This paper reviews the findings of a study commissioned by the California Department of Transportation to evaluate the potential of infrared and passive millimeter-wave imaging technologies for traffic surveillance and automated detection. Images formed from radiation at infrared and millimeter wavelengths are characterized by fundamentally different information compared with visible-spectrum images, and generally improved ability to penetrate obscured atmospheres such as fog or dust.
Ten examples of commercially available infrared (IR) imaging technologies and one experimental passive millimeter-wave (MMW) radiometric imaging apparatus were evaluated with respect to the specific requirements of highway monitoring and traffic management. A suite of traffic images and performance-related test data were acquired for each imaging system over a range of traffic and environmental conditions. Evaluation criteria included the usable information content of images in both clear and obscured atmospheres, image noise, EIA/ NTSC standard video test metrics, advantages and limitations related to technical features, and human interface factors. A general metric was developed to facilitate the comparison of the quality and information content of the video images produced by imaging systems operating in different spectral bands. A software-based image processing program was developed to analyze digitized video samples produced by each imaging system with respect to this metric. Results are classified by spectral band, scene condition, and imaging technology. Recommendations are made regarding the attributes, and technical advantages and limitations of each imaging technology for specific traffic monitoring and management situations.