Publications

Current U.S. weather and aircraft surveillance radar networks vary in age from 10 to more than 40 years. Ongoing sustainment and upgrade programs can keep these operating in the near to mid-term, but the responsible agencies National Weather Service (NWS), Federal Aviation Administration (FAA), and the Departments of Defense (DoD) and Homeland Security (DHS) recognize that large-scale replacement activities must begin during the next decade. The National Weather Radar Testbed (NWRT) in Norman, Oklahoma, is a multiagency project demonstrating operational weather measurements capability enhancements that could be realized using electronically steered phased-array radars as a replacement for the current Weather Surveillance Radar-1988 Doppler (WSR-88D). FAA support for the NWRT and related efforts address air traffic control (ATC) and homeland defense surveillance missions that could be simultaneously accomplished using the agile-beam capability of a phased array weather radar network. In this paper, we discuss technology issues, operational considerations, and cost trades associated with the concept of replacing current national surveillance radars with a single network of multimission phased array radars (MPAR). We begin by describing the current U.S. national weather and aircraft surveillance radar networks and their technical parameters. The airspace coverage and surveillance capabilities of these existing radars provide a starting point for defining requirements for the next-generation airspace surveillance system. We next describe a conceptual MPAR high-level system design and our initial development and testing of critical subsystems. This work, in turn, has provided a solid basis for estimating MPAR costs for comparison with existing, mechanically scanned operational surveillance radars. To assess the numbers of MPARs that would need to be procured, we present a conceptual MPAR network configuration that duplicates airspace coverage provided by current operational radars. Finally, we discuss how the improved surveillance capabilities of MPAR could be utilized to more effectively meet the weather and aircraft surveillance needs of U.S. civil and military agencies.

Operational testing of the Runway Status Lights (RWSL) system at the Dallas-Fort Worth (DFW) airport has detected a number of cases where faults in the ASDE-X/DFW surveillance data have led to erroneous operation of the status lights. Among the surveillance problems noted during testing at DFW were: (a) false tracks, (b) track positional jumps to false locations, (c) Mode S track splits, (d) ATCRBS track splits, (e) invalid Mode C altitudes, (f) invalid track velocities, and (g) spurious Mode 3/a 06078 code tracks. The RWSL surveillance improvement algorithms package in this document is placed between the ASDE-X/DFW surveillance data source and the RESL safety logic. The surveillance improvement algorithms perform a variety of reasonableness and consistency checks on the input data and set validity flags and report status values for each input report which are then passed on to the RWSL safety logic. These flags and status values allow the RWSL to ignore erroneous reports and to avoid using questionable report components in the subsequent RWSL logic. This document illustrates the performance of the RWSL surveillance improvement algorithms package with examples from DFW analysis. It is shown that the RWSL surveillance improvement algorithms package substantially reduces the impact of the known ASDE-X/DFW surveillance anomalies on the performance of the RWSL safety logic. The RWSL surveillance improvement algorithms package may also host future algorithms necessary to mitigate further problems that might be detected in the surveillance data.

Current U.S. weather and aircraft surveillance radar networks vary in age from 10 to more than 40 years. Ongoing sustainment and upgrade programs can keep these operating in the near to mid term, but the responsible agencies (FAA, NWS and DoD/DHS) recognize that large-scale replacement activities must begin during the next decade. In addition, these agencies are re-evaluating their operational requirements for radar surveillance. FAA has announced that next generation air traffic control (ATC) will be based on Automatic Dependent Surveillance - Broadcast (ADS-B) (Scardina, 2002) rather than current primary and secondary radars. ADS-B, however, requires verification and back-up services which could be provided by retaining or replacing primary ATC radars.

The Federal Aviation Administration is modernizing the Air Traffic Control system to improve flight efficiency, to increase capacity, to reduce flight delays, and to control operating costs as the demand for air travel continues to grow. Promising new surveillance technologies such as Automatic Dependent Surveillance Broadcast, (ADS-B), multisensor track fusion, and multifunction phased array radar offer the potential for increased efficiency in the National Airspace System (NAS). However, the introduction of these surveillance systems into the NAS is hampered because the FAA Order containing the surveillance requirements to support separation services assumes surveillance is provided by radar technology. The requirements are stated in terms that don't apply to new surveillance technologies. In order to take advantage of new surveillance technologies, the surveillance requirements to support separation services in the NAS must be articulated from a performance perspective that is not technology specific. This will allow the FAA to make the investment and performance trade-off analysis necessary to support the introduction of new surveillance technologies. [not complete]

