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All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Recommended reference figures for geophysics and geodesy

Specific reference figures are recommended for consistent use in geophysics and geodesy. The selection of appropriate reference figure for geophysical studies suggests a relationship between the Antarctic negative gravity anomaly and the great shrinkage of the Antarctic ice cap about 4-5 million years ago. The depression of the south polar regions relative to the north polar regions makes the Southern Hemisphere flatter than the Northern Hemisphere, thus producing the third harmonic (pear-shaped) contribution to the earth's figure.

Khan, M. A.↗
NASA NTRS1973

Microwave spectrometer on the Nimbus 5 satellite - Meteorological and geophysical data

The Nimbus 5 microwave spectrometer has been used to measure thermal radiation in five frequency bands between 22.235 and 58.8 gigahertz, and has yielded both the temperature profile and, over ocean, the vapor and liquid water content of the terrestrial atmosphere, even in overcast conditions. Information has also been obtained on geophysical parameters that affect the surface emissivity, such as ice type, sea roughness, and snow cover. The experiment demonstrates the considerable potential of passive microwave sensing of meteorological and geophysical parameters.

Staelin, D. H.↗
NASA NTRS1974

Geophysical, geochemical, and geological investigations of the Dunes geothermal system, Imperial Valley, California

The Dunes anomaly is a water-dominated geothermal system in the alluvium of the Salton Trough, lacking any surface expression. It was discovered by shallow-temperature gradient measurements. A 612-meter-deep test well encountered several temperature-gradient reversals, with a maximum of 105 C at 114 meters. The program involves surface geophysics, including electrical, gravity, and seismic methods, down-hole geophysics and petrophysics of core samples, isotopic and chemical studies of water samples, and petrological and geochemical studies of the cores and cuttings. The aim is (1) to determine the source and temperature history of the brines, (2) to understand the interaction between the brines and rocks, and (3) to determine the areal extent, nature, origin, and history of the geothermal system. These studies are designed to provide better definition of exploration targets for hidden geothermal anomalies and to contribute to improved techniques of exploration and resource assessment.

Elders, W. A.↗
NASA NTRS1974

Solar flare emissions and geophysical disturbances

Various geophysical phenomena are produced by both wave and particle emission from solar flares. In understanding these phenomena, it is necessary to investigate the nature of these emissions and solar flare phenomena. Using the observed data for these emissions, a review is given on the nature of solar flares and their development. Geophysical phenomena are discussed by referring to the results for solar flare phenomena.

Sakurai, K.↗
NASA NTRS1977

An array processing system for lunar geochemical and geophysical data

A computerized array processing system has been developed to reduce, analyze, display, and correlate a large number of orbital and earth-based geochemical, geophysical, and geological measurements of the moon on a global scale. The system supports the activities of a consortium of about 30 lunar scientists involved in data synthesis studies. The system was modeled after standard digital image-processing techniques but differs in that processing is performed with floating point precision rather than integer precision. Because of flexibility in floating-point image processing, a series of techniques that are impossible or cumbersome in conventional integer processing were developed to perform optimum interpolation and smoothing of data. Recently color maps of about 25 lunar geophysical and geochemical variables have been generated.

Eliason, E. M.↗
NASA NTRS1980

Geophysical and astronomical models applied in the analysis of very long baseline interferometry

Very long baseline interferometry presents an opportunity to measure at the centimeter level such geodetic parameters as baseline length and instantaneous pole position. In order to achieve such precision, the geophysical and astronomical models used in data analysis must be as accurate as possible. The Mark-3 interactive data analysis system includes a number of refinements beyond conventional practice in modeling precession, nutation, diurnal polar motion, UT1, solid Earth tides, relativistic light deflection, and reduction to solar system barycentric coordinates. The algorithms and their effects on the recovered geodetic, geophysical, and astrometric parameters are discussed.

Ma, C.↗
NASA NTRS1981

Ultimate limits to error probabilities for ionospheric models based on solar geophysical indices and how these compare with the state of the art

An ideal model based on a given set of geophysical indices is defined as a model that provides a least squares fit to the data set as a function of the indices considered. Satellite measurements of electron content for three stations at different magnetic latitudes were used to provide such data sets which were each fitted to the geophysical indices. The magnitude of the difference between the measured value and the derived equation for the data set was used to estimate the probability of making an error greater than a given magnitude for such an ideal model. Atmospheric Explorer C data is used to examine the causes of the fluctuations and suggestions are made about how real improvements can be made in ionospheric forecasting ability. Joule heating inputs in the auroral electrojets are related to the AL and AU magnetic indices. Magnetic indices based on the time integral of the energy deposited in the electrojets are proposed for modeling processes affected by auroral zone heating.

