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The separation of transmitter and receiver in bistatic and multistatic radar sensors offers the system designer new and additional degrees of freedom to tailor solutions to specific applications. The receivers may be passive and hence largely immune to jamming. Passive systems that also use ‘illuminators of opportunity’ do not have to provide a potentially expensive transmitter. Multiple transmitters and or receivers can improve sensitivity, coverage, and importantly improve the opportunity to acquire a line of site to the target (without which detection is impossible). These advantages make this form of radar attractive for a variety of applications, many of which fit well with the needs of homeland security. Equally, however, the additional complexity of having a number of separated transmitters and receivers brings about new challenges that require careful understanding if these forms of sensors are to be routinely adopted for operational use.

Recent terrorist attacks demonstrated that even sophisticated terrorists capable of planning and executing multiple, coordinated attacks continue to rely on traditional weapons rather than risk the uncertainty of chemical, biological, radiological or nuclear (CBRN) weapons. While some terrorist organizations have the motivations and capabilities to conduct large attacks worldwide, we have not yet witnessed the use of so called weapons of mass destruction (WMD) foreshadowed by the 1995 Sarin attacks in Tokyo, the discovery of al Qaeda’s crude biological weapons program in Afghanistan, and the anthrax attacks in the United States in the fall of 2001. Anti-Western extremists pose a global threat, but what do the use of traditional weapons and innovative tactics mean for the future of terrorism? This chapter describes our current understanding of the global terrorist threat including the use of CBRN weapons. A discussion of the implications for sensor research, particularly for chemical and biological agents and radioactive materials then follows.

This is a short review of how neuronal sensors fit in the broader biological context of animal survival. This may help those involved in the development of engineered sensors to put in perspective their task with what the evolutionary process has achieved. Most of the information reported here is available in the educational field of neuroscience, with mention of some recent relevant findings. I have attempted to place these findings in an evolutionary perspective as it clarifies better the intrinsic role of some of the extraordinary particularities of the biological solutions of neuronal sensors.

Chemical sensors are becoming more and more important in any area where the measurement of concentrations of volatile compounds is relevant for both control and analytical purposes. They have also found many applications in sensor systems called electronic noses and tongues.

In this chapter, the sensing coverage area of surveillance wireless sensor networks is considered. The sensing coverage is determined by applying Neyman-Pearson detection and de.ning the breach probability on a grid-modeled field. Using a graph model for the perimeter, Dijkstra’s shortest path algorithm is used to find the weakest breach path. The breach probability is linked to parameters such as the false alarm rate, size of the data record and the signal-to-noise ratio. Consequently, the required number of sensor nodes and the surveillance performance of the network are determined. For target tracking applications, small wireless sensors provide accurate information since they can be deployed and operated near the phenomenon. These sensing devices have the opportunity of collaboration amongst themselves to improve the target localization and tracking accuracies. Distributed data fusion architecture provides a collaborative tracking framework. Due to the present energy constraints of these small sensing and wireless communicating devices, a common trend is to put some of them into a dormant state. We adopt a mutual information based metric to select the most informative subset of the sensors to achieve reduction in the energy consumption, while preserving the desired accuracies of the target position estimation.

In order to realise scalability of chemical sensors in extensively deployed wireless sensor networks, considerable materials challenges must be overcome. Conventional devices are currently far too expensive and unreliable for massive long-term field deployment. Cost can be driven down by imaginative approaches to transduction and instrument design. For example, we have produced a complete instrument based on LED measurement of colour changes that has sub-micromolar detection limits for a number of heavy metals for around $1.2 In its current form, the device also has a short distance wireless communications functionality and very low power consumption. However, chemical sensors capable of long-term reliability will require imaginative solutions to the key issue – how can the sensing films/membranes in chemical sensors maintain predictable characteristics in long term deployment?

Arrays were introduced in the mid-eighties as a method to counteract the cross-selectivity of gas sensors. Their use has since become a common practice in sensor applications [1]. The great advantage of this technique is that once arrays are matched with proper multivariate data analysis, the use of non-selective sensors for practical applications becomes possible. Again in the eighties, Persaud and Dodds argued that such arrays has a very close connection with mammalian olfaction systems. This conjecture opened the way to the advent of electronic noses [2], a popular name for chemical sensor arrays used for qualitative analysis of complex samples.

Radar, and in particular imaging radar, has many and varied applications to security. Radar is a day/night all-weather sensor, and imaging radars carried by aircraft or satellites are routinely able to achieve highresolution images of target scenes, and to detect and classify stationary and moving targets at operational ranges. Different frequency bands may be used, for example high frequencies (X-band) may be used to support high bandwidths to give high range resolution, while low frequencies (HF or VHF) are used for foliage penetration to detect targets hidden in forests, or for ground penetration to detect buried targets.

A Space-Based Radar (SBR) is a reconnaissance, surveillance, and target acquisition system capable of supporting a wide variety of joint missions and tasks simultaneously, including battle management, command and control, target detection and tracking, wide area surveillance and attack operations. SBR also supports traditional intelligence, surveillance and reconnaissance missions such as indications, warning, and assessment. These mission areas cover the strategic, operational, and tactical levels of operations of interest. SBR systems are also used for earth science projects. However, an SBR system, by virtue of its motion, generates a Doppler frequency component to the clutter return from any point on the earth as a function of the SBR-earth geometry. The effect of earth’s rotation around its own axis is shown to add an additional component to this Doppler frequency. The overall effect of the earth’s rotation on the Doppler turns out to be two correction factors in terms of a crab angle affecting the azimuth angle, and a crab magnitude scaling the Doppler magnitude of the clutter patch. Interestingly both factors depend only on the SBR orbit inclination and its latitude and not on the specific location of the clutter patch of interest.

Radar technology was designed to increase public safety on sea and in the air. Today radars are used in many .elds of application, such as airdefense, air-tra.c-control, zone protection (in military bases, airports, industry), people search and others. Classic pulse radars are often being replaced by continuous wave radars. Unique features of continuous wave radars, such as the lack of ambiguity, very low transmitted power and good electromagnetic compatibility with other radio-devices, enhance this trend. This chapter presents the theoretical background of continuous wave radar signal processing (for FMCW and noise radars), highlights the most important features of this type of radar and shows their abilities in the field of security.