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Throughout the past few decades, advancements in global navigation satellite systems (GNSS), such as the Global Positioning System (GPS), have resulted in real-time planimetric accuracy at the centimetre level, whether achieved using Real-Time Kinematic (RTK) or Real-Time Network (RTN) approaches. This study examines and characterizes the performance of RTK and RTN solutions at three test sites in Los Angeles County, California, in the United States of America. The solutions were characterized to examine the dispersion of vertical measurements in the context of different environments. The results from this study suggest that both methods have advantages and drawbacks; in particular, the data showed that the distribution and density of the network stations, cellular network coverage and environmental dynamics have significant impacts on RTN vertical precision, where the vertical precision for the RTN measurements were observed to be 2–4 times lower in comparison to the RTK measurements. [ABSTRACT FROM AUTHOR]

Northeast Japan is a typical island arc related to the Pacific plate subduction. The 2011 Mw 9.0 Tohoku-oki earthquake provided a unique opportunity to analyze crustal deformation with different boundary conditions, similar to a gigantic rock deformation experiment. We review findings obtained through various observations and data analyses in Northeast Japan, focusing on the crustal deformation in different timescales. The occurrence of the M9 earthquake solved the ongoing paradox that the geodetic strain rate is an order of magnitude larger than the geologic estimate, showing that the centennial geodetic observation had mainly captured the elastic strain accumulation. Along the localized contraction zone along the Japan Sea coast, a comparison of postseismic and interseismic deformation patterns revealed a significant contribution of inelastic deformation, which plays an essential role in long-term deformation. Along the Pacific coast, rapid interseismic subsidence and unexpected coseismic subsidence were followed by a rapid postseismic uplift, indicating that viscous relaxation in the mantle is of essential importance. These findings advance our understanding of plate interactions and the tectonic evolution of the island arc. The 2011 Tohoku-oki earthquake provided the most complete crustal deformation data set ever for interseismic, coseismic, and postseismic periods. The discrepancy between the geologic and geodetic deformation rates in Northeast Japan is attributed to an elastic strain due to interplate locking. A significant contribution of inelastic deformation in the island arc crust is identified through a comparison of interseismic and postseismic deformations. [ABSTRACT FROM AUTHOR]

Spatial data is constantly evolving, and the accuracy of spatial data is constantly changing. The latest GRPK and orthophotographic map were used in the study. Accuracy is also affected by technological advances, which are driven by improvements in working methods, which include the development of work tools and the development of data sets that contain structured data. The data contained in the data sets are determined by a variety of methods, such as field measurements (GPNS receiver or tacheometer) and analysis of digital photographic images, which are determined using aircraft or satellite systems. The determined data is processed with the help of specialized software, which is selected depending on its functionality and capabilities, and with the help of which the determined data is processed as accurately as possible. Accurate spatial data in densely populated areas makes it easier to carry out planning and design work correctly. The study is performed to determine the accuracy of the coordinates of the selected structures using remote methods. The more similar studies are conducted, the more confident the GRPK data generated remotely will be of the required accuracy, reliability, and applicability to planning, forecasting, and other important tasks. The article compares geodetic measurements and GRPK data and geodetic measurements and ORT10LT data, identifies coordinate differences, the size of the discrepancy and its average, and calculates the root mean square error. The object of the research is spatial and cartographic data of different buildings. The aim of the research is to determine and evaluate the accuracy of the coordinates obtained using remote sensing methods. [ABSTRACT FROM AUTHOR]

For millennia, the geodesic industry has improved methods and technologies for obtaining information on the location of objects on the Earth's surface, whose key task has been to improve the accuracy and reliability of measurements. At the same time, in recent decades, the rapid development of positioning technologies based on satellite radio navigation systems has created prerequisites for a situation where the acceptable accuracy of determining the geodetic characteristics of real estate becomes quite affordable even when using non-specialized geodetic equipment, including personal mobile devices. The article shows that the error in determining the area of land for registration of rights to real estate has its own "cost", which depends on the value of real estate in the area of survey. By the example of model sites, it is shown that further improvement of the accuracy of engineering surveying to determine the spatial characteristics of real estate objects would be economically feasible only if the cost of geodetic surveys (including the cost of purchasing new geodetic equipment, payment for labor of specially trained engineers, additional technical services and etc.) will not exceed the "cost of error" to determine the area of the site. Using the example of Ukraine, it is shown that the most accurate geodetic surveys (determining turning points of land borders with an accuracy of more than 0.02 m) are economically feasible only when the market value of a land plot exceeds USD 208 per square meter. [ABSTRACT FROM AUTHOR]

Investments in the development and improvement of the Romanian road network were made recently to ensure enhanced comfort, safety, and efficiency in transport conditions while observing sustainable development policies. The most important objective for Romanian road authorities has been improving the safety of the road system to achieve a secure and efficient movement of people and goods within the public network while effectively managing risks associated with road transport operations. Infrastructure-related risks include personnel injuries and material damages, which can result from physical and natural hazards, accidents, and engineering failures. In this context, this paper brings forward the applicability of state-of-the-art geodetic technologies in adjacent domains, such as civil engineering and road infrastructure works, while explaining that the best solution can be found only by thorough interdisciplinary collaboration between specialists. Thus, the study focuses on complex monitoring methods and the models used for a road structure in Romania. The main objective of the paper is to describe the methodologies (geodetic and laser scanning) used for assessing the deformations of a real road structure. By using these technologies, the authors found real deformations and their underlying causes and thereby managed to adopt the optimal technical solution for rehabilitating the road structure. Finally, the discussed case study provided highly accurate results because the methods and technologies used allow for millimeter-precise measurements of displacements and linear and angular deformations suffered by the construction. [ABSTRACT FROM AUTHOR]

