Showing papers on "Geodetic datum published in 1997"

The Development of the NASA GSFC and NIMA Joint Geopotential Model

Abstract: The NASA Goddard Space Flight Center, the National Imagery and Mapping Agency (NIMA; formerly the Defense Mapping Agency or DMA) and The Ohio State University have collaborated to produce EGM96, an improved degree 360 spherical harmonic model representing the Earth’s gravitational potential. This model was developed using: (1) satellite tracking data from more than 20 satellites, including new data from GPS and TDRSS, as well as altimeter data from TOPEX, GEOSAT and ERS-1. (2) 30’ x 30’ terrestrial gravity data from NIMA’s comprehensive archives, including new measurements from areas such as the former Soviet Union, South America, Africa, Greenland, and elsewhere. (3) 30’ x 30’ gravity anomalies derived from the GEOSAT Geodetic Mission altimeter data, as well as altimeter derived anomalies derived from ERS-1 by KMS (Kort and Matrikelstyrelsen, Denmark) in regions outside the GEOSAT coverage. The high degree solutions were developed using two different model estimation techniques: quadrature, and block diagonal. The final model is a composite solution consisting a combination solution to degree 70, a block diagonal solution to degree 359, and the quadrature model at degree 360. This new model will be used to define an undulation model that will be the basis for an update of the WGS-84 geoid. In addition, the model will contribute to oceanographic studies by improving the modeling of the ocean geoid and to geodetic positioning using the Global Positioning System (GPS).

Use of potential coefficient models for geoid undulation determinations using a spherical harmonic representation of the height anomaly/geoid undulation difference

Abstract: This paper suggests that potential coefficient models of the Earth's gravitational potential be used to calculate height anomalies which are then reduced to geoid undulations where such quantities are needed for orthometric height determination and vertical datum definition through a potential coefficient realization of the geoid. The process of the conversion of the height anomaly into a geoid undulation is represented by a height anomaly gradient term and the usual N–ζ term that is dependent on elevation and the Bouguer anomaly. Using a degree 360 expansion of 30′ elevations and the OSU91A potential coefficient model, a degree 360 representation of the correction terms was computed. The magnitude of N–ζ reached –3.4 m in the Himalaya Mountains with smaller, but still significant, magnitudes in other mountainous regions.

Geodetic Boundary Value Problems in View of the One Centimeter Geoid

Abstract: Potential theory.- Boundary value problems for harmonic random fields.- Free boundary problems.- Formulation and linearization of boundary value problems: From observables to a mathematical model.- The hierarchy of geodetic BVPs.- GBVP-Classical solutions and implementation.- Topographic effects in gravity field modelling for BVP.- Global models for the 1cm geoid - Present status and near term prospects.- An introduction to airborne gravimetry and its boundary value problems.- Spherical spectral properties of the earth's gravitational potential and its first and second derivatives.- Satellite altimetry, ocean dynamics and the marine geoid.- Stochastic boundary value problem theory: An elementary example.- Variational methods for geodetic boundary value problems.- Topics on boundary element methods.- Solving geodetic boundary value problems with parallel computers.- Application of boundary value techniques to satellite gradiometry.- The polar gap.- European capabilities and prospects for a spaceborne gravimetric mission.

Integrated satellite interferometry in Southern California

Abstract: Geodetic studies of crustal deformation and earthquakes in California, which began with the analysis of repeated triangulation measurements after the 1906 San Francisco earthquake, have been revolutionized by new satellite interferometric techniques in space geodesy and remote sensing. Today, space geodetic monitoring of crustal deformation at regional scales relies on a combination of continuous Global Positioning System regional arrays (CGPS), such as the Southern California Integrated GPS Network (SCIGN), and less frequent field GPS surveys. A global continuous GPS array, the International GPS Service for Geodynamics (IGS), provides precise satellite ephemerides and a well-defined terrestrial reference frame. Data from CGPS arrays can also be used to map tropospheric water vapor and ionospheric disturbances.

