fields
karst caves and caverns
Submerged beach rock
plains
Reef fro
nt
Reef front
Kailua ReefKailua Reef
NN
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Data collectionData collection
January 10, 1998– Light winds– No rain– Minimal ocean swell– 9:30 to 10:30 a.m.– 20 to 30 m horizontal visibility in water– Ocean floor visible to 30 m
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Data collection (continued)Data collection (continued)
Low flying (1400 m) airplane– ThunderChicken
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Data collection (continued)Data collection (continued) Application Specific Multi-Spectral
Camera System (TerraSystems, Inc.)• 8-bit precision
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Data collection (continued)Data collection (continued) Multi-spectral
images collected along a north-west to south-east transect
60% overlap along flight path
20% overlap across flight path
NN
OahuOahu
KailuaKailua
335˚335˚
1 m1 m
2 m2 m
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Data collection (continued)Data collection (continued)An image from the 6th flight path 1 pixel = 1 m
578 m
740 m
488 nm
551 nm
557 nm
10 nm full width half maximun
Hochberg and Hochberg and Atkinson, 2000Atkinson, 2000
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OutlineOutline
Introduction• Study Site• Data Collection
Methods• Data Processing• Radiative Transfer Theory• Depth and Bottom-type by Band Difference• Applying the Model
Results• Depth Predictions• Percent Living Coral Predictions
Conclusion
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Data processingData processing PCI Geomatics TM
••11
••11
••22
••33
••22••33
1:5000 aerial photographs
Coyne et al., 1998Coyne et al., 1998RMS = 0.5 m
NN
OahuOahu
KailuaKailua
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Radiative Transfer TheoryRadiative Transfer Theory
Irradiance: time rate of change of sunlight energy with area (W m-2 nm -1)
Radiance: flux per projected area per unit solid angle (W m-2 nm -1 sr-1)
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irradiance reflectanceupwelling irradiance
downwelling irradiance
Remote Sensing Reflectance,
Mobley, 1994Mobley, 1994
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reflectance beneath the water surface
wavelength
reflectance of infinitely deep ocean
bottom albedo(R just above the ocean
bottom)
water attenuation
distribution function for the underwater light
field
depth
Philpot, 1989Philpot, 1989
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Two-Flow ModelTwo-Flow Model
Gordon, 1989Gordon, 1989
Gregg and Gregg and Carder, 1991Carder, 1991
Elterman, 1968Elterman, 1968
Elterman, 1968Elterman, 1968Burt, Burt, 19541954
Mobley, Mobley, 19941994
Mobley, Mobley, 19941994
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can be written in a simple equation in terms of Radiance:
If
where
Lb is the radiance of the ocean substrate
Lw is the radiance of the ocean
is the water attenuation coefficient
D is the water distribution function
z is depth
Ld = Lb exp -Dz + Lw
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From the simplified equation:
A derivative band, Xi, can be defined:
(1) solve for the water attenuation coefficient,
(2) solve for depth and bottom-type
Ld = Lb exp -Dz + Lw
Xi ln((Ld-Lw) = lnLb-Dz
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Solve for water Solve for water attenuation attenuation coefficient, coefficient,
-10 m-20 m-30 m
X488
X551
X557
-10 m-20 m-30 m
-10 m-20 m-30 m
Depth*D
600
200
y = 0.05 x + 8.00
y = 0.07 x + 8.84
y = 0.07 x + 8.78
Xi ln((Ld-Lw) = lnLb-Dz
Y-axis X-axis
slopeintercept
Sand
In agreement with Maritorena, 1996Maritorena, 1996
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Solve for depth (Solve for depth (zz) and bottom-type () and bottom-type (YY))from the “difference” in two bands (from the “difference” in two bands (ii,,jj))
Assumptions:(1) Homogeneous water quality(2) Bottom reflectance is the same in two bands
(Frazer)(Frazer)
where g = D X = derivative band
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How do we apply the model to multi-spectral data?How do we apply the model to multi-spectral data?
