Abstract

Disclosed is a method and apparatus for enhancing target detection, particularly in the millimeter wave frequency range, through the utilization of an imaging radiometer. The radiometer, which is a passive thermal receiver, detects the reflected and emitted thermal radiation of targets within a predetermined antenna/receiver beamwidth. By scanning the radiometer over a target area, a thermal image is created. At millimeter wave frequencies, the received emissions from the target area are highly dependent on the emissivity of the target of interest. Foliage will appear "hot" due to its high emissivity and metals will appear cold due to their low emissivities. A noise power illuminator is periodically actuated to illuminate the target of interest. When the illuminator is actuated, the role of emissivity is reversed, namely poorly emissive targets will generally be good reflectors which in the presence of an illuminator will appear "hot". The highly emissive targets (such as foliage and dirt) which absorb most of the transmitted energy will appear almost the same as in a non-illuminated, passive image. Using a data processor, the intensity of the passive image is subtracted from the intensity of the illuminated, active image which thereby cancels the background foliage, dirt, etc. and the reflective metallic targets are enhanced.

Other References

• Gonzalez et al., Digital Image Processing, pp. 6-11, and 199-207, Addison-Wesley Publishing Co., Reading, Massachusetts, 1977
• The Coming of MM-Wave Forward Looking Imaging Radiometers, Schuchardt et al., Microwave Journal, Jun. 1981, pp. 45-62