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

1. 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’.

2. 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

3. 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 ?!

4. 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

5. Sample area
275 km2

6. Sample area

7. Sample area

8. 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
−
+

9. Results
o Satellite image covered 94.3% of the sample area
o 10.9 km2 water surface and saturated surface
o 4% of the whole Rétköz

10. Results

11. Results

12. Results
Threshold: 0

13. Results
NDVI values

14. Results
Threshold: 0.15
Water: 1.24 km2,
0.45% of Rétköz

15. Thank you for your
attention!
geo.bb@mailbox.hu
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