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At least 811 records · Page 45

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NASA NTRS1974

Earth's gravity field to the eighteenth degree and geocentric coordinates for 104 stations from satellite and terrestrial data

Geodetic parameters describing the earth's gravity field and the positions of satellite-tracking stations in a geocentric reference frame have been computed. These parameters were estimated by means of a combination of five different types of data: routine and simultaneous satellite observations, observations of deep space probes, measurements of terrestrial gravity, and surface triangulation data. The combination gives better parameters than does any subset of data types. The dynamic solution used precision-reduced Baker-Nunn observations and laser range data of 25 satellites. Data from the 49-station National Oceanic and Atmospheric Administration BC-4 network, the 19-station Smithsonian Astrophysical Observatory Baker-Nunn network, and independent camera stations were employed in the geometrical solution.

Gaposchkin, E. M.↗

NASA NTRS1974

Present and future NASA earth resources related satellite programs

Ongoing and presently contemplated earth resources related space programs are discussed, and the evolution of present programs is presented. Nimbus, ERTS (earth resources technology satellite), Skylab, and GEOS C (geodetic earth-orbiting satellite C) are the ongoing programs described. Future projects explained comprise ERS (earth resources survey operational satellite), Nimbus G, EOS (earth observatory satellite), SEASAT (sea satellite), and shuttle sortie. The objectives and instrument payloads for each of the missions are detailed. A number of high-altitude color satellite photographs supplements the treatment.

Branchflower, G. A.↗

NASA NTRS1974

Marine geodesy - Problem areas and solution concepts

This paper deals with a conceptional geodetic approach to solve various oceanic problems, such as submersible navigation under iced seas, demarcation/determination of boundaries in open ocean, resolving sea-level slope discrepancy, improving tsunami warning system, ecology, etc., etc. The required instrumentation is not described here. The achieved as well as desired positional accuracy estimates in open ocean for various tasks are also given.

Saxena, N.↗

NASA NTRS1974

Post-earthquake dilatancy recovery

Geodetic measurements of the 1964 Niigata, Japan earthquake and of three other examples are briefly examined. They show exponentially decaying subsidence for a year after the quakes. The observations confirm the dilatancy-fluid diffusion model of earthquake precursors and clarify the extent and properties of the dilatant zone. An analysis using one-dimensional consolidation theory is included which agrees well with this interpretation.

Scholz, C. H.↗

NASA NTRS1974

Techniques for the analysis of geodynamic effects using laser data

A technique is described by which laser measurements may be used in an explicit definition of geodetic parameters at the one-meter level of resolution. Observations made by a tracking station at the Goddard Space Flight Center of the Beacon Explorer C satellite are analyzed with this technique to yield highly precise measures of perturbations in the satellite's inclination, including the effect of earth and ocean tides and variations in the station's latitude due to polar motion. The tracking configuration is described, and the basic technique is outlined (analysis of six-hour observations with a weighted least squares orbit determination method). Techniques for analyzing orbital errors and inclination perturbations are described, and it is shown that quarter-day spans of laser data can be employed to monitor the inclination of the satellite to the order of 0.01 arcseconds precision over a period of 17 months.

Dunn, P. J.↗

NASA NTRS1974

A global station coordinate solution based upon camera and laser data - GSFC 1973

The results of a determination of the coordinates of about 70 tracking stations are presented. The data were deived with the aid of dynamical techniques from precise reduced optical and laser observations of geodetic satellites. It is attempted to establish a reasonable accuracy estimate through a comparison of the data with other independent solutions. A brief description is given of the independent solutions used as a source of comparison.

Marsh, J. G.↗

NASA NTRS1975

Planetary geodesy

Work related to planetary geodesy conducted during the period from 1971 to 1975 is reviewed, taking into account the traditional subjects of geometrical and physical geodesy. Particular attention is given to the size and shape of the planets and to their masses and gravity fields. Improvements in the principal geodetic parameters of Mercury, Venus, and Mars are considered. Studies of the planets Jupiter, Saturn, Uranus, and Neptune are also discussed.

Anderson, J. D.↗

NASA NTRS1975

Satellite altimetry applied to marine geoid determination

The pioneering satellite radar altimeter aboard Skylab has provided a wealth of information about ocean surface topography for both the oceanographic and geodetic communities. This report describes typical satellite altimetry concepts and discusses the parameters measured, geometry utilized, and techniques employed to generate ocean geoid estimates. The standard deviation of the noise on the altitude measurements is shown to range from one to three meters when the altimeter antenna is nadir aligned. The altimeter is shown to sense short wavelength ocean surface features which are not included in present conventional global geoids. An estimate of a local geoid in the Atlantic, using only altimeter data, is presented. Finally, results demonstrate that the Skylab radar altimeter system capability is less than 10 meters RMS.

Leitao, C. D.↗

NASA NTRS1974

Scientific value of Seasat for geodesy

SEASAT altimetry data which relate directly to geoid heights provide the means to obtain information on the geoid on a global scale which is not attenuated by height or by high frequency averaging. The most important geodetic application of these data is to provide a standard reference surface for oceans.

Chovitz, B. H.↗

NASA NTRS1974

Civil and scientific applications of the geoid

SEASAT-A can be used for determining the geoid to much higher accuracy on a world wide basis and in a relatively short time. Two basic objectives can be considered: (1) determination of the geoid to at least 1 meter. This accuracy will satisfy most geodetic requirements for applications purposes; and (2) determination of the geoid to better than 1-meter an oceanographic objective required for measurement of sea surface topography and sea slope, quasi-stationary departure from the geoid, ocean circulation, air and sea interaction, etc. The geodesy objective in this case will be to define a reference equipotential surface as a means by which the oceanographic requirements can be achieved.

