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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

National Geodetic Satellite Program, Part II: Ohio State University

Data analysis was carried out to obtain an improved global network combining all participating tracking stations in a single worldwide coordinate system. Mathematical formulations were derived, programmed, and tested. Observational data were used to determine the relative positions of tracking stations in an arbitrary Cartesian coordinate system. The position of this coordinate system was estimated with respect to an absolute system. A primary network was established in which station positions were known to an internal consistency of 10 meters or better for the following purposes: (1) to establish the relative relationships between the various geodetic datums in use around the world; and (2) to connect isolated tracking stations, islands, navigational beacons, and other points of interest. Results are presented.

Mueller, I. I.↗
NASA NTRS1977

National Geodetic Satellite Program, Part II: Evaluation

The National Geodetic Satellite Program (NGSP) was evaluated to see if the program objectives were actually met. An inspection of the results shows that the general objectives were met. It is concluded that the specific results of the NGSP were too generally stated to allow one to tell whether they were met or were unobtainable. Analysis of methods and results shows that the standard deviations assigned to the results are indications of precision, not accuracy, and cannot be used to rank the various sets of coordinates in order of accuracy.

Henriksen, S. W.↗
NASA NTRS1978

Monitoring regional crustal deformation with horizontal geodetic data

The National Ocean Survey is developing an automated system to derive parameters of horizontal crustal motion from existing geodetic data by the process of least squares estimation. The estimated parameter will describe crustal motion as a function of geographic position. The system will first be tested in the Imperial Valley region of southern California, using data from 8 individual field projects spanning four decades of time.

Snay, R. A.↗
NASA NTRS1979

Geodetic interferometry submission for the IUGG Quadrennial Report

The present paper reviews the activities of two major VLBI (Very Long Baseline Interferometry) groups, within the United States, which have been concentrating on geodetic measurements for a number of years. The activities have resulted in the development of transportable VLBI terminals for regional surveying applications; development of VLBI techniques for obtaining station positions; establishment of relative epochs and rates of the hydrogen maser clocks at the stations; the acquisition of polar motion and earth rotation data in support of deep space tracking functions; and the development of VLBI techniques necessary for tectonic measurements on trans- and intercontinental baselines and for astrometry, polar-motion and earth-rotation observations.

Clark, T. A.↗
NASA NTRS1980

Geodetic measurements with a mobile VLBI system

The Project ARIES 9 meter transportable antenna was used as one element of very long baseline interferometer (VLBI) to begin monitoring locations of six sites in California relative to large diameter fixed antennas at the NASA Deep Space Network, Goldstone, California, and at the Caltech Owens Valley Radio Observatory, Big Pine, California. An accuracy of about 6 cm in the horizontal components was demonstrated by comparison with measurements of the National Geodetic Survey. The root of mean square scatter of the lengths of the baselines between any pair of antennas was about 3 cm except for the Goldstone-JPL (Pasadena) baseline. In the period August 1974 to August 1977 the length of this baseline increased by 15 + or - 5 cm as JPL moved westward relative to Goldstone at the rate of 6 + or - 2 cm/year. The baseline lengths were unaffected by the uncertainties of UT1, polar motion, and tropospheric water vapor, which are the limitations to present three dimensional vector accuracies.

Niell, A. E.↗
NASA NTRS1980

Scandinavia studies of recent crustal movements and the space geodetic baseline network

A brief review of crustal movements within the Fenno-Scandia shield is given. Results from postglacial studies, projects for measuring active fault regions, and dynamic ocean loading experiments are presented. The 1979 Scandinavian Doppler Campaign Network is discussed. This network includes Doppler translocation baseline determination of future very long baseline interferometry baselines to be measured in Scandinavia. Intercomparison of earlier Doppler translocation measurements with a high precision terrestrial geodetic baseline in Scandinavia has yielded internal agreement of 6 cm over 887 km. This is a precision of better than 1 part in to the 7th power.

Anderson, A. J.↗
NASA NTRS1980

Water vapor as an error source in microwave geodetic systems: Background and survey of calibration techniques

Water vapor as an error source in radio interferometry systems is briefly examined. At microwave frequencies, the delay imposed by tropospheric water vapor becomes a limiting error source for high accuracy geodetic systems. The mapping of tropospheric induced errors into 'solved-for' parameters depends upon baseline length and observing strategy. Simulation analysis (and experience) indicates that in some cases, errors in estimating tropospheric delay can be magnified in their effect on baseline components. The various techniques by which tropospheric water can be estimated or measured are surveyed with particular consideration to their possible use as a calibration technique in support to very long baseline interferometry experiments. The method of remote sensing using a microwave radiometer seems to be the most effective way to provide an accurate estimate of water vapor delay.

Claflin, E. S.↗
NASA NTRS1980

NASA geodetic applications of the Mark 3 VLBI system

The Mark 3 very long baseline interferometer system was used in monitoring the following geodetic phenomena: the regional deformation and strain accumulation related to large earthquakes in the plate boundary region of the western United States; contemporary relative plate tectonic motions of the North American, Pacific, South American, Eurasian, and Australian Plates; the internal deformation of continental and oceanic lithospheric plates with particular emphasis on North America and the Pacific; the rotational dynamics of the Earth and their possible correlation to earthquakes, plate motions, and other geophysical phenomena; and motions and deformation occurring in regions of high earthquake activity.

