Layover

If, in the case of a very steep slope, targets in the valley have a larger slant range than related mountain tops, then the foreslope is "reversed" in the slant range image
This phenomenon is called layover: the ordering of surface elements on the radar image is the reverse of the ordering on the ground . Generally, these layover zones, facing radar illumination, appear as bright features on the image due to the low incidence angle.
Ambiguity occurs between targets hit in the valley and in the foreland of the mountain, in case they have the same slant-range distance. For steep incidence angles this might also include targets on the backslope.
Geocoding can not resolve the ambiguities due to the representation of several points on the ground by one single point on the image; these zones also appear bright on the geocoded image.

These images were acquired over a mountainous zone close to the city of Udine (I), by ERS-1 and Landsat-5 respectively.
The effect of layover is visible in the whole SAR image, in particular on the two mountains that are on the right of the lake. The height of the upper one (San Simeone) is about 1000 m above the valley bottom (1220 msl), while the height of the lower one (Brancot) is 1015 msl.

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry