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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Analyses for precision reduced optical observations from the international satellite geodesy experiment (ISAGEX)

During the time period of December 1970 to September 1971 an International Satllite Geodesy Experiment (ISAGEX) was conducted. Over fifty optical and laser tracking stations participated in the data gathering portion of this experiment. Data from some of the stations had not been previously available for dynamical orbit computations. With the recent availability of new data from the Astrosoviet, East European and other optical stations, orbital analyses were conducted to insure compatibility with the previously available laser data. These data have also been analyzed using dynamical orbital techniques for the estimation of estimation of geocentric coordinates for six camera stations (for Astrosoviet, two East European). Thirteen arcs of GEOS-1 and 2 observations between two and four days in length were used. The uncertainty in these new station values is considered to be about 20 meters in each coordinate. Adjustments to the previously available values were generally a few hundred meters. With these geocentric coordinates these data will now be used to supplement earth physics investigations during the ISAGEX.

Marsh, J. G.↗
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 NTRS1971

The gravimetric geodesy investigation

The Gravimetric Geodesy Investigation which will utilize altimeter and satellite-to-satellite tracking data from GEOS-C, ATS-F, and other spacecraft as appropriate to improve our knowledge of the earth's gravitational field is discussed. This investigation is interrelated with the study of oceanographic phenomena such as those associated with tides and currents, hence the latter are considered together with gravitational effects in the analysis of the data. The oceanographic effects, each of the order of a meter or two in amplitude and with still smaller uncertainties does not seriously hamper the altimeter gravimetric studies at the five meter level. Laser and satellite-to-satellite tracking data, when combined with the altimeter results, should provide the basis for such studies over wide areas of the ocean surface. Laser and conventional geodetic tracking data from ISAGEX and succeeding campaigns will provide a valuable framework for these analyses.

Siry, J. W.↗
NASA NTRS1974

Marine geodesy a multipurpose approach to solve oceanic problems

Various current and future problem areas of marine geodesy are identified. These oceanic problem areas are highly diversified and include submersible navigation under ice seas, demarcation and determination of boundaries in deep ocean, tsunamis, ecology, etc., etc. Their achieved as well as desired positional accuracy estimates, based upon publications and discussions, are also given. A multipurpose approach to solve these problems is described. An optimum configuration of an ocean-bottom control-net unit is provided.

Saxena, N.↗
NASA NTRS1975

Dynamic satellite geodesy

It is pointed out that during the time since the last quadrennial report dynamic satellite geodesy has been continually refined with several new and independent solutions for the gravity field and station coordination. The generalized geoid seems to be known to about 3 m. Satellite-to-satellite tracking has been investigated as a means of determining the fine structure of the gravity field. The earth tide continues to be studied with satellite perturbation analysis. Investigations of polar motion are also considered.

Gaposchkin, E. M.↗
NASA NTRS1976

Probabilistic and deterministic aspects of linear estimation in geodesy

Recent advances in observational techniques related to geodetic work (VLBI, laser ranging) make it imperative that more consideration should be given to modeling problems. Uncertainties in the effect of atmospheric refraction, polar motion and precession-nutation parameters, cannot be dispensed with in the context of centimeter level geodesy. Even physical processes that have generally been previously altogether neglected (station motions) must now be taken into consideration. The problem of modeling functions of time or space, or at least their values at observation points (epochs) is explored. When the nature of the function to be modeled is unknown. The need to include a limited number of terms and to a priori decide upon a specific form may result in a representation which fails to sufficiently approximate the unknown function. An alternative approach of increasing application is the modeling of unknown functions as stochastic processes.

Dermanis, A.↗
NASA NTRS1977

Phobos and Deimos - Geodesy

Results of geodesy studies of Phobos and Deimos based on Mariner 9 imaging data are presented. This analysis includes a review of the surface coverage and high resolution pictures obtained and the determined sizes, shapes, topographies, and librations of the two Martian satellites. Also, exploration of Phobos and Deimos by missions such as Viking is discussed.

Duxbury, T. C.↗
NASA NTRS1978

Investigations of Mars dynamics and geodesy via the Viking spacecraft

Results are reported for analyses of Doppler, ranging, and tracking data from the Viking landers and orbiters of relevance to the dynamics and geodesy of Mars. Highly improved numerical results are given for the orientation of the spin axis of Mars, the planet's sidereal rotation rate, and the earth-Mars ephemeris. A refined definition of the global gravitational field of Mars is discussed, a local gravitational survey based on Viking Orbiter 2 tracking data is described, and a mass anomaly near Olympus Mons is noted. Radius data are examined which suggest an asymmetry in the figure of Mars characterized by generally higher topography in the southern than in the northern hemisphere. The mass of Phobos is determined on the basis of Orbiter 1 orbital perturbations, and the mean density of this Martian satellite is found to be approximately 2.0 g/cu cm, which is suggestive of primitive carbonaceous chondrites and, if true, implies that Phobos was formed in the asteroid belt.

Michael, W. H., Jr.↗
NASA NTRS1978

Applications of Geodesy to Geodynamics, an International Symposium

Geodetic techniques in detecting and monitoring geodynamic phenomena are reviewed. Specific areas covered include: rotation of the earth and polar motion; tectonic plate movements and crustal deformations (space techniques); horizontal crustal movements (terrestrial techniques); vertical crustal movements (terrestrial techniques); gravity field, geoid, and ocean surface by space techniques; surface gravity and new techniques for the geophysical interpretation of gravity and geoid undulation; and earth tides and geodesy.

Mueller, I. I.↗
NASA NTRS1979

Multivariate approximation methods and applications to geophysics and geodesy

The first report in a series is presented which is intended to be written by the author with the purpose of treating a class of approximation methods of functions in one and several variables and ways of applying them to geophysics and geodesy. The first report is divided in three parts and is devoted to the presentation of the mathematical theory and formulas. Various optimal ways of representing functions in one and several variables and the associated error when information is had about the function such as satellite data of different kinds are discussed. The framework chosen is Hilbert spaces. Experiments were performed on satellite altimeter data and on satellite to satellite tracking data.

Munteanu, M. J.↗
NASA NTRS1979

Investigations on the hierarchy of reference frames in geodesy and geodynamics

Problems related to reference directions were investigated. Space and time variant angular parameters are illustrated in hierarchic structures or towers. Using least squares techniques, model towers of triads are presented which allow the formation of linear observation equations. Translational and rotational degrees of freedom (origin and orientation) are discussed along with and the notion of length and scale degrees of freedom. According to the notion of scale parallelism, scale factors with respect to a unit length are given. Three-dimensional geodesy was constructed from the set of three base vectors (gravity, earth-rotation and the ecliptic normal vector). Space and time variations are given with respect to a polar and singular value decomposition or in terms of changes in translation, rotation, deformation (shear, dilatation or angular and scale distortions).

Grafarend, E. W.↗
NASA NTRS1981

Superconducting tensor gravity gradiometer for satellite geodesy and inertial navigation

A sensitive gravity gradiometer can provide much needed gravity data of the earth and improve the accuracy of inertial navigation. Superconductivity and other properties of materials at low temperatures can be used to obtain a sensitive, low-drift gravity gradiometer; by differencing the outputs of accelerometer pairs using superconducting circuits, it is possible to construct a tensor gravity gradiometer which measures all the in-line and cross components of the tensor simultaneously. Additional superconducting circuits can be provided to determine the linear and angular acceleration vectors. A tensor gravity gradiometer with these features is being developed for satellite geodesy. The device constitutes a complete package of inertial navigation instruments with angular and linear acceleration readouts as well as gravity signals.

Paik, H. J.↗