An object-based approach for flood area delineation in a transboundary area using ENVISAT ASAR and LANDSAT TM data

Figures & data

Figure 1. Location of the Evros river and satellite imagery processed for delineating the flood extent.

Table 1. Confusion matrices and accuracy measures of the three classification approaches.

	Reference data
	Not water	Water	UA (%)	PA (%)	OA (%)	Khat
NDWI, TM bands
Not water	93	8	92.07	96.87	92.67	0.84
Water	3	46	93.87	85.18
dNDWI
Not water	94	11	89.52	97.91	91.33	0.80
Water	2	43	95.55	79.62
ENVISAT ASAR
Not water	91	17	84.03	94.79	85.33	0.66
Water	5	37	88.09	68.51

Figure 2. Differences observed from the overlay of the official flood extent map and the classification following the bi-level OBIA approach using the NDWI and the post-flood LANDSAT bands, highlighted using the post-flood (upper right) and pre-flood image (lower right).

Table 2. Area-based comparison and agreement of the uni-level Geographic Object-Based Image Analysis (GEOBIA) post-NDWI/LANDSAT, dNDWI, ENVISAT and bi-level GEOBIA post-NDWI/LANDSAT classifications with the official flood map.

	Flooded area in common with the flood extent map of the GSCP (km^2)	Agreement (%)	Overestimation (km^2)	Underestimation (km^2)
NDWI, TM bands (uni-level)	267.62	73.34	30.38	97.28
dNDWI	243.19	66.65	29.77	121.71
ENVISAT ASAR	195.46	53.57	23.66	169.44
NDWI, TM bands (bi-level)	336.21	92.14	52.19	28.69