hydrological investigations in the rétköz, hungary

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

Thank you for your attention!

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