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Introduction
Trex is a world renowned expert in high resolution optical imaging through atmosphere. Since its inception, Trex has been developing electro-optical techniques (passive and active) which leads to component (cameras and lasers) and systems development and field deployment. It is through more than 35 years, > US $300M research and development experience, Trex concluded Electro-Optics System is not suitable for FOD detection in the airport environment. Below are a few examples that explain the ineffectiveness of Electro-Optics Systems.
Heat Haze
Heat haze refers to the inferior image experienced when viewing objects through a layer of heated air; like viewing objects across hot asphalt or through the exhaust gases produced by jet engines. Heat haze is the wavy, watery, rippling, shimmering effect you see both in person, and in your photos, most often associated with hot days. In reality, and somewhat counter-intuitively, heat haze can and does occur on very cold days too. That’s because heat haze occurs when relatively warm air mixes with relatively cool air. The warmer air rises through the cooler air causing the disturbance in the air that we perceive as “heat haze”. The greater the difference in temperature between the warm air and the cool air, the more noticeable the heat haze becomes.
Hot Asphalt Surfaces
Convection causes the temperature of the air to vary, producing a blurred shimmering effect, which affects the ability to resolve objects, the effect being exacerbated when the image is magnified through optical lenses.
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 Figure 1: Shimmering Effects due to Heat Haze & Hot Asphalt Surfaces
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Sandstorm
A sandstorm or dust storm is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface. Particles are transported by saltation and suspension, a process that moves soil from one place and deposits it in another.
Weather affects the image quality in outdoor electro-optics surveillances. Fog, mist, haze, smoke, dust and sandstorms, which are composed of smaller droplets or particles than snow and rain, have an impact on visibility, making images white and blurred by scattering light.
Conclusion
Hence, Trex concluded that the primary FOD detection must be accomplished by the all-weather millimeter wave sensor which is supplemented by an Electro-optics System such as CCD camera as secondary tool for identification.
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