Publications
Pilot evaluation of TCAS in the Long Ranger helicopter
June 3, 1986
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-136
Topic:
R&D area:
R&D group:
Summary
A specially modified version of the Traffic Alert and Collision Avoidance System (TCAS) was installed in a Bell Long Ranger helicopter in order to investigate the feasibility of TCAS operation in rotorcraft. This installation employed TCAS air-to-air surveillance to provide automated traffic advisories that were displayed in the cockpit on a color cathod ray tube display. As part of this study, 12 subject pilots evaluated the utility of the installation thorugh brief test flights in the vicinity of a major airport. Among the topics investigated were the rate of alarms, the computer logic for issuing advisories, the bearing accuracy, and the display symbology. Several recommendations for adapting TCAS to the rotorcraft environment resulted from the testing.
Summary
A specially modified version of the Traffic Alert and Collision Avoidance System (TCAS) was installed in a Bell Long Ranger helicopter in order to investigate the feasibility of TCAS operation in rotorcraft. This installation employed TCAS air-to-air surveillance to provide automated traffic advisories that were displayed in the cockpit on...
READ MORE
Robust HMM-based techniques for recognition of speech produced under stress and in noise
April 30, 1986
Conference Paper
Published in:
Proc. Speech Tech '86, 28-30 April 1986, pp. 241-249.
Topic:
R&D area:
Summary
Substantial improvements in speech recognition performance on speech produced under stress and in noise have been achieved through the development of techniques for enhancing the robustness of a base-line isolated-word Hidden Markov Model recognizer. The baseline HMM is a continuous-observation system using mel-frequency cepstra as the observation parameters. Enhancement techniques which were developed and tested include: placing a lower limit on the estimated variances of the observations; addition of temporal difference parameters; improved duration modelling; use of fixed diagonal covariance distance functions, with variances adjusted according to perceptual considerations; cepstral domain stress compensation; and multi-style training, where the system is trained on speech spoken with a variety of talking styles. With perceptually-motivated covariance and a combination of normal (single-frame) and differential cepstral observations, average error rates over five simulated-stress conditions were reduced from 20% (baseline) to 2.5% on a simulated-stress data base (105-word vocabulary, eight talkers, five conditions). With variance limiting, normal plus differential observations, and multi-style training, an error rate of 1.8% was achieved. Additional tests were conducted on a data base including nine talkers, eight talking styles, with speech produced under two levels of motor-workload stress. Substantial reductions in error rate were demonstrated for the noise and workload conditions, when multiple talking styles, rather than only normal speech, were used in training. In experiments conducted in simulated fighter cockpit noise, it was shown that error rates could be reduced significantly by training under multiple noise exposure conditions.
Summary
Substantial improvements in speech recognition performance on speech produced under stress and in noise have been achieved through the development of techniques for enhancing the robustness of a base-line isolated-word Hidden Markov Model recognizer. The baseline HMM is a continuous-observation system using mel-frequency cepstra as the observation parameters. Enhancement techniques...
READ MORE
The Cooperative Huntsville Meteorological Experiment (COHMEX)
April 1, 1986
Journal Article
Published in:
Bull. Am. Meteorol. Soc., Vol. 67, No. 4, April 1986, pp. 417-419.
Topic:
R&D area:
R&D group:
Summary
A unique meteorological field experiment (COHMEX) is scheduled to be conducted from March-July 1986 with a core period of operation in June and July. It is taking place in the region covering northern Alabama and the adjoining portion of central Tennessee. The experiment's uniqueness derives from the fact that it is actually composed of three distinct experiments sponsored by National Aeronautics and Space Administration (NASA), the National Science Foundation (NSF), and the Federal Aviation Administration (FAA), respectively, with extensive sharing of resources and data. A diagram of the experiment's domain with observational coverage is included in Fig. 1.
Summary
A unique meteorological field experiment (COHMEX) is scheduled to be conducted from March-July 1986 with a core period of operation in June and July. It is taking place in the region covering northern Alabama and the adjoining portion of central Tennessee. The experiment's uniqueness derives from the fact that it...
READ MORE
A new application of adaptive noise cancellation
February 1, 1986
Journal Article
Published in:
IEEE Trans. Acoust., Speech, Sig Process., Vol. ASSP-34, No. 1, February 1986, pp. 21-7.
Topic:
R&D area:
Summary
A new application of Widrow's adaptive noise cancellation (ANC) is presented in this paper. Specifically, the method is applied to the case where an acoustic barrier exists between the primary and reference microphones. By updating the coefficients of the noise estimation filter only during silence, it is shown that ANC can provide substantial noise reduction with little speech distortion even when the acoustic barrier provides only moderate attenuation of acoustic signals. The use of the modified ANC method is evaluated using an oxygen facemask worn by fighter aircraft pilots. Experiments demonstrate that if a noise field is created using a single source, 11 dB signal-to-noise ratio improvements can be achieved by attaching a reference microphone to the exterior of the facemask. The length of the ANC filter required for this particular environment is only 50 points.
