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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Active control of fan noise from a turbofan engine

A three channel active control system is applied to an operational turbofan engine in order to reduce tonal noise produced by both the fan and high pressure compressor. The control approach is the feedforward filtered-x least-mean-square algorithm implemented on a digital signal processing board. Reference transducers mounted on the engine case provides blade passing and harmonics frequency information to the controller. Error information is provided by large area microphones placed in the acoustic far field. In order to minimize the error signal, the controller actuates loudspeakers mounted on the inlet to produce destructive interference. The sound pressure level of the fundamental tone of the fan was reduced using the three channel controller by up to 16 dB over a 60 deg angle about the engine axis. A single channel controller could produce reduction over a 30 deg angle. The experimental results show the control to be robust. Simultaneous control of two tones is done with parallel controllers. The fundamental and the first harmonic tones of the fan were controlled simultaneously with reductions of 12 dBA and 5 dBA, respectively, measured on the engine axis. Simultaneous control was also demonstrated for the fan fundamental and the high pressure compressor fundamental tones.

Thomas, Russell H.↗
NASA NTRS1991

Report of the sensor readout electronics panel

The findings of the Sensor Readout Electronics Panel are summarized in regard to technology assessment and recommended development plans. In addition to two specific readout issues, cryogenic readouts and sub-electron noise, the panel considered three advanced technology areas that impact the ability to achieve large format sensor arrays. These are mega-pixel focal plane packaging issues, focal plane to data processing module interfaces, and event driven readout architectures. Development in each of these five areas was judged to have significant impact in enabling the sensor performance desired for the Astrotech 21 mission set. Other readout issues, such as focal plane signal processing or other high volume data acquisition applications important for Eos-type mapping, were determined not to be relevant for astrophysics science goals.

Fossum, Eric R.↗
NASA NTRS1999

Root gravitropism: a complex response to a simple stimulus?

Roots avoid depleting their immediate environment of essential nutrients by continuous growth. Root growth is directed by environmental cues, including gravity. Gravity sensing occurs mainly in the columella cells of the root cap. Upon reorientation within the gravity field, the root-cap amyloplasts sediment, generating a physiological signal that promotes the development of a curvature at the root elongation zones. Recent molecular genetic studies in Arabidopsis have allowed the identification of genes that play important roles in root gravitropism. Among them, the ARG1 gene encodes a DnaJ-like protein involved in gravity signal transduction, whereas the AUX1 and AGR1 genes encode proteins involved in polar auxin transport. These studies have important implications for understanding the intra- and inter-cellular signaling processes that underlie root gravitropism.

Review, Tutorial↗
NASA NTRS1974

Photolysis of spacecraft contaminants

A molecular beam facility, which was designed to measure photochemical cross-sections, has been constructed at the Athens College science facility. The integration of this vacuum system into an operational photochemical instrument was performed with signal processing consisting of both dc and ac techniques. Of the experiments performed to date on the vacuum ultraviolet photolysis of water vapor, it is apparent that a larger pumping capacity (preferably with differential pumping) is required to improve upon the background signal. Both phase-sensitive detection and ion-counting techniques are recommended for future studies.

Workman, G. L.↗
NASA NTRS1976

Signal design study for shuttle/TDRSS Ku-band uplink

The adequacy of the signal design approach chosen for the TDRSS/orbiter uplink was evaluated. Critical functions and/or components associated with the baseline design were identified, and design alternatives were developed for those areas considered high risk. A detailed set of RF and signal processing performance specifications for the orbiter hardware associated with the TDRSS/orbiter Ku band uplink was analyzed. Performances of a detailed design of the PN despreader, the PSK carrier synchronization loop, and the symbol synchronizer are identified. The performance of the downlink signal by means of computer simulation to obtain a realistic determination of bit error rate degradations was studied. The three channel PM downlink signal was detailed by means of analysis and computer simulation.

Source record↗
NASA NTRS1976

Conference on Charge-Coupled Device Technology and Applications

Papers were presented from the conference on charge coupled device technology and applications. The following topics were investigated: data processing; infrared; devices and testing; electron-in, x-ray, radiation; and applications. The emphasis was on the advances of mutual relevance and potential significance both to industry and NASA's current and future requirements in all fields of imaging, signal processing and memory.

Source record↗
NASA NTRS1978

A sequential method for spline approximation with variable knots

In this paper we describe a method for approximating a waveform by a spline. The method is quite efficient, as the data are processed sequentially. The basis of the approach is to view the approximation problem as a question of estimation of a polynomial in noise, with the possibility of abrupt changes in the highest derivative. This allows us to bring several powerful statistical signal processing tools into play. We also present some initial results on the application of our technique to the processing of electrocardiograms, where the knot locations themselves may be some of the most important pieces of diagnostic information.