W0: an estimate in the Finnish Height Datum N60, epoch 1993.4, from twenty-five GPS points of the Baltic Sea Level Project

Abstract: Based upon a data set of 25 points of the Baltic Sea Level Project, second campaign 1993.4, which are close to mareographic stations, described by (1) GPS derived Cartesian coordinates in the World Geodetic Reference System 1984 and (2) orthometric heights in the Finnish Height Datum N60, epoch 1993.4, we have computed the primary geodetic parameter W 0(1993.4) for the epoch 1993.4 according to the following model. The Cartesian coordinates of the GPS stations have been converted into spheroidal coordinates. The gravity potential as the additive decomposition of the gravitational potential and the centrifugal potential has been computed for any GPS station in spheroidal coordinates, namely for a global spheroidal model of the gravitational potential field. For a global set of spheroidal harmonic coefficients a transformation of spherical harmonic coefficients into spheroidal harmonic coefficients has been implemented and applied to the global spherical model OSU 91A up to degree/order 360/360. The gravity potential with respect to a global spheroidal model of degree/order 360/360 has been finally transformed by means of the orthometric heights of the GPS stations with respect to the Finnish Height Datum N60, epoch 1993.4, in terms of the spheroidal “free-air” potential reduction in order to produce the spheroidal W 0(1993.4) value. As a mean of those 25 W 0(1993.4) data as well as a root mean square error estimation we computed W 0(1993.4)=(6 263 685.58 ± 0.36) kgal × m. Finally a comparison of different W 0 data with respect to a spherical harmonic global model and spheroidal harmonic global model of Somigliana-Pizetti type (level ellipsoid as a reference, degree/order 2/0) according to The Geodesist's Handbook 1992 has been made.

Geoid of the Nordic and Baltic Region from Gravimetry and Satellite Altimetry

Abstract: An updated high-resolution geoid model for the Scandinavian and Baltic region has been done by spherical FFT approaches, taking topography into account by a hybrid RTM/Helmert condensation approach. Significant new data sources have entered the geoid solution: a new spherical harmonic reference model, new gravity data over many regions, including the Baltic republics and the Russian border regions, and new high-resolution topographic sources. ERS-1 geodetic mission satellite altimetry has been included in the Baltic, using Fourier-based draping techniques, and taking sea surface topography from tide gauge levellings into account. Compared to more than 300 GPS-levelling points across the region the geoid shows a fit at the 10 cm level, thus being a major improvement over earlier models. In local regions with good gravity coverage, such as Denmark, the geoid fitted to the national GPS net yields accuracies at the 1 cm-level, thus allowing accurate operational levelling by GPS.

La nuova rete geodetica nazionale IGM95 : risultati e prospettive di utilizzazione

Abstract: IGM95 was a strategic geodetic project, developed by the Author and started in 1992 to determine a new fundamental network covering the whole country. The aim was to realize: - a GPS.3D network consisting of about one thousand uniformly distributed points, all of them placed in easily accessible sites and most of them belonging to the national fundamental triangulation and levelling networks; - the determination of the astronomical latitude and longitude of a significant part of the above points with the method of equal heigths for the evaluation of vertical deflections. At the end of 1995, after an intensive work lasted four years, 1236 points were monumented and GPS-observed, using 11 Trimble 4000SSE receivers. About 66% of the points have been placed in coincidence, or directly connected, with points of the triangulation network, while over 34 % of them have been given the height above m.s.l. through their connection to the fundamental levelling net. In 1996, additional baselines were measured, in order to strenghten the geometry of the IGM95 network in those parts which experienced problems of electromagnetic interference. In the meanwhile, adjustment computations in WGS84, relevant to large parts of the network, were executed as preliminary steps to the final block adjustment, and the problem of the transformation between the local geodetic system and WGS84 was being faced locally. At the end of 1996 the block adjustment of the whole network was carried out, producing the coordinates of all network points with centimeter precision. Presently (May 1997), the determination of local transformation parameters for each point of IGM95 network is almost completed, in order to make possible to pass from WGS84 to national Datum and viceversa, as far as geodetic φ and coordinates are concerned. Furtherly, the integration of IGM95 altimetric observed data (GEOTRAV sub-project) and the ITALGEO95 geoid model data is in a phase of analysis and preliminary computation, in order to get an effective solution of the problem of GPS levelling. IGM95 is the most important geodetic project in Italy and one of the most meaningful examples of GPS network in Europe. It constitutes a precise reference frame to support geodetic and topographic surveys as well as research purposes.

