An algorithm to remove anomalous propagation clutter returns from ASR-9 weather channel data using pencil beam radar data
The Integrated Terminal Weather System (ITWS), currently under development by the Federal Aviation Administration (FAA), will produce a fully automated, integrated terminal weather information system to improve the safety, efficiency and capacity of terminal area aviation operations. The ITWS will acquire data from FAA and National Weather Service sensors as well as from aircraft in flight in the terminal area. The ITWS will provide products to Air Traffic personnel that are immediately usable without further meteorological interpretation. These products include current terminal-area weather and short-term (0-30 minute) predictions of significant weather phenomena. The ASR (Airport Surveillance Radar)-9 radar is used in the terminal area to control aircraft. This radar has a weather channel that provides the location and intensity of precipitation (6-level) on the air traffic controllers' radar screen. Controllers use the weather information to aid aircraft in avoiding weather. The ASR-9 radar data are often contaminated by anomalous propagation (AP). Due to the smoothing process used in the ASR-9, controllers are unable to distinguish between AP and valid weather returns. As a result controllers may attempt to vector aircraft around AP, resulting in increased controller workload and decreased terminal airspace capacity. The ITWS product suite includes two precipitation products: ITWS Precipitation (AP removed) and the ASR-9 Precipitation (AP flagged in black). The basis for these products is the ASR-9 weather channel output. Both of these products are created by an algorithm called AP-edit. The ITWS precipitation product is a representation of the location and intensity of precipitation in the TRACON (Terminal Radar Approach Control) area and may be used for situational awareness and as a planning aid for air traffic managers by showing where weather is located relative to traffic flow patterns. The ASR-9 precipitation product explicitly shows where AP clutter is located relative to any ASR-9 radar. Since the ITWS precipitation product docs not replace the ASR-9 weather display on any controllers' displays, the Air Traffic Control (ATC) supervisor or traffic manager may use the ASR-9 precipitation product to indicate the location of AP clutter to any individual controller. The products were demonstrated during the ITWS Demonstration and Validation Operational Test and Evaluation (OT&E) conducted at Memphis and Orlando International Airports during the summer of 1994. This paper describes the AP-edit algorithm and provides a preliminary evaluation of the performance of the algorithm.