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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

NASA-SETI microwave observing project: Targeted Search Element (TSE)

The Targeted Search Element (TSE) performs one of two complimentary search strategies of the NASA-SETI Microwave Observing Project (MOP): the targeted search. The principle objective of the targeted search strategy is to scan the microwave window between the frequencies of one and three gigahertz for narrowband microwave emissions eminating from the direction of 773 specifically targeted stars. The scanning process is accomplished at a minimum resolution of one or two Hertz at very high sensitivity. Detectable signals will be of a continuous wave or pulsed form and may also drift in frequency. The TSE will possess extensive radio frequency interference (RFI) mitigation and verification capability as the majority of signals detected by the TSE will be of local origin. Any signal passing through RFI classification and classifiable as an extraterrestrial intelligence (ETI) candidate will be further validated at non-MOP observatories using established protocol. The targeted search will be conducted using the capability provided by the TSE. The TSE provides six Targeted Search Systems (TSS) which independently or cooperatively perform automated collection, analysis, storage, and archive of signal data. Data is collected in 10 megahertz chunks and signal processing is performed at a rate of 160 megabits per second. Signal data is obtained utilizing the largest radio telescopes available for the Targeted Search such as those at Arecibo and Nancay or at the dedicated NASA-SETI facility. This latter facility will allow continuous collection of data. The TSE also provides for TSS utilization planning, logistics, remote operation, and for off-line data analysis and permanent archive of both the Targeted Search and Sky Survey data.

Webster, L. D.↗
NASA NTRS1991

Microwave conductivity of laser ablated YBa2Cu3O(7-delta) superconducting films and its relation to microstrip transmission line performance

The discovery of high temperature superconductor oxides has raised the possibility of a new class of millimeter and microwave devices operating at temperatures considerably higher than liquid helium temperatures. Therefore, materials properties such as conductivity, current density, and sheet resistance as a function of temperature and frequency, possible anisotropies, moisture absorption, thermal expansion, and others, have to be well characterized and understood. The millimeter wave response of laser ablated YBa2Cu3O(7-delta)/LaAlO3 thin films was studied as a function of temperature and frequency. In particular, the evaluation of their microwave conductivity was emphasized, since knowledge of this parameter provides a basis for the derivation of other relevant properties of these superconducting oxides, and for using them in the fabrication of actual passive circuits. The microwave conductivity for these films was measured at frequencies from 26.5 to 40.0 GHz, in the temperature range from 20 to 300 K. The values of the conductivity are obtained from the millimeter wave power transmitted through the films, using a two fluid model.

Bhasin, K. B.↗
NASA NTRS1991

Magnetic field effects on microwave absorbing materials

The objective of this program was to gather information to formulate a microwave absorber that can work in the presence of strong constant direct current (DC) magnetic fields. The program was conducted in four steps. The first step was to investigate the electrical and magnetic properties of magnetic and ferrite microwave absorbers in the presence of strong magnetic fields. This included both experimental measurements and a literature survey of properties that may be applicable to finding an appropriate absorbing material. The second step was to identify those material properties that will produce desirable absorptive properties in the presence of intense magnetic fields and determine the range of magnetic field in which the absorbers remain effective. The third step was to establish ferrite absorber designs that will produce low reflection and adequate absorption in the presence of intense inhomogeneous static magnetic fields. The fourth and final step was to prepare and test samples of such magnetic microwave absorbers if such designs seem practical.

Goldberg, Ira↗
NASA NTRS1992

Laboratory evaluation and application of microwave absorption properties under simulated conditions for planetary atmospheres

Radio absorptivity data for planetary atmospheres obtained from spacecraft radio occultation experiments and earth-based radio astronomical observations can be used to infer abundances of microwave absorbing atmospheric constituents in those atmospheres, as long as reliable information regarding the microwave absorbing properties of potential constituents is available. The use of theoretically derived microwave absorption properties for such atmospheric constituents, or using laboratory measurements of such properties under environmental conditions which are significantly different than those of the planetary atmosphere being studied, often leads to significant misinterpretation of available opacity data. The recognition of the need to make such laboratory measurements of simulated planetary atmospheres over a range of temperatures and pressures which correspond to the altitudes probed by both radio occultation experiments and radio astronomical observations, and over a range of frequencies which correspond to those used in both radio occultation experiments and radio astronomical observations, has led to the development of a facility at Georgia Tech which is capable of making such measurements. The goal of this investigation was to conduct such measurements and to apply the results to a wide range of planetary observations, both spacecraft and earth-based, in order to determine the identity and abundance profiles of constituents in those planetary atmospheres.

