Perimeter Surveillance Radars (PSR)
Endro SUNARSO, ASIS-CPP?, PMI-PMP?, FSyl, F.ISRM
Highly effective security professional with extensive experience in corporate & physical security operations & management across APAC & ME.
The threat of terrorism at critical and/or sensitive facilities makes maintaining awareness of unusual activity around perimeters increasingly important. Terrorist attacks such as the bombing of the USS Cole (Oct 2000) & the sabotage of a French oil tanker in Yemen (Oct 2002) could have been avoided if an early warning system capable of detecting & tracking the motion of intruders on the ground or in the water had been deployed. Early identification & location of potential ground & marine threats is vital for taking appropriate countermeasures to stop such attacks.
Intrusion detection technology aims to monitor human intruders entering the protected area to prevent their theft & destruction. It has been widely used in the security protection of important places such as warehouses, museums, banks, airports & transformer substations. Common intrusion detection technologies include infrared sensors, video surveillance systems, electronic fences, vibration cable transducers, optical fiber vibration sensors, leaky coaxial cable (LCX) sensors & radar.
Security practitioners are pulling intrusion detection systems at the perimeter & going to longer-range detection systems, eliminating the threat of having a system that is visible on the outside. The system on the inside is under lock & key, & is protected from hackers & those with bad intentions.
Perimeter security has moved on from simply triggering after the event when a line has been crossed, to deploying technology that reacts before the intrusion has even happened.
Perimeter intrusion is about detecting objects on the ground, on water & in the air. Perimeter monitoring needs to be 360 degrees & should include a system that can position objects. Most are based on radio frequencies (RF) or radar. However, a combination of RF & radar can be good for determining the position of UAWs or drones.
Convenience plays a large part in solutions working together. Convenience in perimeter security & access control is important for ease of use which equates to increased compliance. People tend to work around things that are inconvenient.
Unmanned Aerial Vehicle (UAV) and Drone detection
Drone detection has become an important part of perimeter security. Security personnel must first be made aware of the presence of the drone before any action can be taken to bring it down. The ability to deploy countermeasures are greatly enhanced if you know the drone’s (&/or the controller’s) exact location. Countermeasures can be grouped as either:
Although the technology is available, current regulations in most countries forbid the use of any of the following technologies to be used for neutralising drones.
Of course, exceptions are made for military &/or law enforcement agencies.
Drone jamming devices work by disrupting the communication between the drone & its operator. The drone will either land automatically or fly erratically until it crashes. This device works on any Wi-Fi or cellular?connected drone?regardless of brand or model but only within line-of-sight range. It is imperative to employ such measures when the drone is low enough for security personnel to see clearly.
Perimeter intrusion detection systems (PIDS) typically employ CCTV but adverse environmental & imaging conditions can impede the performance of traditional camera sensors. Radars address these challenges, detecting intruders 24/7 even in harsh weather & low-light or no-light scenarios. Radars are ideal for monitoring large, exposed spaces with harsh weather, & where the perimeter environment is too complex for deployment of only?CCTV. It was only a matter of time before radar’s integration into physical security systems to improve the protection of assets at critical infrastructure locations.
Radar
Radar?is a radiolocation system that uses?radio waves?to determine the distance (ranging), angle (azimuth), & radial velocity of objects relative to the site. It is used to detect & track aircraft, ships, spacecraft, guided missiles & motor besides mapping weather formations & terrain. A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves?domain, a transmitting antenna, a receiving antenna (often the same antenna is used for transmitting & receiving) and a?receiver & processor to determine properties of the objects. Radio waves (pulsed or continuous) from the transmitter reflect off the objects & return to the receiver, giving information about the objects' locations and speeds.
Historically radars have been seen as expensive, complex & suitable for operation only by highly trained specialist staff. However modern ground movement radars are different as they are relatively affordable, simple to operate & can be integrated into existing security systems, with intuitive operator interfaces allowing straightforward control of the sensor & interpretation of results. The main benefits of radar are:
Such radars offer an invaluable strategic advantage: a right-sized system built to deliver high-end technical performance while increasing accessibility to broader range of commercial applications.
