|MadSci Network: Engineering|
Excellent question Adarsh. Infrared radiation are photons with wavelengths that vary from a little less than 1 micron to about 1 millimeter. All objects with a temperature above absolute zero emit these photons as a function of the temperature and material characteristics. Can the infrared signature of a human body be person-specific? First what is infrared signature? Its the characteristic irradiance of an object in the infrared spectrum - and may include both emission and reflection. Is it unique? Its not certain that the infrared signature would be 100% unique to an individual. It is however likely to be quite variable. On most humans, that infrared signature will be modified by attire. Different fabrics and clothing styles will modify/transmit the internal heat of the body differently. For example, this will sometimes allow the novelty of discriminating a person's gender by their heat signature. However, that would not be 100% reliable. Since photons are just light at a lower frequency, the person's shape would be resolved to within the resolution limits of the sensor system. Furthermore, the person's particular state of health, skin and circulatory system as well as that person's metabolic and emotional state as well as their physiologic response to external conditions (extreme cold, for example) will cause variations in thermal signature which could be unique. However, it would seem unlikely that these minor differences would be consistent enough to provide a unique identification test for the sensor. So to the extent that a person's general shape and general features are unique in the test group, one can descriminate individuals. Still, there are infrared differences between humans and other species. And certain physiological conditions can manifest themselves in observable variations of a person's thermal emission. Thus the use of themal imaging for medical diagnosis is a developing field. So it is doubtful the human infrared signature would be consistently unique enough to differentiate between individuals in general. Perhaps where some external information is added, such as limiting the group out of which the person would need to be indentified and by adding a priori data (such as knowledge of the person's attire), it might be possible. But that would be very limiting. Differentiating between humans and other animals and other objects in the scene is more practical as is use of thermal imaging where a physiologic response could be detected (say in conjunction with a polygraph test). And use of infrared imaging in medicine is an emerging technology which offers promise. http://meweb.ecn.purdue.edu/~image/research/Gupta_files/Thermography .pdf http://web.mit.edu/newsoffice/1997/infrared-0924.html
Try the links in the MadSci Library for more information on Engineering.