There are now 29 thermal imaging systems deployed at Singapore's land, air and sea checkpoints.

These heat detectors used to spot people with a fever may soon become more commonplace as more commercial buildings begin to use them for SARS screening.

Two different types of thermal imaging systems are being deployed.

The scanner being used to screen travellers at Changi Airport is jointly developed by Singapore's Defence Science and Technology Agency (DSTA), and ST Electronics.

This thermal imaging system is a quick way to spot a person with a fever, one of the symptoms of SARS.

Once the requirements were set for the system, the engineers took about a week to develop and deploy their first machine.

A unique feature of this system is that it uses a thermal imager that was initially designed for military use.

It was designed for the military to find enemy targets in low visibility with a limited temperature range.

Because of this, the system's specifications are very stringent, and can measure minute temperature differences.

The system has a pre-set temperature and anyone with a higher temperature appears red on the monitor.

"This system deployed at the airport does not convert infra red energy into a temperature reading. It captures the raw IR radiation and compares it with a preset raw IR energy level," said Teo Chee Wah, programme manager, sensor division, DSTA.

However, to screen ground crew and other staff, the airport uses a commercially available radiometric thermal scanner.

This is different because it measures a wide temperature band, from zero to a thousand degrees Celsius.

"The radiometric thermometer has to be calibrated carefully, the accuracy as well the stability of the reading has to be carefully evaluated and assessed," Mr Teo said.

"It provides an absolute reading of the object and compares the temperature with a preset threshhold. One has to be careful in the conversion process."

This means some temperatures readings may have a small error at very low or very high temperatures.

DSTA, however, is looking to develop a commercial version based on the technology used by its military thermal scanners.

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