On the use of passive microwave systems for the defence against terrorism

Abstract

International terrorism has reached a level where adequate countermeasures to protect the population have to be provided by the authorities. Similarly, the improved surveillance and protection of sensitive infrastructures, like for instance nuclear power plants or hazardous materials industries, attracts increased attention. The efficient inspection of people with respect to weapons and explosives is of increasing interest particularly for transportation services or public events. Hence, research on these new challenges had been animated through various organizations. Microwaves in the range of 1-300 GHz are used in many respects for remote sensing applications. Besides radar sensors particularly passive measurement methods are used for two-dimensional imaging. Microwaves can penetrate clothing and a multitude of other materials and allow the detection of hidden objects by monitoring dielectric anomalies. Passive microwave remote sensing allows a daytime independent non-destructive observation and examination of the objects of interest under nearly all weather conditions without artificial exposure of persons or areas. Imaging and profiling systems have been developed in the past for a multitude of applications. The development of suitable high-resolution and real-time capable instruments is supported by the extensive use of adequate experimental sensors as precursors for advanced operational equipment. An introduction to the problem and to microwave radiometry is given. The application of some radiometer systems for the defence against terrorism is illustrated. Imaging examples are shown for various frequencies and applications.