Crowds behaving badly

A laser radar used by the military could be adapted for monitoring civilian activity following research carried out in Sweden.

The technology would identify early signs of violent behaviour by individuals in large crowds.

Lidar, as the system is known, has previously been used for long-range vehicle detection and identification. But a research project at the Swedish Defence Research Agency has come up with potential civilian uses.

The laser sends out a sweeping beam of light which is reflected by the target and detected by sensors to produce an image. Any movement within the image is analysed to determine the presence of vehicles or people.

Researcher Lena Klasen has developed a new image analysis system for the Lidar, details of which are be presented to the agency next week. Klasen’s system involves compression algorithms, which have been able to detect people in the cabs of vehicles from 10km away.

This involves ‘change detection’ where differences in separate pictures can indicate movement and the presence of people. Klasen said the system has many possible civilian applications including security surveillance.

‘The change detection technology could be used for airport crowd monitoring or watching for suspicious movement or unusual activity such as somebody running out of a bank.’

But watching suspicious people is not just limited to running or other physical movement. Klasen also explained that the laser system could analyse faces. Research suggests that national populations have distinct common facial movements.

By comparing laser images to a set of characteristics the system would be able to distinguish genuine expressions from fake ones in order to indicate when somebody was lying.

Klasen’s system was originally developed to generate 3D images from existing military Lidar systems which are 2D.

The image analysis technology was to have been an intermediate step between today’s 2D sensors and the 3D sensors which are still being developed.

That 3D sensor is called the focal plane array. Using this, a full 3D image of an enemy vehicle and its occupants can be generated using just one laser pulse. Thesingle pulse of light could be sent out to a distance of 10km.

Normally Lidar relies on a sweeping laser beam that covers a large area. The single pulse laser illuminates an area just 15m in diameter. This minimises the chances of the beam being detected by the enemy target.

Other active detection systems such as radar which send out a signal can be easily detected by the enemy. Missiles are also capable of homing in on radar signals.

To avoid this fate armed forces can use passive systems. But these only receive signals from heat or noise, or vibration from enemy vehicles.

They do not emit anything themselves. But they are prone to rain, snow, cloud or fog cover and defensive measures taken by the enemy.