Nightingales don't sing in Grosvenor Square.

On the battlefield there are recognised front lines and soldiers who wear distinctive uniforms. But in today's world where peacekeeping operations and anti-terrorist precautions are major tasks, soldiers and security forces face the unenviable task of protecting areas such as airports, embassies, military bases and other sensitive areas, and must do so without losing the respect and co-operation of the nearby civilian populace.

A popular song of the 1940s claimed, "The Nightingale Sang in Berkley Square". Now sixty years on, if that London-based nightingale feels like bursting into song, he'd better stay in Berkley Square, and not move a few blocks to the west. London's Grosvenor Square is no place for singing--home of the American Embassy, it is an area now noted for its security fences, concrete barriers and armed police. Let the nightingale choose the wrong nearby street to live in, and our nocturnal songbird had better carry an identity card to present to those armed police before leaving home to begin his nightly serenade.

The American Embassy in London and the British 'bobbies' on the street who guard it face a classic problem of the present day--how do you protect a sensitive facility in the depth of a modern city, and at a time when terrorists may have it marked for attack?

As these words were being written in October 2004, area security was a problem for more than the inhabitants of Grosvenor Square and the surrounding streets. Israeli armoured units were pressing deep into the Gaza Strip in an attempt to deny launch sites to Hamas Qassam rocket teams, unmanned air vehicles were patrolling the United States/Mexico border, an airship loaded with surveillance gear was flying over Washington and bombs were exploding in the closely-guarded 'Green Zone' in Baghdad. The title pictures of this article shows a Qassam launch which was taken from a Hamas video obtained via the Israeli Defence Forces, which explains their poor resolution.

Today's armed forces simply don't have the numbers of 'boots on the ground' that the armies of the past could muster. But where the stakes are high, there is no substitute for the firepower of heavily armed guards.

Strategic nuclear weapon facilities such as the silos that house intercontinental ballistic missiles (ICBM) are an example of the sort of installation that needs a strong guard force. The operating methods of such defenders were illustrated in the summer of 2004, when the US Air Force's 91st Space Wing installed new launch codes in its force of Boeing Minuteman III ICBMs.

Each maintenance team that went to a missile site to conduct the code change was accompanied by a two-person security escort team from the 791st Missile Security Forces Squadron. "We have five four-person fire teams and airborne fire teams that sweep the area before the (fire and maintenance) teams even go out," explained 1st Lt David Mays, the 791st Missile Security Forces Squadron operations officer.

Once the site area is secured, technicians are able to access the ICBMs. "At the actual site, one person on the security escort teams continuously walks around the LF ]Launch Facility] while the other person monitors the radio and, depending on how long the maintenance team takes, the security airmen could be working a 12 to 16-hour day."

Confronting terrorism is a major task for many armies, as countless rear-area and civil facilities require a secure perimeter. One of the basic tools of area security is the physical barrier. This can take forms such as fences, barbed wire and ribbon tape, concrete obstacles and ditches.

Wire obstacles first saw significant military use during World War I, and saw continued use on a smaller scale during World War II and the Korean War. In modern mobile warfare they are largely used as simple, temporary barriers, but are still important for the defence of rear-situated areas, sensitive installations and national borders.

Terrorist tactics include parking explosive-laden vehicles just outside the building to be attacked, or even crashing explosive-laden vehicles into buildings. The counter to such tactics is to prevent unauthorised vehicles (or even all vehicles) from coming within critical distances.

Ditches and obstacles can be used in locations through which no vehicle should pass, while security fences around the overall perimeter can be equipped with reinforcing cables to prevent vehicle penetration.

All gates used to admit vehicles must be able to resist vehicle impacts. In May 2004, the Canadian company Vanguard Response Systems achieved the US Department of State's certification rating of 'K12', which is recognised worldwide as the highest certification standard for vehicle barrier systems used to stop threats such as vehicle bombers from penetrating high-risk facilities. In September Vanguard reported having received contracts worth C$1.1 million to supply barriers for use at one foreign embassy and three nuclear facilities in North America. One contract from an unspecified US federal agency was for the development of a barrier system able to isolate and contain persons who have breached a secure area. The company says that its Vehicle Barrier Bar can stop a 6800 kg vehicle travelling at 80 km/h.

Today, the best-known example of a physical barrier (and certainly the one most often in the news) is the barrier that Israel is constructing between its own territory and that of the Palestinian areas in the West Bank. As seen on TV news reports, it is a nine metre-high concrete wall, but this relatively expensive form of construction is used only in critical areas, and at points where there is a risk of sniper fire. It makes up about three per cent of the total. News reports often fail to indicate that for much of its length, the barrier is a lower-cost construction that combines fences, massed razor wire, a ditch and a 'trace path'--a cleared area whose sand surface is intended to show the footprints of anyone who has crossed.

