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A Remote Sensing Study of Coral Reefs; Kailua Bay, Oahu. Ebitari Isoun, Charles Fletcher, Neil Frazer, Jonathan Gradie, Scott Rowland.

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Presentation on theme: "A Remote Sensing Study of Coral Reefs; Kailua Bay, Oahu. Ebitari Isoun, Charles Fletcher, Neil Frazer, Jonathan Gradie, Scott Rowland."— Presentation transcript:

1 A Remote Sensing Study of Coral Reefs; Kailua Bay, Oahu. Ebitari Isoun, Charles Fletcher, Neil Frazer, Jonathan Gradie, Scott Rowland

2 Acknowledgements 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

3 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

4 Topical Overview n High-resolution multi-spectral imagery n Map bathymetry and percent living coral N Kailua Bay, Oahu

5 Topical Overview (continued) n Passive remote sensing n Radiative transfer model Atmosphere, ocean surface, water, and ocean substrate n “Differencing” of two spectral bands

6 Topical Overview (continued) n Error Assessment Depth: hydrographic survey Percent living coral: diver-obtained ground truth

7 Topical Overview (continued) n Correlation of predictions to environmental and human factors n 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

8 n Introduction Study Site Data Collection n Methods Data Processing Radiative Transfer Theory Depth and Bottom-type by Band Difference Applying the Model n Results Depth Predictions Percent Living Coral Predictions n ConclusionOutline

9 Study Site Oahu Kailua Bay 0 10 km 21.5˚ 158˚ 21˚ 158˚ Hawaiian Islands Oahu N km

10 m E m E m N m N m N m E m E m N. sand channel spur and groove Sand fields karst caves and caverns Submerged beach rock plains Reef front Kailua Reef N

11 Data collection n 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

12 Data collection (continued) n Low flying (1400 m) airplane –ThunderChicken

13 Data collection (continued) n Application Specific Multi-Spectral Camera System (TerraSystems, Inc.) 8-bit precision

14 Data collection (continued) n Multi-spectral images collected along a north-west to south-east transect n 60% overlap along flight path n 20% overlap across flight path N Oahu Kailua 335˚ 1 m 2 m

15 Data collection (continued) An image from the 6th flight path1 pixel = 1 m 578 m 740 m 488 nm 551 nm 557 nm 10 nm full width half maximun Hochberg and Atkinson, 2000

16 Outline n Introduction Study Site Data Collection n Methods Data Processing Radiative Transfer Theory Depth and Bottom-type by Band Difference Applying the Model n Results Depth Predictions Percent Living Coral Predictions n Conclusion

17 Data processing n PCI Geomatics TM :5000 aerial photographs Coyne et al., 1998 RMS = 0.5 m N Oahu Kailua

18 Radiative Transfer Theory n Irradiance: time rate of change of sunlight energy with area (W m -2 nm -1 ) n Radiance: flux per projected area per unit solid angle (W m -2 nm -1 sr -1 )

19 irradiance reflectance upwelling irradiance downwelling irradiance Remote Sensing Reflectance, Mobley, 1994

20 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, 1989

21 Two-Flow Model Gordon, 1989 Gregg and Carder, 1991 Elterman, 1968 Burt, 1954 Mobley, 1994

22 can be written in a simple equation in terms of Radiance : If where L b is the radiance of the ocean substrate L w is the radiance of the ocean  is the water attenuation coefficient D is the water distribution function z is depth L d = L b exp -  Dz + L w

23 From the simplified equation: A derivative band, X i, can be defined: (1) solve for the water attenuation coefficient,  (2) solve for depth and bottom-type L d = L b exp -  Dz + L w X i  ln((L d -L w ) = lnL b -  Dz

24 Solve for water attenuation coefficient,  -10 m -20 m-30 m X 488 X 551 X m -20 m-30 m -10 m -20 m-30 m Depth*D y = 0.05 x y = 0.07 x y = 0.07 x X i  ln((L d -L w ) = lnL b -  Dz Y-axisX-axis slope intercept Sand Maritorena, 1996 In agreement with Maritorena, 1996

25 Solve for depth (z) and bottom-type (Y) from the “difference” in two bands (i,j) Assumptions: (1) Homogeneous water quality (2) Bottom reflectance is the same in two bands (Frazer) where g =  D X = derivative band

26 How do we apply the model to multi-spectral data? bit 32-bit 488 nm 551 nm 557 nm  ca  cw t(  cw   ca )  sa  sw T sun D eb06aj.pix

27 Mosaic_model.pix 1, 2, bit 32-bit 488 nm, 551 nm, 557 nm D  ca  cw t(  cw   ca )  sa  sw T sun

28 A eb06aj.pix B eb07aj.pix Relative Difference in Overlap Before After 488 nm 7% 0.9% 551 nm 4% 0.7%

29 n Introduction Study Site Data Collection n Methods Data Processing Radiative Transfer Theory Depth and Bottom-type by Band Difference Applying the Model n Results Depth Predictions Percent Living Coral Predictions n ConclusionOutline

30 157˚44’00”W157˚42’50”W 157˚43’30”W 157˚44’00”W157˚42’50”W 157˚43’30”W 157˚44’00”W157˚42’50”W157˚43’30”W 21˚25’20”N 21˚24’55”N 21˚25’20”N 21˚24’55”N 21˚25’20”N 21˚24’55”N 21˚25’20”N 21˚24’55”N -3 m-6 m-9 m-12 m-15 m-18 m-21 m-24 m Predicted Depth (z 488/551 ) Hydrographic Survey Depth (USGS data, E. Grossman)

31 Percent Error 157˚44’00”W157˚42’50”W 157˚43’30”W 157˚44’00”W157˚42’50”W 157˚43’30”W 21˚25’20”N 21˚24’55”N 21˚25’20”N 21˚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

32 Percent Living Coral Zones (Harney, 2000) hardgrounds sand Living Coral <15% 15-25% 25-40% 40-75% >75% ˚44’00”W157˚42’45”W30”15” 157˚44’00”W157˚42’45”W30”15” 21˚25’30” 21˚25’00” 21˚25’30” 21˚25’00” line-intercept transect percent living coral value

33 hardgrounds sand Living Coral <15% 15-25% 25-40% 40-75% >75% ˚44’00”W157˚42’45”W30”15” 157˚44’00”W157˚42’45”W30”15” 21˚25’30” 21˚25’00” 21˚25’30” 21˚25’00” Multi-Spectral Percent Living Coral (Y 488/551 ) Map 0.10

34 Accuracy Assessment of Multi-Spectral Percent Living Coral Map R = 0.73, producers accuracy to # reference points Re-sampling loss of detail in 40-75%

35 38% 2% 12% 3% 15% 7% 25% sand 1,500,000 m 2 hardgrounds 70,000 m 2 <15% living coral 500,000 m % living coral 70,000 m % living coral 600,000 m % living coral 300,000 m 2 >75% living coral 1000,000 m 2 Substrate Diversity

36 Outline n Introduction Study Site Data Collection n Methods Data Processing Radiative Transfer Theory Depth and Bottom-type by Band Difference Applying the Model n Results Depth Predictions Percent Living Coral Predictions n Conclusion

37 Conclusion n Radiative transfer model can be used to normalize several multi-spectral images n Bathymetry and percent living coral is predicted with 488 nm and 551 nm n It may be possible to map change through time

38 Tuesday,June 12, 2001


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