At first glance, airborne or spaceborne Synthetic Aperture Radar (SAR) images look like photographs. Only with a closer look do irritating details reveal themselves: shadows don’t match the position of the sun, mountain slopes are cut short or disappear completely, moving vehicles are not located on roads but beside them. “To correctly interpret such radar images you need some experience and expert know-ledge about the physical principles involved”, says Wolfgang Roller of the Fraunhofer Institute for Information and Data Processing IITB in Karlsruhe. He and his team are developing the “SAR Tutor”, a training software for military and civilian interpreters of radar images. Radar devices send out electromagnetic waves in the gigahertz range and receive the echoes from the objects. The main advantage over photos is that radar beams can penetrate clouds, light rain or snow and deliver clear images even at night or in fog. On the basis of the transmit time, a computer calculates how far away the different objects are. By analyzing the echo frequencies, the SAR additionally distinguishes between points which are at the same distance. Finally it compiles an overall picture. Armed forces use SAR images for reconnaissance purposes, civilian users employ them primarily for mapping the earth’s surface. Up to now, to access high resolution satellite images, German institutions are depending on data from the United States. But the first civilian German SAR satellite will be launched into orbit this year and the German Federal Armed Forces plan to develop their own spaceborne reconnaissance system by 2008. The training of photo interpreters within the German Forces is therefore to be extended in the coming autumn. The SAR-Tutor will be used for on-site learning as well as for pre- and post- processing of training courses. The program imparts the basic physical and technical principles of SAR and uses numerous photos and radar images to explain the characteristics of perspective or the shifting of moving objects caused by the Doppler effect. Users can try different settings and observe the results on a monitor. A demo version will be presented at the LEARNTEC exhibition in Karlsruhe from February 14 to 16. A Web-based (WBT) and computer-based (CBT) version of the training program are scheduled to be ready by autumn of this year.
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