To achieve wide area monitoring, a number of wide FOV cameras can be installed on-site. However, cameras with wide-angle lenses have significantly less range, reducing subsequent alarm lead times. In contrast, narrow FOV cameras offer better detection range but yield less coverage. Radar is capable of scanning a full FOV up to 10 times per second for faster target detection is an effective option. The result is reduced infrastructure costs & early warnings of approaching threats.
When intruders are approaching a perimeter from multiple directions, delayed detection or lost visuals can severely limit an operator’s ability to intercept potential threats before they breach the perimeter. Radar is purpose-built to detect, track, and map human or vehicle movement for superior tracking of threats. It delivers continuous target tracking with distance to target accuracy within 1%. Moreover, the time from first detection to intrusion intercept is drastically improved with a radar, enabling a faster, more efficient response. In some cases, a radar detecting a human on foggy day occurs as many as 60 seconds faster than it would take a thermal camera to see the intruder in its line of sight.
The operational principle of radar
Radar stands for RAdio Detection And Ranging. RADAR is fundamentally an electromagnetic sensor used to detect & locate objects that cannot be seen. Radio waves are radiated out from the radar into free space. Some of the radio waves will be intercepted by reflecting objects (targets). The intercepted radio waves that hit the target are reflected back in many different directions. Some of the reflected radio waves (echos) are directed back toward the radar where they are received & amplified. Those measurements include the delay between transmitted & received energy proportional to range & the frequency shift between transmission & reception (TX & RX respectively) proportional to relative velocity, as well as the angle & angle rate available through antenna & gimbal measurements to determine to location of foreign objects. With the aid of signal processing a decision is made as to whether or not a target echo signal has been detected. The target location & other information can then be acquired from the echo signal.
As a radar takes a snapshot picture of the area, it learns the fixed environment. After several scans are recorded, the radar compares the most recent picture with the fixed environment & notes what is different. On the next revolution, it measures any change in the location of any abnormality, & if the difference meets one or more of the criteria for an intruder, it generates an alarm.
How radar measures range to target
Radars transmit invisible electromagnetic radio waves that travel at the speed of light, approximately 300 million metres per second. Although this is extremely quick, there will still be a brief delay between the transmission of the original signal & the reception of the echo. The time delay is directly proportional to the range to the target.
Long-range radars use very short pulses & measure the time difference between the original pulse & echo pulse to establish range to target. At shorter ranges a different technique - Frequency Modulated?Continuous Wave (FMCW) is normally used where the radar constantly transmits but the frequency is modulated so there is a frequency difference between the echo signal & the instantaneous transmitted signal. The radar measures the difference in frequency, which is directly proportional to the range of the target.
In both cases, the radar makes a direct measurement of the echo signal to determine range to the object. Compared to optical systems where a large object at long range appears similar to a small object at close range, radar range measurements are not fooled by target size.
However, if the radar energy passes through the target (the optical analogy being a clear glass window) or is absorbed by the target, it will be difficult to detect using radar. Therefore targets that reflect radar energy strongly will be easier to detect using radar. The direction of the radio waves gives the bearing of the target & this, in conjunction with the range measurement, allows the position of the target to be determined.?
As radar?use electromagnetic waves to detect movement, it is not sensitive to the things that normally trigger false alarms like moving shadows or light beams, raindrops or insects.
How radar measures size of target
Generally larger objects reflect more radio waves than smaller objects, however the target angle & shape also has an effect. Radar Cross Section (RCS) is the term used to describe the combination of shape & size & is usually expressed in square metres. Targets with higher RCS reflect more radio waves & cause a stronger echo signal to be detected by the radar, so this information can be used to aid in target classification. Although echo strength diminishes with increasing range to target, the radar knows the range from the echo so can compensate for this effect.
Typical RCS figures:
In reality the RCS does vary to some extent based on the target angle, so a building or vehicle that is normal to the radar presents a large flat surface & has a slightly higher RCS than one that is angled so less reflected energy is directed back toward the radar.
Radars dynamically map human & vehicle movement to deliver early warnings of intruder activity. Walking humans have an interesting characteristic where the swinging arms & legs causes the RCS to cycle higher & lower in sync with the walking motion. Crawling humans have a lower RCS than walking humans because they have a physically smaller cross section. This can present some difficulties as RCS is similar to small wild animals.