Mier Muth, A. M.↗
NASA NTRS1979

A model for testing centerfinding algorithms for automated optical navigation

An efficient software simulation of the imaging process for optical navigation is presented, illustrating results using simple examples. The problems of image definition and optical system modeling, including ideal image containing features and realistic models of optical filtering performed by the entire camera system, are examined. A digital signal processing technique is applied to the problem of developing methods of automated optical navigation and the subsequent mathematical formulation is presented. Specific objectives such as an analysis of the effects of camera defocusing on centerfinding of planar targets, addition of noise filtering to the algorithm, and implementation of multiple frame capability were investigated.

Griffin, M. D.↗
NASA NTRS1983

Information theory analysis of sensor-array imaging systems for computer vision

Information theory is used to assess the performance of sensor-array imaging systems, with emphasis on the performance obtained with image-plane signal processing. By electronically controlling the spatial response of the imaging system, as suggested by the mechanism of human vision, it is possible to trade-off edge enhancement for sensitivity, increase dynamic range, and reduce data transmission. Computational results show that: signal information density varies little with large variations in the statistical properties of random radiance fields; most information (generally about 85 to 95 percent) is contained in the signal intensity transitions rather than levels; and performance is optimized when the OTF of the imaging system is nearly limited to the sampling passband to minimize aliasing at the cost of blurring, and the SNR is very high to permit the retrieval of small spatial detail from the extensively blurred signal. Shading the lens aperture transmittance to increase depth of field and using a regular hexagonal sensor-array instead of square lattice to decrease sensitivity to edge orientation also improves the signal information density up to about 30 percent at high SNRs.

Huck, F. O.↗
NASA NTRS1993

The solid state detector technology for picosecond laser ranging

We developed an all solid state laser ranging detector technology, which makes the goal of millimeter accuracy achievable. Our design and construction philosophy is to combine the techniques of single photon ranging, ultrashort laser pulses, and fast fixed threshold discrimination while avoiding any analog signal processing within the laser ranging chain. The all solid state laser ranging detector package consists of the START detector and the STOP solid state photon counting module. Both the detectors are working in an optically triggered avalanche switching regime. The optical signal is triggering an avalanche current buildup which results in the generation of a uniform, fast risetime output pulse.

Prochazka, Ivan↗
NASA NTRS1990

Clutter filter design considerations for Airborne Doppler radar detection of windshear

The problem of clutter rejection when processing down-looking Doppler radar returns from a low altitude airborne platform is a paramount problem. With radar as a remote sensor for detecting and predicting windshear in the vicinity of an urban airport, dynamic range requirements can exceed 50 dB because of high clutter to signal ratios. This presentation describes signal processing considerations in the presence of distributed and/or discrete clutter interference. Previous analyses have considered conventional range cell processing of radar returns from a rigidly mounted radar platform using either the Fourier or the pulse-pair method to estimate average windspeed and windspeed variation within a cell. Clutter rejection has been based largely upon analyzing a particular environment in the vicinity of the radar and employing a variety of techniques to reduce interference effects including notch filtering, Fourier domain line editing, and use of clutter maps. For the airborne environment the clutter characteristics may be somewhat different. Conventional clutter rejection methods may have to be changed and new methods will probably be required to provide useful signal to noise ratios. Various considerations are described. A major thrust has been to evaluate the effect of clutter rejection filtering upon the ability to derive useful information from the post-filter radar data. This analysis software is briefly described. Finally, some ideas for future analysis are considered including the use of adaptive filtering for clutter rejection and the estimation of windspeed spatial gradient directly from radar returns as a means of reducing the effects of clutter on the determination of a windshear hazard.

Baxa, Ernest G., Jr.↗
NASA NTRS1984

On Estimating the Phase of Periodic Waveform in Additive Gaussian Noise, Part 2

Motivated by advances in signal processing technology that support more complex algorithms, a new look is taken at the problem of estimating the phase and other parameters of a periodic waveform in additive Gaussian noise. The general problem was introduced and the maximum a posteriori probability criterion with signal space interpretation was used to obtain the structures of optimum and some suboptimum phase estimators for known constant frequency and unknown constant phase with an a priori distribution. Optimal algorithms are obtained for some cases where the frequency is a parameterized function of time with the unknown parameters and phase having a joint a priori distribution. In the last section, the intrinsic and extrinsic geometry of hypersurfaces is introduced to provide insight to the estimation problem for the small noise and large noise cases.

