Surveillance system with a sensor operating according to the reflection method and as a barrier

The open ground surveillance system with automatic alarm uses a bi-or multistatic sensor, passing over the area to be watched, and a monostable sensor bying within the reception range of this sensor. The bi- or multistable sensor works according to the reflection principle and as a barrier. The low- and high-frequency transmitting and receiving oscillations of both sensors are superposed and thus Doppler information is gained. With this control commands to be evaluated can be obtained. This effect may be assisted by putting crawling obstacles in the escape ways forcing the fugitives resp. intruders to adopt different body carriages (upright - bying). As sensors CW-Doppler radar units are suitable. (DG)