This paper is a concept study for possible future utilization of active electronically scanned radars to provide weather and aircraft surveillance functions in U.S. airspace. If critical technology costs decrease sufficiently, multi-function phased array radars might prove to be a cost effective alternative to current surveillance radars, since the number of required radars would be reduced, and maintenance and logistics infrastructure would be consolidated. A radar configuration that provides terminal-area and long-range aircraft surveillance and weather measurement capability is described and a radar network design that replicates or exceeds current airspace coverage is presented. Key technology issues are examined, including transmit-receive elements, overlapped sub-arrays, the digital beamformer, and weather and aircraft post-processing algorithms. We conclude by discussing implications relative to future national weather and non-cooperative aircraft target surveillance needs. The U.S. Government currently operates four separate ground based surveillance radar networks supporting public and aviation-specific weather warnings and advisories, and primary or "skin paint" aircraft surveillance. The separate networks are: (i) The 10-cm wavelength NEXRAD or WSR88-D (Serafin and Wilson, 2000) national-scale weather radar network. This is managed jointly by the National Weather Service (NWS), the Federal Aviation Administration (FAA), and the Department of Defense (DoD). (ii) The 5-cm wavelength Terminal Doppler Weather Radars (TDWR) (Evans and Turnbull, 1989) deployed at large airports to detect low-altitude wind-shear phenomena. (iii) The 10-cm wavelength Airport Surveillance Radars (ASR-9 and ASR-11) (Taylor and Brunins, 1985) providing terminal area primary aircraft surveillance and vertically averaged precipitation reflectivity measurements. (iv) The 30-cm wavelength Air Route Surveillance Radars (ARSR-1, 2, 3 and 4) (Weber, 2005) that provide national-scale primary aircraft surveillance. The latter three networks are managed primarily by the FAA, although the DoD operates a limited number of ASRs and has partial responsibility for maintenance of the ARSR network. In total there are 513 of these radars in the contiguous United States (CONUS), Alaska, and Hawaii. The agencies that maintain these radars conduct various "life extension" activities that are projected to extend their operational life to approximately 2020. At this time, there are no defined programs to acquire replacement radars. The NWS and FAA have recently begun exploratory research on the capabilities and technology issues related to the use of multi-function phased array radar (MPAR) as a possible replacement approach. A key concept is that the MPAR network could provide both weather and primary aircraft surveillance, thereby reducing the total number of ground-based radars. In addition, MPAR surveillance capabilities would likely exceed those of current operational radars, for example, by providing more frequent weather volume scans and by providing vertical resolution and height estimates for primary aircraft targets. Table 1 summarizes the capabilities of current U.S. surveillance radars. These are approximations and do not fully capture variations in capability as a function, for example, of range or operating mode. A key observation is that significant variation in update rates between the aircraft and weather surveillance functions are currently achieved by using fundamentally different antenna patterns--low-gain vertical "fan beams" for aircraft surveillance that are scanned in azimuth only, versus high-gain weather radar "pencil beams" that are scanned volumetrically at much lower update rates. Note also that, if expressed in consistent units, the power-aperture products of the weather radars significantly exceed those of the ASRs and ARSRs. In the next section, we present a concept design for MPAR and demonstrate that it can simultaneously provide the measurement capabilities summarized in Table 1. In Section 3 we present an MPAR network concept that duplicates the airspace coverage provided by the current multiple radar networks. Section 4 discusses technology issues and associated cost considerations. We conclude in Section 5 by discussing implications relative to future national weather and non-cooperative aircraft target surveillance needs.

Surveillance information forms the basis for providing traffic separation services by Air Traffic Control. The consequences of failures in the integrity and availability of surveillance data have been highlighted in near misses and more tragically, by midair collisions. Recognizing the importance and criticality of surveillance information, the U.S. Federal Aviation Administration (FAA) in common with most other Civil Aviation Authorities (CAAs) worldwide has implemented a surveillance architecture that emphasizes the independence of surveillance sources and the availability of crosschecks on all flight critical data. Automatic Dependent Surveillance Broadcast (ADS-B) changes this approach by combining the navigation and surveillance information into a single system element. ADS-B is a system within which individual aircraft distribute position estimates from onboard navigation equipment via a common communications channel. Any ADS-B receiver may then assemble a complete surveillance picture of nearby aircraft by listening to the common channel and combining the received surveillance reports with an onboard estimate of ownership position. This approach makes use of the increasing sophistication and affordability of navigation equipment (e.g. GPS-based avionics) to improve the accuracy and update rate of surveillance information. However, collapsing the surveillance and navigation systems into a common element increases the vulnerability of the system to erroneous information, both due to intentional and unintentional causes.

