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NASA NTRS1993

Use of global positioning system measurements to determine geocentric coordinates and variations in Earth orientation

Geocentric tracking station coordinates and short-period Earth-orientation variations can be measured with Global Positioning System (GPS) measurements. Unless calibrated, geocentric coordinate errors and changes in Earth orientation can lead to significant deep-space tracking errors. Ground-based GPS estimates of daily and subdaily changes in Earth orientation presently show centimeter-level precision. Comparison between GPS-estimated Earth-rotation variations, which are the differences between Universal Time 1 and Universal Coordinated Time (UT1-UTC), and those calculated from ocean tide models suggests that observed subdaily variations in Earth rotation are dominated by oceanic tidal effects. Preliminary GPS estimates for the geocenter location (from a 3-week experiment) agree with independent satellite laser-ranging estimates to better than 10 cm. Covariance analysis predicts that temporal resolution of GPS estimates for Earth orientation and geocenter improves significantly when data collected from low Earth-orbiting satellites as well as from ground sites are combined. The low Earth GPS tracking data enhance the accuracy and resolution for measuring high-frequency global geodynamical signals over time scales of less than 1 day.

R P Malla↗

NASA NTRS1973

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 were 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. Data from the tracking of deep-space probes were converted to relative longitudes and distances to the earth's axis of rotation of the tracking stations. Surface-gravity data in the form of 550-km squares were derived from 19,328 1 deg X 1 deg mean gravity anomalies.

Gaposchkin, E. M.↗

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 NTRS1988

Determination of a geocentric coordinate frame for GPS measurements

Two strategies for determining the offset from the geocenter for GPS measurements are considered. In the first strategy, VLBI-determined relative positions are used to fix the frame orientation and the absolute scaling, while the geocenter offset is determined from GPS measurements. In the second strategy, the absolute scaling is determined by the adopted gravitational constant of earth and the adjusted periods of GPS orbits, with the latitude being obtained from the time signature of earth rotation in the GPS measurements. The results indicate that geocentric positioning to an accuracy of a few centimeters can be achieved with just one day of precise GPS pseudorange and carrier phase data.

Wu, S. C.↗

NASA NTRS1971

Applications of laser ranging and VLBI observations for selenodetic control

The observation equations necessary to utilize lunar laser ranging and very long baseline interferometry measurements were developed for the establishment of a primary control network on the moon. The network consists of coordinates of moon points in the selenodetic Cartesian coordinate system, which is fixed to the lunar body, oriented along the three principal axes of inertia of the moon, and centered at the lunar center of mass. The observation equations derived are based on a general model in which the unknown parameters included: the selenodetic Cartesian coordinates, the geocentric coordinates of earth stations, parameters of the orientation of the selenodetic coordinate system with respect to a fixed celestial system, the parameters of the orientation of the average terrestrial coordinate system with respect to a fixed celestial coordinate system, and the geocentric coordinates of the center of mass of the moon, given by a lunar ephemeris.

Fajemirokun, F. A.↗

NASA NTRS1991

Comparison of VLBI and SLR geocentric site coordinates

Results are reported from a systematic comparison of the geocentric coordinates determined for 18 pairs of VLBI and satellite laser ranging (SLR) sites. The data and results are presented in tables and briefly characterized. The rms differences in the X, Y, and Z coordinates are found, after a 7-parameter frame adjustment, to be 15, 22, and 22 mm, respectively. The potential usefulness of a combined VLBI-SLR reference frame for spacecraft tracking and similar applications is indicated.

Ray, J. R.↗

NASA NTRS1986

The coordinate frame of the lunar laser ranging network

The geocentric coordinates for four instruments, which were derived using lunar laser ranging, are compared with the 84L02 coordinates determined from the Lageos satellite. The determination of the geocentric coordinates for the 2.7 m and McDonald Observatory laser ranging system telescopes at McDonald Observatory, the Haleakala site, and the CERGA site near Grasse, France is described. Consideration is given to the McDonald Observatory colocation and station motion due to continential drift. A rms difference of 18 cm is determined for the two sets of geocentric coordinates; however, removing a data anomaly reduces the rms difference to 13 cm.

Williams, J. G.↗

NASA NTRS1974

Derivation of transformation formulas between geocentric and geodetic coordinates for nonzero altitudes

Four formulas, for the nonzero altitude transformation from geodetic coordinates (geodetic latitude and altitude) to geocentric coordinates (geocentric latitude and geocentric distance) and vice versa, are derived. The set of four formulas is expressed in each of the three useful forms: series expansion in powers of the earth's flattening; series expansion in powers of the earth's eccentricity; and Fourier series expansion in terms of the geodetic latitude or the geocentric latitude. The error incurred in these series expansions is of the order of one part in 3 x 10 to the 7th power.

Long, S. A. T.↗

NASA NTRS1976

Study of Arctic sea ice drift from L-band synthetic aperture radar

As part of the Arctic Ice Dynamics Joint Experiment (AIDJEX) several repetitive coverages of L-band (25 cm wavelength) side-looking airborne radar images have been flown over coastal areas of Alaska and a test area in the Arctic. These images allow the analysis of sea ice and its drift. Radar is particularly suited for the mapping and interpretation of Arctic sea ice due to independence from sunlight and the capability to penetrate clouds. Ice floes and leads can be readily identified on the radar images. Measurement of ice floe drift is based on the transformation of radar image coordinates into a geocentric coordinate system using inertial guidance data from the survey aircraft. The paper will demonstrate an example of Arctic ice drift measurements from L-band synthetic aperture radar imagery with an absolute accuracy of about 5%. The conclusions are of particular value in view of planned spaceborne side-looking radar missions in polar orbits.

