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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 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Voids in Jovian magnetosphere revisited - Evidence of spacecraft charging

The Voyager 2 Plasma Science Instrument (PLS) measuring cold plasma number density observed about a dozen 'voids', lasting from a few minutes to 20 min, in the vicinity of the Ganymede-orbit crossing, when the low-energy ion and electron fluxes recorded fell to very low levels. Original interpretations associated these 'voids' with Ganymede wake effects. In the present study, the PLS data are reexamined, in conjunction with data from the magnetic field experiment and the low-energy charged particle (LECP) experiment. The LECP data showed that the PLS voids were accompanied by large enhancements of the flux of energetic electrons and ions, while the magnetic data exhibited no systematic signatures. It is suggested that increased energetic electron fluxes in the void regions intermittently charged the spacecraft negatively to values between a few kV and a few tens of kV, and that spacecraft charging could have produce dropouts in the measured cold ion and electron fluxes and enhancements in the measured fluxes of hot particles consistent with the observations.

Khurana, K. K.↗
NASA NTRS1987

Low-frequency magnetic field fluctuations in comet P/Halley's magnetosheath - Giotto observations

The interaction region between comets and the solar wind is characterized by large amplitude, low frequency magnetic field fluctuations, both within the upstream region as well as in the magnetosheath. Magnetosheath observations of the magnetic field experiment onboard Giotto indicate values of delta B/B equal to about O(1). Power spectral peaks appear at frequencies of 10mHz with the spectrum exhibiting a power law dependence with an exponent of the order 2. Radial variation of the fluctuation level does not clearly increase with decreasing distance from the cometary nucleus as observed by the magnetometer onboard Vega-1 and as expected from quasi-linear theory. The entrance into the cometary bow shock is furthermore characterized by an order of magnitude increase of the fluctuation level, both on the in- and outbound pass of Giotto.

Glassmeier, K. H.↗
NASA NTRS1988

Trace gas emissions from a mid-latitude prescribed chaparral fire

Smoke-plume gas samples were collected at altitudes from 35-670 m above the ground over the San Dimas Experimental Forest during a 400-acre prescribed chaparral fire. Mean emission ratios relative to CO2 for CO, H2, CH4, and total nonmethane hydrocarbons were lower than previous values obtained for large biomass-burning field experiments. Comparison of samples from vigorously flaming and mixed stages of combustion revealed little differences in CO2 normalized emission ratios for these gases (except for N2O).

Cofer, Wesley R., III↗
NASA NTRS1988

An unusual charging event on ISEE 1

Electrostatic cleanliness requirements on ISEE 1 were expected to prevent negative charging in sunlight. This has largely been true, but on three occasions, ISEE 1 has been observed to charge to significant negative potentials in sunlight. Data from the two electric field experiments and from the plasma composition experiment on ISEE 1 show that the spacecraft charged to close to -70 V in sunlight at about 0700 UT on March 17, 1978. Data from the electron spectrometer experiment show that there was a potential barrier of some -10 to -20 V about the spacecraft during this event. The potential barrier was effective in turning back emitted photoelectrons to the spacecraft. Potential barriers can be formed by differential charging on the spacecraft or by the presence of excess space charge in the plasma. The shape of the barrier suggests that it is due to the former, even though electrostatic cleanliness specifications imposed on ISEE were intended to eliminate differential charging. Modeling of this event showed that the barrier could not be produced by the presence of space charge but that it was most likely produced by differential charging of the solar arrays.

Olsen, R. C.↗
NASA NTRS1989

Digital 8-DPSK Modem For Trellis-Coded Communication

Digital real-time modem processes octuple differential-phase-shift-keyed trellis-coded modulation. Intended for use in communicating data at rate up to 4.8 kb/s in land-mobile satellite channel (Rician fading) of 5-kHz bandwidth at carrier frequency of 1 to 2 GHz. Modulator and demodulator contain digital signal processors performing modem functions. Design flexible in that functions altered via software. Modem successfully tested and evaluated in both laboratory and field experiments, including recent full-scale satellite experiment. In all cases, modem performed within 1 dB of theory. Other communication systems benefitting from this type of modem include land mobile (without satellites), paging, digitized voice, and frequency-modulation subcarrier data broadcasting.

Jedrey, T. C.↗
NASA NTRS1988

Proceedings of the Twelfth NASA Propagation Experimenters Meeting (NAPEX 12)

The NASA Propagation Experimenters Meeting was convened on June 9 and 10, 1988. Pilot Field Experiments propagation studies, mobile communication systems, signal fading, communication satellites rain gauge network measurements, atmospheric attenuation studies, optical communication through the atmosphere, and digital beacon receivers were among the topics discussed.

