Perimeter surveillance radar
Perimeter surveillance radar (PSR) is a class of radar sensors that monitor activity surrounding or on critical infrastructure areas such as airports,[1] seaports, military installations, national borders, refineries and other critical industry and the like. 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.[2]
Alternate technologies include laser-based systems. These have the potential for very high target position accuracy, however they are less effective in the presence of fog and other obscurants.
Characteristics
PSR's usually have the following required characteristics:
- No operator required: The radar autonomously detects movement in a defined area, tracks those targets and raises an alarm if the targets cross into alarm areas.
- Export of target data: The radar not only has its own dedicated display and alarm system, but also outputs data to other systems that form the security network. A typical interface system today would include target data output over Extensible Markup Language (XML) at a useful target data rate (0.1 Hz to 1 Hz).
- Coverage: a radar that covers more area can be potentially more useful than a radar that covers a limited sector. Most PSRs cover a 360° area and some are limited to sectors of 80 to 180° by their design.
- Resolution: a radar that operates at higher frequencies and with narrower beams will determine target positions most accurately.
- Low false alarm rates: a radar that puts out false targets is at best an irritant and tactically can confuse the security team. A good PSR should have a designed false alarm rate of two or less false alarms per day. (A false alarm should not be confused with a nuisance alarm caused by, for example, an animal).
Characteristics of some perimeter surveillance radar systems:
- Carrier frequencies range from X-band (about 10 GHz) to W band (about 77 GHz).
- Modulation characteristics include CW, FMCW, and pulsed. FMCW based systems typically have very high range resolution, often better than 1 metre.
- Ranges from 300 meters to over 10 km.
- Detection methods include Doppler (requiring movement relative to the transmitter) and clutter mapping (movement in any direction).
- Area coverage rates: from 360° per second down to 30° per second. (Note: some Doppler based sensors tend to have lower scan rates.)
Challenges to PSR
Challenges to perimeter surveillance radar include high clutter area operations. In the range of frequencies used almost all objects return some reflection from the radar. So foliage presents 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 high signal return from the foliage. To a degree, Doppler based radars 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.
Integration with other systems typically involves security control room plots of target position and control of one or more cameras. In turn, the cameras may be daylight or thermal.