Steffes, Paul G.↗
NASA NTRS1991

Utilization of surface cover composition to improve the microwave determination of snow water equivalent in a mountain basin

Satellite microwave data have been used to derive areal snow water equivalent in flat homogeneous areas. Over heterogeneous mountainous areas different algorithms are needed to retrieve the water equivalent of the snow cover. A mixed pixel model based on the percentage of vegetation cover within a pixel has been developed to simulate the microwave brightness temperatures for the Rio Grande basin in southwestern Colorado. A relationship between the difference in microwave-brightness temperature at two different frequencies (37- and 18-GHz horizontal polarization), and the basin-wide average snow water equivalent was obtained. The areal snow-water equivalent values derived from the model were consistent with values generated by a reliable snowmelt run-off model using snow-cover extent data.

Chang, A. T. C.↗
NASA NTRS1990

Aircraft observations and cloud-microwave radiative model simulations of a deep convective system

A 3D cloud model is used to simulate the storm structure of the June 29, 1986 storm system observed during the Cooperative Huntsville Meteorological Experiment (Dodge et al., 1986), and the results are linked to a microwave radiative transfer model for simulating aircraft observations. The results of cloud and radiative model simulations are then compared with radar data and aircraft microwave observations, respectively. It is shown that the degree of agreement between model simulations and the aircraft microwave observations depends on the model-derived microphysics of cloud and precipitation. It is found that the calculated values of the brightness temperature (Tb) at 92 GHz are close to the observed temperatures, while the calculated Tb values at 18 and 37 GHz are lower than the observed Tb.

Yeh, H.-Y. M.↗
NASA NTRS1991

Microwave absorption by a lossy dielectric sphere in a rectangular cavity

A new theory of absorption of microwave power by a lossy dielectric sphere in a resonant rectangular chamber is developed here. In this treatment, resonant modes of the cavity are resolved into traveling plane-wave fields, and Mie's theory of scattering and absorption of a plane electromagnetic wave by a sphere is utilized. The fields in the cavity containing the sphere are found by superposition of results for the individual scattering problem for each traveling plane wave. Absorbed power is then calculated by evaluating the time-averaged Poynting vector and integrating over the surface of the sphere. Applications of microwave power absorption are discussed, with particular emphasis on processing of materials. Numerical studies based on the newly derived formulas are presented. The results exhibit the manner in which microwave absorption is influenced by a number of different experimentally controllable parameters. The examples considered were chosen with a view toward designing experiments and apparatus for containerless processing of materials in the microgravity environment of space.

Jackson, H. W.↗
NASA NTRS1991

Microwave properties of YBa2Cu3O(7-delta) high-transition-temperature superconducting thin films measured by the power transmission method

The microwave response of YBa2Cu3O(7-delta) superconducting thin films deposited on LaAlO3, MgO, YSZ, and LaGaO3 substrates are studied. It is found that the microwave transmission properties are very weakly dependent on temperature in the normal state but change drastically upon transition to the superconducting state. In particular, the transmission decreases and there is a negative phase shift with respect to the phase at room temperature when the sample is cooled through its transition temperature. The magnetic penetration depth for all the films was determined from the surface reactance of the films. The microwave complex conductivity is determined in both the normal and the superconducting state. It is observed that both sigma1 and sigma2 increase in transition to the superconducting state. The surface resistivity is calculated for all the films.

