4.1 Background

Probability of intercept (POI) is a key performance feature of EW surveillance and reconnaissance systems; it relates to the probability of time coincidence of two or more parametric window functions, such as scanning antennas, sweeping or stepping receivers, and frequency agile emitters.

Many publications and examples that examine POI and its associated intercept time statistics invariably quote examples involving crystal video (wide open) receivers (CVRs), scanning superheterodyne (SSH) receivers, and the implications of scanning, directional antennae. However, over the last 20 years, significant developments in technology have occurred as have several armed conflicts. These have dictated radical changes in requirements, force modus operandi, and other issues.

In previous chapters, the impact of receiver developments, the impact of more recent conflicts (such as the Gulf War), and the emergence of a number of new threats such as the low probability of intercept (LPI) emitter have been examined. Clearly, there is a significant POI issue associated with such emitters in the presence of the littoral electromagnetic environment. Finally, as shown in the USS Cole incident, the new threat (now referred to as the asymmetric threat ) from fast attack craft (FAC), for example, is significant and must be accounted for in tasks, combat strategies, weapons, sensors, and so on, for fast reaction and adequate firepower.

So today s EW systems have to deal with increasing complexity and density of the electromagnetic environment; comprising multimode emitters, high and low ERPs, increased signal agilities (RF, PRI, and so forth), complex...