#perimeter video surveillance
Video surveillance system on the perimeter of an object.
States have traditionally paid the greatest attention to protecting the perimeter or borders of a city. A large number of ancient fortress walls and fortifications marking the borders of old cities have survived to this day.
This is understandable, — preventing an intruder or enemy from entering a protected area is the basis of security for any territory.
There are many borders in our country and they know how to guard them; we have plenty of experience in this, in general.
After all, Russia has the longest state border. And there are more than enough objects with guarded perimeters inside the country.
Specifics of perimeter protection
As a rule, the perimeter of an object has a significant length, from several hundred meters to several tens of kilometers and more, if we are talking, for example, about a state border.
In this regard, it is necessary to solve the problem of transmitting information over such distances. And the organization of power supply for equipment on the perimeter can also cause problems.
All technical security equipment must be suitable for outdoor use, otherwise the issue of heating the equipment in winter will have to be resolved.
If we talk about video surveillance, then we should also think about and decide how the stage lighting will be organized.
Perimeter video surveillance tasks
I believe that it is possible and necessary to use a video surveillance system for perimeter security.
It is only necessary to clearly define the tasks solved with the help of video surveillance.
In my opinion, it is most appropriate to use video cameras as another line of security in addition to traditional perimeter detectors.
Here, two operating modes are possible: verification of alarms from the main security lines and use of the video camera as an independent security detector.
In the first case, after any alarm is triggered, the operator analyzes the image received from a video camera installed in the same section of the perimeter and makes a final decision on the alarm level and further actions.
Here, the coordinated operation of the security alarm and video surveillance is extremely important: the image from the required camera should be automatically displayed on the alarm monitor of the system so that the operator does not waste time searching for the required image. Even in this, generally speaking, simplest mode of operation, the benefits of the video surveillance system can be invaluable.
It is no secret that the percentage of false alarms of perimeter detectors is quite high, — difficult operating conditions have an effect. And the ability to quickly obtain an image from the protected area significantly increases the efficiency of the security system as a whole. In the second mode of operation, the intelligent capabilities of the video surveillance system are used.
Despite the assurances of all leading manufacturers, not everything is so great here yet, but in recent years progress has been obvious, and using a video camera as a security alarm no longer seems utopian.
Modern motion detectors already work quite stably in difficult outdoor conditions, they can tune out many natural obstacles, such as rain, snow, light pollution, etc. It is also a good idea to provide a sufficiently wide exclusion zone when constructing a perimeter fence, so that as few foreign objects as possible fall into the field of view of video cameras: bushes, trees, passing cars, etc.
Among other things, multi-zone detectors can help with this, which register movement only in the necessary areas of the frame. Many systems today can classify objects in the frame.
For example, determine that a person is approaching the fence or identify a whole group of violators.
However, I would not recommend using a video camera as the only or primary detector of attempts to breach the perimeter boundary.
In general, each section of the perimeter should be protected by two or three independent security lines built on different principles of intrusion detection, and the use of video surveillance is no exception to this rule.
Placement of video cameras
Typically, video cameras are placed along the perimeter, with 2-4 fixed cameras on each section. The typical length of a section is about 200 meters, although of course, everything depends on the terrain and the direct visibility distance on a particular section.
To cover the entire section, video cameras with wide-angle and narrow-angle lenses are often installed in pairs.
A wide-angle lens provides surveillance at a distance of approximately 50 meters from the camera installation location, a narrow-angle lens “shoots” the next 50 meters. Sometimes the following scheme is used: several controlled PTZ cameras are placed inside the security facility so that all sections of the perimeter are in the visibility zone.
When an alarm occurs, the corresponding PTZ camera preset is automatically selected, and the image of the triggered section is displayed on the operator’s screen. A specific method is selected based on the facility’s configuration; a combination of both methods can also be used.
Data transmission
Since the perimeter length can be quite significant, the question arises about the method of delivering the video signal from the camera to the security post.
The maximum length of a coaxial cable for transmitting an analog video signal is about 300 meters, the length of a UTP CAT5e or CAT6 cable for IP video cameras is even less, about 100 m.
It is possible to use signal repeater amplifiers, but the maximum number of such repeaters installed in series in the communication line is limited, and it is also necessary to provide power to these devices.
Therefore, video signal converters are most often used. For analog video cameras, signal converters with transmission via twisted pair can be used.
The length of such a connection with acceptable image quality can reach a kilometer or even more. There are solutions for transmitting an analog signal via fiber optics. In the case of using multimode fiber, the transmission distance is about several kilometers, for a single-mode optical cable it can be tens of kilometers.
In addition to the long transmission range, optics removes almost all issues regarding the noise immunity of the video signal. Although this solution is still more expensive than using copper cable, at long distances there is essentially no alternative to optics. The same physical transmission media are also used for digital data in IP systems.
For twisted pair, DSL technology is used, which provides a flow of about 10 Mbit over a distance of up to several kilometers. For fiber optics, Ethernet media converters from copper to optics are used. Sometimes, for transmission over long distances, a radio channel is used: Wi-Fi or WiMAX.
Power supply and protection of video surveillance communication lines on the perimeter
Large distances impose their own peculiarities on the organization of power supply for equipment installed on the perimeter.
In order to eliminate voltage losses on long wires, 220V is often pulled along the perimeter and low-voltage power supplies are installed on the sites. In this case, power is backed up either directly by high voltage, or uninterruptible power supplies are used on-site.
In this case, care must be taken to maintain the operability of the batteries at sub-zero temperatures.
Here you can use either battery compartment heating or batteries that operate at low temperatures. It should be noted that such batteries are significantly more expensive than conventional ones. The task of lightning protection is extremely important for equipment and all communication lines in perimeter systems.
With a large perimeter length, the probability of system failure from lightning discharges increases significantly.
This applies equally to both signal lines and power cables. And here you should not save on protection under any circumstances, otherwise serious problems are inevitable.
By the way, the use of fiber optics can significantly reduce such risks.
Perimeter Lighting
To get the most out of a video surveillance system, it makes sense to work hard on perimeter lighting.
In the simplest case, you can use infrared spotlights, which will allow you to get acceptable image quality at night at a relatively low cost. Although more often, full-fledged lighting in the visible range is organized, since it is important to ensure visual inspection of the protected areas when sentries patrol the perimeter.
Do not forget that no lighting will help if fog has descended over the protected area. Thermal imaging cameras can help here.
Thermal imagers are based on a completely different principle of obtaining visual information about an object: in fact, the operator sees a temperature distribution map in the frame.
This allows for fairly clear identification of a person and other objects whose temperature differs from the background temperature. The image obtained from a thermal imager is practically unaffected by weather conditions and illumination levels.
But this pleasure is very, very expensive, so such solutions are used only in particularly important cases.
The use of video surveillance significantly increases the security of the boundaries of an object. And despite the fact that building a well-functioning system is a technically complex task, taking into account the difficult operating conditions of the equipment, the costs are worth it.
However, there is no need to overestimate the capabilities of modern video surveillance systems, although they are great, they are not yet unlimited.
Therefore, the use of traditional perimeter detectors remains mandatory.
If you follow these recommendations, the perimeter will be reliably protected.