Miranda, F. A.↗
NASA NTRS1991

Diurnal change in trees as observed by optical and microwave sensors - The EOS Synergism Study

The EOS (Earth Observing System) Synergism Study examined the temporal variability of the optical and microwave backscatter due to diurnal change in canopy properties of interest to ecosystem modelers. The experiment was designed to address diurnal changes in canopy water status that relate to transpiration. Multispectral optical and multifrequency, multipolarization microwave measurements were acquired using boom-truck-based systems over a two-week period. Sensor and canopy properties were collected around the clock. The canopy studied was a walnut orchard in the San Joaquin Valley of California. The results demonstrate a large diurnal variation in the dielectric properties of the tree that in turn produces significant diurnal changes in the microwave backscatter. The results suggest that permanently orbiting spaceborne sensors such as those on EOS should be placed in orbits that are optimized for the individual sensor and need not be tied together by a tight simultaneity requirement on the order of minutes to hours for the purpose of monitoring ecosystem properties.

Way, Jobea↗
NASA NTRS1990

Tropical Rainfall Measuring Mission (TRMM) project. VI - Spacecraft, scientific instruments, and launching rocket. Part 3 - The electrically Scanning Microwave Radiometer and the Special Sensor Microwave/Imager

The two microwave radiometers for TRMM are designed to measure thermal microwave radiation upwelling from the earth. The Electrically Scanning Microwave Radiometer (ESMR) scans from 50 deg to the left through nadir to 50 deg to the right in 78 steps with no moving mechanical parts in a band centered at 19.35 GHz. The TRMM concept uses the radar to develop a climatology of rain-layer thickness which can be used for the interpretation of the radiometer data over a swath wider than the radar. The ESMR data are useful for estimating rain intensity only over an ocean background. The Special Sensor Microwave/Imager (SSM/I), which scans conically with three dual polarized channels at 19, 37, and 85 GHz and a single polarized channel at 22 GHz, provides a wider range of rainfall intensities. The SSM/I spins about an axis parallel to the local spacecraft vector and 128 uniformly spaced samples of the 85 GHz data are taken on each scan over a 112-deg scan region simultaneously with 64 samples of the other frequencies.

Wilheit, Thomas T.↗
NASA NTRS1991

MACHYDRO-90 - The microwave aircraft experiment for hydrology

MACHYDRO-90 is a multisensor aircraft campaign (MAC) that was held in central Pennsylvania over an eleven day period in July 1990. The emphasis of the campaign was on the microwave measurements of soil moisture, although other aspects of hydrology and microwave-target interactions were also studied. A description is given of the experiment, its organization, and the meteorological conditions during the eleven days. Preliminary results are also presented from PBMR (Push-Broom Microwave Radiometer) and SAR (synthetic aperture radar) measurements of soil moisture. These results are portrayed in the context of the hydrology, which, during this experiment, exhibited dry and wet extremes.

Engman, Edwin T.↗
NASA NTRS1992

Beamed microwave power transmission and its application to space

The general principles and special components of beamed microwave power transmission systems are outlined and their application to the space program are discussed. The beamed system is defined as starting with a dc source of power at the transmitting end, converting it to a microwave beam for transmission through space, and ending with the dc power output at the receiving end. An experimentally measured and certified dc-to-dc efficiency of 54 percent has been achieved, using this definition. The application discussed is that of a LEO to GEO transportation system that depends upon vehicles propelled by electric thrusters whose power is supplied by a microwave beam originating at the earth's surface. The advantages of the all-electronic system over a chemically propelled system are enumerated. The principles of space propulsion, particularly as they relate to electric propulsion, are outlined. Key components of the system and environmental considerations are discussed.

Brown, William C.↗
NASA NTRS1989

Passive microwave remote sensing of precipitation from space - Impact of cloud microphysics

Numerical experiments to investigate the impact of time-dependent cloud microphysical structure on the transfer to space of passive microwave radiation are carried out, using a vertically and angularly detailed, plane-parallel radiative transfer model for unpolarized microwave radiation. The object is to explore the feasibility of multichannel passive-microwave retrieval techniques to estimate precipitation from space. Results on the time-dependent influence of large graupel-size ice particles on top-of-atmosphere brightness temperature - rainfall rate relationships at 6.6, 10.7, 18, 19.35, 22.235, 37, 89.5, 130, and 231 GHz are given. Frequency-dependent vertical profiles of a generalized brightness-temperature weighting function, introduced to vertically resolve the contributions by individual cloud and precipitation layers to the brightness temperatures, are also shown.

