LiDAR system from researchers at Heriot-Watt University impresses with extremely high resolution: Comparison of a LiDAR image with the original (Photo: Aongus McCarthy, hw.ac.uk)

In the future, it will be possible to recognise a face from a distance of hundreds of metres, at least for trained eyes. This will even work if it is hidden behind a camouflage net and in fog. This has been achieved with the ‘single-photon time-of-flight LiDAR’, developed by a team led by Aongus McCarthy of Heriot-Watt University (https://www.hw.ac.uk/ ). The detector that captures the reflected light is crucial. It is designed to respond to individual photons. The researchers opted for infrared light with a wavelength of 1,550 nanometres, which penetrates the atmosphere even in adverse conditions.

LiDAR for autonomous driving

LiDAR is a laser-based range-finding device used, for example, in self-driving cars. It emits laser beams that are reflected by obstacles. The system determines the distance to the obstacle to an accuracy of centimetres based on the time-of-flight of the light. The high resolution of the advanced LiDAR system is based on the separation of the photons.

‘Our system uses a single-photon detector that is about twice as efficient as detectors used in similar LiDAR systems and has at least ten times better system time resolution. This allows the imaging system to capture more scattered photons from the target object and achieve a much higher spatial resolution,’ says McCarthy.

Exactly 325 metres away

However, technological progress comes at a price. To reduce noise, i.e. distortions of the measurements due to interference signals, the detector must be cooled to a temperature of minus 272 degrees Celsius (one Kelvin). This means that the system is relatively immobile because it requires a sophisticated cooling system.

The researchers also use measuring instruments that record the time of flight of the photons with extreme precision, accurate to a trillionth of a second (a picosecond). By way of comparison, light can travel about 300 millimetres in just 1,000 picoseconds. This level of precision makes it possible to distinguish surfaces with a height difference of just one millimetre from a distance of 325 metres. Due to the high cost of the equipment, the new LiDAR system seems to be primarily useful for military purposes for the time being.