Publications

The Federal Aviation Administration (F.A.A.) is currently embarking on programs, such as the Integrated Terminal Weather System (ITWS) and Terminal Doppler Weather Radar (TDWR), that will significantly improve the aviation weather information in the terminal area. Given the great increase in the quantity and quality of terminal weather information, it would be highly desirable to provide this information directly to pilots rather than having to rely on voice communications. Providing terminal weather information automatically via data link would both enhance pilot awareness of weather hazards and reduce air traffic controller workload. This paper will describe current work in the area of providing direct pilot access to terminal weather information via existing data link capabilities, such as ACARS (Addressing, Communications and Reporting System). During the summer of 1994, the ITWS testbed systems at Orlando, FL and Memphis, TN provided real–time terminal weather information to pilots in the form of text and character graphics–based products via the ACARS VHF data link. This effort follows an earlier successful demonstration during the summer of 1993 at Orlando (Campbell, 1994). Two types of Terminal Weather lnformation for Pilots (TWIP) messages are generated: a text-only message and a character graphics map. In order to ensure their operational utility, these products were developed in consultation with an ad hoc pilot user group. The TWIP Text Message is intended for typical ACARS cockpit displays, which are roughly 20 characters wide by 10 lines high. The TWIP Character Graphics Depiction is intended for the cockpit printers available on some aircraft that are at least 40 characters wide. Both products are intended to provide strategic information to pilots about terminal weather conditions to aid flight planning and improve situational awareness of potential hazards.

A successful demonstration of providing a text-based message via VHF data link (ACARS) was carried out at Orlando, FL during the summer of 1993. Five airlines participated in the three-month demonstration, which included an average of 145 Terminal Weather message requests per day. During a heavily-impacted weather day, a total of 220 Terminal Weather requests were made. The format of the Terminal Weather message was developed by an ad hoc committee of pilots, dispatchers, controllers and researchers. The format required a balance between the need for including important information and the need to fit the information into a limited number of characters. The approach was to divide the message into several blocks and to prioritize the potential message elements by importance and immediacy. The most important and timely elements are listed first, and the others appear only if more important elements are not present or else were deleted altogether. Pilot reaction to the demonstration was assessed from questionnaire responses. Overall, pilots thought that the system should be deployed operationally and found that it increased situational awareness. They felt that it provided some help in decision making and did not adversely affect cockpit workload. They also strongly endorsed the need for a graphical version of the Terminal Weather service. Controllers were initially concerned that the data link demonstration would result in increased radio traffic and concomitant controller workload. Prior to the demonstration, changes were made in the Terminal Weather message format to help allay these concerns. Consequently, controllers were surprosed to find that requests for weather information actually decreases over what they normally would expect during a period of heavy weather impact. Thus, evidence was obtained that delivery of Terminal Weather information by data link could decrease controller workload. Dispatchers took a strong and unanticipated interest in the Terminal Weather message. The dispatchers for one airline used the Terminal Weather message to monitor weather conditions at Orlando during a period of heavy weather impact. Special messages also were sent to dispatchers to alert them when wind shear or microburst hazards initially impacted the Orlando airport. Additional demonstration of the Terminal Weather message service are planned for the summer of 1994 at Memphis, TN and Orlando, FL. Results of hte summer 1993 demonstration are being used to make improvements to the message content. A demonstration of a grpahical version of the Terminal Weather message is also planned.

Flight crews need tiimely information about terminal weather conditions when approaching or departing airports. This paper describes a new concept in providing this information from new ground-based terminal weather sensors currently being deployed via new and existing data link systems. Currently, pilots rely on ATIS (Automatic Terminal Information System) for airport weather conditions. However, the Surface Observation (SAO) contained in the ATIS message is nominally only updated once per hour. Special observations are issued more frequently, but are difficult to keep current manually in rapidly changing conditions. The Automated Surface Observing System (ASOS) and Automated Weather Observing Systems (AWOS) are beginning to supplant manual surface observations in many locations. These automated systems offer the advantage of providing continuous , automated surface observations. However, the surface observations issued by these units lack the remarks section provided by manual observers, including such information as the location and motion of storm activity in the airport area. The shortcomings of the current ATIS system were illustrated by an incident at Kansas City International Airport (MCI) in the evening of September 8, 1989. An aircraft approaching from the west received an ATIS message indicating 10 miles visibility at the airport. However, unknown to the crew, an intense storm was approaching the airport from the East. By the time the aircraft reached the airport (about 30 minutes after the initial ATIS message was received), the visibility had dropped to 1/2 nmi, but the flight crew was not notified. The aircraft subsequently struck power lines while on final approach and was forced to make an emergency landing at an alternate airport. This example provides a vivid example of current shortcomings in the generation and dissemination of terminal weather information to the flight deck. Besides improving safety, improved access to terminal weather information would provide economic benefits by allowing more efficient flight planning and utilization of air space.