123
456
789
10
8-bit
32-bit
32-bit
32-bit
488 nm551 nm557 nm
ca
cw
t(cw ca)
sa
sw
Tsun
D
eb06aj.pixeb06aj.pix
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Mosaic_model.pixMosaic_model.pix
1, 2, 3
4
567
89
10
8-bit
32-bit
32-bit
32-bit
488 nm, 551 nm, 557 nm
D
ca
cw
t(cw ca)
sa
sw
Tsun
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Aeb06aj.pix
Beb07aj.pix
Relative Difference in Overlap
Before After488 nm 7% 0.9%
551 nm 4% 0.7%
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Introduction• Study Site• Data Collection
Methods• Data Processing• Radiative Transfer Theory• Depth and Bottom-type by Band Difference• Applying the Model
Results• Depth Predictions• Percent Living Coral Predictions
Conclusion
OutlineOutline
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157˚44’00”W 157˚42’50”W157˚43’30”W
157˚44’00”W 157˚42’50”W157˚43’30”W
157˚44’00”W 157˚42’50”W157˚43’30”W
21˚2
5’20
”N21
˚24’
55”N
21˚2
5’20
”N21
˚24’
55”N
21˚25’20”N21˚24’55”N
21˚25’20”N21˚24’55”N
-3 m -6 m -9 m -12 m -15 m -18 m -21 m -24 m
Predicted Depth (z488/551)
Hydrographic Survey Depth(USGS data, E. Grossman)
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Percent Error
157˚44’00”W 157˚42’50”W157˚43’30”W
157˚44’00”W 157˚42’50”W157˚43’30”W
21˚2
5’20
”N21
˚24’
55”N
21˚25’20”N21˚24’55”N
0-5% 6-10% 11-15% 16-20% 21-25% 26-30% 31-35% >35%
Median = 11% Mean = 14% Std. Dev. = 11
•Percent error to depth R = 0.21•Boundaries sand channel
•Difference in water quality•Bottom-type assumption
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Percent Living Coral Zones Percent Living Coral Zones (Harney, 2000)(Harney, 2000)
hardgroundssand
Living Coral<15%
15-25%
25-40%
40-75%
>75%0.730.851.0
0.76
0.760.58
0.620.74
0.44
0.54
0
0
00
0
00
0.67 0.74
0.42
0.160.3
0.16
0.53
0.730.42
0.20.65
0.380.12
0.47
0.07
0.03 0.57
0.12
0.490.710.82
0.4
157˚44’00”W 157˚42’45”W30” 15”
157˚44’00”W 157˚42’45”W30” 15”
21˚2
5’30
”21
˚25’
00”
21˚25’ 30”21˚25’ 00”
line-intercept transect percent living coral value
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hardgroundssand
Living Coral<15%
15-25%
25-40%
40-75%
>75%0.730.851.0
0.76
0.760.58
0.620.74
0.44
0.54
0
0
00
0
00
0.67 0.74
0.42
0.160.3
0.16
0.53
0.730.42
0.20.65
0.380.12
0.47
0.07
0.03 0.57
0.12
0.490.710.82
0.4
157˚44’00”W 157˚42’45”W30” 15”
157˚44’00”W 157˚42’45”W30” 15”
21˚2
5’30
”21
˚25’
00”
21˚25’ 30”21˚25’ 00”
Multi-Spectral Percent Living Coral (Multi-Spectral Percent Living Coral (YY488/551488/551) Map) Map
0.10
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Accuracy Assessment of Multi-Spectral Percent Living Accuracy Assessment of Multi-Spectral Percent Living Coral MapCoral Map
•R = 0.73, producers accuracy to # reference points•Re-sampling loss of detail in 40-75%
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38%
2% 12%3%
15%
7%
25%
sand1,500,000 m2
hardgrounds70,000 m2
<15% living coral
500,000 m215-25% living
coral70,000 m2
25-40% living coral
600,000 m2
40-75% living coral
300,000 m2>75% living
coral1000,000 m2
Substrate DiversitySubstrate Diversity
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OutlineOutline
Introduction• Study Site• Data Collection
Methods• Data Processing• Radiative Transfer Theory• Depth and Bottom-type by Band Difference• Applying the Model
Results• Depth Predictions• Percent Living Coral Predictions
Conclusion
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ConclusionConclusion Radiative transfer model can be used to
normalize several multi-spectral images
Bathymetry and percent living coral is predicted with 488 nm and 551 nm
It may be possible to map change through time
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Tuesday,June Tuesday,June 12, 200112, 2001