Nisbet, J. S.↗
NASA NTRS1981

Geophysical fluid dynamics

Systematic scaling or dimensional analysis reveals that certain scales of geophysical fluid flows (such as stellar, ocean, and planetary atmosphere circulations) can be accurately modeled in the laboratory using a procedure which differs from conventional engineering modeling. Rather than building a model to obtain numbers for a specific design problem, the relative effects of the significant forces are systematically varied in an attempt to deepen understanding of the effects of these forces. Topics covered include: (1) modeling a large-scale planetary atmospheric flow in a rotating cylindrical annulus; (2) achieving a radial dielectric body force; (3) spherical geophysical fluid dynamics experiments for Spacelab flights; (4) measuring flow and temperature; and (5) the possible effect of rotational or precessional disturbances on the flow in the rotating spherical containers.

Fowlis, W. W.↗
NASA NTRS1982

Geophysical fluid flow cell experiment

The primary purpose of the geophysical flow experiments is to simulate large-scale baroclinic (density-stratified) flows which occur naturally in the atmospheres of rotating planets and stars and to gain insights and obtain answers to crucial questions concerning the large-scale nonlinear mechanics of the global geophysical flows. Those external conditions related to fluid viscosity, rotation, gravity are identified, which allow qualitatively different modes of instability or waves in the model.

Hart, J. E.↗
NASA NTRS1983

A two step linear statistical technique using leaps and bounds procedure for retrieval of geophysical parameters from microwave radiometric data

A linear statistical technique using a 'leaps and bounds' procedure (Furnival and Wilson, 1974) is developed for retrieving geophysical parameters from remote measurements. It is used for retrieving sea surface temperatures from the Scaning Multichannel Microwave Radiometer (SMMR) on Seasat. The technique uses an efficient algorithm to select the best fixed-size subset of the 10 SMMR channels for linearly retrieving a given geophysical parameter. The 5-channel subset (6.6V, 6.6H 10H, 18V, 21H), where V and H refer to, respectively, the vertical and horizontal polarizations and the numbers are the channel frequencies in gigahertz, gives the minimum rms error in estimating the sea surface temperature. A comparison with ground truth indicates that the algorithm infers the temperature with an rms accuracy of better than 1.5 K under most environmental conditions. A quality control procedure which is seen as holding promise for further improving the accuracy is proposed.

Kakar, R. K.↗
NASA NTRS1984

Alternative experiments using the geophysical fluid flow cell

This study addresses the possibility of doing large scale dynamics experiments using the Geophysical Fluid Flow Cell. In particular, cases where the forcing generates a statically stable stratification almost everywhere in the spherical shell are evaluated. This situation is typical of the Earth's atmosphere and oceans. By calculating the strongest meridional circulation expected in the spacelab experiments, and testing its stability using quasi-geostrophic stability theory, it is shown that strongly nonlinear baroclinic waves on a zonally symmetric modified thermal wind will not occur. The Geophysical Fluid Flow Cell does not have a deep enough fluid layer to permit useful studies of large scale planetary wave processes arising from instability. It is argued, however, that by introducing suitable meridional barriers, a significant contribution to the understanding of the oceanic thermocline problem could be made.

Hart, J. E.↗
NASA NTRS1983

Geophysical consequences of phanerozoic and Archean crustal evolution: Evidence from crustal cross-sections

Geophysical properties of continental crust depend on the nature of crustal evolution. This is well illustrated by examination of two crustal cross-sections (1), the combined Ivrea-Verbano zone (IVZ) and Strona-Ceneri zone (SCZ) of northern Italy and the Pikwitonei granulite belt (PGB) and Cross Lake subprovince (CLS) of Manitoba. These two cross-sections are of particular interest because the IVZ and SCZ developed during Phanerozoic time whereas the PGB-CLS is an example of Archean crustal evolution. Consequently, each cross-section is geologically distinctive and, thus, exhibits very different geophysical properties such as density, seismic velocity, heat production, and magnetism. Results of geological investigations of each area are given.

Fountain, D. M.↗
NASA NTRS1986

Geophysical constraints on the lunar interior

Geophysical constraints relating to the structure, composition, and thermal state of the moon are reviewed in an attempt to evaluate lunar origin models. Particular attention is given to constraints on the bulk composition of the crust and mantle, on the existence and size of a possible metallic core, and on the depth of initial melting and differentiation. It is noted that models such as the binary accretion hypothesis would be capable of producing a bulk moon in accordance with available geophysical constraints.

