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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

A model for radar images and its application to adaptive digital filtering of multiplicative noise

Standard image processing techniques which are used to enhance noncoherent optically produced images are not applicable to radar images due to the coherent nature of the radar imaging process. A model for the radar imaging process is derived in this paper and a method for smoothing noisy radar images is also presented. The imaging model shows that the radar image is corrupted by multiplicative noise. The model leads to the functional form of an optimum (minimum MSE) filter for smoothing radar images. By using locally estimated parameter values the filter is made adaptive so that it provides minimum MSE estimates inside homogeneous areas of an image while preserving the edge structure. It is shown that the filter can be easily implemented in the spatial domain and is computationally efficient. The performance of the adaptive filter is compared (qualitatively and quantitatively) with several standard filters using real and simulated radar images.

Frost, V. S.↗
NASA NTRS1982

Abell 2069 - An X-ray cluster of galaxies with multiple subcondensations

X-ray and optical observations of the cluster Abell 2069 are presented. The cluster is at a mean redshift of 0.116. The cluster shows multiple condensations in both the X-ray emission and in the galaxy surface density and, thus, does not appear to be relaxed. There is a close correspondence between the gas and galaxy distributions which indicates that the galaxies in this system do map the mass distribution, contrary to what might be expected if low-mass neutrinos dominate the cluster mass.

Gioia, I. M.↗
NASA NTRS1982

A model of human decisionmaking in multiple process monitoring situations

It is proposed that human decisionmaking performance in multiple process monitoring situations can be modeled in terms of the detection of process related events and the allocation of attention among processes once events are felt to have occurred. An elementary pattern recognition technique, discriminant analysis, is used to generate estimates of event occurrence probability. A queueing theory framework is then utilized to incorporate these probabilities as well as other task characteristics into the solution of the attention allocation problem. The performance of the model is compared with that of subjects in two experiments.

Greenstein, J. S.↗
NASA NTRS1982

The effects of isotropic multiple scattering and surface albedo on the photochemistry of the troposphere

The present study is believed to be the first investigation which combines a detailed tropospheric photochemical model with a radiative code that realistically considers the important physical processes in the cloudless troposphere which control the transfer of incoming solar radiation. It is found in most cases that the inclusion of the multiple scattering code significantly alters the photolytic reaction frequencies. This in turn alters the vertical distribution of some key tropospheric species. In the case of ozone a decrease was found, while O(1D) and OH showed increased concentrations. The increases are especially evident for the species which are highly dependent on photolysis processes that occur shortward of about 320 nm. The photolysis frequencies for ozone photolysis calculated with the Anderson-Meier model are in general in excellent agreement with recent measurements

Augustsson, T. R.↗
NASA NTRS1982

Galaxy clusters with multiple components. I - The dynamics of Abell 98

The nature and evolution of rich galaxy clusters containing multiple condensations is studied. Velocities for 13 members of A98 are presented and the determination of dynamical properties of the individual subclusters is substantially improved. The application of techniques for quantifying gravitational scale lengths are stressed without invocation of the symmetry arguments demanded by the usual parameter fitting procedures. The entire A98 cluster is modeled as a two-body system. The probability that A98 is bound is found to be 98 percent. From this model and the results of previous N-body simulations, it is shown that the most likely description of the system is that it reached maximum expansion about 3.5 billion years ago and is presently in a state of collapse. The subclusters will merge in another three billion years.

Beers, T. C.↗
NASA NTRS1982

Outline of a multiple-access communication network based on adaptive arrays

Attention is given to a narrow-band communication system consisting of a central station trying to receive signals simultaneously from K spatially distinct mobile users sharing the same frequencies. One example of such a system is a group of aircraft and ships transmitting messages to a communication satellite. A reasonable approach to such a multiple access system may be based on equipping the central station with an n-element antenna array where n is equal to or greater than K. The array employs K sets of n weights to segregate the signals received from the K users. The weights are determined by direct computation based on position information transmitted by the users. A description is presented of an improved technique which makes it possible to reduce significantly the number of required computer operations in comparison to currently known techniques.

Zohar, S.↗
NASA NTRS1982

Multiple-spacecraft and correlated riometer study of magnetospheric substorm phenomena

Double-spacecraft observations presented suggest that growth phase phenomena are widespread in the outer magnetosphere and can occur simultaneously at nightside locations 4-5 hours apart in local time. Evidence is also adduced from multiple-spacecraft data and comprehensive magnetometer and riometer data against the concept that growth phase features are not generally due to substorm activity at other locations in the auroral or polar regions. A close relationship is noted between putative energy input to the magnetosphere and the sensitive response of the magnetic field and energetic particles at pre- and near-midnight geostationary orbit locations. This relationship is shown explicitly for the cases of three event periods. Data are also presented which suggest that growth phase features at synchronous orbit can be strictly controlled by IMF orientations.

Baker, D. N.↗
NASA NTRS1984

Multiple-Wavelength Metal/Halide Laser

Single device produces multiple lasing lines. Laser capable of producing many lasing lines has several reservoirs of halide lasant mixed with chlorides of copper, manganese and iron. Convection-control technique possible to rapidly change from one metal halide to another at maximum energy.

