Detection and feature extraction of bridges in airborne and spaceborne SAR image data

Operational SAR satellite systems such as ENVISAT-ASAR and RADARSAT-1 deliver image data of a rather coarse resolution, which allows the recognition or feature extraction only for large man-made objects. State of the art airborne SAR sensors on the other hand provide spatial resolution in the order well below a half meter. In such data many features of urban objects can be identified and used for recognition. Core elements of man-made infrastructure are bridges. In case of bridges over water, the oblique side looking imaging geometry of SAR sensors may lead to special signature in a SAR image depending on the aspect. In this paper, the appearance of bridges over water in SAR data is discussed. Geometric constraints concerning the changing of this signature are investigated using simulation techniques based on an adapted ray tracing. Furthermore, an approach is presented to detect bridges over water and to derive object features from spaceborne and airborne SAR images in the context of disaster management. RADARSAT-1 data with a spatial resolution of about 9 in as well as high-resolution airborne SAR data of geometric sampling distance better than 40 cm are investigated.