Lincoln Laboratory was tasked by the FAA to measure the performance of a representative sample of current commercial off-the-shelf (COTS) fusion trackers. This effort included cataloging the companies that have available ATC fusion trackers, acquiring executable tracker images from as many as possible of these trackers, running the commercial tracker code on the test sets, and evaluating the performance achieved. This report presents an overall review of the state-of-the-art of fusion tracker as applied to the FAA surveillance problem. Average statistics of performance, as well as performance in special situations, are included. In each case, the performance of fusion is compared against the performance of single sensor and mosaic tracking. Thus, the advantages and disadvantages of fusion will be evident. The statistics may also permit the generation of a fusion tracker specification should the FAA decide to procure one as part of a future automation system.

This report documents the analysis of and subsequent improvements to the performance of the ASR-8/TDX-2000 digitizer equipment combination. Working at the FAA's Palm Springs, CA and Williams (Mesa, AZ) ASR-8 facilities, data was methodically collected and analyzed to isolate the causes of reported correlated radar-only tracks that were being dropped or were never initiated. These problems were subsequently fixed via hard and soft parameter changes in the TDX-2000. A significant study was also undertaken in conjunction with the Sensis Corporation to improve the TDX-2000's capability to reject returns from multiple-time-around detections. The details of that algorithm modification and the results of follow-on testing and analysis are described. Final conclusions on the status of the project are also included.

In response to concerns over the number of runway incursions and runway conflicts at U.S. airports, the FAA is sponsoring research and development of safety systems for the airport surface. Two types of safety systems are being actively pursued, a tower cab alerting system and a runway status light system. The tower cab alerting system, called the Airport Movement Area Safety System (AMASS) is currently undergoing initial operational evaluation at several major airports. It provides aural and visual alerts to the tower cab to warn the controllers of potential traffic conflicts. The runway status light system is currently in the development phase, with initial operational suitability demonstrations planned at Dallas/Fort Worth International Airport during FY2003. Intended to offer protection in time-critical conflict scenarios where there is not enough time to warn the aircrews indirectly via the tower cab, the runway status light system provides visual indication of runway status directly to the cockpit; runway entrance lights warn pilots not to enter a runway on which there is approaching high-speed traffic; takeoff-hold lights warn pilots not to start takeoff if a conflict could occur. Both systems operate automatically, requiring no controller inputs. Activation commands for alerts and lights are generated by the systems' safety logic, which in turn receives airport traffic inputs from a surface surveillance and target tracking system. Accurate traffic representation is essential to meet system requirements, which include high conflict detection rate, prompt and accurate alerting and light activation, low nuisance and false alarm rates, and negligible interference with normal operations. This report analyzes the effect of the two fundamental surveillance performance parameters-position accuracy and surveillance update rate - on the performance of three different surface safety systems. The first two are the above-mentioned tower cab alerting and runway status light systems. The third system is a hypothetical cockpit alerting system that delivers alerts directly to the cockpit rather than to the tower cab. The surveillance accuracy and update rate requirements of these three systems are analyzed for three of the most common runway conflict scenarios, using realistic parameter values for aircraft motion. The scenarios are 1) a runway incursion by a taxiing aircraft in front of a departure or arrival, 2) a departure on an occupied runway, and 3) an arrival on an occupied runway. Runway status lights are especially effective at preventing incursions and accidents between takeoff or arrival aircraft and intersection taxi aircraft. Tower cab alerts are effective at alerting controllers to aircraft crossing or on a runway during an arrival. Runway status information provided directly to the cockpit will be required for the case where a previous arrival or a taxi aircraft fails to exit the runway as anticipated shortly before the arrival crossed the threshold. (not complete)

Taxi delay is the largest of all aviation movement delays. However, taxi-out delays have not received attention equal to that focused on airborne delays because taxi-out delays often result from downstream problems. Also, until recently, there was no practical means of tracking surface movements. New surface surveillance technology will revolutionize surface management by providing data for planning, timing, and monitoring surface operations. This paper proposes a simple aid to help manage departure taxi queues and help exploit existing departure capacity, while avoiding the delays that result from saturated queues and unbalanced runways. The proposed decision aide will use archived surveillance data to quantify queuing behavior and model departure capacity, and it will use real-time surveillance to track capacity changes and monitor the state of the taxi queues.