Summary
A new application of Widrow's adaptive noise cancellation (ANC) is presented in this paper. Specifically, the method is applied to the case where an acoustic barrier exists between the primary and reference microphones. By updating the coefficients of the noise estimation filter only during silence, it is shown that ANC...
READ MORE
WX1 - an expert system for weather radar interpretation
January 1, 1986
Conference Paper
Published in:
Coupling Symbolic and Numerical Computing in Expert Systems, Elsevier Science Publ. B. V., 1986.
Topic:
R&D area:
R&D group:
Summary
This paper describes work performed by M.I.T. Lincoln Laboratory for the Federal Aviation Administration to investigate the use of expert system techniques for weather radar interpretation. The design of WX1, a prototype system for recognizing low-altitude wind shear hazards from Doppler weather radar data, is presented. The WX1 system consists of a rule-based expert system coupled to an object-oriented image processing package. Initial results for recognition of two types of low-altitude wind shear are provided.
Summary
This paper describes work performed by M.I.T. Lincoln Laboratory for the Federal Aviation Administration to investigate the use of expert system techniques for weather radar interpretation. The design of WX1, a prototype system for recognizing low-altitude wind shear hazards from Doppler weather radar data, is presented. The WX1 system consists...
READ MORE
Low-altitude wind shear characteristics in the Memphis, TN area based on mesonet and LLWAS data
November 1, 1985
Conference Paper
Published in:
Proc. 14th Conf. on Severe Local Storms, 29 October -1 November 1985, pp. 322-327.
Topic:
R&D area:
R&D group:
Summary
As part of the 1984-85 FLOWS (FAA-Lincoln Laboratory Operational Weather Studies) Project, mesonet and Doppler radar data are being collected on rain and thunderstorms in the Memphis, TN area. One of the key goals of the FLOWS Project is to characterize and evaluate the various form of potentially aviation-hazardous low-altitude wind shear in parts of the country where this type of high spatial and temporal resolution meteorological data have not previously been collected. The 1982 JAWS (Joint Airport Weather Studies) Project revealed that the "microburst", a small scale, intense downdraft which hits the surface and causes a strong divergent outflow of wind, has been the source of much of the hazardous wind shear in the Denver area. The 1978 NIMROD (Northern Illinois Meteorological Research on Downbursts) Project revealed that microbursts occur there on convectively unstable days along with gust fronts and "macrobursts" (scale 4-40 km). Other experiments have largely failed to detect microbursts because their observational networks have not been dense enough to resolve this small scale. A compilation of pioneering studies of microburst-related aircraft accidents around the world by Fujita (1985) illustrates clearly the inherent danger of the microburst wind pattern to jet aircraft, wherever it occurs. In developing ways to best meet the goal of providing warning and protection from low-altitude wind shear in the airport terminal areas, the FAA will need to characterize the problem in different parts of the country. It may be misleading, for example, to use the results on wind shear in the Denver area, or any other single geographical locale, to typify the requirements for microburst warnings at all airports in the country. An important region in terms of its frequency of commercial air traffic control and of thunderstorms, in which high resolution measurements capable of revealing microburts have never before been collected, is the southeastern part of the United States (excluding Florida). During 1984 Lincoln Laboratory continuously collected surface meteorological data from 25-30 mesonet stations and FAA Low Level Wind Shear Alert System (LLWAS) data from the 6 anemometers at the Memphis International Airport from May through November (212 days total). Presented here are preliminary results on the characteristics of wind shear events in the Memphis area. Microburst statistics for Memphis are contrasted with those computed by Fujita and Wakimoto (1983) for the Denver area during JAWS and the Chicago area during NUMROD. A detailed analysis of a microburst that occurred on August 11, 1984 is also presented.
Summary
As part of the 1984-85 FLOWS (FAA-Lincoln Laboratory Operational Weather Studies) Project, mesonet and Doppler radar data are being collected on rain and thunderstorms in the Memphis, TN area. One of the key goals of the FLOWS Project is to characterize and evaluate the various form of potentially aviation-hazardous low-altitude...
READ MORE
Effect of interference on the performance of a minimum TCAS II
September 5, 1985
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-132
Topic:
R&D area:
R&D group:
Summary
Minimum TCAS II equipment is required to operate reliably in all aircraft densities up to the 0.3 transponder-equipped aircraft per square nautical mile anticipated in the Los Angeles Basin in the year 2000. Prototype TCAS equipment has been developed and shown to be capable of providing reliable surveillance in today's highest densities, which reach an average of about 0.1 aircraft per square nmi. Since there are no existing environments that reach the density of asynchronous interference anticipated for the Los Angeles Basin in the year 2000, it is necessary to generate simulated interference to determine the performance of the TCAS II design in that environment. A series of bench tests were conducted at Lincoln Laboratory for this purpose. Special sources were used to generate asynchronous ATCRBS and Mode S reply signals (Fruit) and TCAN/DME squitter and interrogation signals. Synchronous ATCRBS and Mode S reply sequences were also generated to simulate airborne encounters. The performance was evaluated by observing hoe the interference signals either degraded the ability of a TCAS II unit to receive, process, and track the desired synchronous reply sequences, or caused the TCAS II unit to generate false tracks.
