Airport Perimeters: a look at modern intrusion detection technology

In today’s increasingly fragile airport security environment, the perimeter is the first line of defence. Eugene Gerstein offers an overview of perimeter intrusion detection technologies and provides some integration advice.

The perimeter is one of the most important aspects of the airport security environment. Some airports are fortunate and have natural barriers, such as rivers, creeks and in some cases even mountains. While these are wonderful aids, they are not a solution. The only way to effectively protect an airport is by having a proper fence, supplemented by technological means – specifically, a perimeter intrusion detection system (PIDS).

Whilst the International Civil Aviation Organisation’s (ICAO) guidelines on fences are fairly straightforward, suggesting a minimum height of 2.44m, along with barbed or razor wire at the top, their PIDS guidelines, on the other hand, are fairly loose, and this is where it gets interesting.

There are lots of technologies to choose from, among which you can find microwave, buried cable, fence mounted cable systems, fibre optics, different types of acoustic sensors (both cable-based and separate wireless sensors, with exceptionally long battery life) and even radars (not to mention infrared, as well as infrared/Doppler combinations; however, in my experience, they are not reliable enough to be used in an airport environment). Each has its own advantages and disadvantages, and often mixing and matching is the right way to go.

It is crucial that each technology is paired with technological means of alarm verification, such as CCTV, as it is inevitable that ‘nuisance’ alarms will occur. These can be caused by many factors, and it is an vital task to verify them, thus separating them from ‘false’ alarms, which raise completely different concerns (e.g. whether you are using the right system for the environment, and whether it was installed properly etc.) This article does not address the use of advanced video analytics as a means of perimeter protection on purpose, as we are looking at purely technological means, rather than an add-on to another security system component, namely CCTV.

Buried cable (a.k.a. ported ‘leaky’ coax) is a venerable solution, having proven itself over decades of service, and it continues to see some degree of innovation even today. Its main benefits are that it is tried, tested and true; it is covert, it can easily compensate for changes in the terrain, and it can pinpoint intrusions fairly accurately. The intrusion detection occurs through the use of time and spatial signatures of legitimate targets, while ignoring small animals and environmental factors (i.e. rain, snow, etc.). Basically, transmitter and receiver cables are used to create an invisible electromagnetic detection field, used to detect an intruder. The cables are designed with apertures in the transmit cable’s outer conductor, which allow energy to escape and be retrieved by the corresponding parallel receiver cable. Its main disadvantage is the cost of installation as a lot of digging is required.

Most fence-mounted cable systems are a lot faster to install then buried cable, as they are attached to a fence using tie wraps (unless the airport in question has a concrete fence, reducing the effectiveness of this solution). It works through using signals generated by flexing the sensor cable and then analysing these to determine if a legitimate intrusion is taking place.

For years I was a staunch advocate of microwave sensors, however, these days I also recommend fibre optic solutions. If you do not already have an infrastructure at and around the perimeter with which to put up CCTV and other IP based solutions, you can really kill two birds with one stone, as you can utilise the perimeter solution as your infrastructure. This method is tremendously economical, convenient and the installation becomes a lot less labour intensive, especially if carrying out both projects at or around the same time.

A common objection to an all-in-one solution is that of cutting, however a properly designed network (read: perimeter protection solution) will mitigate and/or eliminate these issues, with self-healing capabilities and redundancy (more on this in the sample solution description below).

While the all-in-one solution is a significant advantage, the main disadvantage would be cost. However, again, if you are also facing the need to install infrastructure for CCTV and other IP-based solutions around your perimeter, the cost balances itself out.

On the subject of microwave sensors, these are divided into two categories – bi-static (transmitter and receiver) and monostatic (transceiver). There are various types of bi-static sensors, with detection zones ranging from 10 metres in the traditional type, to 800 metres in some of the modern systems, creating long and narrow zones. This style of detection gives you the ability to establish a kind of ‘invisible fence’, where the detection field serves to identify intrusions. Intruders create a sort of a ‘void’ in a detection zone, which is analysed by the system through the use of complex algorithms, which compare it to a matrix populated with parameters equalling various human ‘shapes’ (it is a lot more complex in reality, however this is an easy way of explaining it in lay terms).

Monostatic sensors are also known as volumetric, named for their mass sensing capabilities. Traditionally, these devices were used to protect enclosed spaces, such as rooftops, garbage dumps, etc. Modern applications are a lot more diverse, with an ability to protect individual objects, such as aircraft, vehicles etc.