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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

The response of SAR imagery to azimuth travelling ocean surface waves as determined from shuttle SAR imagery

Comparisons between two-dimensional ocean wave spectra, derived from synthetic aperture radar (SAR) imagery, and two-dimensional wave spectra from independent instruments have shown good agreement. The procedure by which raw SAR image intensity-variance spectra are converted to estimates of wave spectra is dependent upon models of how a SAR is able to image ocean waves. The greatest uncertainty exists about the mechanism by which azimuth (along track) traveling waves are imaged. In this paper, independent wave spectra from an airborne, radar ocean wave spectrometer (ROWS) are systematically compared with spatially and temporally coincident shuttle SAR image intensity-variance spectra to determine an optimum description of the relationship between the two. The result of these comparisons is to demonstrate that a SAR image intensity-variance spectrum is nearly proportional to the ocean wave slope-variance spectrum for azimuth traveling waves.

Monaldo, Frank M.↗
NASA NTRS1988

The Surface Wave Dynamics Experiment (SWADE)

SWADE was developed to study the dynamics of the wave field development in the open ocean with the following specific objectives: (1) to understand the development of the wave directional spectrum under various conditions; (2) to determine the effect of waves on the air/sea transfers of momentum, heat, and mass; (3) to determine breaking distributions as a function of sea state, wind, and boundary stability; and (4) to provide data and analyses for ERS-1 validation. The experiment is designed for the winter of 1990 to 1991. Four buoys will be deployed for 6 months starting October 1990 and ending March 1991. During that time period, three intensive periods of 2 weeks duration each will be selected for frequent aircraft flights for wave data collection to satisfy scientific studies, as well as ERS-1 validation needs.

Long, S. R.↗
NASA NTRS1992

The local properties of ocean surface waves by the phase-time method

A new approach using phase information to view and study the properties of frequency modulation, wave group structures, and wave breaking is presented. The method is applied to ocean wave time series data and a new type of wave group (containing the large 'rogue' waves) is identified. The method also has the capability of broad applications in the analysis of time series data in general.

Huang, Norden E.↗
NASA NTRS1995

Analysis of a disk-on-rod surface wave element inside a corrugated horn using the mode-matching technique

A disk-on-rod inside a corrugated horn is one of the horn configurations for dual-frequency or wide-band operation. A mode-matching analysis method is described. A disk-on-rod inside a corrugated horn is represented as a series of coaxial waveguide sections and circular waveguide sections connected to each other. Three kinds of junctions need to be considered: coaxial-to-coaxial, coaxial-to-circular, and circular-to-circular. A computer program was developed to calculate the scattering matrix and the radiation pattern of a disk-on-rod inside a corrugated horn. The software as verified by experiment, and good agreement between calculation and measurement was obtained. The disk-on-rod inside a corrugated horn design gives an option to the Deep Space Network dual-frequency operation system, which currently is a two-horn/one-dichroic plate system.

Chen, J. C.↗
NASA NTRS2009

Comparison of Transmission Line Methods for Surface Acoustic Wave Modeling

Surface Acoustic Wave (SAW) technology is low cost, rugged, lightweight, extremely low power and can be used to develop passive wireless sensors. For these reasons, NASA is investigating the use of SAW technology for Integrated Vehicle Health Monitoring (IVHM) of aerospace structures. To facilitate rapid prototyping of passive SAW sensors for aerospace applications, SAW models have been developed. This paper reports on the comparison of three methods of modeling SAWs. The three models are the Impulse Response Method (a first order model), and two second order matrix methods; the conventional matrix approach, and a modified matrix approach that is extended to include internal finger reflections. The second order models are based upon matrices that were originally developed for analyzing microwave circuits using transmission line theory. Results from the models are presented with measured data from devices. Keywords: Surface Acoustic Wave, SAW, transmission line models, Impulse Response Method.

