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In this research the Modified Normalized Difference Water Index was used to enhance and map the open water features in a Hungarian sample area. Two Landsat-7 ETM+ images from 23. April and 30. September 2000 were used to derive the final maps. The sample area is highly endangered by excess water inundation therefore the rapid mapping of water surfaces is necessary. As result the MNDWI can be used for quick mapping, the result maps matched the distrubution of water closely. Presented by Balázs Boglárka, assistant professor at Debrecen University
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Hydrological Investigations in The Rétköz, Hungary
Boglárka Balázs ‒ Gábor Türk
29-31 May, 2014 Hungarian GIS Conference with MapWindow
This research was supported by the European Union and the State of Hungary, co-financed by the European Social Fund in
the framework of TÁMOP 4.2.4.A/2-11-1-2012-0001 ‘National Excellence Program’.
Intro ─ Remote Sensing in Mapping Surface Water
Different materials reflect differently at different wavelenghts
Widely used for surface analysing Opportunity to map surface water Monitor the dynamics of surface water Different methods to extract water features:
Single-band method – threshold? under/over-estimation
Multi-band methods (reflective differences between bands)
If-then-else logic tree (analysing signature among different
spectral bands, find differences, then use the tree)
Band-ratio approach – spectral indexes
Intro ─ Spectral indexes
Single number derived from an arithmetic operation NDVI = (NIR−Red)/(NIR+Red) NDWI McFeeters = (Green−NIR)/(Green+NIR) -1 ≤ NDWI ≤ 1
Threshold: 0
NDWI Gao= (NIR−SWIR)/(NIR+SWIR) water content of vegetation
canopy
MNDWI= (Green−SWIR)/(Green+SWIR)Threshold: 0, but more accurate results can be achieved by manual adjustment
Threshold ?!
Why could the NDWI be so important in Hungary? More than half is flatland Inundation hazard map of Hungary by Pálfai, I. (2003) 60% of the flatland is differently endangered by inundation
5% highly endangered 26% medium risk 29% low risk 40% barely endangered
Sample area
275 km2
Sample area
Sample area
Satellite images
Landsat-7 ETM+ images 23. April 2000 30. September 2000
Seasons with different aspect
MNDWI= (B2−B5)/(B2+B5)
Water ≥0; non-water ≤0
−
+
Resultso Satellite image covered 94.3% of the sample areao 10.9 km2 water surface and saturated surfaceo 4% of the whole Rétköz
Results
Results
Results
Threshold: 0
Results
NDVI values
Results
Threshold: 0.15
Water: 1.24 km2,0.45% of Rétköz