While the Israeli barrier regularly features in the news headlines, other less-publicised barriers have been built or are planned. In the US, a security fence along the border with Mexico is close to completion, while planned schemes include a barrier between Saudi Arabia and Yemen, and a security fence that India plans to build along the border between Indian and Pakistani-administered portions of Kashmir.

In the area between Egypt and the Gaza Strip, a different sort of barrier is being planned. Organisations such as Hamas dig tunnels that start on Egyptian territory, pass under the Israeli-patrolled border and terminate in the Palestinian-controlled area. These tunnels are used to smuggle weapons to the insurgents involved in the current Intifada (uprising).

Although the Israel Defense Forces try to locate such tunnels and close them down, one solution being considered would involve digging a ditch along the border that would be deep enough to intercept existing tunnels and prevent the creation of new ones.

Ideally, a barrier needs to be positioned so that all the assets to be protected are on one side, and all likely attackers are on the other, with all access between the two areas tightly controlled by the defenders. In the real world this may be impractical. For example, although the 'Green Zone' in Baghdad is a walled area that contains the offices of the interim Iraqi government plus a former palace of Saddam Hussein (now part of the US Embassy), it is also home to around 12,000 Iraqi citizens. While there are security checks at all entrances and exits to the zone, many of the searches are conducted by Iraqi personnel. A successful attack on 14 October 2004, apparently by suicide bombers, penetrated this defensive screen.

When fencing is used without intrusion-detection devices, it has limited ability to detect unauthorised entry. The concrete walls and razor-wire fences that make up Israel's security barrier are the most obvious part of the defensive system, but the latter also includes what the Israeli Ministry of Defense describes as "various observation systems ... with varying performance requirements (range, all weather, day/night)".

The Challenge: Exploiting Images

Thermal imaging technology provides good long-range detection, but a thermal image is not as useful for target identification as that from a shorter-ranged, extreme low-light or integrated day/night camera. If the budget permits, a mixture of integrated day/night and thermal cameras should be used. If the cost of thermal cameras is too high, a combination of day/night cameras and infrared illuminators can be used, but performance will be degraded by weather conditions such as heavy snow and fog.

Cameras and sensors can be interconnected by a dedicated network, or via commercially available systems such as intranets or even the Internet. The Swedish company Axis Communications specialises in network video systems and recently announced the availability of its 213 PTZ Network Camera. This offers pan/tilt/zoom (PTZ) capabilities, a built-in 26x optical zoom auto-focus lens, plus an IR mode for nighttime conditions. The 213 also incorporates a built-in Web server, compression chip and operating system, allowing it to transmit motion Jpeg and Mpeg-4 image streams over an intranet or the Internet, and to be controlled via the same connection.

It is one thing to gather imagery, but another to effectively exploit it. As any regular air traveller will testify, the airport personnel responsible for x-raying hand luggage bring varying degrees of concentration to the task. Viewing a screen for hours on end is boring, and short spells on duty are needed so that the operator is relieved before his or her efficiency has become too degraded.

Another approach would be to let a computer handle routine screen-monitoring tasks. Automated video surveillance (AVS) techniques use computer software to monitor video streams, watching for activities, events or behaviour that might be considered suspicious.

Video Motion Detection (VMD) technology analyses video imagery and determines where there is motion in the scene. This seemed promising, the theory being that anything that moves is likely to be of interest. In practice, real-world scenes often have large amounts of motion that can confuse VMD systems. For example, cameras being used to detect watercraft are monitoring scenes in which almost the entire image is moving. An operationally effective AVS system must be able to extract tactically significant motion from a background of generic motion.

For the last 25 years, the US Defense Advanced Research Projects Agency has funded research into technologies that would allow a single human operator to monitor activities over a broad area using a distributed network of active video sensors. Operating mainly autonomously, these sensors would notify the operator of salient information as it occurs.

The three-year Video Surveillance and Monitoring (Vsam) programme began in 1997 was intended to develop state-of-the-art algorithms for automated video surveillance systems suitable for use in future urban and battlefield surveillance applications. A team composed of Carnegie Mellon University Robotics Institute and the Sarnoff Corporation was chosen to develop an end-to-end testbed system demonstrating capabilities such as real-time moving object detection and tracking from stationary and moving camera platforms, recognition of generic object classes (e.g. human, lorry), human gait analysis and recognition of simple multi-agent activities.