Wilson, William↗
NASA NTRS1988

Resonance absorption of compressible magnetohydrodynamic waves at thin 'surfaces'

The behavior of plasma and fields in the transition layer supporting MHD surface waves is analyzed, assuming that the total pressure fluctuations, delta-P(tot), can be taken to be nearly constant across this thin transition layer, with a value nearly the same as would be obtained if the MHD wave were supported by a truly discontinuous surface. Regarding therefore delta-P(tot) as known, the plasma and field equations in the transition layer were cast into a form in which delta-P(tot) appeared as a driving term. Among the two resonances that appear (the cusp resonance and the Alfven resonance) special attention is given to the Alfven resonance, which affects the velocity and magnetic field components normal to the background magnetic field. The effects of three types of viscosity on the Alfven resonance are considered, and it is shown that energy is pumped out of the surface wave into thin layers surrounding the resonant field lines.

Hollweg, Joseph V.↗
NASA NTRS1993

An oxygen pressure sensor using surface acoustic wave devices

Surface acoustic wave (SAW) piezoelectric devices are finding widespread applications in many arenas, particularly in the area of chemical sensing. We have developed an oxygen pressure sensor based on coating a SAW device with an oxygen binding agent which can be tailored to provide variable sensitivity. The coating is prepared by dissolving an oxygen binding agent in a toluene solution of a copolymer which is then sprayed onto the surface of the SAW device. Experimental data shows the feasibility of tailoring sensors to measure the partial pressure of oxygen from 2.6 to 67 KPa (20 to 500 torr). Potential applications of this technology are discussed.

Leighty, Bradley D.↗
NASA NTRS1971

Surface elastic wave detectors

The potential applications of acoustic surface wave technology to multiplex communication systems such as data-bus, are examined. The goals are primarily to characterize certain aspects of surface wave trapped delay lines, surface wave modulation techniques, and surface wave applications that are relevant to the evaluation of surface wave devices in multiplex systems. The results indicate that there is a potential for the application of surface wave technology in data-bus type systems.

Lawson, R. L.↗
NASA NTRS1977

The distribution of seismic velocities and attenuation in the earth

Estimates of the radial distribution of seismic velocities and density and of seismic attenuation within the earth are obtained through inversion of body wave, surface wave, and normal mode data. The effect of attenuation related dispersion on gross earth structure, and on the reliability of eigenperiod identifications is discussed. The travel time baseline discrepancies between body waves and free oscillation models are examined and largely resolved.

Hart, R. S.↗
NASA NTRS1981

Absorption band Q model for the Earth

Attenuation in solids and liquids, as measured by the quality factor Q, is typically frequency dependent. In seismology, however, Q is usually assumed to be independent of frequency. Body wave, surface wave, and normal mode data are used to place constraints on the frequency dependence of Q in the mantle. Specific features of the absorption band model are: low-Q in the seismic band at both the top and the base of the mantle, low-Q for long-period body waves in the outer core, an inner core Q sub s that increases with period, and low Q sub p/Q sub s at short periods in the middle mantle.

Anderson, D. L.↗
NASA NTRS1986

A multidisciplinary study of planetary, solar and astrophysical radio emissions

Combination of the related fields of planetary, solar, and astrophysical radio emissions was attempted in order to more fully understand the radio emission processes. Topics addressed include: remote sensing of astrophysical plasma turbulence; Alfven waves; astrophysical shock waves; surface waves; very long base interferometry results; very large array observations; solar magnetic flux; and magnetohydrodynamic waves as a tool for solar corona diagnostics.

Gurnett, D. A.↗
NASA NTRS1983

An all fiber-optic sensor for surface acoustic wave measurements

A surface acoustic wave (SAW) sensor constructed from single-mode fiber-optic components is described. An analysis of reciprocal and nonreciprocal modes of operation of the sensor is presented. Results from measurements on a variety of SAW devices illustrate the use of the sensor. The amplitude sensitivity is 0.0003 A for an integration time of 0.1 s.

Bowers, J. E.↗