Topography

Today, world-wide, there is'nt a consistent Digital Elevation Model (DEM).

Among the several advantages of the Synthetic Aperture Radar (SAR) Interferometry technology with respect to competing ones, the active nature of SAR systems provide weather independency, allowing to map large areas of the terrain in limited timeframes, not depending on the weather and solar illumination conditions. Although complex, the processing of interferometric SAR data is, at large extent, automated, providing accurate and cost-effective products in reduced time.

From Space

Already in the late 90's, sarmap has produced the first country-wide DEM using this technology. The Swiss DEM has a spatial resolution of 25 metres and a height accuracy ranging from 7 (moderate topography) to 15 metres (steep topography).

From Airborne

The combination of interferometric SAR acquired simultaneously at high frequency (X-Band), non penetrating through the tree leaves, together with lower frequency (P-Band) data allows to obtain at the same time and directly information on the surface (DSM) and terrain (DTM) height of a vegetated area.

The generation of the DSM and DTM is performed by exploiting interferometric data acquired by the OrbiSAR-1 SAR system. This system, mounted on a small airplane, is capable of acquiring three X-Band and one P-Band images of a same are simultaneously, allowing to generate DSMs with single-pass acquisitions. If DTMs shall also be generated, a repeat-pass acquisition scheme has to be implemented. The system is capable of acquiring X-Band with a selectable horizontal resolution of up to 0.5 by 0.5 m and P-Band data up to 2.5 by 2.5 m. An example of a high resolution DSM is shown in the figure below.

For further information refer to the publications

• National-Scale DEM generation using ERS Tandem data in alpine regions, ERS-ENVISAT Symposium, 2000.
• Automatic Generation and Quality Assessment of Digital Surface Models generated from AeS-1 InSAR data, EUSAR Symposium, 1998.