Davarian, Faramaz↗
NASA NTRS1988

Comparison of measured and modeled radiation, heat and water vapor fluxes: FIFE pilot study

The primary objectives of the 1985 study were to test the feasibility of using radio frequency receivers to collect data from automated weather stations and to evaluate the use of the data collected by the automated weather stations for modeling the fluxes of latent heat, sensible heat, and radiation over wheat. The model Cupid was used to calculate these fluxes which were compared with fluxes of these entities measured using micrometeorological techniques. The primary objectives of the 1986 study were to measure and model reflected and emitted radiation streams at a few locations within the First International Satellite Land-Surface Climatology Project Field Experiment (FIFE) site and to compare modeled and measured latent heat and sensible heat fluxes from the prairie vegetation.

Blad, Blaine L.↗
NASA NTRS1988

High-resolution Interferometer Sounder (HIS), phase 2

The High-resolution Interferometer Sounder (HIS) was successfully built, tested, and flight proven on the NASA U-2/ER-2 high altitude aircraft. The HIS demonstration has shown that, by using the technology of Fourier Transform Spectroscopy (FTS), it is possible to measure the spectrum of upwelling infrared radiance needed for temperature and humidity sounding with high spectral resolution and high radiometric precision. By resolving individual carbon dioxide lines, the retrieved temperature profiles have vertical resolutions of 1 to 2 km and RMS errors less than 1 C, about 2 to 4 times better than possible with current sounders. Implementing this capability on satellite sounders will greatly enhance the dynamical information content of temperature measurements from space. The aircraft model HIS is now a resource which should be used to support field experiments in mesoscale meteorology, to monitor trace gas concentrations and to better understand their effects on climate, to monitor the surface radiation budget and the radiative effects of clouds, and to collect data for research into retrieval techniques, especially under partially cloudy conditions.

Source record↗
NASA NTRS1988

Observed effects of soil organic matter content on the microwave intensity of soils

In order to determine the significance of organic matter content on the microwave emissivity of soils when estimating soil moisture, field experiments were conducted in which 1.4 GHz microwave emissivity data were collected over test plots of sandy loam soil with different organic matter levels (1.8, 4.0, and 6.1 percent) for a range of soil moisture values. Analyses of the observed data show only minor variation in microwave emissivity due to a change in organic matter content at a given moisture level for soils with similar texture and structure. Predictions of microwave emissivity made using a dielectric model for aggregated soils exhibit the same trends and type of response as the measured data when appropriate values for the input parameters were utilized.

Jackson, T. J.↗
NASA NTRS1989

Rotordynamic Instability Problems in High-Performance Turbomachinery, 1988

The continuing trend toward a unified view is supported with several developments in the design and manufacture of turbomachines with enhanced stability characteristics along with data and associated numerical/theoretical results. The intent is to provide a continuing impetus for an understanding and resolution of these problems. Topics addressed include: field experience, dampers, seals, impeller forces, bearings, and compressor and rotor modeling.

Source record↗
NASA NTRS1988

Microwave remote sensing of sea ice

The long term objectives are: (1) to understand the physics of the multispectral microwave radiative characteristics of sea ice as it goes through different phases; (2) to improve characterization of sea ice cover using satellite microwave sensors; and (3) to study ice/ocean physical and biological processes associated with polynya formations and variability of the marginal sea ice region. Two field experiments were conducted to pursue these objectives. One involved measurements of radiative and physical characteristics of sea ice from a ship during a 3-month long cruise through the Weddell Sea ice pack during the Austral winter of 1986. The other involved similar measurements from two aircrafts and a submarine over the Central Arctic and Greenland Sea region. Preliminary results have already led to an enhanced understanding of the microwave signatures of pancake ice, nilas, first year ice, multiyear ice and effects of snow cover. Coastal and deep ocean polynyas and their role in bottom water formation and ocean circulation were studied using a time series of ice images from SMMR. An unsupervised cluster analysis of Arctic sea ice using SMMR and THIR emissivity and brightness temperature data was implemented. The analysis indicates the existence of several unique and persistent clusters in the Central Arctic region during winter and that the sum of the area of these clusters excluding those of first year ice is about 20 percent less than minimum ice cover area inferred from a previous summer data. This result is consistent with saline surface for some multiyear ice floes as observed during MIZEZ and suggests that a significant fraction of multiyear ice floes in the Arctic have first year ice signatures.

