Events in early 2010 at Newark Liberty International Airport (EWR) provide a clear demonstration of the vulnerability of civil GPS infrastructure to intentional interference. An interdiction effort was launched to catch an offender using advanced interference detection equipment and multiple surveillance cameras. An offender, a truck driver, was caught and arrested. In his possession: a widely available GPS jammer that plugs directly into the cigarette lighter. To prevent future incidents, the FAA is relocating the GBAS system to a more protected location away from the freeway. There are strong privacy and financial motivations to use GPS jamming. Conventional emitter location techniques perform poorly in the ground mobile environment and are unaffordable if wide area geographic coverage is needed. Without effective interdiction, we may reach a point where low power GPS jamming becomes chronic. Cell phones could include GPS Jam to Noise (J/N) ratio detectors to provide timely interference detection. Given measurements from several cell phones, the jammer's location can be estimated by examining measured jamming power as a function of observer positions. This paper explores how viable such a concept might be, how accurately jammer location can be determined and what it would take to implement such a system. The influences of cell phone J/N measurement accuracy, cell phone position accuracy, propagation, and cell phone density on jammer location accuracy are examined. The relative advantages of smart phones, dumb phones, and smart meters as measurement devices are also considered. It appears feasible and cost effective to provide jamming detection in under 10 seconds and provide real-time jammer location to better than 40 meters but it will require an act of national will. IOC could happen as early as 2016 with full national coverage by 2018. Concepts discussed in this paper can be extended to locating cellular jammers, explosives, and radiation sources
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