Traffic Density Monitoring Using Passive Radars

Today the main applications of ground based passive coherent location (PCL) systems are in the domain of air traffic surveillance-air target detection, tracking, and localization. Interest in using PCL radars in these applications is expressed primarily by military users, mainly because of the great advantages of silent and covert operation that passive radars provide. In this regard, passive radars benefit from the fact that they operate by using emissions already present (e.g. FM radio, DAB, DVB-T, GSM, Wi-Fi, etc.) rather than their own. Other advantages of passive radars relate to the possibilities of stealth target detection and gap filling in areas not covered by active radars. Another huge advantage of the passive radar lies in the fact that there is no need for requirements for spectrum allocation or powerful transmitters. Consequently, as the aforementioned points make passive radars great representatives of green technology, one can install them in sanctuaries-specific or specialized places such as high-density urban areas, sites located in the vicinities of hospitals, and/or other places where electromagnetic emissions are limited by law because of the risk of interference or simply through the public's fear of electromagnetic fields. Also, it is worth mentioning that PCL systems can be cheaper than active ones as the passive radar does not have its own transmitter and typically consists of a simple radio receiver with commercial off-the-shelf (COTS) hardware, and uses a commercially available PC as a computation. © 2017 IEEE.