Comiso, J. C.↗
NASA NTRS1988

Advanced Solidstate Array Spectroradiometer

During the Summer of 1987, the Advanced Solidstate Array Spectroradiometer (ASAS) was installed and flown on the NASA Ames C-130 in support of the First International Field Experiment (FIFE) missions. The study site was over the grassland areas of the Konza Prairie in Kansas. The data collected with ASAS during these flights has been used to produce the first nearly simultaneous multiangular/multispectral images of selected terrestrial study sites. This data will be valuable in the study of surface bidirectional reflectance and albedo. The data will also be useful for the development of data analysis algorithms for future spaceborne instruments such as the Goddard MODIS-T and JPL's HIRIS. The flight data acquired is further analyzed.

Huegel, F. G.↗
NASA NTRS1988

Airborne lidar detection of subsurface oceanic scattering layers

The airborne lidar detection and cross-sectional mapping of submerged oceanic scattering layers are reported. The field experiment was conducted in the Atlantic Ocean southeast of Assateague Island, VA. NASA's Airborne Oceanographic Lidar was operated in the bathymetric mode to acquire on-wavelength 532-nm depth-resolved backscatter signals from shelf/slope waters. Unwanted laser pulse reflection from the air-water interface was minimized by spatial filtering and off-nadir operation. The presence of thermal stratification over the shelf was verified by the deployment of airborne expendable bathythermographs. Optical beam transmission measurements acquired from a surface truthing vessel indicated the presence of a layer of turbid water near the sea floor over the inner portion of the shelf.

Hoge, Frank E.↗
NASA NTRS1987

Low cost, microcomputer-based interactive analysis system for direct-reception and archived remote sensing data

A hardware/software system has been developed for use in meteorological field experiments and by developing countries which need low-cost remote sensing data analysis capabilities. The system can directly receive satellite transmissions of the AVHRR, TOVS, Argos, GOES, GMS, and Meteosat systems. Also, the system can process computer tapes from Landsat. Received data are ingested directly into the computer's disk storage, eliminating the need for a wide-band analog tape drive. Data may be interpreted in terms of cloud imagery, cloudtop temperature, sea surface temperature, vegetation index, and temperature/humidity profiles with overlays of geographic boundaries and latitude/longitude grids. The image processing, enhancement functions, and modeling capabilities of the system are discussed.

Vermillion, Charles H.↗
NASA NTRS1988

Radiometric calibration of the reflective bands of NS001-Thematic Mapper Simulator (TMS) and modular multispectral radiometers (MMR)

The NS001 Thematic Mapper Simulator scanner (TMS) and several modular multispectral radiometers (MMRs) are among the primary instruments used in the First ISLSCP (International Satellite Land Surface Climatology Project) Field Experiment (FIFE). The NS001 has a continuously variable gain setting. Calibration of the NS001 data is influenced by drift in the dark current level of up to six counts during a mirror scan at typical gain settings. The MMR instruments are being used in their 1 deg FOV configuration on the helicopter and 15 deg FOV on the ground.

Markham, Brian L.↗
NASA NTRS1989

Differential absorption lidar sensing of ozone

The differential absorption lidar (DIAL) technique for deriving O3 profiles from lidar measurements is discussed. The NASA airborne DIAL system is described, and examples of a broad range of O3 and aerosol measurements are presented from a number of field experiments. These airborne and ground-based DIAL measurements demonstrate the outstanding capability of lidar for conducting O3 investigations throughout the troposphere and lower stratosphere under widely different atmospheric conditions.

Browell, Edward V.↗
NASA NTRS1989

Demonstration of sub-meter GPS orbit determination and 1.5 parts in 10 to the 8th three-dimensional baseline accuracy

Strategies for the estimation of precise GPS orbits and ground baselines, designed to minimize error sources related to the GPS orbit accuracy and the tropospheric delay, are demonstrated. Using GPS data from field experiments conducted in 1985 and 1986, it is shown that, by carefully selecting well-known stations to serve as reference points and by using the GPS data to determine high-accuracy GPS orbits and to solve for wet tropospheric delay fluctuations, the 2000-km baselines in North America can now be estimated with the accuracy better than 1.5 parts in 10 to the 8th. Using these strategies, better than l-m accuracy was achieved for the two best-tracked satellites (of the seven total operational GPS satellites).

Lichten, Stephen M.↗
NASA NTRS1990

Data-Management Software For PiFEx

UNIX Based Data Management System is collection of computer programs for use in Pilot Field Experiment (PiFEx), which attempts to mimic mobile/satellite-communications (MSAT) scenario. Major purposes to define mobile-communications channels and test workability of new concepts used to design various components of receiver system. Results, large amounts of raw data that must be retrieved according to researcher's needs. Intended to manage PiFEx data in interactive way. Written in either FORTRAN-77 or UNIX shell-scripts.

Kantak, Anil V.↗