Leberl, F.↗

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 NTRS1991

A picosecond accuracy relativistic VLBI model via Fermi normal coordinates

Fermi normal coordinates are used to construct transformations relating solar system barycentric coordinates to local inertial geocentric coordinates. Relativistic corrections to terrestrial VLBI measurements are calculated, and this formalism is developed to include corrections needed for picosecond accuracy. A calculation of photon time delay which includes effects arising from the motion of gravitational sources is given.

Shahid-Saless, Bahman↗

NASA NTRS1980

Geophysical parameters of the earth-moon system

Doppler tracking data from Lunar Orbiter 4 have been combined with laser ranging data from lunar retroreflectors to yield a number of geophysical and geodetic parameters for the earth and moon. This joint solution gives values of (1) the lunar principal polar moment C/M R squared = 0.3905 plus or minus 0.0023, (2) GM(E) = 398600.461 plus or minus 0.026 cu km/sq s, and (3) an earth/moon mass ratio at 81.300587 plus or minus 0.000049. Also determined are the harmonics of a complete lunar gravity field through degree and order 5, the obliquity of the lunar pole, selenocentric coordinates of the lunar retroreflectors, geocentric coordinates of the McDonald Observatory, and the lunar secular acceleration. The lunar potential Love number is weakly determined at 0.022 plus or minus 0.013, and a suprisingly large dissipation of rotational energy is inferred, though either solid body tidal dissipation or liquid core mantle interactions could be causes.

Ferrari, A. J.↗

NASA NTRS1984

2 Pallas - 1982 and 1983 lightcurves and a new pole solution

Photoelectric lightcurves of the asteroid 2 Pallas obtained in March 1982 and May 1983 display amplitudes of 0.04 and 0.10 mag respectively. The latter lightcurve shows that Pallas was at V(1.0) mag of 4.51 + or -0.02 when it occulted 1 Vulpeculae on May 29, 1983. A least-squares best fit to an amplitude-aspect relation for all available lightcurve observations of Pallas between 1951 and 1983 yields two solutions for its pole position: lambda = 200, beta = 40 and lambda = 220, beta = 15, where the uncertainty regions correspond to an overall error estimate of + or -10 deg. Use of phase angle bisector coordinates give lower residuals than geocentric coordinates. The (220, 15) pole position is favored since it is in very good agreement with an independent pole solution obtained by photometric astrometry. This pole position implies that the latitude of the sub-earth point at the time of occultation was 22 deg.

Binzel, R. P.↗

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.↗

NASA NTRS1976

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

Schutz, B. E.↗

NASA NTRS1991

JPL 1990-3: A 5-nrad extragalactic source catalog based on combined radio interferometric observations

A combined analysis merges 17,000 Deep Space Network (DSN) Very Long Baseline Interferometric (VLBI) observations with 303,000 observations from the Crustal Dynamics Project (CDP) and the International Radio Interferometric Surveying (IRIS) project. Observations from the Radio Reference Frame Development (RRFD) and Time and Earth Motion Precision Observations (TEMPO) programs through late 1990 form the DSN VLBI data set. The combined analysis yields angular coordinates of extragalactic radio sources with a precision of a few nanoradians, as compared with 5 to 10 nrad precision for coordinates derived in the past solely from DSN data. The improvement in the combined analysis is due to the new Mark III DSN data, as well as to increased statistical strength from the large volume of observations from non-DSN experiments. Such a unified analysis is made possible by recent improvements in parameter estimation software efficiency. The terrestrial reference frame is based on joint VLBI experiments using both DSN and CDP antennas, and on specifying the coordinates of VLBI antennas in a proper geocentric coordinate system by means of Global Positioning System (GPS) collocation of VLBI, LLR, and SLR (Laser Ranging) sites.

Sovers, O. J.↗

NASA NTRS1973

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

Results for the geocentric coordinates of 72 globally distributed satellite tracking stations consisting of 58 cameras and 14 lasers are presented. The observational data for this solution consists of over 65,000 optical observations and more than 350 laser passes recorded during the National Geodetic Satellite Program, the 1968 Centre National d'Etudes Spatiales/Smithsonian Astrophysical Observatory (SAO) Program, and International Satellite Geodesy Experiment Program. Dynamic methods were used. The data were analyzed with the GSFC GEM and SAO 1969 Standard Earth Gravity Models. The recent value of GM = 398600.8 cu km/sec square derived at the Jet Propulsion Laboratory (JPL) gave the best results for this combination laser/optical solution. Solutions are made with the deep space solution of JPL (LS-25 solution) including results obtained at GSFC from Mariner-9 Unified B-Band tracking. Datum transformation parameters relating North America, Europe, South America, and Australia are given, enabling the positions of some 200 other tracking stations to be placed in the geocentric system.

Marsh, J. G.↗

NASA NTRS1976

Improved gravity field and station-coordinate estimates from laser tracking data

Knowledge of the long-wavelength features of the geopotential and the geocentric coordinates of satellite-tracking stations is significantly improved by the use of precision satellite tracking with lasers. Tracking data on nine satellites are combined with terrestrial gravimetry to obtain a spherical-harmonics representation of the geopotential complete through degree and order 24. Laser tracking data are used to determine the coordinates of tracking stations. This coordinate system is referred to an inertial reference frame by use of camera observations and observations of deep-space probes. Resulting geodetic parameters provide better satellite ephemerides and a reference for analyzing satellite-to-sea-surface altimetry.

Gaposchkin, E. M.↗