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Heat-seeking vipers may help with U.S. defense, UT Austin researcher finds

University Of Texas At Austin : 31 May, 2001  (Technical Article)
An engineering professor at The University of Texas at Austin is helping the U.S. Air Force learn techniques to build better missile detectors by studying poisonous snakes. Dr. John Pearce, the Temple Foundation Endowed Professor in Electrical and Computer Engineering, studies Crotalines, better known as pit vipers. This family of reptiles includes rattlesnakes, copperheads and cottonmouths.
Pearce's research focuses on the unusual 'pit organs' that Crotalines use to locate their warm-blooded prey. A tiny nerve-rich depression, called the pit, is located in front of the snake's eye. It harbors a sophisticated, heat-sensing system so sensitive the snake can detect a mouse several meters away, even in total darkness.

Researchers hope that when they unravel the secrets of the pit viper's intricate search-and-destroy mechanism, the principles may be applied on a much larger scale to protect the nation from enemy missiles, and to help pilots flying dangerous missions evade enemy weaponry.

'The Air Force wants to see if they can mimic the biological system and get a better missile dectector,' Pearce said.

Pearce's specialty is called thermography, the measurement of the heat energy that is radiated by any object above a temperature of Absolute Zero (minus 273 degrees Centigrade). Pearce said the viper's remarkable heat sensing system responds to temperature changes much less than one-thousandth of a degree centigrade.

Pearce devises mathematical models that can predict both the level of heat or energy emitted by the prey and the impact this would have at a given distance from the snake's powerful receptors. He also builds ideal radiation sources, simple devices fashioned from copper pipe and black paint and heated by water, that emit thermal energy. The aim is to produce a desired combination of infrared wavelength and power output.

Pearce explained that the United States already has heat-seeking detectors, but the equipment has many limitations. 'They don't tell you how far away the missile is, they just tell you there's something hot back there!'

The equipment is fragile and needs frequent servicing because it is subject to tremendous vibrations in the aircraft tail. The equipment must be cooled to temperatures well below minus 200 degrees Centigrade. In contrast, Pearce said, the snake's heat detector operates at normal temperatures.

Pearce is a co-principal investigator in a $5 million project funded by the U.S. Air Force to study remote sensing abilities found in several types of beetles and snakes. Dr. Ashley J. Welch, the Marion E. Forsman Centennial Professor in Engineering, is the director of the overall project, which is administered through the UT Austin College of Engineering. Researchers in Iowa, Germany, Florida and The University of Texas Medical Branch at Galveston are collaborating with Pearce.

'We trade information with each other periodically, and it always amazes me how well everything dovetails. Together, we have learned what the mechanism of the pit membrane is,' Pearce said.

UTMB's Dr. Burgess Christensen and Dr. Massoud Motamedi work directly with the snakes, stimulating the snakes' receptors and measuring the snake's response. A pair of thermal video cameras capture infrared pictures of what the snake senses. Measurements are taken at bandwidths of 3-to-5 microns and 8-to-12 microns, the two channels used by today's heat-sensing equipment. Pearce said experiments at Galveston have verified his modeling.

Pearce compares the complexity of the process to 'putting electrodes on a large telephone cable and trying to figure out the individual conversations.' Pearce's mathematical models quantify the relationship between stimulus and response. He has developed one mathematical model for source infrared signal strength and one for the corresponding temperature increase in the receptor.

'We're basically modeling the sensitivity of the snake organ. You can measure nerve impulses, but the question is, what do those impulses mean? We use a numerical model to tell us: there's this much infrared hitting the organ, and that means this many nerve pulses.'

The snake's pit is a very thin membrane rich in blood vessels and nerve bundles. The membrane is so sensitive, and the variations in the responses so minute and subtle, that Pearce said 'I had to write my whole program in double-precision arithmetic or the signal would disappear.'

To develop a good mathematical picture of the pit organ, he drew upon delicate measurements and photomicrographs (pictures taken through a high-powered microscope) provided by Dr. Anke Schmidt of the Institut fur Zoologie in Bonn, Germany. Dr. Vladimir Tsukruk of Iowa State University contributed important information about the thermal properties of the viper's membrane itself.
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