Mugnai, Alberto↗
NASA NTRS1992

Retrieval of nonprecipitating liquid water cloud parameters from microwave data - A simulation study

A new microwave algorithm, analogous to the IR 'radiance-ratioing' method of Eyre and Menzel (1989) is developed to retrieve the height and 'effective' fraction (defined as the product of the emissivity times the actual physical fractional coverage) of nonprecipitating water clouds using various pairs of the 20 microwave channels planned for the Advanced Microwave Sounding Unit (AMSU), an instrument slated to fly on polar-orbiting satellites beginning in 1994. The results of a simulation study are presented to provide some insights into the potentials of this technique using different AMSU channel combinations. This study suggests that the use of the oxygen channels 3 and 5 and water vapor channels 19 and 20 will produce the most accurate retrievals of liquid water cloud parameters and the highest percentage of good-quality retrievals over a range of meteorological and cloud conditions.

Huang, Hung-Lung↗
NASA NTRS1991

Microwave polarization inversion observed

Observations of an inversion of solar-active-region microwave polarization are described as they occurred during the Coronal Magnetic Structures Observing Campaign. Data regarding the microwave frequencies, soft X-ray emissions, brightness temperatures, and column emissions are obtained with the observations. The data are employed in the potential-field extrapolation procedure by Sakurai (1982) to calculate the coronal magnetic-field vector, and the microwave polarization observations yield reasonable coronal densities and evidence of an inversion.

Brosius, Jeffrey W.↗
NASA NTRS1993

Measuring Microwave Conductivities Of Superconducting Films

Microwave conductivities of thin films of high-temperature superconductors like YBa(3)Cu(3)O(7-delta) measured by noninvasive, nondestructive microwave-power-transmission method. Measurements yield useful information on superconducting and normal states of films and contribute to evaluation of films for use in microwave devices.

Bhasin, K. B.↗
NASA NTRS1992

Laboratory evaluation and application of microwave absorption properties under simulated conditions for planetary atmospheres

Radio absorptivity data for planetary atmospheres obtained from spacecraft radio occultation experiments and earth-based radio astronomical observations can be used to infer abundances of microwave absorbing atmospheric constituents in those atmospheres, as long as reliable information regarding the microwave absorbing properties of potential constituents is available. The use of theoretically-derived microwave absorption properties for such atmospheric constituents, or using laboratory measurements of such properties under environmental conditions which are significantly different than those of the planetary atmosphere being studied, often leads to significant misinterpretation of available opacity data. For example, laboratory measurements performed by Fahd and Steffes have shown that the opacity from gaseous SO2 under simulated Venus conditions can be well described by the Van Vleck-Weisskopf lineshape at wavelengths shortward of 2 cm, but that the opacity of wavelengths greater than 2 cm is best described by a different lineshape that was previously used in theoretical predictions. The recognition of the need to make such laboratory measurements of simulated planetary atmospheres over a range of temperatures and pressures which correspond to the altitudes probed by both radio occultation experiments and radio astronomical observations, and over a range of frequencies which correspond to those used in both radio occultation experiments and radio astronomical observations, has led to the development of a facility at Georgia Tech which is capable of making such measurements. It has been the goal of this investigation to conduct such measurements and to apply the results to a wide range of planetary observations, both spacecraft and earth-based, in order to determine the identity and abundance profiles of constituents in those planetary atmospheres.

Steffes, Paul G.↗
NASA NTRS1993

Development of Si(1-x)Ge(x) technology for microwave sensing applications

The progress for the first year of the work done under the Director's Discretionary Fund (DDF) research project entitled, 'Development of Si(1-x)Ge(x) Technology for Microwave Sensing Applications.' This project includes basic material characterization studies of silicon-germanium (SiGe), device processing on both silicon (Si) and SiGe substrates, and microwave characterization of transmission lines on silicon substrates. The material characterization studies consisted of ellipsometric and magneto-transport measurements and theoretical calculations of the SiGe band-structure. The device fabrication efforts consisted of establishing SiGe device processing capabilities in the Lewis cleanroom. The characterization of microwave transmission lines included studying the losses of various coplanar transmission lines and the development of transitions on silicon. Each part of the project is discussed individually and the findings for each part are presented. Future directions are also discussed.

Mena, Rafael A.↗