Practical geodesy : using computers

Abstract: Preamble BASIC Guidelines & Algorithms Datums and Reference Systems Geodetic Arc Distances Conformal Projections in General Gauss-Kruger Projection Lambert's Conformal Conical Projection Oblique Mercator Projection Spatial Coordinate Calculations Miscellaneous Coordinate Systems Appendix Bibliography Indices.

A Comparison of Existing Co-ordinate Transformation Models and Parameters in Australia

Abstract: Editor's note: This paper is a joint publication by the Institution of Surveyors, Australia and the Mapping Sciences Institute, Australia. Four standard procedures to transform curvilinear co-ordinates from the Australian Geodetic Datum 1984 to the World Geodetic System 1984 are compared. These comprise the Bursa-Wolf model with the national set of seven parameters currently used by Federal and State surveying and mapping authorities, the standard Molodensky model with the five parameters used by the United States Defense Mapping Agency, the simple three-parameter model with the origin shifts taken from the Bursa-Wolf and standard Molodensky models, and the multiple regression equations as determined by the Defense Mapping Agency. The differences between the resulting co-ordinates can reach 4.2 metres over continental Australia, which has implications for the final approach adopted to transform to the Geocentric Datum of Australia. The arguments are presented in favour of more suitable transformation stra...

Introduction to Geodesy: The History and Concepts of Modern Geodesy

Abstract: History of Geodesy. Earth's Shape. Units of Measure. Traditional Survey Positioning Techniques. Geodetic Systems. Physical Geodesy. World Geodetic System. Satellite Geodesy. Very Long Baseline Interferometry. Global Positioning System. Gravity. Gyroscope. Inertial Surveying. Velocity of Light, EDM, and Laser Ranging. Projections. Examples of Modern Projects. Bibliography. About the Author. Index.

The precision of geodetic GPS and one way of improving it

Abstract: We analyse the effect of the combined estimation/elimination of station coordinates, tropospheric zenith delay, dispersive ionosphere and station clock error on the precision achievable with geodetic GPS. We also sketch a method to eliminate the major part of the precision deteriorating effect of this combined estimation of the unknowns, by a dual antenna arrangement.

The importance of including the Geoid in Terrestrial Survey Data Reduction to the Geocentric Datum of Australia

Abstract: The complete reduction of terrestrial survey data to the Geodetic Reference System 1980 spheroid will become an important consideration after the implementation of the Geocentric Datum of Australia. Three examples are used to illustrate that when data reduction, which incorporates the effects of the Earth’s gravity field, is not applied, errors of approximately 10ppm, 200m and 3” can be introduced into terrain distances, astrogeodetic coordinates and azimuths respectively.

Geodetic determination of the surface topography of the Baltic Sea

Abstract: The Baltic Sea Level Project is an international scientific observation program to unify the vertical datums of the countries of the Baltic Sea with GPS measurements. In total, 35 tide gauges on shores and islands of the Baltic were occupied with GPS in 1993. After computing a new gravimetric geoid over the Baltic Sea, it was possible to unify the datums as well as to calculate the orthometric heights and the sea surface topography values for the tide gauge stations. The results obtained are shown.

Electrically erasable and programmable memory that allows data update without prior erasure of the memory

Abstract: A processor-implemented method is described for updating a datum stored in a nonvolatile memory, bits of which cannot be overwritten from a first logical state to a second logical state without a prior erasure. A first storage location in the memory that stores a first version of the datum is accessed. A status field of the first storage location is checked to determine whether the first version of the datum has been superseded. If the status field of the first storage location indicates that the first version of the datum has not been superseded, then a most recent version of the datum is stored in a second storage location of the memory. An address of the second storage location is then written into a next location address field of the first storage location and the status field of the first storage location is written to indicate that the first version of the datum has been superseded such that the datum is updated without the prior erasure of the memory. If the status field of the first storage location indicates that the first version of the datum has been superseded, then the next location address field of the first storage location is accessed to obtain the address of a next storage location that stores a second version of the datum that supersedes the first version of the datum. The next storage location is then caused to be the first storage location and the method repeats itself to access the first storage location. An apparatus for storing a datum is also described.

