<title>Passive millimeter-wave imaging: seeing in very poor visibility</title>

Abstract

It is more common to use the visible or infrared regions to image although it is possible to use millimeter waves. Passive millimeter wave imaging, however, has the advantage of being able to see in poor weather conditions such as in thick fog. The images, unlike radar signatures, have a natural appearance that can be easily interpreted. The spatial resolution of these imagers is limited by the aperture size and choice of operating frequency. Novel signal processing algorithms have been applied to improve the spatial resolution. Millimeter wave imagers detect slight temperature differences in the scene and using current technology it is possible to sense changes as low as 0.2 K whilst the contrast between an aircraft and its background can be as high as 200 K. A millimetric imager has been used at London Heathrow airport to demonstrate the high quality of the images that can be obtained. Aircraft can be recognized, runways and grass delineated and complex areas such as gates imaged. A qualitative comparison has been made of radar, thermal imaging and passive millimeter wave imaging for ground movement control. The possibility of deploying a passive millimeter wave imager on a commercial aircraft and of using it as part of an enhanced vision system is also discussed.