A study of primary surveillance radar traffic and its utility via ADS-B uplink

A pilot flying with a typical Cockpit Display of Traffic Information (CDTI) can see traffic positions broadcast air-to-air via Automatic Dependent Surveillance - Broadcast (ADS-B) or broadcast ground-to-air via the Traffic Information Service - Broadcast (TIS-B) or ADS-B Rebroadcast (ADS-R). The TIS-B service broadcasts position information of all transponding aircraft seen by a secondary surveillance radar. Aircraft operating under visual flight rules who are not transponding are only sensed by primary surveillance radars and are not broadcast via TIS-B today. One method to provide a more complete traffic picture to pilots and to aid in future integration of Unmanned Aircraft Systems (UAS) in the National Airspace System (NAS) is to broadcast primary radar traffic information as a primary TIS-B (pTIS-B) message. Numerous questions need to be addressed about the nature of non-cooperative, i.e., non-transponding, primary aircraft before their positions can be broadcast and influence the decision making of pilots, UAS pilots, or automatic sense-and-avoid algorithms on-board unmanned aircraft. This paper presents an in-depth analysis of primary radar targets from an Air Route Surveillance Radar (ARSR-4) in Finley, North Dakota to help gain insight to these questions. Eight months of radar data were collected from January through August, 2012. Numerous methods were used to distinguish real aircraft from primary radar clutter so that a good estimate of the total number of primary aircraft flights could be calculated and the nature of the flights assessed. ADS-B reports were also collected over the same eight month period, mostly containing the flight data from operations by the University of North Dakota flight training school. The ADS-B and primary aircraft datasets were merged to study the frequency and nature of situations in which the two aircraft types encounter each other at various ranges to assess inherent safety risk and pilot workload visually acquiring traffic. The results indicate a large number of non-transponder flight operations in the eastern half of North Dakota. While a rare occurrence, ADS-B aircraft did occasionally operate within close proximity to non-transponding aircraft. This paper will present the analysis methodology and statistical results of the study performed researching the application of primary radar data in TIS-B as a potential source for uplink to ADS-B equipped aircraft. MITRE also developed a test platform to further investigate the end-to-end possibilities of broadcasting pTIS-B messages. The work to construct this test platform is described and some thoughts on future work are considered.