Military research goes back to nature

An engineering professor at The University of Texas at Austin is helping the US 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, a family of reptiles that includes rattlesnakes, copperheads and cottonmouths.

Pearce’s research focuses on the ‘pit organs’ that Crotalines use to locate their warm-blooded prey. A tiny nerve-rich depression – the pit – is located in front of the snake’s eye and harbours a sophisticated, heat-sensing system.

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’ he said.

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

Pearce’s colleagues 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 and measurements are taken at bandwidths of 3-to-5 microns and 8-to-12 to microns, which are the two channels used by current heat-sensing equipment.

Pearce devises mathematical models that can predict both the levels 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 that emit thermal energy with the aim of producing a desired combination of infrared wavelength and power output.

His mathematical models quantify the relationship between stimulus and response and he has developed one mathematical model for source infrared signal strength and one for the corresponding temperature increase in the receptor.

‘We’re basically modelling 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 concluded: ‘I had to write my whole program in double-precision arithmetic or the signal would disappear.’