How radar measures direction of target
Radar antennas typically have a narrow field of view that is scanned across a wider area. When a target is seen the direction in which the antenna is pointing corresponds to the direction of the target.
There are many possible antenna methods that can be used, with choice being determined by required size, weight, power & cost.
The simplest method is to physically rotate the antenna. When the radar sees the target echo, the direction of the antenna directly corresponds to the direction of the target. Rotating antennas do have moving parts that can wear, however with clever engineering & use of very small & light materials, the expected lifetime can be extremely long.
Some radars have fixed antennas that are steered electronically - phased array -although this is often much more expensive than simple physical rotation.
Another method uses 2 or more antennas to mathematically calculate the angle of arrival by comparing 2 or more echo signals. This method is cheaper than a phased array, but has limitations such as inability to distinguish multiple targets at the same distance & lower sensitivity.
Integrating a ground-based commercial radar as another essential sensor within a PIDS to complement visible & thermal cameras maximizes detection coverage by receiving early warnings of threats & gain position intelligence of threats for an effective security solution.
Site Security Radar or Perimeter Surveillance Radars (PSR)
PSR are a class of radar sensors that monitor activity surrounding or on critical infrastructure areas such as airports,?seaports, military installations, national borders, refineries & other critical industries. Such radars are characterized by their ability to detect movement at ground level of targets such as an individual walking or crawling towards a facility. Such radars typically have ranges of several hundred metres to over 10 kilometres, & offer significant opportunities for improving site security
A surveillance radar can track a target or track multiple targets. As the surveillance radar passes each target, its position is reported to the radar processor. After consecutive scans & reports, the targets' positions can be smoothed, & their future locations can be predicted. A surveillance radar that develops tracks on targets is sometimes called a?track-while-scan?(TWS)?radar. In a modern radar, the target detection & tracking can be automatically processed by a data processor called?automatic detection & tracking?(ADS). An ADS system can perform the functions of target detection, track initiation, track association, track update, track smoothing & track termination.
Research carried out by UK's Centre for the Protection of National Infrastructure (CPNI) showed that radar technology can be a key element in the provision of enhanced detection & tracking of threats at many different types of national infrastructure. Site security radars can generally be divided into 2 categories:
These radars use a very high frequency beam to detect & monitor movements within the defined area. Along with detection & tracking, radars can also trigger alarms if the moving object crosses into certain areas.
Radar is most effective when used with CCTV, PIDS & thermal imagers. While alerting security personnel to the presence of multiple potential threats, radar can determine the precise location of those threats & advanced systems can track their positions over time. This multiple target detection & tracking capability is available day or night.
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Typically, alert zones may be defined within which all targets detected by the radar will be flagged as potential threats & highlighted to security personnel. Advanced ground movement radars may provide a target classification capability, to distinguish between pedestrians & vehicles. However, radar classification is rarely totally reliable.
While a camera cannot see far enough, it is more effective to use radar to track the objects & when they get close enough, the camera can focus on them. Note that radar does not have enough resolution to identify one person from another, so cannot be used as a substitute for CCTV.
To verify whether the threat is genuine, security personnel are required to verify the target. Most radar systems work in conjunction with CCTV, allowing video images to be activated to the target. This makes them highly efficient systems & allows for security personnel monitoring the system to quickly decide whether human intervention is needed on the ground. It is far more efficient to perform initial verification remotely via CCTV, than to dispatch guards to investigate all alarms/targets. Target location data from the radar can be used to cue the appropriate camera system & direct it accurately at the target. Only when a target has been inspected & declared by the operator to be a potential threat, need guards be sent out. By including radar as part of an integrated sensor system, security practitioners can maximize the use of valuable manpower resources.
When intruders are approaching a perimeter from multiple directions, delayed detection or lost visuals can severely limit an operator’s ability to intercept potential threats before they breach the perimeter. Radar is purpose-built to detect, track, and map human or vehicle movement for superior tracking of threats. It delivers continuous target tracking with distance to target accuracy within 1%. Moreover, the time from first detection to intrusion intercept is drastically improved with a radar, enabling a faster, more efficient response. In some cases, a radar detecting a human on foggy day occurs as many as 60 seconds faster than it would take a thermal camera to see the intruder in its line of sight.