Coates, R.↗
NASA NTRS1980

Geodetic distance measuring apparatus

A geodetic distance measuring apparatus which compensates for the refractive index of the atmosphere is discussed. A mode locked laser system with a laser device and its peripheral components is utilized to derive two mutually phase locked optical wavelength signals and one phase locked microwave CW signal which respectively traverse the same distance measurement path. The optical signals are comprised of pulse type signals. Phase comparison of the two optical wavelength pulse signals is used to provide the dry air density while phase comparison of one of the optical wavelength pulse signals and the microwave CW signal issued to provide wet or water vapor density of the air. The distance to be measured corrected for the atmospheric dry air and water vapor densities in the measurement path is computed from these measurements. A time interval unit is included for measuring transit time of individual optical pulses for resolving the phase ambiguity needed with the phase measurements to give the true target distance.

Abshire, J. B.↗
NASA NTRS1981

Baseline mathematics and geodetics for tracking operations

Various geodetic and mapping algorithms are analyzed as they apply to radar tracking systems and tested in extended BASIC computer language for real time computer applications. Closed-form approaches to the solution of converting Earth centered coordinates to latitude, longitude, and altitude are compared with classical approximations. A simplified approach to atmospheric refractivity called gradient refraction is compared with conventional ray tracing processes. An extremely detailed set of documentation which provides the theory, derivations, and application of algorithms used in the programs is included. Validation methods are also presented for testing the accuracy of the algorithms.

James, R.↗
NASA NTRS1981

Transformation formulas relating geodetic coordinates to a tangent to Earth, plane coordinate system

Formulas and their approximation were developed to map geodetic position to an Earth tangent plane with an airport centered rectangular coordinate system. The transformations were developed for use in a terminal area air traffic model with deterministic aircraft traffic. The exact configured vehicle's approximation equations used in their precision microwave landing system navigation experiments.

Credeur, L.↗
NASA NTRS1981

Geodetic monitoring of tectonic deformation: Toward a strategy

Issues of interest and importance to society and science are presented. The problems considered are of national concern; their solutions may contribute to a better understanding of tectonic deformation and earthquake hazards. The need for additional field data, the role of geodetic measurements, the importance of both ground and space techniques, and the need for advanced instrumentation development are discussed.

Source record↗
NASA NTRS1982

A case for inherent geometric and geodetic accuracy in remotely sensed VNIR and SWIR imaging products

Significant aberrations can occur in acquired images which, unless compensated on board the spacecraft, can seriously impair throughput and timeliness for typical Earth observation missions. Conceptual compensations options are advanced to enable acquisition of images with inherent geometric and geodetic accuracy. Research needs are identified which, when implemented, can provide inherently accurate images. Agressive pursuit of these research needs is recommended.

Driver, J. M.↗
NASA NTRS1982

On the geodetic applications of simultaneous range-differencing to LAGEOS

The possibility of improving the accuracy of geodetic results by use of simultaneously observed ranges to Lageos, in a differencing mode, from pairs of stations was studied. Simulation tests show that model errors can be effectively minimized by simultaneous range differencing (SRD) for a rather broad class of network satellite pass configurations. The methods of least squares approximation are compared with monomials and Chebyshev polynomials and the cubic spline interpolation. Analysis of three types of orbital biases (radial, along- and across track) shows that radial biases are the ones most efficiently minimized in the SRC mode. The degree to which the other two can be minimized depends on the type of parameters under estimation and the geometry of the problem. Sensitivity analyses of the SRD observation show that for baseline length estimations the most useful data are those collected in a direction parallel to the baseline and at a low elevation. Estimating individual baseline lengths with respect to an assumed but fixed orbit not only decreases the cost, but it further reduces the effects of model biases on the results as opposed to a network solution. Analogous results and conclusions are obtained for the estimates of the coordinates of the pole.

Pablis, E. C.↗
NASA NTRS1982

Application of a recursive distortion estimator to the geodetic correction of thematic mapper imagery

It is pointed out that the higher resolution provided by the Thematic Mapper increases the demands on the accuracy needed by the ground processing in correcting for geodetic errors deriving from internal misalignments and uncertainties in the knowledge of spacecraft ephemeris and attitude. In addition, the Thematic Mapper will also process longer imagery intervals than previous missions. The recursive distortion estimator to be used is a Kalman filter. Here, a minimum variance spacecraft state error vector is estimated for known initial covariance of the elements of that vector and known image noise. Tests of the recursive distortion estimator with various spacecraft models carried out using a simulation of real world state vector dynamics are described. A determination is made of the density of control points needed to meet specified geometric correction requirements; it is expressed as a function of imagery interval length and control point measurement error.

Arnold, P.↗
NASA NTRS1983

A comparison of geodetic Doppler satellite receivers

A great number of geodetic Doppler satellite receivers of various types have been employed since early 1970s. In October and November 1979, a comparison was conducted of three more recent types of receivers, including the CMA-751, the JMR-1A, and the MX-1502. A description of the studies involved in conducting the comparison is presented, taking into account the preliminary results obtained on the basis of the processing of the collected data. Attention is given to tracking statistics, chord difference results, range rate measurement errors, residual tests, station position repeatability, and absolute differences to ground control. Recommendations for future comparisons are also provided.

Archinal, B.↗
NASA NTRS1985

Geodetic and geophysical results from Lageos

Seven years of laser tracking of the Lageos spacecraft have been used to derive geodetic quantities describing the earth and its rotational motion. The dynamical motions of the solid-earth on its axis have been derived continuously since launch and changes in the length-of-day show very high correlation with variations in the atmospheric zonal winds between 1000 and 50 mbars. A significant improvement in the determination of the product of the earth's mass and the gravitational constant has been made. The high accuracy of the orbit determination of Lageos over the 7 years since launch has permitted the identification of a small deceleration in the nodal precession of the orbit. This deceleration is being caused by a small reduction in the flattening of the earth arising from the rebound of the earth after the last ice age. Measurements of the distances between the tracking stations over several years are showing changes consistent with tectonic plate motion and with general ideas of vertical movements.

Smith, D. E.↗