Slant range / ground range

The figure shows two types of radar data display:
- slant range image, in which distances are measured between the antenna and the target.
- ground range image, in which distances are measured between the platform ground track and the target, and placed in the correct position on the chosen reference plane.
Slant range data is the natural result of radar range measurements. Transformation to ground range requires correction at each data point for local terrain slope and elevation.
This figure illustrates an example of SAR data using a Seasat scene of Geneva (Switzerland). The slant range image is displayed on the left of the screen, while the ground range image is on the right side.
The geometric distortions present on a radar image can be divided into:
- Range distortions: Radar measures slant ranges but, for an image to represent correctly the surface, it must be ground range corrected.
- Elevation distortions: this occurs in those cases where points have an elevation different from the mean terrain elevation.

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