A sensor about the size of a large briefcase weighing less than 30 pounds might soon make near-zero-visibility landings routine at just about any airport. Vision enhancement systems are not new to aviation. Most rely on measuring infrared light, enhancing the available visible light, and often a combination of these. In each case, pilot vision improves, but clouds and fog remain a problem. Water droplets are usually smaller than 100 microns, which is small, but still much larger than the span of an infrared or visible-light wave, so neither infrared light nor visible light can pass easily through clouds.
A millimeter wave of electromagnetic energy is much longer than 100 microns, so it readily penetrates clouds, fog, and other visible forms of water. Just about every physical object, including you, emits electromagnetic energy in this wavelength range.
Like enhanced flight vision systems, passive millimeter wave detection and imaging systems are also not new to aviation; however, to date, the most useful application of the technology has been airport security scanners, the sort in which one stands like a criminal with hands up while a machine swiftly scans what’s under your clothing (and strips whatever shreds of dignity the rest of the commercial air travel experience has left intact). Your imperfect flesh has a different millimeter wave energy signature than the things around it, including objects you may have neglected to remove from your pockets. READ MORE (AOPA)