Twelve other contracts were awarded to university and industry laboratories to conduct research in areas that included sensor design, human activity recognition, and vehicle tracking/counting.

Software to the Rescue

The results of the above-mentioned research are now being incorporated in operational products. ObjectVideo has developed video surveillance software based on an artificial intelligence concept which it calls 'computer vision'. This checks all objects in a camera's view against threat-specific pre-programmed rules. When an object violates a rule, for example, when a small boat loiters near a ship or an airport passenger enters an off-limits area, the software alerts security personnel by phone, pager, email or an alert console.

Algorithms monitor the video streams, detecting and tracking all relevant objects in the camera's view and classifying these into specific types. The basic capability classifies objects as 'human' or 'vehicle', but custom classification algorithms can be developed for users with more specific needs such as to distinguish humans from animals or lorries from aircraft.

On 14 September 2004 ObjectVideo announced that it had won a $ 750,000 award from the US Defense Advanced Research Projects Agency (Darpa) Small Business Technology Transfer Phase II programme to continue to research and develop night vision video surveillance technologies. The company hopes to use the new funding to develop technologies needed to overcome some of the challenges that a nighttime environment presents as people or objects are tracked from one camera view to the next across a security system. These include strange lighting effects, headlights, low-light conditions and other phenomena.

Small radars can also be used to detect intruders. This can be a task for the traditional tripod-mounted surveillance radar deployed by infantry, or a small unmanned sensor such as the Elta eight to twelve GHz EL/M-2128 Minder (MINiature DEtection Radar) that can be hung on a fence or mounted on a post. High cost is a traditional problem with radar sensors, but the British systems house Plextek is trying to sharply reduce the cost of such hardware by using commercial off-the-shelf (cots) technologies and techniques wherever possible in the development of its BlightER series of infantry-deployable radars. BlightER 100 is a motion-alert sensor for use on fences or similar locations.

BlightER 200 is a small electronically scanned radar covering sectors of typically 15[degrees] to 45[degrees], while the BlightER 300 uses a mechanically rotated narrow-beam antenna to provide full 360 [degrees] coverage. At the top of the range is BlightER 400 which offers electronic scanning of a 90 [degrees] sector. All four can be either deployed individually or linked together via a wireless or wired network connection to monitor a larger area.

Intrusion sensors such as motion detectors, pressure sensors and vibration detectors can be used to warn of intruders. If teamed with a fence or other physical barrier, they can be used to automatically turn on lights or to direct cameras to the area where an intrusion has been detected.

A recently updated report by the US Congressional Research Service noted that "the military's demand for persistent surveillance, a function for which aerostats appear to be well suited, is growing ... increased emphasis on homeland security, and growing force protection demands in urban environments all call for dominant battlespace awareness."

Securiton in Switzerland, after two years of tests with a pilot system at the Suva Reka camp in Kosovo, is now marketing the M3Syst. In the M3Syst, the surveillance and observation cameras record any movement on the ground surrounding the protected outer zone. Attempts to penetrate this zone are detected and reported by the open space and fence surveillance sensors. All sensors transmit their signals/alarms to the central monitoring unit container that includes, inter alia, programmable logic controllers, image recorders and displays. The surveillance team in this unit assesses the alarms, processes them and deploys the intervention teams. On the other hand three access-control units in the individual-control container provide controlled access to the protected inner zone. Checking equipment includes metal detectors, fingerprint scanners, a deadman door plus a baggage X-ray system and video surveillance (see diagram below).

Drones

In recent articles, Armada International has documented the growing role of unmanned air vehicles in providing lowcost aerial surveillance. The US is using small drones such as the Lockheed Martin Desert Hawk (originally known as the Force Protection Airborne Surveillance System) to monitor areas around facilities in southwest Asia, and other small drones are being developed for similar tasks.

In June 2004 the US Department of Homeland Security Customs and Border Protection (CBP) began to use the long endurance Elbit Hermes 450 to patrol Arizona's border with Mexico. Under a lease contract, the Israeli company and its Texas-based subsidiary EFW are providing drones, ground control stations, operational crews and support personnel for these border patrol operations. This initial pilot programme may be extended into 2005 and could be expanded by the CBP to include the northern American border with Canada.

Balloons

The US Army has deployed small aerostats (tethered balloons) in Afghanistan and Iraq to help protect US forces there. The Rapidly Elevated Aerostat Platform (Reap) is a 7.6-metre-long aerostat that operates only 300 feet above the ground. Designed for rapid deployment (approximately 4 minutes), it carries TV and night vision cameras. A similar payload is also carried by the much larger Rapid Aerostat Initial Development (Raid) system, which is reported to have been sent to Afghanistan. This aerostat operates at approximately 1000 feet.

