Vision+

The TerraSAR-X satellite also operates in the novel so-called Staring Spotlight mode, which acquires SAR images at very high resolutions. Such images can be used to derive digital elevation models using the principles of radargrammetry. Airbus DS and JOANNEUM RESEARCH joint their work forces to assess the possible quality increase when employing such very high resolution images in comparison to other TerraSAR-X acquisition modes. Additionally, the processing chain was custom-tailored and enhanced for optimized performance.

Objective

The objective of this project that started in August 2014 was to assess the potential of the novel TerraSAR-X Staring Spotlight (ST) mode w.r.t. radargrammetric digital elevation modelling. This mode is available since the end of 2013 and provides synthetic aperture radar (SAR) images at different look angles and at very high resolution of 0.85 to 1.77 m in range and 0.24 m in azimuth, when operating in the full performance range of 20 to 45°.

Many images were acquired over two test sites and airborne LiDAR data was used as reference for validation purposes.

Results

Evaluation of the 2D and 3D geo-local accuracy revealed that sensor models are highly accurate and interpreted correctly. The stereo-radargrammetric pipeline was enhanced by according multi-looking, epipolar rectification, enhanced semi-global image matching, and DSM fusion.

For all ST stereo and triplets the standard deviation of error was below 4m and thus significantly better than using Spotlight mode images for reconstruction.

Thus, the Staring Spotlight mode allows highly accurate 3D mapping.

Fig. 1: Tri-stereo (triplet) configuration for DSM extraction.

Fig. 2: Surface models derived from TerraSAR-X Starlight Spotlight
triplet data and the reference LiDAR DSM

Fig. 3: Comparison of stereo DSMs resulting from Staring Spotlight mode (left)
and from standard Spotlight mode (right).