Recent advances in millimeter-wave (MMW), microwave, and infrared (IR) technologies provide the means to detect concealed wapons remotely through clothing and in some cases through walls. Since the development of forward-looking infrared (FLIR) instruments, work has been ongoing in attempting to use these devices for concealed weapon detection based on temperature differences between metallic weapons and the background body temperature of the person carrying the weapon; however, the poor transmissio nproperties of clothing in the infrared has led to the development of techniques based on lower frequencies. Focal plane arrays operating at MMW frequencies are becoming available which eliminate the need for a costly and slow mechanical scanner for generating images. These radiometric sensors also detect temperature differences between weapons and the human body background. Holographic imaging systems operating at both microwave and MMW frequencies have been developed which generate images of near photographic quality through clothing and through thin, non-metallic walls. Finally, a real-aperture radar is useful for observing people and detectign weapons through walls and in the field under reduced visibility conditions.
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