GPS-Squitter is a technology for surveillance of aircraft via broadcast of their GPS-determined positions to all listeners, using the Mode S data link. It can be used to provide traffic displays, on the ground for controllers and in the cockpit for pilots, and will enhance TCAS performance. It is compatible with the existing ground-based beacon interrogator radar system and is an evolutionary way to more from ground-based-radar surveillance to satellite-based surveillance. GPS-Squitter takes advantage of the substantial investment made by the U.S. in the powerful GPS position-determining system and has the potential to free the Federal Aviation Administration from having to continue maintaining a precise position-determining capability in ground-based radar. This would permit phasing out the ground-based secondary surveillance radar system over a period of 10 to 20 years and replacing it with much simpler ground stations, resulting in cost savings of hundreds of millions of dollars.
The Laser Centerline Localizer (LCL) uses a series of low power, but highly visible laser beams to illuminate approach corridors to provide a pilot on final approach to landing with precise centerline guidance. The LCL was initially developed for aircraft carrier flight operations, but it has dual-use in the civilian sector. The first operational deployment of the LCL was on the U.S.S. Constellation, CV-64, in March 1994. The installation of the LCL on the U.S.S. Constellation is discussed along with the results and conclusions from the flight operations to date. Quantitative analysis from 110 naval aviators who have flown the LCL at sea is presented. Pilot acceptance has been overwhelmingly positive. Civil applications of the LCL are described. The LCL provides definitive traffic separation for parallel runways, which are a common feature at larger airports where the incursion of aircraft into airspace reserved for the other runway is an ongoing concern. The LCL is extremely beneficial and safety enhancing at airports that have no good visual access at night due to terrain. Helicopter landing pads, particularly on oil platforms, greatly benefit from the LCL. Because of its small size, portability, and low power consumption, the LCL is ideal for civil disaster relief operations.
Technologies for communications, navigation and surveillance are emerging at an astonishing rate. Keeping up with the changes in technology is a full time effort; efficiently applying technology to satisfy the needs of aviation users is another effort entirely. This paper describes a methodology currently seeing limited use by the Federal Aviation Administration to identify current and future weather and surveillance system needs and to extend the use of this needs information to a process of technical requirements definition. The methodology can be used to: identify user needs in a manner that facilitates the selection of technology, (2) translate user needs into operational and technical requirements, and (3) `match' system technological capabilities to the identified needs and requirements of aviation users. This methodology permits system engineers to optimize benefits attained from the infusion of new capabilities into today's National Airspace System by capitalizing on technologies appropriate to user decision making.
Simulated signatures of aircraft wakes as detected by a scanning coherent short wavelength lidar are presented and characterized for a number of candidate surveillance scenarios. Ground based and airborne scanning configurations that emulate candidate operational detection and warning systems are compared for spatial coverage and detection capability as a function of system design parameters and atmospheric conditions. Examples of trailing geometries characteristic of onboard wake detection and warning systems are presented. The dependence of predicted detection capability on hydrodynamic parameters, such as vortex circulation, axial motion in the wake vortices, and ambient turbulence is discussed. Simulated wake signatures are compared to observations for wakes observed at Denver's Stapleton International Airport in 1993.
Atmospheric turbulence environments can adversely affect the operation of both commercial and military supersonic aircraft. Future aircraft designs, such as the High Speed Civil Transport will aim to alleviate the effects of supersonic engine inlet unstart. Fluctuations in air temperature, longitudinal and transverse velocity all can trigger inlet unstarts. With fore- knowledge of the turbulence, a feed-forward control system can be used to re-configure the propulsion systems to avoid unstarts. The same technology can be used to counteract gust effects to improve ride quality and reduce gust loads. A coherent lidar sensor is being developed to demonstrate that the atmospheric turbulence can be measured with sufficient reliability, fidelity, and pre-encounter time for these feed-forward control solutions. The NASA Airborne Coherent Lidar for Advanced In-flight Measurements (ACLAIM) program will develop and flight test a sensor on NASA research aircraft, including the SR-71, and investigate the atmospheric environment to establish the feasibility of a lidar sensor. The paper will present an overview of the ACLAIM program including: the scope and content of the program, lidar measurement challenges, atmospheric environment, technology choices, and anticipated problem areas.
Coherent lidar systems based on eyesafe solid-state laser technology are rapidly emerging in ruggedized packages. The airport terminal area presents several measurement scenarios appropriate for application of pulsed coherent lidar sensors. This paper briefly reviews the status of coherent lidar technology and presents results produced with a mobile flashlamp- pumped 2.09 micrometers coherent lidar sensor for windshear detection and measurement, wind turbulence estimation, and wake vortex detection and tracking.
A diode-pumped 2 micrometers LIDAR was installed aboard the NASA Ames DC-8 Flying Laboratory. The LIDAR was used to measure true airspeed through a variety of flight operating conditions. Data was successfully obtained during all four six-hour flights.