Summary
Minimum TCAS II equipment is required to operate reliably in all aircraft densities up to the 0.3 transponder-equipped aircraft per square nautical mile anticipated in the Los Angeles Basin in the year 2000. Prototype TCAS equipment has been developed and shown to be capable of providing reliable surveillance in today's...
READ MORE
Evaluation of the ASR-9 weather reflectivity product
June 21, 1985
Conference Paper
Published in:
Proc. Second Int. Conf. on the Aviation Weather System, 19-21 June 1985, pp. 196-202.
Topic:
R&D area:
R&D group:
Summary
The ASR-9 is a modern airport surveillance radar (ASR) under procurement by the United States Federal Aviation Agency. The radar operates at S-band, providing range-azimuth position information on aircraft targets within a 111-km radius. A fully-coherent klystron amplifier, large dynamic range and digital signal processing enable high integrity target processing and display under condition of ground clutter, weather, angel clutter, RF interference and ground vehicular traffic. To aid controllers in the identification of hazardous weather conditions, the processor will also generate two- or six-level weather reflectivity contours for display at the terminal radar control center and (potentially) remote sites. In this paper, we present an overview of the ASR-9 and its weather processor, emphasizing those features that raise issues with respect to the utility of the weather reflectivity product in an air-traffic control environment. We then describe a simulation procedure that utilizes pencil-beam Doppler weather radar data and ground clutter measurements to preview the ASR-9 product and assess the effects of the radar's configuration on the weather intensity reports. Examples of the simulated weather reports are used to illustrate" (a) partial beamfilling die to the fan-shaped surveillance antenna pattern; (b) attenuation of low velocity weather by the clutter filters' (c) the effects of the spatial filters used in weather processing.
Summary
The ASR-9 is a modern airport surveillance radar (ASR) under procurement by the United States Federal Aviation Agency. The radar operates at S-band, providing range-azimuth position information on aircraft targets within a 111-km radius. A fully-coherent klystron amplifier, large dynamic range and digital signal processing enable high integrity target processing...
READ MORE
The FAA/MIT Lincoln Laboratory Doppler Weather Radar Program
June 21, 1985
Conference Paper
Published in:
Proc. Second Int. Conf. on the Aviation Weather Systems, 19-21 June 1985, pp. 76-79.
Topic:
R&D area:
R&D group:
Summary
Adverse weather is the leading cause of aircraft accidents in the United States. In order to improve hazardous weather detection and warning capability for aviation, the Federal Aviation Administration (FAA) is pursuing a two part Doppler weather radar program. The first part consists of a joint program with the National Weather Service (NWS) and United States Air Force Weather Service (AWS) is to develop and install the Next Generation Weather Radar (NEXRAD). The NEXRAD Systems will meet the FAA enroutw hazardous weather detection requirements and will replace the existing obsolete NWS and AWS weather radars. The second part of the FAA program is the development of a Terminal Doppler Weather Radar (TDWR), which could be procured and installed at major airports to detect weather hazards to terminal aviation operations. The TDWR couls be either a derivative of NEXRAD or a separate radar system. In order to support both of these efforts, the FAA contracted with M.I.T. Lincoln Laboratory to develop and fabricate a NEXRAD-like transportable weather radar support facility. This facility along with a second Doppler radar and a network of meteorological measurement stations are installed near Memphis, Tennessee. These facilities will be used to validate and refine scanning strategies, data processing techniques, and weather detection algorithms. The utility of weather radar products for air traffic control (especially for pilots and controllers) will be evaluated.
Summary
Adverse weather is the leading cause of aircraft accidents in the United States. In order to improve hazardous weather detection and warning capability for aviation, the Federal Aviation Administration (FAA) is pursuing a two part Doppler weather radar program. The first part consists of a joint program with the National...
READ MORE
Collision avoidance for Naval training aircraft
March 8, 1985
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-125
Topic:
R&D area:
R&D group:
Summary
Lincoln Laboratory was tasked by the FAA to assist the Naval Air Training Command in evaluating the feasibility of using the FAA's TCAS I concept as the document summarizes the results of a brief study and flight test activity conducted to that end. It begins with a review of Lincoln Laboratory's understanding of the nature of the mid-air collision problem at the Naval Air Training Center. This is followed by a brief analysis of a set of documented collisions and near-miss encounters involving aircraft of Navy Training Air Wing 5 at Whiting Naval Air Station in Florida in 1982 and 1983. Experience gained from FAA and Lincoln Laboratory flight tests of similar encounters is reviewed and applied to the Navy encounter data base. This is followed by a review of the results obtained when a Lincoln Laboratory aircraft equipped with a TCAS Experimental Unit (TEU) was flown to Whiting Field to evaluate the ability of TCAS I equipment to perform reliable surveillance in the Naval training environment. Flight test results show that the environment is quite unlike typical civil environments, but that the TCAS surveillance design would be capable of providing a significant degree of protection to Naval trainers.
Summary
Lincoln Laboratory was tasked by the FAA to assist the Naval Air Training Command in evaluating the feasibility of using the FAA's TCAS I concept as the document summarizes the results of a brief study and flight test activity conducted to that end. It begins with a review of Lincoln...
READ MORE