A general solution in geodetic nonlinear rank-defect models

Abstract: The adjustment of free networks has been one of main research topics in geodesy since Meissl' paper of 1962, with many important applications in deformation analysis. It has been based on the linearized observation model. So far, nonlinearity of the nonlinear rank-defect model seems to have been completely ignored, mathematically. After accounting for the effect of nonlinearity on nonlinear rank-defect adjustment, we obtain a geodetically general solution of coordinates to describe a free geodetic network. It provides us with the maximum possible solution set of coordinates in free net adjustment, with the present general solution set as its subset. The general solution obtained also recovers all the coordinates of the free network satisfying the configuration of the adjusted network, with all possible coordinate corrections and within all possible coordinate systems. The relationship between a particular solution of free geodetic network adjustment and a coordinate system will be uniquely established.

Method and device for geodetic surveying and/or earth imaging by satellite signal processing

Abstract: The invention concerns a method for geodetic surveying and/or earth imaging, characterised in that a radio satellite signal reflected on the ground is picked up by a shaped-beam antenna (2) and this signal is processed, with a reference signal corresponding to the radio satellite signal, for obtaining a geodetic measurement and/or an image of the zone (Z) towards which the shaped-beam antenna (2) is oriented.

Study of Earth's rotation and geophysical fluids progresses

Abstract: Variations in the Earth's speed of rotation and the position and orientation of the rotation axis—known collectively as Earth orientation parameters—are observed by a variety of space geodetic techniques coordinated by the International Earth Rotation Service (IERS). Observations of Earth orientation parameters provide fundamental information about the physical properties of the Earth's interior and the variability of fluids in the atmosphere, oceans, and liquid core, and on land. Participants at a workshop held October 14–18, 1996, at the Paris Observatory, where IERS is headquartered, called for extending IERS activities [Reigber and Feissel, 1997] to include the monitoring of geodetically important properties of the oceans, the liquid core, and terrestrial water to supplement current atmospheric angular momentum variation (AAM) measurements. Given the success of the IERS, expansion of its activities into other areas is not only natural for understanding the observed Earth orientation parameters, but essential for fulfilling its mission of improving the underlying space geodetic observations.

A New Detailed Geoid for Latvia

Abstract: A new geoid of Latvia, computed from available gravity data and newly digitised data, as well as gravity data derived from ERS-1 geodetic mission data in the Baltic Sea is described. Computations were carried out by spherical FFT techniques on a 1.5′ × 3.0′ grid. Results for Latvia show a marked improvement due to the new digitised gravity data, and a minor improvement due to inclusion of ERS-1 data. The overall fit of the gravimetric geoid to 32 Latvian GPS/levelling stations is 8 cm RMS.

Multi-representational data structure for recognition in computer systems

Abstract: An improved recognition data structure is described that is particularly well suited for use in a computer system having recognition abilities. The data structure includes a multi-representational data list section arranged to store a multiplicity of datum. Each datum includes a datum reference number that uniquely identifies that datum and is arranged to contain a plurality of representation zones. Each representation zone is arranged to hold data indicative of a particular representation of the data stored in the datum. The data structure also includes a trellis based recognition results section arranged to accommodate trellis based recognition results at a plurality of different trellis levels.

A vision-aided alignment datum system for coordinate measuring machines

Abstract: This paper presents the development of a CAD-based and vision-aided precision measurement system. A new coordinate system alignment technique for coordinate measuring machines (CMMs) is described. This alignment technique involves a machine vision system with CAD-based planning and execution of inspection. The determination method for measuring datums for the coordinate measuring technique, using the AutoCAD development system, is described in more detail. To improve image quality in the machine vision system, a contrast enhancement technique is used on the image background to reduce image noise, and an on-line calibration technique is applied. Some systematic errors may be caused by imperfect geometric features in components during coordinate system alignment. This measurement system approach, with its new measuring coordinate alignment method, can be used for high-precision measurement to overcome such errors.

Improved Recovery of the Global Marine Gravity Field from the GEOSAT and the ERS-1 Geodetic Mission Altimetry

Abstract: Satellite altimetry from the GEOSAT and the ERS-1 Geodetic Mission provides altimeter data with a very dense coverage. Hence, the gravity field may be recovered very detailed. However, since neighbouring ground tracks are located very closely, cross track variations in the sea surface heights are extremely sensible to sea surface variability. In order to avoid errors in the gravity field caused by such effects, sea surface variability need to be carefully eliminated from the observations. Initially, a crossover adjustment was carried out using bias and tilt terms. Then gross errors and outliers were detected by comparing the data with estimated values obtained using collocation. Subsequently, the altimetry was crossover re-adjusted. The re-adjusted sea surface heights were gridded using local collocation in which residual ocean variability was considered. The conversion of the heights into gravity anomalies was carried out using FFT. Through this process a filtering was performed in the spectral domain in order to avoid the so-called “orange skin” characteristics. This technique was applied to recover the global marine gravity field.