This paper describes an experimental system for cockpit display of Terminal Doppler Weather Radar (TDWR) wind shear warnings. The TDWR is a ground-based system for detecting wind shear hazards that pose a threat to aviation, During the Summer of 1990, wind shear warnings generated by the Lincoln-operated TDWR testbed radar at Orlando, Florida were transmitted in real-time to a research aircraft performing microburst penetrations. This test marks a milestone as being the first time that TDWR wind shear warnings were successfully transmitted and displayed in an aircraft in real-time. This effort was supported by NASA Langley Research Center as part of a program to investigate techniques for integrating airborne and ground-based wind shear information for aircrew alerting. The three main goals for 1990 were 1) to conduct microburst penetrations with an instrumented aircraft, 2) to compare a hazard estimate called the F factor (Bowles, 1990) for airborne and TDWR data, and 3) demonstrate real-time data link and cockpit display of TDWR warnings. All three of these goals were successfully carried out. The research aircraft, a Cessna Citation II operated by the University of North Dakota (UND) Center for Aerospace Sciences conducted over 80 microburst penetrations in Orlando over a six week period with TDWR testbed radar surveillance. Initial post-processing analysis in comparing the aircraft and TDWR F factors has begun. The cockpit display system was operated during the latter part of the flight test period, and proved useful in aiding the Citation crew in locating microburst and gust front events. There were three main objectives in the development of the cockpit display system. First, the real-time display was intended to aid the Citation crew in locating microburst and gust front events. This capability was desired both to aid the crew in locating events to penetrate, and to improve safety by providing a better information about the location of the wind shear events. A second objective was to demonstrate the feasibility of transmitting TDWR wind shear warnings to aircraft in real-time. This demonstration is an important element in the eventual development of an integrated aircrew alerting procedure incorporating both airborne and ground-based wind shear information. This study marks the first successful demonstration of real-time transmission of TDWR wind-shear warnings to an aircraft in flight. A third objective was to demonstrate the desirability of transmitting TDWR wind shear warnings to aircraft in real-time. Currently, the TDWR provides these warnings to controllers as textual messages, which are then relayed to pilots via voice communications. The TDWR also includes graphical displays of wind shear and precipitation products but these are only provided currently to the Tower and TRACON supervisors. A potential use of Mod S Data Link (or other ground-to-air data link systems) is to provide TDWR wind shear warnings directly to pilots, Automatic delivery of TDWR wind shear warnings potentially result in decreased controller workload and improved pilot information. Mode S Data Link is currently planned to provide textual wind shear warnings only. However, studies by Wanke and Hansman (1990) show that pilots substantially prefer graphical presentation of wind shear warnings over textual presentation. The paper will first describe the organization of the system, including the process of generating the display messages in the TDWR testbed and data linking them to the aircraft. Second, the display format and operation of the cockpit display will be described. Next, an example of the operational use of the cockpit display will be presented, along with initial F factor results. Finally, the paper will conclude with a summary and plans for future work.

The Terminal Doppler Weather Radar (TDWR) is a ground-based system for providing automated warnings of aviation wind shear hazards. This paper describes a proposed new TDWR product for microburst prediction. The proposed Microburst Prediction (MBP) product provides the ability to predict microbursts prior to the onset of surface outflow. The MBP product uses the ability of the TDWR to scan aloft for precursor signatures which indicate that a microburst is about to occur. The proposed MBP product provides a complementary capability to the other TDWR wind shear detection and prediction algorithms. As shown in Figure 1, the Microburst and Gust Front algorithms provide safety benefits by detecting wind shear hazards. The Wind Shift Prediction product provides an economic benefit by predicting runway wind shifts up to 20 minutes in advance. The MBP product provides both safety and economic benefits by predicting microburst hazards about 5 minutes in advance. The development of the MBP product is intended to be evolutionary. The initial implementation of the product relies on TDWR radar data only. Later versions are expected to also employ thermodynamic information, as part of the Integrated Terminal Weather System (ITWS). However, the radar-only version discussed in this paper will provide a useful interim capability. The organization of the paper is as follows. Section 2 provides a discussion of the potential operational benefits of the MBP product in improving safety and reducing delay. Section 3 describes the current MBP product algorithm, and section 4 provides performance results for two environments: Kansas City, KS and Orlando, FL. Section 5 provides an example of the product operation in predicting a 50 knot microburst which had substantial impact on airport operations. Section 6 will provide a summary and discuss future work.

