Counter Terror Gazette

Man vs. Nature: taking back perimeter security through enhanced technologies

14 Jun 2011

Nuisance alarms, caused by natural and benign environmental events, have been unavoidable in an uncontrolled perimeter setting, without sacrificing detection capabilities, and are notoriously resource-intensive to resolve. Anna Hamilton explores improvements in security technologies that help abate nuisance alarms, and, with them, the ongoing monitoring costs that have long deterred many airports from installing technology-based perimeter security systems.

An airport’s perimeter, though understood to be a major concern for security vulnerabilities, is often protected by little more than a fence line and security patrols. Even major airports with technology-based perimeter security programmes will concede to gaps within their systems. For most facilities, the costs to install, maintain, and monitor perimeter security devices have long been more than are viable for the relative risk of the areas they would be installed to protect.

When we think about threats to an airport’s perimeter, we can imagine any number of potential dangers – stealthy intruders scaling fences in the dead of the night, armoured vehicles tearing through concrete barriers, explosive projectiles landing on active runways. Being in the security industry, fuelled by insider experience with a healthy touch of paranoia, our first thoughts form around the characters and events that might lead directly to loss of life and property.

But what about the events that inhibit security? If environmental interferences consume resources and distract from the security process, it might be argued that they are as significant as actual threats. Following this train of thought in the context of perimeter security technologies, we might revise our threat list to include things like rabbits, rain, miscellaneous debris, or passing traffic – benign events that have the potential to masquerade as threats.

It’s highly doubtful that heads of state and security professionals lie awake at night worrying about the rabbit population or have an ongoing terror of precipitation. Perimeter security device vendors, however, are in agreement. If trends in product development are anything by which to infer the major concerns of the airport community, then addressing natural phenomena is equally as important as addressing sophisticated invasion plans.

What we’re talking about here are nuisance alarms: one of the three key performance characteristics of any perimeter intrusion detection system. Along with its Probability of Detection (POD) and vulnerability to defeat, a device’s Nuisance Alarm Rate (NAR) is a major consideration in whether it has a practical application. The perfect perimeter solution would detect every intruder (100% POD) and never alarm unnecessarily (zero NAR). This ideal device, however, with current perimeter security technologies, can only exist in a completely controlled environment.

A device’s POD – its ability to detect an intrusion within its protected area – would seem to be the most important performance characteristic. After all, detecting threats is the objective of the system in the first place. This number is, however, highly conditional. The sensor’s characteristics, the environment where it has been installed, the method of its installation and calibration, and assumptions about the intruder’s behaviour all factor into the POD rating. In ideal conditions, a 99.9% POD is actually quite easy to achieve:  turn up the sensitivity and ignore the environment. Developmentally, this is perfectly acceptable; operationally, on the other hand, not so much…

This leads us to the NAR – the expected rate of alarms not attributable to legitimate intrusion activity. Turning up the sensitivity might increase the POD, but indiscriminately. Assuring protection from every possible, potential, would-be intruder comes with the undesirable side effect of also detecting every raindrop, groundhog, and tumbleweed that violates the protected area. Unless an airport has the staff, time, resources, and patience to resolve hundreds of nuisance alarms every shift, some trade-offs have to be made. POD or NAR? It’s a difficult decision.

As a matter of principle, most sites opt for a high POD. As a matter of practicality, they later readjust the system for a lower NAR. This isn’t because the principles of protection are no longer important, but, rather, that frequent unnecessary alerts drain valuable security resources. A sensor that cries wolf is unreliable, a hindrance to security in its incessant bleating. That’s why furry critters become Public Enemy #1 – not because they are dangerous in themselves, but because they have the ability to fake-out a security device; a rabbit in terrorist’s clothing, so to speak. A system that alarms too frequently ultimately jades the security personnel’s confidence in it, and potentially masks real intrusion events. And that’s also why perimeter security system vendors, for the most part, are focusing on improving the NARs and capabilities of legacy systems, more so than developing entirely new technologies. That’s not to say that new technologies are not being developed, but that the fundamental principles of detection are staying pretty constant, while their accuracy and NARs are improving.

Technology Overview

Legacy perimeter security sensor systems (disregarding physical barriers and basic surveillance, such as CCTV) usually fit into one of four major deployment categories: Fence-mounted, Buried, Open Area, or Video (Figure 1).

Figure 1. Basic Classification of Perimeter Intrusion Detection Technologies by Deployment Strategy. Adapted from Future Fibre Technologies

Fence-mounted systems, as a matter of function, all operate pretty much alike: vibrations imparted onto the fence should alert the system. Operating principles of the individual technologies, however, dictate their respective strengths and weaknesses, installation needs, and maintenance requirements.

Many of the technologies in this category are not affected by electromagnetic and radiofrequency interferences or lightening strikes that cause nuisance alarms in the other categories. Fence-mounted sensors, however, are very susceptible to weather forces, like wind and rain that move the fence or sensor cable. Likewise, debris, animals and vegetation may also affect NARs.

Recent advances in fence-mounted systems include refinements within each technology type, such as Bragg Grating optics, an emerging concept in the fibre optic family. The most notable improvements are that some devices are now capable of pinpointing intrusion locations to varying degrees of accuracy. The software that analyses the sensor input has also improved in its ability to distinguish between environmental effects and potential intruder attempts.

Buried and open area sensors are typically installed in areas where mounting infrastructures are not practical due to terrain or safety restrictions. Operationally, whether installed above the ground or below, they all detect changes (e.g. movement, energy fluctuations, and disturbances) within a specified field. The technologies that make up these categories, however, vary widely. Active sensors project an energy field (e.g. infrared, microwave), then measure the changes in that field; passive sensors measure the changes to the ambient energy field. As with any device, each has its own benefits and drawbacks to installation requirements, reliability and accuracy and interference issues.

The variety of buried and open area sensor options widens the potential for nuisance alarms. Depending on the operating principles of the technology, its NAR might be affected by anything from seismic activity (as in the case of Geophone technology), to vegetation, fog, poor drainage, animals, or electromagnetic or radiofrequency interference. Any consideration for these devices should be carefully researched to ensure that the technology is compatible with its proposed installation site.

As with fence-based systems, buried and open area sensors are improving with time. They too are implementing locator capabilities that can determine where the alarm was instigated, as well as improved processing capabilities that can eliminate many nuisance alarm causes.

Video sensors, beyond general surveillance tools, and not to be confused with motion-detection systems, are computer analytic programmes with capabilities that include automatic detection, tracking and alarming on movements in camera images. These technologies operate with both thermal cameras, which image heat signatures, as well as visual-based cameras, which operate within the spectrum of visible light.

NARs for video sensors that monitor visual-based cameras can be affected by changes in lighting in the camera’s field of view, including sudden brightness or shadowing caused by clouds, birds, headlights and security lighting. Thermal cameras, operating independently of lighting sources, are not susceptible to these same issues, but their rates may still be affected by objects with sufficiently significant heat signatures that enter the field of view. Warm-blooded creatures – animals and birds – are common causes for nuisance alarms, but other objects might register alarms so long as they meet the camera’s detection criteria for temperature, size, and speed.

Video analytics are improving rapidly. Within the past few years, the technology has emerged from the research and development realm and entered the mainstream market as a relatively reliable and stable security solution. Many of the systems are highly customisable, allowing the user to set their own criteria, such as direction of movement, speed, and time of day, which must all be met before the system will alarm. Being able to require a higher specificity for the type of intrusion greatly decreases the potential for nuisance alarms.

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