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By Mark Radford, Director of Security Products, Plextek Limited

20 Aug 10. The term persistent surveillance describes the need to keep ‘eyes’ constantly focused on critical areas where activity should never be missed.

Effective persistent surveillance requires the ability to accurately understand the type of threat(s) being faced and ensure that appropriate sensors are selected to take account of the vastly different speeds at which different threats approach. Solutions need to be able to capture situational status accurately, whether that’s a plane flying overhead or a lone person popping their head out from behind a rock and using evasive ‘crawler’ tactics. They must also provide the optimal trade off between timeliness of information, update rates, range and the ability to react, as there is no use in being able to identify a threat if, by then, it is too late to intercept.

Information bandwidth also needs to be properly managed. For example power and wireless coverage challenges must be overcome when persistent surveillance is required in remote environments.

This article presents the limitations of traditional surveillance sensors and mechanically-scanned ground radars for persistent surveillance provision and advocates the use of superior e-scan Doppler systems to deliver significant situational awareness improvements for force protection and homeland security environments.

Traditional solutions for persistent surveillance

Cameras and sensors

Traditional security technologies, such as distributed short-range unattended ground sensors (UGS) or remote still/video cameras and thermal imagers, continue to be integrated at the heart of most modern surveillance systems for intruder detection and target identification. Improvements in image processing and the move to HD are raising the quality of these devices, however there are still fundamental weaknesses that can render these systems ineffective or impractical for some force protection and homeland security environments or scenarios.

UGS can be challenging to deploy, whilst the limited view of cameras reduce its ability to detect intruders over a wide area and are generally not capable of operating in all-weathers. Furthermore, whilst HD has improved the image capture capability of cameras, it is creating a different set of problems further down the chain, in terms of how to manage/store/transmit the vast quantity of data gathered.


Until recently radar had not been considered a realistic option for many security applications due to its high cost, large size and lack of portability. But this has started to change.

Radar is in principle capable of providing great situational awareness by immediately indicating movement, detecting threats at long range, glimpses of a person in the hills or covert targets, whilst also being able to follow the rapid evasive manoeuvres of vehicles.

The problem is that nearly all existing Doppler ground surveillance radars (GSR), employ a flawed mechanical-scan approach taking as long as 30 seconds to scan an area. While this may not sound that long, put in context, that’s easily enough time to miss an intruding car or person moving behind rocks. The physical rotation of conventional mechanically-scanned GSRs can also mask the slow ‘crawler’ movement of covert targets behind the radar return from ground clutter.

For the most effective radar-based persistent surveillance, we need low-speed detection and high-speed scanning – a compromise usually restricted by the laws of physics. Fast scanning allows quick detection of moving targets yet it reduces the radar’s ability to see slow covert-movement, which requires slow scanning.

Rise of the e-scan/Doppler GSR

Historically many GSR radars have struggled to achieve this balance, but the latest Blighter electronic-scanning Doppler GSRs, make ultra effective radar-based persistent su

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