Mourad, A. G.↗

NASA NTRS1974

The Earth and Ocean Physics Applications Program (EOPAP). Ocean dynamics program

SEASAT-A is a research oriented program consisting of a spacecraft, precision ground tracking systems, and data processing and modelling capabilities that address both scientific and application programs problems in ocean surface dynamics for the EOPAP program. An array of active radar and passive microwave and infrared instruments allows for quantitative measurements of oceanic, atmospheric, and geodetic parameters under stormy wind and wave conditions, as well as over regions lying under a cloud cover.

Apel, J. R.↗

NASA NTRS1975

Error analysis for the proposed close grid geodynamic satellite measurement system (CLOGEOS)

The close grid geodynamic measurement system experiment which envisages an active ranging satellite and a grid of retro-reflectors or transponders in the San Andreas fault area is a detailed simulated study for recovering the relative positions in the grid. The close grid geodynamic measurement system for determining the relative motion of two plates in the California region (if feasible) could be used in other areas of the world to delineate and complete the picture of crustal motions over the entire globe and serve as a geodetic survey system. In addition, with less stringent accuracy standards, the system would also find usage in allied geological and marine geodesy fields.

Mueller, I. I.↗

NASA NTRS1975

Marking LANDSAT images with small mirror reflectors

Uniquely identifiable artificial landmarks were generated in LANDSAT imagery by making use of specular solar reflection from small, easily transportable mirrors. The results are impressive in well-registered color composite enlargements, where the mirror returns appear as bright white spots. The signatures are unique enough that returns can be readily located in the computer compatible tape records either manually or by machine search. As embodied in experiments to date, the system is entirely passive. Mirrors must be carefully positioned prior to each satellite pass, but the required angle calculations are simple enough to be made on a hand calculator and the required input data are easily available. Possible applications of the technique include providing site identification and geodetic control in remote regions of the earth, enhancement of small targets such as offshore oil derricks, providing atmospheric transmission data coincident with other LANDSAT experiments, and providing a nearly perfect optical point source for overall system checkout.

Evans, W. E.↗

NASA NTRS1976

Site evaluation for laser satellite-tracking stations

Twenty-six locations for potential laser satellite-tracking stations, four of them actually already occupied in this role, are reviewed in terms of their known local and regional geology and geophysics. The sites are also considered briefly in terms of weather and operational factors. Fifteen of the sites qualify as suitable for a stable station whose motions are likely to reflect only gross plate motion. The others, including two of the present laser station sites (Arequipa and Athens), fail to qualify unless extra monitoring schemes can be included, such as precise geodetic surveying of ground deformation.

Mao, N. H.↗

NASA NTRS1975

User requirements for project-oriented remote sensing

Registration of remotely sensed data to geodetic coordinates provides for overlay analysis of land use data. For aerial photographs of a large area, differences in scales, dates, and film types are reconciled, and multispectral scanner data are machine registered at the time of acquisition.

Hitchcock, H. C.↗

NASA NTRS1976

Viking telecommunication effects of GEOS satellite interference based on testing at the Madrid deep space station

In support of the ongoing NASA-European Space Agency (ESA) effort to understand and control possible interference between missions, testing was conducted at the Madrid Deep Space Station from July 1975 to February 1976 to characterize the effect on Viking 1975 telecommunication link performance of Geodetic Earth-Orbiting Satellite (GEOS) downlink signals. The prime use of the data was to develop a capability to predict GEOS interference effects for evaluation of Viking 1975 mission impacts and possible temporary GEOS shutdown. Also, the data would serve as a basis for assessment of the GEOS impact on missions other than Viking as well as for more general interference applications. Performances of the reference receiver, telemetry, and planetary ranging were measured in the presence of various types of GEOS-related interference, including an unmodulated GEOS carrier and simulation of the actual spectrum by an ESA-supplied GEOS suitcase model.

Stuhr, F. V.↗

NASA NTRS1976

Recursive partitioned inversion of large (1500 x 1500) symmetric matrices

A recursive algorithm was designed to invert large, dense, symmetric, positive definite matrices using small amounts of computer core, i.e., a small fraction of the core needed to store the complete matrix. The described algorithm is a generalized Gaussian elimination technique. Other algorithms are also discussed for the Cholesky decomposition and step inversion techniques. The purpose of the inversion algorithm is to solve large linear systems of normal equations generated by working geodetic problems. The algorithm was incorporated into a computer program called SOLVE. In the past the SOLVE program has been used in obtaining solutions published as the Goddard earth models.

Putney, B. H.↗

NASA NTRS1975

Sensitivity analysis of short-arc station coordinate determinations from range data

The accurate determination of the geocentric coordinates of a tracking station is essential for most geodetic and geophysical satellite applications. Since most of these satellites are close to the earth, the geopotential model is a dominant source of error which significantly influences station coordinate determinations. Other sources, such as GM error and drag, also influence the accuracy of the station coordinate determination. One technique for reducing the effect of these errors is to use short-arcs consisting of a few passes of the satellite over the tracking station. This paper analyzes the sensitivity of short-arc station coordinate estimates to various errors in the physical model, to the number of observations, and to the station-satellite geometry using simulated as well as real data.

Schutz, B. E.↗