Hood, L. L.↗
NASA NTRS1991

GEOSIM: A numerical model for geophysical fluid flow simulation

A numerical model which simulates geophysical fluid flow in a wide range of problems is described in detail, and comparisons of some of the model's results are made with previous experimental and numerical studies. The model is based upon the Boussinesq Navier-Stokes equations in spherical coordinates, which can be reduced to a cylindrical system when latitudinal walls are used near the pole and the ratio of latitudinal length to the radius of the sphere is small. The equations are approximated by finite differences in the meridional plane and spectral decomposition in the azimuthal direction. The user can specify a variety of boundary and initial conditions, and there are five different spectral truncation options. The results of five validation cases are presented: (1) the transition between axisymmetric flow and baroclinic wave flow in the side heated annulus; (2) the steady baroclinic wave of the side heated annulus; (3) the wave amplitude vacillation of the side heated annulus; (4) transition to baroclinic wave flow in a bottom heated annulus; and (5) the Spacelab Geophysical Fluid Flow Cell (spherical) experiment.

Butler, Karen A.↗
NASA NTRS1990

Evaluation of geophysical properties of the lunar regolith for the design of precursor scientific missions for the space exploration initiative

The following topics are addressed: (1) the frequency of encountering boulders that represent hazards to lunar operations; (2) the ease of lunar soil excavation; (3) the use of explosives in excavation operation; (4) the trafficability of the regolith; (5) problems encountered in mining (probably strip mining) of the regolith; (6) the stable angle(s) of repose in excavation of the regolith; (7) the layering to be encountered in the subsurface; (8) knowledge of the regolith site and the possibility of its general application to any site on the lunar surface; (9) the data needed to characterize a site for a lunar base; (10) the influence of regolith properties on the design of geophysical experiments from the lunar base; and (11) terrestrial analogues for the geophysical properties of the lunar regolith.

Morgan, Paul↗
NASA NTRS1991

Validating a large geophysical data set - Experiences with satellite-derived cloud parameters

The goal of this study is to validate the global cloud parameters derived from the satellite-borne HIRS2 and MSU atmospheric sounding instrument measurements, and to use the analysis of these data as one prototype for studying large geophysical data sets in general. The HIRS2/MSU data set contains a total of 40 physical parameters, filling 25 MB/day; raw HIRS2/MSU data are available for a period exceeding 10 years. Validation involves developing a quantitative sense for the physical meaning of the derived parameters over the range of environmental conditions sampled. This is accomplished by comparing the spatial and temporal distributions of the derived quantities with similar measurements made using other techniques, and with model results. The need to work with Level 2 (point) data, rather than Level 3 (gridded) data for validation purposes is discussed, and some techniques developed for charting the assumptions made in deriving an algorithm and generating a code to produce geophysical quantities from measured radiances are presented.

Kahn, Ralph↗
NASA NTRS1993

A study of the impact of the Space Shuttle environment on faint far-UV geophysical and astronomical phenomena

FAUST is a far ultraviolet (1400-1800 A) photon-counting imaging telescope featuring a wide field of view (7.6 deg) and a high sensitivity to extended emission features. During its flight as part of the ATLAS-1 payload aboard the STS-45 mission in March 1992, 19 deep-space nighttime viewing opportunities were utilized by FAUST. Here we report the observed fluxes and their time and space variations, and identify the signatures of postsunset airglow phenomena and Orbiter Vernier attitude control thruster firing events. We find that the Space Shuttle nighttime environment at 296 km altitude is often sufficiently dark to permit geophysical and astronomical UV observations down to levels on the order of 1000 photons/sq cm sr A sec, or 0.01 Rayleighs/A. We also find evidence for occasional geophysical fluxes of some tens or hundreds of Rayleighs in the upward-looking direction.

Lampton, Michael↗
NASA NTRS1993

Geophysical signature of the Pretoria saltpan impact structure and a possible satellite crater

The Pretoria Saltpan Crater is located in the southern portion of the Bushveld Igneous Complex, some 40 km NNW of Pretoria, South Africa, at 25 deg 24 min 30 sec S/28 deg 4 min 59 sec E. An origin by impact for this crater structure was recently confirmed. The results of the only gravity reconnaissance carried out over the crater to date failed to support an impact origin. With the aid of recent results obtained from a central drill-core, it was necessary to carry out more geophysical work which would include a gravity profile of higher resolution. A second, smaller, circular depression (about 400 m in diameter) to the SW of the crater is suggestive of a twin crater. This site had never been investigated, and thus various geophysical surveys were conducted.

Brandt, D.↗