Improved characterization of scenes with a combination of MMW radar and radiometer information

Abstract

For security related applications MMW radar and radiometer systems in remote sensing or stand-off configurations are well established techniques. The range of development stages extends from experimental to commercial systems on the civil and military market. Typical examples are systems for personnel screening at airports for concealed object detection under clothing, enhanced vision or landing aid for helicopter and vehicle based systems for suspicious object or IED detection along roads. Due to the physical principle of active (radar) and passive (radiometer) MMW measurement techniques the appearance of single objects and thus the complete scenario is rather different for radar and radiometer images. A radar system consists of a transmitter and a receiver path. It performs an active illumination of a scenario and records the reflected signals. It delivers a range measurement in combination with information about the objects reflectivity properties. A radiometer system has only a receiver path in order to measure the natural thermal radiation power of objects. The measured signal provides information on the emission and reflection properties of objects whereas the cosmic background radiation and the complete environment act as illumination source for a scenario. The illumination and imaging principles of the both techniques and the related scattering behavior of objects will deliver different and often complementary information of a scenario. A reasonable combination of both measurement techniques could lead to enhanced object information. However, some technical requirements should be taken into account. The imaging geometry should be nearly identical, the geometrical resolution and the wavelength should be similar and at best the imaging process should be carried out simultaneously. Therefore theoretical and experimental investigations on a suitable combination of MMW radar and radiometer information have been conducted. The antenna system of an existing mechanical linescanner was improved in order to provide a similar imaging geometry for radar and radiometer system. The investigations concentrate on rather basic scenarios with canonical targets like flat plates, spheres, corner reflectors and cylinders. Experimental results of different image products are shown and discussed.