Active Geolocation Using the Small Airport Surveillance Sensor (SASS) System

Tower controllers at small airports often rely on visual surveillance to manage aircraft traffic because current surveillance systems are too expensive. As a result, runway incursions and in-flight safety near small airports are important issues that need to be addressed. The Small Airport Surveillance Sensor (SASS) system leverages current aircraft transponder technology to provide tower controllers at smaller airports with low-cost, real-time, all-weather aircraft surveillance of the airport surface and surrounding airspace. The SASS system consists of three pieces: two phased array Sensor Units that detect and demodulate signals from FAA-mandated transponders on all aircraft, and a Master Unit that fuses data from the two Sensor Units together and tracks aircraft in order to give tower controllers better situational awareness. Position accuracy within 30 feet at the surface and 0.2 nautical miles (nmi) aloft has been demonstrated. The designs of the SASS system and 8-element phased array are described, along with techniques used for detecting and demodulating signals of interest, estimating angle of arrival and time of arrival, and geolocating surface and airborne aircraft with an emphasis on active geolocation. Position accuracy results are also presented from a SASS experimental system installed at Hanscom Air Field in Bedford, MA.