Once the radar has emitted a microwave signal, the power reflected by the objects hit by the signal is measured. This is called the backscatter . But also ships appear as bright points since they are made of metal and have a lot of right angles. There are of course other factors involved, as we'll see in some of the Exercises. The interpretation of images of land is in many ways similar.
Cities are very rough surfaces and appear generally very bright.
Forests are also bright features, with gray levels being rather high and even. Even smoother are runways and highways, which appear nearly black. The accompany figure shows a radar satellite image of a cultivated area in The Netherlands, where a network of roads is clearly visible as dark linear features. But you may also find a fine bright line in this image. Of course it is a railway - made of iron, reflecting microwave strongly.