Comparison of ASR-11 and ASR-9 surveillance radar azimuth error

To ensure aviation safety, air traffic safety agencies have required minimum aircraft separation standards. Currently, the FAA requires a minimum separation of 3 nautical miles (NM) when aircraft are within 40 NM of an air traffic control surveillance radar and a separation of 5 NM when aircraft are located beyond 40 NM from the radar. At the same time, the FAA permits a separation of 3 NM out to 60 NM for single sensor terminal systems using an ASR-9 Mode S MSSR. The ASR-9 Mode S and ASR-11 Monopulse Secondary Surveillance Radar (MSSR) are similar monopulse systems and the 40 NM limit on terminal separation minima for the ASR-11 may be unnecessarily restrictive. In this paper, we seek to determine if there are any differences in radar azimuth performance between the ASR-9 Mode S and the ASR-11 at ranges of 40 to 60 NM. To perform this analysis we implement a method that estimates radar error from raw time-stamped range and azimuth reports of aircraft flying through the airspace (targets of opportunity). The method filters the data to extract radar reports from aircraft traveling at nearly constant heading, velocity and altitude, and then utilizes knowledge of the aircraft dynamics to accurately estimate the true aircraft position. Our analysis employs a reference system approach comparing the performance of the alternative system, the ASR-11, against the performance of the approved legacy system, the ASR-9 Mode S, to determine if the alternative system's performance is equivalent or better.