Small airport surveillance sensor (SASS)

This paper describes a low-cost real-time geo location system that uses two multiple-antenna sites to provide secondary surveillance at small to medium size airports. Tower controllers at these airports currently rely primarily on visual surveillance to maintain situational awareness, which can be impaired at night and during bad weather. While the nations busiest airports have the ASDE-X radar surveillance capability, it is too expensive to deploy at the remaining 500+ towered airports. The Small Airport Surveillance Sensor (SASS) leverages current aircraft transponder technology to provide tower controllers at smaller airports with low-cost all-weather surveillance of aircraft on the airport surface and in the surrounding airspace. The SASS system consists of two phased-array Sensor Units and a Master Processing Unit located on the airport property. The sensors utilize a novel 8-element monopole array to provide high accuracy direction of arrival (DOA) measurements of transponder replies, as well as high precision GPS-synced clocks to determine the signal's time of arrival (TOA). The Master Unit obtains the transponder reply information via WiFi and uses that information to compute the target location. Position accuracy goals are 30' at the surface and 0.2 nm aloft, out to 20 nm, at a 1 second update interval. The design of the 8-element monopole array and its measured performance are described, along with the techniques used for DOA and position estimation. Position accuracy results are presented from a SASS experimental system installed at Hanscom Field in Bedford, MA.