Rocky Kaku, Vanuatu Fisheries Department & Franck Magron...
Transcript of Rocky Kaku, Vanuatu Fisheries Department & Franck Magron...
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GIS/RS multi-scale approach for the assessment of mangrove species composition and coverage
Rocky Kaku, Vanuatu Fisheries Department& Franck Magron, Pacific Community
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Methodology
1. Preparation of field survey using satellite imagery (WV2 – 8 bands)
2. Sampling points in the mangrove (field work)
3. GIS mapping and analysis
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WV2 spectral bands
Mangrove classification
Visible bands Red edge & NIR bandsVisible bands PCA all bands
Masked image
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Mangrove remote sensing
Mangroves areas are wet and appear darker than bare soil, urban areas and grass fields on near-infrared bands.
Visible bands 4,3,2 NIR-1 band (7)
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Mangrove remote sensing
A PCA* on all bands excluding water furtherly highlight differences between bare soil (orange), urban areas (magenta), grass fields (light green, khaki) and mangrove areas (sea green, aquamarine).
* PCA = Principal Component Analysis
PCA excluding water Mangrove map (from NC Atlas)
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Mangrove remote sensing
Using the non water it is possible to do a first classification and extract areas with similar signatures. This might include vegetation not belonging to the mangrove area.
Classification from PCA
Mangrove
Grass fields
Forest
Bare soil
Urban area
PCA excluding water
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Mangrove remote sensing
The classification can be used as a mask to select only pixels with a signature belonging to the mangrove classes
Classification from PCA Reflectances for mangrove classes
Mangrove
Grass fields
Forest
Bare soil
Urban area
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Mangrove remote sensing
Finally a PCA on the mangrove class pixels highlights the differences(species composition, cover and exposed soils)
PCA on selected pixelsPixels for mangrove classes
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Mangrove remote sensing
Field survey is then necessary to determine what species correspond to the PCA
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Application to North Efate mangrove
4 km
PCA on mangrove area
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Sampling points in the mangrove
Sampled points for the area
Web database interface
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Species composition for sampled points
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PCA vs species composition for sampled points
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Delineation of zones based on PCA and species composition and extraction of polygon area in Ha
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Intersection of mapping points and polygons
AcAu AcSp AvMa BaRa ExAg HeLi LuLi RhAp RhSa XyGr Poly id Area Ha
20 0 0 0 5 0 2 0 0 0 14 15.94
90 0 0 0 2 0 0 0 0 0 14 15.94
40 0 0 0 3 0 30 0 0 0 14 15.94
1 0 0 0 1 0 1 0 0 0 14 15.94
2 0 1 0 0 0 2 0 0 0 14 15.94
0 0 0 0 2 0 5 0 0 0 14 15.94
0 0 20 0 0 0 0 0 0 0 14 15.94
0 0 40 0 0 0 0 0 0 0 14 15.94
0 0 20 0 1 0 10 0 0 0 14 15.94
0 0 0 0 0 0 1 0 95 0 13 7.15
0 0 10 0 0 0 0 0 40 0 13 7.15
0 0 0 0 0 0 10 0 30 20 12 0.4
0 0 0 0 10 1 1 0 0 20 12 0.4
0 0 0 0 0 0 0 0 70 20 13 7.15
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Averaging species composition by polygonand calculation of a weighted average (using area Ha) for the whole area
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Similar methodology applied for Aniwa & Emae
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Tank yu tumas