Rauch, L. L.↗
NASA NTRS2009

Two-Stage Variable Sample-Rate Conversion System

A two-stage variable sample-rate conversion (SRC) system has been pro posed as part of a digital signal-processing system in a digital com munication radio receiver that utilizes a variety of data rates. The proposed system would be used as an interface between (1) an analog- todigital converter used in the front end of the receiver to sample an intermediatefrequency signal at a fixed input rate and (2) digita lly implemented tracking loops in subsequent stages that operate at v arious sample rates that are generally lower than the input sample r ate. This Two-Stage System would be capable of converting from an input sample rate to a desired lower output sample rate that could be var iable and not necessarily a rational fraction of the input rate.

Tkacenko, Andre↗
NASA NTRSDate not supplied

NASA's Unsteady Pressure-Sensitive Paint Research and Operational Capability Developments

In the last three years, several advancements have been made to produce a new state-of-the-art capability in the field of Aerosciences. NASA’s Aerosciences Evaluations and Test Capabilities (AETC) Portfolio Office has funded a multi-year project to produce the unsteady Pressure-Sensitive Paint (uPSP) technology as an operational capability in key ground test facilities at NASA. The research and development has primarily been conducted at NASA Ames Research Center’s (ARC) Unitary Plan Wind Tunnel (UPWT) 11-by 11-ft Transonic Wind Tunnel (TWT). The NASA ARC UPWT is one of the ground test facilities under NASA AETC’s Portfolio Office. AETC’s goals are to provide the tools to deliver the technology innovations and breakthroughs necessary to address increasingly complex research and development challenges. AETC’s integrated approach will consider the complimentary high-end compute capabilities necessary to advance analysis in conjunction with ground experimental capabilities. The uPSP Capability Challenge Project is a demonstration of several different technologies: 1) the unsteady Pressure-Sensitive Paint (uPSP) technology, and 2) Project: Red Rover, establishing a secure, reliable, fast connection between experimental and computation facilities, leveraging NASA’s computational resources within the High-End Compute Capability (HECC) Project for processing, storing, and sharing data efficiently. This project demonstrates the technical diversity and technical inclusion need to advance the field of Aerosciences. The approach to combine subject matter experts in experimental methods, optical methods, production wind tunnel testing, network engineering, high-end computing, signal processing, grid generation, and visualization while establishing the required infrastructure for subject matter experts to have access to the data while the wind tunnel test is being conducted. The most recent advancements for the uPSP technology have focused on three key areas: development of data products, robust processing pipeline, operational efficiencies and uncertainty quantification.

buffet↗
NASA NTRS1977

DKDP /potassium dideuterium phosphate/ light valves

The use of potassium dideuterium phosphate (DKDP) light valves for optical data processing is discussed. The operating principles and structure of optically and electron beam addressed DKDPs are compared, and specifications for both devices given. Optically addressed DKDPs are capable of higher resolution and contrast, but both systems represent viable real time spatial light modulators adaptable to optical processing. Examples of real time data processing performed by the DKDPs include: image addition and subtraction; reduction of noise introduced by scattered light in recording media; reconstruction of computer generated and acoustic holograms; reconstruction of synthetic aperture radar data; retrieval of three-dimensional information in X-ray diagnoses; radar signal processing and display; and optical pattern recognition and correlation of images, which has applications for missile guidance systems.

Casasent, D.↗
NASA NTRS1985

Application of digital pulse shaping by least squares method to ultrasonic signals in composites

For ultrasonic testing in composites, a signal processing tool is identified that can significantly enhance the sharpness of ultrasonic waveforms and provide clearer pictures of the nature of the material flaw. The technique artificially improves the resolution of the system to discrete events by pulse shaping the measured waveform based on the signal from a reference. The optimum pulse shape operator is determined from a least-squares method in the z-domain.

Kishoni, D.↗
NASA NTRS1991

Multiresponse imaging system design for improved resolution

Multiresponse imaging is a process that acquires A images, each with a different optical response, and reassembles them into a single image with an improved resolution that can approach 1/sq rt A times the photodetector-array sampling lattice. Our goals are to optimize the performance of this process in terms of the resolution and fidelity of the restored image and to assess the amount of information required to do so. The theoretical approach is based on the extension of both image restoration and rate-distortion theories from their traditional realm of signal processing to image processing which includes image gathering and display.

Alter-Gartenberg, Rachel↗
NASA NTRS1984

Phased-Antenna-Array Conical Scanning

Antenna pointing faster than mechanical scanning. Three antenna phased array connected to receiving signal-processing system through two phase-shifting networks. Two networks simultaneously steer phased array in two slightly-different beam directions; one for scanning, one for tracking. Technique has many uses in military and civilian radar, principally in tracking aircraft, balloonborne weather instruments, and other moving signal sources or reflectors.

Lesh, J. R.↗