This paper describes a prototype microburst prediction product for the Terminal Doppler Weather Radar (TDWR). The prediction product was evaluated for microbursts observed during the spring and summer of 1989 at Kansas City. Results are presented demonstrating reliable prediction of high reflectivity microbursts of at least 15 m/s outflow intensity from single-Doppler radar data. The ability of the algorithm to predict microbursts approximately five minutes prior to the onset of surface outflow could be used to improve air traffic control (ATC) planning and to improve hazard warning time to pilots. In particular, this product could allow aircraft to avoid an impending microburst hazard, rather than penetrating it. The present TDWR microburst recognition algorithm uses features aloft such as reflectivity cores and convergence to recognize microburst precursors. The algorithm uses precursors to make a microburst declaration while the surface outflow is still weak, thereby improving the hazard warning time (Campbell, 1989). The microburst prediction product is an extension of the algorithm to predict microbursts from these precursor signatures. The prototype prediction product is tuned to predict the high reflectivity microburst typical of humid regions of the United States. The paper begins by reviewing conceptual models for microburst development and comparing them to the observed characteristics of Kansas City microbursts. The prototype prediction product is then described, and performance statistics are presented. Finally, failure mechanisms and future work are discussed.

This paper describes the use of features aloft in the Terminal Doppler Weather Radar (TWDR) microburst recognition algorithm. The paper is divided into three sections: algorithm description, scan strategy and recent results. The prototype algorithm recognizes features aloft associated with microbursts, such as descending reflectivity cores and convergence aloft. The algorithm uses these signatures to improve the detection performance and timeliness of microburst hazard warnings. For example, the algorithm can use features aloft to make a microburst declaration while the surface outflow is still weak, thereby increasing the hazard warning time. An important factor in microburst recognition algorithm performance is the scan strategy employed. The TDWR scan strategy is designed for timely detection of microburst surface outflows and features aloft. The rationale for the prototype TDWR scan strategy is presented using Denver's Stapleton airport as an example. Recent results are presented demonstrating the ability of the system to recognize features aloft for microburst events observed during the summer of 1988 at Denver, CO. It is shown that the ability to recognize features aloft improved the probability of detection and hazard warning time for these events.

The Terminal Doppler Weather Radar (TDWR) has an operational requirement to provide a one minute advance warning for aircraft encountering a hazardous wind shear. This paper describes the use of features aloft in the prototype TDWR microburst recognition algorithm to improve the timeliness of microburst hazard warnings. The use of features aloft allows the algorithm to make a microburst declaration while the surface outflow is still weak, thereby increasing the hazard warning time. In addition, current work indicates that these signatures can also be used to predict the onset of surface outflow for high-reflectivity events. An initial version of the microburst recognition algorithm using surface velocity data only was described by Merritt (1987). Initial work on the use of features aloft to increase the reliability and timeliness of microburst alarms was described in Campbell, 1988. This work was motivated by the desire to emulate the ability of human experts to use features aloft to enhance the timeliness of microburst warnings (McCarthy & Wilson, 1986). This research was further influences by the conceptual models for the evolution of low, medium and high reflectivity microburst events in the Denver area proposed by Roberts and Wilson (1986), and by studies of features aloft associated with microbursts in the Southeast (Isaminger, 1987). The current TDWR microburst recognition algorithm is described in Campbell and Merritt, 1988. The present paper presents results demonstrating the ability of the prototype algorithm to recognize features aloft for microburst events observed at Huntsville, AL and Denver, CO. It is shown that the ability to recognize features aloft improved the hazard warning time for these events. Initial results for microburst prediction are also presented.

This paper describes current work in assessing the microburst recognition performance of the Terminal Doppler Weather Radar (TDWR) operational testbed. The paper is divided into three main sections: microburst recognition algorithm, performance assessment methodology and results. The first section provides an overview of the prototype TDWR microburst recognition algorithm The algorithm uses radar data from both surface scans and scans aloft to identify microburst events. The surface scan is used to identify microburst outflows, and the scans aloft provide information concerning reflectivity and velocity structures associated with microbursts to improve recognition rate and timeliness. The second section of the paper describes the methodology for assessing the recognition performance of the system. The performance of the testbed system is addressed from two viewpoints: radar detectability and pattern recognition capability. The issue of radar detectability is examined by comparing radar and mesonet data to determine if any events observed by the mesonet fail to be observed by the radar. The issue of pattern recognition performance is assessed by comparing microburst recognition algorithm outputs with truth as determined by expert radar meteorologists. The final section of the paper provides performance results for data collected by the testbed radar at Huntsville, AL and Denver, CO.

Abrupt changes in the winds near the ground pose serious hazards to aircraft during approach or departure operations. Doppler weather radars can measure regions of winds and precipitation around airports, and automatically provide air traffic controllers and pilots with important warnings of hazardous weather events. Lincoln Laboratory, as one of several organizations under contract to the Federal Aviation Administration, has been instrumental in the design and development of radar systems and automated weather-hazard recognition techniques for this application. The Terminal Doppler Weather Radar (TDWR) system uses automatic computer algorithms to ident* hazardous weather signatures. TDWR detects and warns aviation users about low-altitude wind shear hazards caused by microbursts and gust fronts. It also provides advance warning of the arrival of wind shifts at the airport complex. Extensive weather radar observations, obtained from a Lincoln-built transportable testbed radar system operated at several sites, have validated the TDWR system. As a result, the Federal Aviation Administration has issued a procurement contract for the installation of 47 TDWR radar systems around the country.