Use of a Millimeter Wave Radiometer for Detecting Pedestrian and Bicycle Traffic

A total-power radiometer at 48 GHz has been constructed and used for detecting pedestrian and bicycle traffic. The high operating frequency was selected in order to obtain a high angular resolution. The best way to distinguish a human being from the background is to direct the antenna to the road from above in an angle of 40-70 degrees. Hereby the road reflects the cold sky and thus the brightness temperature of the road is low. On the other hand, the brightness temperature of a human being at millimeter waves is almost the same as his physical temperature. Cars among human beings can be detected radiometrically because the brightness temperature versus the car position has a specific feature. First the front of the car reflects the high brightness temperature of the surroundings and then the top reflects the low brightness temperature of the sky.