NASA and the FAA have expressed interest in laser radar's capabilities to detect wind profiles at altitude. A number of programs have been addressing the technical feasibility and utility of laser radar atmospheric backscatter data to determine wind profiles and wind hazards for aircraft guidance and navigation. In addition, the U.S. Air Force is investigating the use of airborne lidar to achieve precision air drop capability, and to increase the accuracy of the AC- 130 gunship and the B-52 bomber by measuring the wind field from the aircraft to the ground. There are emerging capabilities of airborne laser radar to measure wind velocities and detect turbulence and other atmospheric disturbances out in front of an aircraft in real time. The measurement of these parameters can significantly increase fuel efficiency, flight safety, airframe lifetime, and terminal area capacity for new and existing aircraft. This is achieved through wind velocity detection, turbulence avoidance, active control utilization to alleviate gust loading, and detection of wingtip wake vortices produced by landing aircraft. This paper presents the first flight test results of an all solid-state 2-micrometers laser radar system measuring the wind field profile 1 to 2 km in front of an aircraft in real time. We find 0.7-m/s wind measurement accuracy for the system which is configured in a rugged, light weight, high- performance ARINC package.
Boeing Defense & Space Group has developed and validated a LIDAR system for optically measuring air speed over a wide variety of altitudes and atmospheric conditions. Our technique uses a focused beam to backscatter the doppler shifted light off of a single atmospheric aerosol particle, thereby enhancing the return signal by over four orders of magnitude compared with non-focused LIDARS. We successfully demonstrated this approach on flight tests aboard a NASA Ames DC-8 where we measured airspeed over a broad range of test parameters (0 to 40 kft altitude, 1 to 500 knots airspeed in clear air and clouds). This paper summarizes the results of these flight tests.
This paper discusses a systems engineering approach to design and implementation of Air Traffic Control Systems (ATCS). Preservation of situational awareness by optimum use of available sensors is used as a unifying paradigm for airspace structural design which yields significant increases in reliability of operation as measured by the potential to detect collisions and effect avoidance. Strategic and tactical data required for continuous situational awareness is dependent on efficient and timely capture of sensor information. Analytical relationships between airspace structure and sensor search and acquisition functions were mathematically related. The reliability of ATCS airspace structures as mission critical components and probability of failure of these functions are derived. Modelling is used to show strong interdependencies between visual acquisition, cruising rule and tactical communications. The limitations of various airspace structures in use are identified. System reliability is baselined against well-known acceptance standards. Improvements of five orders of magnitude in performance and reliability are demonstrated with flow on effects to the reliability of overall ATCS design. The sensor paradigm is used to postulate an extension to current separation criteria and facilitate identification of fundamental failure modes for ATCS design. New flow model criteria enabling critical airspace structures, performance and geographic areas to be identified by simulation or real time performance monitoring are identified thus enabling quantitative measures required to baseline and improve system performance. The paper concludes by showing how modelling/real time monitoring can be used to predict system trends and capacity problems well in advance of actual system failure.
The integration of modern imaging sensors (EVS sensors) makes it possible to solve the problem of a fully bordautonomous navigation and control of airborne vehicles by means of analyzing images only. In runway referenced applications, where the flight trajectory of an aircraft has to be measured, independence from ground-based sensors can be regarded as a great advantage. The calibration of radio navigation aids, such as instrument landing systems (ILS) or differential satellite navigation systems, needs high precision and stable reference measurement methods. The photogrammetric evaluation of the center of projection of a camera which is fixed to the vehicle, offers one possibility for such a reference system, that is recently developed at DLR-Braunschweig. This system automatically analyzes and interprets on-board images. By different simulations and experiments it is shown, that such a system can meet the strong requirements for runway-reference measurements of flight path trajectories, especially for the calibration of ILS.
Command and control within the ATC environment remains primarily voice-based. Hence, automatic real time, speaker independent, continuous speech recognition (CSR) has many obvious applications and implied benefits to the ATC community: automated target tagging, aircraft compliance monitoring, controller training, automatic alarm disabling, display management, and many others. However, while current state-of-the-art CSR systems provide upwards of 98% word accuracy in laboratory environments, recent low-intrusion experiments in the ATCT environments demonstrated less than 70% word accuracy in spite of significant investments in recognizer tuning. Acoustic channel irregularities and controller/pilot grammar verities impact current CSR algorithms at their weakest points. It will be shown herein, however, that real time context- and environment-sensitive gisting can provide key command phrase recognition rates of greater than 95% using the same low-intrusion approach. The combination of real time inexact syntactic pattern recognition techniques and a tight integration of CSR, gisting, and ATC database accessor system components is the key to these high phase recognition rates. A system concept for real time gisting in the ATC context is presented herein. After establishing an application context, discussion presents a minimal CSR technology context then focuses on the gisting mechanism, desirable interfaces into the ATCT database environment, and data and control flow within the prototype system. Results of recent tests for a subset of the functionality are presented together with suggestions for further research.
The APALSTM system is a precision approach and landing system designed to enable low visibility landings at many more airports than is now possible. It is an autonomous navigation system which uses standard avionics equipment to determine the aircraft position and altitude with respect to unique features over which the aircraft flies. The primary measurement is made with the aircraft's weather radar and provides the range and range rate information necessary to update the precision navigation system. The system makes use of stored terrain map data as references for map matching with Synthetic Aperture Radar maps.
For several decades, airlines have relied on autopilots to guide and land aircraft in very low visibility conditions. In the 1990s, new technology such as the satellite-based, U.S. Global Positioning System and imaging systems based on infrared and millimeter wave radar, provide an opportunity to dramatically change the low-visibility landing paradigm. While the technology may be available, however, the challenge is to apply it in a way that is workable operationally and is sensitive to current airline economic reality.