A?surveillance radar can track a target or track multiple targets. As the surveillance radar passes each target, its position is reported to the?radar processor. After consecutive scans & reports, the targets' positions can be smoothed, & their future locations can be predicted. A surveillance radar that develops tracks on targets is sometimes called a?track-while-scan?(TWS)?radar. In a modern radar, the target detection & tracking can be automatically processed by a data processor called?automatic detection & tracking?(ADS). An ADS system can perform the functions of target detection, track initiation, track association, track update, track smoothing & track termination.
Physical Requirements
While it is important not to compromise the system performance by including too many physical constraints, there are some significant installation requirements that must be considered. The following factors can have a substantial impact on the suitability of a radar-based solution:
Although each radar will be programmed differently to suit security needs, there are key features which are almost universal. Most radars will be able to tell the difference between human & animal intrusion due to size & movement patterns & speed & would not raise the alarm in the event of a cat getting too close to the premises.
PSR may operate in areas with high?clutter levels. In the range of frequencies used almost all objects return some reflection from the radar, as does the ground itself. Foliage presents a particular problem as it is both a barrier to the radar energy, as well as an area in which it is difficult to detect a moving target due to the foliage being blown by the wind appearing as multiple moving targets.?
Doppler Radar
A?Doppler radar?is a specialized?radar?that sends the energy in pulses & listens for any returned signal. It does this by bouncing a microwave signal off a desired target & analyzing how the object's motion has altered the frequency of the returned signal. This variation gives direct & highly accurate measurements of the?radial?component of a target's velocity relative to the radar. Doppler radar pulses have an average transmitted power of about 450,000 watts, compared to a typical home microwave oven generating about 1,000 watts of energy. Despite the wattage, each pulse only lasts about 0.00000157 seconds (1.57x10-6), with a 0.00099843-second (998.43x10-6) "listening period" in between.
Therefore, the total time the radar is actually transmitting a signal (when the duration of all pulse transmissions are added together), the radar is transmitting for a little over 7 seconds each hour. The remaining 59 minutes & 53 seconds are spent listening for any returned signals.
The Doppler shift or the Doppler effect, is defined as?the change in the wavelength or frequency of the waves with respect to the observer who is in motion relative to the wave source. With the "Doppler shift", the sound pitch of an object moving toward your location is higher due to compression (a change in the phase) of sound waves. As an object moves away from your location, sound waves are stretched, resulting in a lower frequency.
The reason for the Doppler effect is that?when the source of the waves is moving towards the observer, each successive wave crest is emitted from a position closer to the observer than the crest of the previous wave. Therefore, each wave takes slightly less time to reach the observer than the previous wave.
To a degree, Doppler?based radar can detect movement in such areas, as long as the component of movement velocity towards or away from the radar is significant enough to generate a signal that overcomes the foliage return signal. All modern radars are Doppler radars.
When integrated with sophisticated management software, the radar displays this data on a dynamic map, delivering real-time insights to security personnel monitoring the device; it then sends coordinates to integrated cameras & initiates slew-to-cue functionality, using the cameras for visual assessment of intruders.
The layering of intrusion detection sensors enables redundancy & prevents false alarms by verifying intrusion events with 2 data points; it also prioritizes multiple targets to provide PTZ cameras with logic, such as “follow closest” or “follow furthest,” taking the operator out of the equation & allowing security personnel to focus on responding to the identified object.
A PIDS system solely relying on PTZ cameras for target tracking often requires multiple hand-offs to effectively follow a target over a large area. However, the ability for a radar to locate an intruder’s geolocation with extreme accuracy improves the entire PIDS’ capability to respond. The radar tells every integrated PTZ exactly where to aim, guaranteeing fewer hand-offs from one target tracking sensor to another, eliminating the chance of a lost visual on target. Users who overlap multiple radar FOVs gain uninterrupted coverage. Target consolidation helps to eliminate confusion & undesired multiple alarms, as a target inside the coverage area of overlapping radar beams will only show as a single target.
Redundancy
Integrating radar with multiple PTZ cameras helps to create a fail proof solution. A radar would continue to track & deliver an intruder’s geolocation to the other PTZ cameras. In other words, by integrating radar into your PIDS, the system is far less likely to lose target’s location.
