Problems of installing security alarm systems in difficult operating conditions.
Problems of installing security alarm systems in difficult operating conditions
As noted in the materials of the Carnahan Conference on Security, the choice of a perimeter control system for a protected facility is always a compromise between the probability of detecting a true intruder and the level of false alarms. Usually, when creating perimeter control systems, a careful selection of sensors is carried out taking into account the conditions of a specific protected facility. Often, the costs of preparing the territory for the installation of a control system exceed the cost of the control system itself. However, a situation often arises when a perimeter protection system has to be deployed in the absence of time (or funds) for proper preparation of the territory. Such a situation occurs when the value of the facility suddenly increases sharply, the level of threats changes, or the need arises to organize temporary protection. Sometimes it is necessary to work under conditions of strict restrictions on the impact of the environment. At the same time, the developer of perimeter control systems usually proceeds from a certain ideal state of the facility, which does not happen in practice.
In a time-sensitive situation, commercially available equipment is often used. In Australia, the choice is limited to equipment that is suitable for local conditions. The country's terrain, climate and wildlife often preclude the use of the experience of users of systems in the Northern Hemisphere. Devices that have proven themselves in Europe and North America are ineffective in Australia. Australia is a country with a low population density spread over a vast area. Therefore, local companies specialising in the supply and installation of perimeter control systems are generally unable to accumulate sufficient information on the operation of the systems. In this regard, Government agencies constantly carry out testing programmes for new and existing systems. However, the results of these programmes are of little use in a situation where equipment must be installed almost immediately in a less than ideal environment and in the absence of data on the use of the systems in the conditions of the facility.
The installation of perimeter protection systems for individual households in Australia located on the coast has a special specificity. Usually it is necessary to proceed from the fact that in this case the possibility of cutting down trees is excluded. Damage to other green spaces should be minimal, the sensors of the alarm system should be invisible to others. In the interests of preserving the rights of residents, it is often necessary to exclude the use of television surveillance systems.
The ban on excavation work excludes the use of sensors buried in the ground. For aesthetic reasons, it is necessary to refuse to install sensors on top of the fence or on individual posts. Therefore, in the interests of minimizing the number of connections of signal lines and electrical outlets, monostatic sensors are used, in particular, passive IR sensors. The total area of dead zones on rough terrain is reduced to a minimum by choosing a sufficiently high sensor installation height.
When deploying a passive IR sensor system, there is often a concern that the sensor's field of view will be limited by a wall of dense vegetation in motion, especially during thunderstorms with heavy rain and wind. To assess the background activity during operation of passive IR sensors, background temperature measurements are taken at selected points where the sensors could be installed. Static and dynamic temperature checks on buildings, trees, grass, and dense vegetation conducted at a coastal facility show that the vegetation structure has a certain homogeneity and creates a relatively uniform IR background at wind speeds of up to 65 km/h. The IR temperature of the vegetation in the sensor's field of view varied within no more than ±5°C.
The available experience in operating passive IR sensors shows that one of the sources of false alarms of this type are large IR emitters located outside the field of view of the sensors. For coastal facilities, these may be passing ships. This circumstance necessitates very precise adjustment of the sensor's field of view.
The experience of subsequent operation of the passive IR sensor system for protecting coastal households has shown the correctness of the choice of technical solution. The level of false alarms was minimal, with the exception of one sector in which there was a fruit-bearing tree that attracted many bats at dawn.
After some time had passed since the coastal property control system had been put into operation, it became clear that a television surveillance system was needed. Since the owner of the house was against installing additional lighting devices, it was decided to install IR floodlights. However, tests showed that the floodlights attracted many representatives of the local nocturnal fauna, which made it impossible to use them at the site. As a result, the issue of using television surveillance equipment remained unresolved.
One of the promising means of territory control is video motion sensors, which at the dawn of their appearance were considered unsuitable for outdoor use. When the task was set to create a system for monitoring the territory of an oil terminal well lit at night, it was video motion sensors that turned out to be a means of covering large working areas with minimal installation costs. They can be installed beyond the reach of intruders, allow visual surveillance and immediately after triggering, identify the source of the alarm.
The main concern when installing video motion sensors was the glare of reflections from sea water getting into the field of view of the television cameras. The tests showed that the latest models of video motion sensors operate quite reliably under these conditions. The latest models of spatial detection video sensors make it possible to significantly reduce the level of false alarms from passing vehicles, lightning flashes, insects and raindrops getting on the optics of television cameras, and camera vibrations caused by wind or transport. The efficiency of this type of system depends greatly on the nature of the soil. In the countries of Europe and North America, the humus layers of the upper A-horizon and the alkaline soils of the lower B-horizon with a small content of insoluble iron and aluminum oxides are located relatively deep. In Australia, a large area is occupied by arid and semi-arid lands with a relatively thin humus layer or even complete absence of the latter. In a number of areas, the A-horizon consists of red desert soils with a high content of oxides. In other areas, high temperatures lead to intense evaporation of soil moisture and salinization of the A-horizon. Under these conditions, active systems provide an unusually irregular detection zone with virtually complete failures of sensitivity in some places. In this case, an overall increase in the sensitivity of the system only leads to an increase in the level of false alarms. In addition, in the absence of vegetation, the soil is subject to intense erosion, which can change the homogeneity of the soil composition and cause physical damage to the sensor. Therefore, when using systems of this type, intensive research is required on a specific site.
The same can be said about passive buried systems. They can be used only if the soil is well prepared. In arid areas, the clayey topsoil cracks in the summer and disables the pressure sensors, making the cable vulnerable to damage by animals, pedestrians and vehicles. However, recent tests of fiber-optic cables have shown the effectiveness of laying the cable on a composite pad with an asphalt covering on top. Asphalt remains flexible at temperatures down to minus 4° C, the system effectively detects people walking or crawling across the cable installation site, and the asphalt can withstand the weight of a vehicle.
Seasonal shifts in clay soils lead to misalignment of active IR systems and misalignment of sensors installed on high wire fences. Soil shifts can also occur under the influence of artificial causes, for example, in places where soil was backfilled during construction. All this leads to undesirable misalignment of the sensors.
Various insects may affect the operation of the devices. Birds are a particular problem, so when using sensors installed on a fence, a separate idle wire should be provided for birds. The organization of a «sterile» zone may be hampered by animals that easily jump over the fence.