The aviation industry has been investigating the potential of synthetic and enhanced vision systems (SVS and EVS) to increase the situational awareness of pilots who are operating in low-visibility weather conditions. Synthetic vision displays provide a real-time depiction of a terrain model from the pilot's perspective. To ensure the integrity of this terrain depiction, consistency checking using remote sensing of the terrain environment has been suggested. This requires the detection and extraction of terrain features from both the model and the sensor measurements. Further, the features must be represented in the same reference domain.

Terrain shadowing occurs when areas are not in the line-of-sight of the observer. It is these shadowed regions and their morphological characteristics that are identified as the feature domain in which consistency can be assessed between two sources of terrain information. This paper describes an algorithm to extract shadow features from digital elevation models during flight to enable direct comparison with x-band radar modus operandi. Results are presented using flight-test data acquired from two platforms with different radar equipment.

The proposed algorithm not only has application to the consistency-checking problem, but also to terrain navigation, image fusion, and digital elevation model accuracy assessments.