Location & Installation Considerations
Height, location & tilt will impact the effectiveness of a radar within a PIDS. It is crucial to be aware of installation best practices to optimize radar performance. Achieving accurate & persistent localization of multiple threats at optimal ranges in all weather & light conditions comes down to accounting for every possible scenario that might limit both camera sensors & radar systems.
Areas with Undulation (Dips)
A difference in ground elevation is one of the most common pitfalls that radars face. A combination of strategic radar height, tilt & layering can mitigate these conditions by minimizing any clutter effect from the ground & by covering any blind spots under the radar.
Placing a radar too high will detect tall targets, while leaving the zone closest to the ground uncovered. Tilting a radar incorrectly will also reduce a radar’s sensitivity by creating ground return interference, where the beam bounces off the earth.
The perfect height & tilt takes into consideration the slope of the covered area as well as the height & location of the desired detection area.
Radar Cluttering
Radar cluttering refers to echoes or reflections not important to a radar’s function that affect its sensitivity & performance.
How clutter affects radar performance
Clutter refers to sources of unwanted echoes generated by objects that reflect radio waves & is caused by reflections from the ground. Any radar that detects targets on, or close to, the ground will see more clutter than radars that look upwards into the air, especially if the clutter moves.
In the ideal case, the ground would be a very flat concrete expanse with a target located in the middle. Unfortunately this is rare. Often there are fixed objects such as cars, posts, walls & fences that all contribute to the background clutter levels. Fixed clutter can mask the presence of a target by reflecting the radio waves before they can reflect off the target.
Radar signal processing tries to ignore fixed clutter either by filtering objects with no Doppler shift or by comparing the current scan to previous scans to identify fixed objects.
Even so, large fixed objects such as tall fences or buildings generate high clutter levels that make it difficult to detect much smaller targets that are next to the clutter due to an effect called scintillation where there are small changes in the echo amplitude of the large object.
Consider a large building with RCS of 10,000 square metres exhibiting 0.1% RCS change due to scintillation. This presents a background RCS variation of 10 square metres that is easily enough to swamp the RCS of a walking human (1 sq. metre). Orientating the radar so the building RCS is reduced will improve the situation.
Moving clutter, such as long grass, bushes, trees & water is very difficult to mitigate using signal processing. Moving clutter generates a Doppler shift & varies from scan to scan so cannot be distinguished easily from real targets. Radar systems will have a higher detection threshold in areas where there is lots of moving clutter to avoid excessive false alarms. The most effective way to improve the performance is to remove or reduce the moving objects that generate the clutter.
Noise is also a problem. The total signal competing with the target return, either electronic, external environmental conditions, or both, is clutter plus noise. The signal-to-noise ratio compares the level of desired signal to the level of background noise, such that a ratio higher than 1:1 (greater than 0 dB) indicates more signal than noise.
Installing a radar in a location where that ratio guarantees more signal than noise is the basic premise of this best practice.
How vertical beam spreading can improve performance
A spread beam is an antenna main beam that has been artificially broadened. This differs to a simplistic wide beam by being designed to distribute the radio waves in a specific pattern to achieve good performance at all ranges.
A spread beam cannot be usefully characterised by comparing -3dB points & is not usually symmetrical. This type of shaping is common for radar systems because the range to target has a large effect on the echo power (every time the range doubles the echo power reduces to 1/16 th of what it was), so spread beams distribute the antenna energy to compensate for this effect. Beam spreading is usually in the elevation (vertical) plane only.
Conclusion
For best radar performance there should be a clear line-of-sight to the target & a low level of clutter around the target.
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Endro Sunarso is an expert in Security Management, Physical Security & Counter Terrorism. He is regularly consulted on matters pertaining to transportation security, off-shore security, critical infrastructure protection, security & threat assessments, & blast mitigation.
Besides being a Certified Protection Professional (CPP?), a Certified Identity & Access Manager (CIAM?), a Project Management Professional (PMP?) & a Certified Scrum Master (CSM?), Endro is also a Fellow of the Security Institute (FSyl) & the Institute of Strategic Risk Management (F.ISRM).
Endro has spent about 2 decades in Corporate Security (executive protection, crisis management, critical infrastructure protection, governance, business continuity, loss mitigation, due diligence, counter corporate espionage, etc). He also has more than a decade of experience in Security & Blast Consultancy work, initially in the Gulf Region & later in South East Asia.
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