Fast space-domain evaluation of geodetic surface integrals

Abstract: Geodetic surface integrals play an important role in the numerical solution of geodetic boundary-value problems. In many cases they can be evaluated using fast methods in the frequency domain (FFT). However, this is not possible in general, because the domain of integration may be non-trivial (as is the surface of the Earth), the kernel function may not be of convolution type, or the data distribution may be heterogeneous. Therefore, fast evaluation strategies are also required in the space domain. They are more difficult to design because only one property is left where a more or less fast evaluation strategy can be built upon: the potential type of the kernel function. Consequently, the idea is not to replace well-established frequency domain techniques, but to supplement them. Our approach to this problem goes in two directions: (1) we use advanced cubature methods where the integration nodes automatically densify in the vicinity of the evaluation points; (2) we use powerful computer hardware, namely MIMD computers with distributed memory. This enables us to evaluate geodetic surface integrals of any practical complexity in reasonable time and accuracy. This is shown in a numerical example.

Datum Shifts for UTM Coordinates

Abstract: The USGS 1 :24,000-scale topographic maps and associated digital map products of the United States are cast on the North American Datum of 1927 (NAD 27). These map products are a national asset used for a variety of mapping, GIS database construction, and land survey tasks. However, NAD 27 has been replaced by the North American Datum of 1983 (NAD 83). While shifts to translate the latitude/longitude (lat/ long) graticule coordinates to NAD 83 are documented, no information is readily available on the shifts in metres needed to convert NAD 27 UTM Northing and Easting grid coordinates to NAD 83 values. These shifts may be determined with computer software such as the U.S. Army Topographic Engineering Center (TEC) CORPSCON package or the commercially available Blue Marble Geographics Geographic Calculator program, and, when plotted at 2" intervals (1atNong) for the contiguous 48 states, show a remarkable consistency within the 6-degree-wide UTM zones, changing gradually from south to north. The shifts depicted in the graphical plots provide the map user with the values needed to quickly convert NAD 27 UTM grid coordinates to NAD 83 values. Because rectangular grid coordinates are preferred for a majority of tasks, it is recommended that the national mapping agencies determine the shift values to convert the NAD 27 UTM coordinates of individual map sheet corners to the datum of choice and make them available through publications and the World Wide Web. When map products are revised, notes defining shifts in rectangular grid coordinates should be included on the map collars or appended to the digital files.

Effects of tropospheric mapping functions on space geodetic data

Abstract: This report is a summary of some of the tropospheric propagation delay mapping function research performed during the past few years at the Geodetic Research Laboratory of the University of New Brunswick (UNB). The work has consisted of modelling the effect of tropospheric delay errors for geodetic and precise airborne GPS positioning. Intercomparison of mapping functions and zenith hydrostatic and wet delay models with extensive radiosonde data sets and flight data has been performed.

A WGS84-AHD Profile over the Darling Fault: Western Australia

Abstract: The Darling Fault near Perth in Western Australia causes a steep geoid gradient of approximately 100mm/km. Existing gravimetric geoid models cannot currently recover this rapidly varying geoid undulation with sufficient accuracy so as to allow the accurate determination of Australian Height Datum (AHD) heights using the Global Positioning System (GPS). As such, the geometrical approach to determine the separation between the AHD and World Geodetic System 1984 (WGS84) ellipsoid is expected to offer improved GPS height determination in this region. A network of 45 carrier-phase GPS baselines, made at 14 first-order AHD benchmarks at ~3km intervals along a 30km profile across the Darling Fault near Perth, was observed in order to test this hypothesis. Several GPS network adjustment strategies were implemented which constrained existing height information in different ways. Due to the poor knowledge of the position of the geoid in this region, the most precise network adjustment used only one fixed ellipsoidal height and all other known stations were held fixed in latitude and longitude only. When the geometrical approach was compared with the results of existing gravimetric geoid solutions, it offers a superior means of determining heights from GPS. However, the geometrical method only satisfies third-order specifications in 5 of the 12 cases tested in this region of the Darling Fault.