Russia's NIIS Scientific Research Institute of System Engineering is heading a team that offers the RKPA aerostat. This combines a Rys captive balloon able to stay at 600 to 800 metres altitude for up to 15 days. The sensor is a 360-degree surveillance radar with a range of 100 km.

Airships can also be used as long-endurance sensors. In September 2004, an American Blimp Corporation A-170 Lightship conducted a 24-hour mission over Washington to demonstrate its suitability as a surveillance platform. Leased from the manufacturer for evaluation trials, it is reported to have carried day and night cameras.

Opponents argue that airships and aerostats are big targets and vulnerable to enemy ground fire; proponents say that in practice the envelope of these craft can endure numerous punctures before the onset of a gradual loss of altitude.

The longer the range of the weapons available to an attacker, the more impractical it becomes to deny the attacker an effective firing site. For years Israel has had a complex system of security fences around the Gaza Strip, but the development and manufacture of Qassam rockets has allowed insurgents to attack targets in Israel from launch points within the Gaza Strip. At time of writing, Israeli forces were completing an operation in the Gaza Strip--an incursion intended to prevent Qassam teams from operating in areas from which they could attack targets such as the town of Sderot (a frequent target for Qassam missiles). In practice, the Qassam attacks were not stopped, just reduced in frequency.

Airport Protection

One current security nightmare is the problem of protecting airports and airliners. A handful of mortar bombs landing on any major airport is enough to bring flight operations to a halt, as the Provisional Irish Republican Army (Pira) demonstrated on 9, 11 and 13 March 1994 at London's Heathrow Airport. During the first attack mortars were fired from a car parked near to the perimeter fence. The second and third involved mortar firings from a wooded area close to the perimeter fence. In all three attacks, the bombs failed to detonate, but operation of the airport was successfully disrupted.

Longer-ranged projectiles would allow such attacks to be mounted from further way, greatly complicating the problem for the security forces. Israel's security barrier runs far enough away from Ben Gurion International Airport (about six miles) to prevent terrorists from threatening civilian aircraft, but the Israeli authorities are only too aware that if the Qassam rockets manufactured in the Gaza strip were to become available in the West Bank, potential firing sites would be uncomfortably close the airport.

In areas at either end of a runway, aircraft are likely to be moving slowly in order to position themselves for takeoff or to leave the runway after landing. At such times, they are particularly vulnerable to enemy ground fire. Attackers will also try to identify sector boundaries and areas like swamps where the defences may not be as extensive. All these locations require particular attention in any defensive plan.

Protecting airliners from attack by man-portable surface-to-air missile systems is another problem that must be tackled. Israel equips at least a portion of the E1 A1 fleet with countermeasures based on infrared flares, but this would be impractical for most operators. The US Department of Homeland Security has funded BAE Systems and Northrop Grumman to develop directional infrared countermeasure systems (now generically called Dircm) that could be installed on American airliners, but such a solution may be too expensive for many nations. Some studies have been conducted in the United Sates of a scheme that would rely on ground-based Dircms.

For the moment, the only solution is to try to deny the terrorist a launch point close to the airport, a measure that involves the 'sanitisation' of what may prove an impractically large area of terrain. A more novel solution has been proposed by the British company Cunning Running Software, which realised in 2003 that the Air Defence Siting Computer software it had developed for the British Ministry of Defence to tackle the problem of finding the best operating sites for surface-to-air missile systems could be used to identify those locations near an airport from which a shoulder-fired missile would be effective. Monitoring of this much smaller area would be a more practical proposition. While the potential terrorists might still be able to fire missiles from other areas close to the airport, attacks from these locations would likely to be unsuccessful, wasting missiles that are probably in short supply and posing a risk that the fleeing firing team might be captured.

Technology may offer newer and better ways to detect intruders, but in the long term, area security depends on motivated personnel who will use their intelligence to observe and analyse the situation. When the Pira decided to attack the headquarters of London's Metropolitan Police at New Scotland Yard, they opted to use a car bomb. After parking the explosive-packed vehicle close to the building, they behaved like law abiding citizens and inserted the appropriate fee into the nearby parking meter. An alert policeman who saw them wondered why anyone would put money into a parking meter on a day when the London authorities had announced that parking charges would be waived because of public transport problems.

New Scotland Yard came out of the experience unscathed, but the story should be part of the training material for all soldiers and guards tasked with area security duties. Observation may be an important part of the anti-terrorist effort, but without intelligent analysis of what is being seen, it will achieve little.