Publications

A fundamental function of any aviation weather system is to provide accurate and timely weather information tailored to the specific air traffic situations for which a system is designed. Weather location and intensity are of prime importance to such systems. Knowledge of the weather provides "nowcasting" functionality in the terminal and en route air spaces. It also is used as input into aviation weather forecasting applications for purposes such as storm tracking, storm growth and decay trends, and convective initiation. Weather radar products are the primary source of the weather location and intensity information used by the aviation weather systems. In the United States, the primary radar sources are the Terminal Doppler Weather Radar (TDWR) and the Weather Surveillance Radar 1988 Doppler (WSR-88D, known as NEXRAD). Additional weather radar products from the Canadian network are used by some of the aviation weather systems. Product quality from all these radars directly impacts the quality of the down stream products created by the aviation weather systems and their utility to air traffic controllers. Four FAA weather systems use some combination of products from the aforementioned radars. They are the Corridor Integrated Weather System (CIWS), the Integrated Terminal Weather System (ITWS), the Weather and Radar Processor (WARP), and the Medium Intensity Airport Weather System (MIAWS). This paper focuses on the improvement of weather radar data quality specific to CIWS. The other mentioned FAA aviation weather systems also benefit either directly or indirectly from the improvements noted in this paper. For CIWS, the legacy data quality practices involve two steps. Step one is the creation of weather radar products of highest possible fidelity. The second step involves creating a mosaic from these products. The mosaic creation process takes advantage of inter-radar product comparisons to interject a further level of improved data quality. The new CIWS data quality plan will use a mounting evidence data quality classifier technique currently being developed. The technique applies a multi-tiered approach to weather radar data quality. Its premise is that no single data quality improvement technique is as effective as a collaboration of many. The evidence will be expanded to include data and products from the radars along with data from additional sensing platforms. The mosaic creation process will correspondingly expand to take advantage of the additional evidence. Section 2 covers data quality of products from the single radar perspective. Section 3 focuses on the use of satellite data as the first additional sensing platform to augment removal of problematic radar contamination. Section 4 describes the data quality procedures associated with creation of mosaics from the single radar products augmented with new satellite masking information. Last, Section 5 discusses future plans for the mounting evidence data quality improvement technique.

This paper describes the Tactical 0-2 hour Convective Weather Forecast (CWF) algorithm developed by the MIT LL for the FAA. We will address the algorithm and focus on the key scientific developments. Future directions will also be discussed.

Operational experience with the Integrated Terminal Weather Systems (ITWS) and Airport Surveillance Radar, Model 9, (ASR-9) Weather System Processor (WSP) demonstration systems, studies of pilot weather avoidance decision making), and recent accidents have demonstrated the need to provide timely, accurate information on the location and movement of storms to air traffic controllers, pilots, and airline dispatch. At medium-intensity airports, generally those with too few flight operations to justify the presence of Doppler radar systems like the Terminal Doppler Weather Radar (TDWR) or the WSP, terminal air traffic surveillance is currently provided with the ASR-7 and ASR-8 radar systems. The ASR-7 and ASR-8 do not provide calibrated precipitation intensity products or any storm motion information. The Medium-Intensity Airport Weather System (MIAWS) program is intended to address these terminal weather information deficiencies. MIAWS-generated products would be displayed to tower and Terminal Radar Approach Control (TRACON) supervisors and delivered to aircraft cockpits and airline dispatchers to assist pilots during landings. Initially, the MIAWS will provide a real time display of storm positions and motion based on Next Generation Weather Radar (NEXRAD) product data using a product generation and display system derived from the WSP. Airport wind and wind shear information will be acquired from an FAA Low Level Wind Shear Alert System (LLWAS). A demonstration system will be installed and demonstrated at experimental sites in Memphis, TN and Jackson, MS in 2000 and potentially at a third site in 2001. This demonstration system will be used to assess technical and operational issues such as compensation for the relatively slow updates of the NEXRAD products and, Anomalous Propagation (AP) ground clutter. The ASR-11 is a replacement for the ASR-7/8 radars that feature a weather reflectivity processing channel. When it becomes available at MIAWS locations, the MIAWS processor will acquire and display precipitation and storm movement products derived from the ASR-11. Likewise, when an LLWAS Relocation/Sustainment (LLWAS-RS) (Nilsen, et al., 1999) becomes available at MIAWS locations, the MIAWS will acquire wind and wind shear information derived from the LLWAS-RS.

A key product within the Integrated Terminal Weather System (ITWS) Initial Operating Capability (IOC) product suite removes anomalous propagation (AP) ground clutter from the ASR-9 precipitation product. This has been identified as a critical component of ITWS due to the frequent occurrence of AP when storms or outflows move over an ASR-9. Editing is accomplished by comparing the raw ASR-9 weather data to composite maps generated by the Next Generation Weather Radar (NEXRAD) and the Terminal Doppler Weather Radar (TDWR). An editing template, containing regions of AP, is created based on the ASR-9 data collected at the middle of the composite volume scan to minimize the difference in update rates. The template is used to edit the ASR-9 scan immediately after the composite map and all subsequent scans until a new composite map is received. This algorithm has been shown to perform quite well, especially if the weather and AP returns are not co-located. During the 1994 Demonstration and Validation Operational Test and Evaluation in Memphis (MEM) and Orlando (MCO), the probability of editing AP (PEAP) in the absence of weather was 0.97 for level 2 and greater returns (Klingle-Wilson, 1995). The probability of editing weather (PEW) for those cases with weather only was quite low, i.e., 0.01. In order to minimize the removal of weather returns in those cases where the AP and weather are located in close proximity, the editing thresholds are quite conservative. This is reflected by the 1994 results which show a PEAP of 0.81 and a PEW of 0.02 for this class of event. Besides the conservative thresholds, another area of concern is the fact that the AP regions can expand or increase in intensity after the AP editing template is created. This rapid variation frequently occurs with convectively generated AP and can cause the performance of the algorithm to decrease with time until a new template is created. In this study, we will examine the algorithm failure mechanisms in detail to identify possible site-adaptable parameter changes that can be used to improve the performance for the mixed weather/AP events. This is especially germane since the parameter set was not re-evaluated after the TDWR composite map was incorporated in 1995. In the critical region over the airport during hazardous weather conditions, this radar updates more frequently than the NEXRAD. Since the parameters were designed to account for the NEXRAD volume update rate, they are probably too conservative for the current algorithm (which uses both composite maps).

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.