ERS-1 quarter scene SLC images from the ice phase in early 1992 (3 day interval) were used to generate a height model of an area close to Bonn, Germany.
The interferometrically calculated digital elevation model (DEM) is presented above as a mixture of the SAR image intensity and colour-coded height values. A colour-cycle here is equivalent to a height difference of 150 metres.
The size of the area is approximately 30km x 40km. Note the Rhine river in the northeast, and open-pit coal mines in the north.
Validation
Geocoding of the interferometric height model enables direct comparison with a reference DEM obtained from another source. In this case, the reference elevation model was provided courtesy of DLR for SAR geocoding research.
The above figure shows colour-coded height differences overlaid on one of the ERS-1 amplitude images, in UTM map geometry. Height differences reach colour saturation at -40m (green), and +40m (red).
Some height differences are due to processing difficulties. The phase unwrapping algorithm was unable to penetrate into the hilly forest at (350,5630), as well as in the south and the extreme southwest of the scene. Open-pit coal mines are visible in the north.
The figure below shows a closeup of height difference map for a portion of the scene. Colour saturation has been made more sensitive: -20m (green) to +20m (red).
There is generally good agreement between the reference DEM and the interferometric height map. Significant departures from such agreement occur in gravel pits at (333,5635), (340.5, 5366.5), and (340,5631), where the reference elevation model no longer reflects the current state of the local landscape. The interferometric heights were error-prone within forested areas (335,5632).
