An enhanced altitude correction technique for improvement of WAM position accuracy

Wide Area Multilateration (WAM) is being considered as one of the primary backup sources of air traffic surveillance to Automatic Dependent Surveillance-Broadcast (ADS-B) in the National Airspace System (NAS). Radar is currently the primary source of air traffic surveillance, with ADS-B poised to succeed radar leading into the FAA ADS-B Out mandate in 2020. WAM service could serve as both a transition to full ADS-B service and a cost-saving backup surveillance alternative to radar maintenance and expansion. One of the challenges associated with WAM is the accuracy of the aircraft's reported altitude. After engaging in a trade study to investigate various alternatives to correcting aircraft altitudes in a wide region for the FAA Colorado WAM Phase II program, Exelis determined that the aircraft altitude errors could be reduced significantly (less than 200') by integrating the Rapid Update Cycle (RUC) weather data grid generated by NOAA. The altitude correction trade study for WAM approach and results are discussed and analyzed.