Nerheim, N. M.↗
NASA NTRS1982

Next generation communications satellites: multiple access and network studies

Efficient resource allocation and network design for satellite systems serving heterogeneous user populations with large numbers of small direct-to-user Earth stations are discussed. Focus is on TDMA systems involving a high degree of frequency reuse by means of satellite-switched multiple beams (SSMB) with varying degrees of onboard processing. Algorithms for the efficient utilization of the satellite resources were developed. The effect of skewed traffic, overlapping beams and batched arrivals in packet-switched SSMB systems, integration of stream and bursty traffic, and optimal circuit scheduling in SSMB systems: performance bounds and computational complexity are discussed.

Meadows, H. E.↗
NASA NTRS1982

Advanced 30/20 GHz multiple-beam antennas for communications satellites

Design concepts under development utilize two separate spacecraft antenna systems, one uplink at 30 GHz and the other a downlink at 20 GHz, where each antenna provides multiple fixed and scanning beams. Two contractors completed configuration trade-off studies and breadboarding of critical technology components, and are fabricating and testing proof-of-concept (POC) models to demonstrate the technology feasibility. Technology developments required for the proposed systems are presented, along with each contractor's progress to date. The technology development areas discussed include: (1) offset Cassegrain and shaped reflector systems for narrow beams with low sidelobes and wideangle off-axis scan; (2) diplexed beam-forming networks for dual polarization, low sidelobes, and fixed and scan-beam operation; (3) fast switching networks for scanning beams; and (4) fabrication of precision feed components and large offset reflectors.

Myhre, R. W.↗
NASA NTRS1982

Noise measurements for single and multiple operation of 50 kw wind turbine generators

The noise characteristics of the U.S. Windpower Inc., 50 kw wind turbine generator were measured at various distances from 30 m to 1100 m and for a range of output power. The generated noise is affected by the aerodynamic wakes of the tower legs at frequencies below about 120 Hz and the blade trailing edge thickness at frequencies of about 2 kHz. Rope strakes and airfoil fairings on the legs did not result in substantial noise reductions. Sharpening the blade trailing edges near the tip was effective in reducing broad band noise near 2 kHz. For multiple machines the sound fields are superposed. A three-fold increase in number of machines (from 1 to 3) results in a predicted increase in he sound pressure level of about 5 dB. The detection threshold for 14 machines operating in a 13 - 20 mph wind is observed to be at approximately 1160 m in the downwind direction.

Hubbard, H. H.↗
NASA NTRS1982

Multiple and variable speed electrical generator systems for large wind turbines

A cost effective method to achieve increased wind turbine generator energy conversion and other operational benefits through variable speed operation is presented. Earlier studies of multiple and variable speed generators in wind turbines were extended for evaluation in the context of a specific large sized conceptual design. System design and simulation have defined the costs and performance benefits which can be expected from both two speed and variable speed configurations.

Andersen, T. S.↗
NASA NTRS1982

Application of MMIC modules in future multiple beam satellite antenna systems

Multiple beam antenna systems for advanced communication satellites operating in the 30/20 GHz frequency bands (30 GHz uplink, 20 GHz downlink) were developed. Up to twenty 0.3 deg HPBW fixed spot beams and six 0.3 deg HPBW scanning spot beams will be required. Array-fed dual reflector antenna systems in which monolithic microwave integrated circuit (MMIC) phase shift and amplifier modules are used with each radiating element of the feed array for beam pointing and power gain were developed. The feasibility of distributed power amplification and beam pointing with MMIC modules in the elements of an array and to develop a data base for future development were demonstrated. The technical discussion centers around the potential advantages of ""monolithic'' antennas for specific applications as compared to systems using high powered TWT's. These include: reduced losses in the beam forming network; advantage of space combining and graceful degradation; dynamic control of beam pointing and illumination contour; and possibilities for cost and weight reduction.

Smetana, J.↗
NASA NTRS1983

Interaction of multiple supersonic jets with a transonic flow field

The influence of multiple high pressure, supersonic, radial or tangential jets, that are injected from the circumference of the base plane of an axisymmetric body, on its longitudinal aerodynamic coefficients in transonic flow is studied experimentally. The interaction of the jets with the body flow field increases the pressures on the forebody, thus altering its lift and static stability characteristics. It is shown that, within the range of parameters studied. This interaction has a stabilizing effect on the body. The contribution to lift and stability is significant at small angles of attack and decreases nonlinearly at higher angles when the crossflow mechanism becomes dominant.

Seginer, A.↗
NASA NTRS1983

Parallel processing in a host plus multiple array processor system for radar

Host plus multiple array processor architecture is demonstrated to yield a modular, fast, and cost-effective system for radar processing. Software methodology for programming such a system is developed. Parallel processing with pipelined data flow among the host, array processors, and discs is implemented. Theoretical analysis of performance is made and experimentally verified. The broad class of problems to which the architecture and methodology can be applied is indicated.

Barkan, B. Z.↗
NASA NTRS1982

A multiple beam antenna concept for a 30/20 GHz satellite communications system

Design and operational performance features of a NASA planned 30/30 GHz flight experiment communications system multiple-beam antenna (MBA) are described. The MBA is a shared aperture offset Cassegrain type with a main reflector diameter of 3 m and physically separated transmit and receive feeds. A planar frequency selective surface is employed which is transmissive to the receive signals and reflective to the transmit signals. Trade-offs and constraints in the MBA feed design are explored, noting the higher feed loss and complexity due to choosing variable power dividers for the beam forming network. Doublet beam coverage of the east coast of the continental U.S. is shown to be possible with a triangular lattice array of feed horns with aperture diameters and element spacings of two wavelengths. The doublet configuration requires ten times the components as a singlet array.

Forman, B. J.↗