features (lines and vehicles) on the dark background of the asphalt (Figure 2.18). In
TerraSAR-X (1 m resolution), the freeway is uniform with a high contrast to the
surrounding terrain. The small house is still visible in 4-m IKONOS data but no longer
identifiable. In TerraSAR-X the small house is not clearly identifiable either, but the
structural characteristics of the two-slope roof (bright spot inside the circle in Figure
2.18) make it possible to infer the presence of a sharp angle, which indicates the
presence of a well-defined structure. The decreasing interpretability of artificial
structures as IKONOS is degraded from 1 to 10 m can be more clearly seen in
the large house (Figure 2.18). At the 10-m IKONOS data only the roads are clearly
identified.
FIGURE 2.18 Comparison of features between TerraSAR-X and degraded IKONOS images.
TABLE 2.4 Comparison of Identifiable Features
Number of Pixels
Visibility
Identifiability
Feature
IKONOS (4 m) TSX IKONOS (4 m) TSX IKONOS (4 m) TSX
Repetitive structure 2
1-2
3-5
x
x
—
—
Repetitive structure
U
6
—
x
—
—
Main road
1–2
8
x
x
x
x
Freeway
7
12
x
x
x
x
Small house
6
18–20
x
—
—
—
Large house
15
53
x
x
—
—
Note: x = possible, — = not possible, U = undetermined number of pixels. The column pixel size shows the
amount of pixel the object has in the specified image.
FUSION OF ELECTRO-OPTICAL AND RADAR DATA
29