In 1997, the National Geodetic Survey (NGS) published static global positioning system (GPS) surveying guidelines for determining ellipsoidal heights on marks. These guidelines, commonly referred to as NGS-58, are used today in the United States for modernizing heights on marks. Later, in 2013, the NGS released OPUS-Projects, a web-based tool for processing GPS surveys. To evaluate OPUS-Projects and compare it with NGS-58, a static GPS survey was conducted in Oregon. The data were used to develop four different networks. For the most part, the recommendations in NGS-58 worked well, but the 1-h observations did not always produce accurate ellipsoidal heights for baselines longer than 7 km. For the other networks that consisted of 5-h observations or greater, the resulting ellipsoidal heights on all of the marks agreed within±1 cm. For these networks, the estimated network accuracy of the ellipsoidal height for each mark was less than 1.2 cm at 95% confidence. Such consistent results indicate that OPUS-Projects can be used for height modernization surveys. [ABSTRACT FROM AUTHOR]

This investigation introduces a rigorous mathematical transformation of variance--covariance matrices between a global geocentric frame and a plate-fixed geodetic frame. A practical example between the geocentric frame of International GNSS Service 2008 (IGS08) epoch 2005.00 and the geodetic frame North American Datum of 1983 (NAD 83) (2011) epoch 2010.00 was implemented. Although the theory is general, the transformation used here is controlled by the assumptions implicit in the definition of NAD 83. However, the same approach could be extended to future definitions of fixed-plate datums used by geodetic organizations for charting and mapping applications. Consequently, because the transformation between these two specific frames is assumed by definition to be a one-toone errorless transformation, the uncertainties for the 14 Helmert transformation parameters between the two frames are assumed to be zero. Nevertheless, the formulation is complete and applicable to other specific datum-transformation situations. [ABSTRACT FROM AUTHOR]

With the advent of global navigation satellite systems (GNSSs), many national geodetic datums have been established with modern technology and referenced to a specific epoch of the international terrestrial reference frame (ITRF) definition. Following the static datum concept, the datum remains unchanged after its publication, which consequently creates problems in datum maintenance. In the recent update of TWD97, the national datum presently used in Taiwan, the resurvey coordinates are transformed back to the original frame but expressed in a recent epoch. In this study, the uncertainties resulting from the transformation between ITRF definitions in the region of Taiwan were investigated. Based on error propagation, a standard error of was estimated due to the transformation of the TWD97 coordinates between ITRF2005(2010.0) and ITRF94(2010.0). The uncertainties propagated from transformation parameters are more significant than those from station coordinates and velocities, and the uncertainty expands with the time interval. The SD is for the transformation between ITRF2005 and ITRF2000. Considering that the uncertainty between later definitions is much smaller than transforming to ITRF94, it may be preferable to replace the ITRF94 with a modern ITRF definition, at least ITRF2000, for the next TWD97 datum maintenance. [ABSTRACT FROM AUTHOR]

A study of deformations, which is based on the use of geodetic measurements, is usually performed by defining a kinematic model. Such a model, when used to describe a complex geophysical environment, can lead to a partial estimation of the deterministic dynamics, which characterize the entire network. Usually, in a case of deterministic nonlinear movements in the network, there is no possibility to determine a stable datum that may serve as a basis for deformation analysis. Today, the concept of stability in time ascribes rigidity to a congruent datum. This paper redefines the concept of the datum congruency and presents the development of a new dynamic datum, which more closely represents geophysical reality. The new datum changes the main characteristics of a traditional datum and successfully overcomes some of its inherent disadvantages. As an example, the proposed algorithm of the dynamic datum is applied to obtain a deformation analysis in the Carmel fault environs, one of the major geological structures in northern Israel. [ABSTRACT FROM AUTHOR]

Knowledge of the actual refraction coefficient is essential in leveling surveys and precise electromagnetic distance measurement reduction. The most common method followed by the surveyor for its determination is based on the use of simultaneous reciprocal zenith observations. The commonly used formula is only an approximation valid for approximately horizontal sightings, whereas the exact geometric solution turns out to be very complicated so that an iterative computation procedure is suggested instead. In the present paper, the goal is to derive a compact formula from the complete solution that is easy to implement and retains the necessary accuracy for horizontal and slanted sightings. In addition, the paper will also focus on the common situation for the surveyor where isolated observations have to be done and no partially compensating procedures-e.g., leap-frog or middle point-are possible. If temperature vertical profiles are unknown then the refraction coefficient cannot be reliably determined. Some surveyors may customarily use then an average value, e.g., , perhaps being unaware of the risks involved in such simplistic assumption. In the present paper, it is also a goal to present a useful and simple formula for approximately estimating the refraction coefficient in terms of easily accessible parameters to correct the bulk of the refraction effect in single observations, always bearing in mind that determination of the refraction coefficient by means of a model may turn out to be somewhat inaccurate, but still better than the blind use of a universal . [ABSTRACT FROM AUTHOR]

In geodetic networks, observations are measured repetitively, and the mean values of these observations are used for network adjustment, outlier detection, deformation analysis, etc. These repetitive observations are independent, and if one of them has outlier, the effect of the outlier decreases depending on the computed mean value. Also, the mean operator-a kind of least-squares estimation-smears the effects of the outlier over other observations. In this case, the detectability and reliability rates of the outlier detection method decrease. Moreover, the undetectable outliers spoil both of the estimated parameters and their standard deviations, causing incorrect results. To form a univariate sample, the same quantity must be measured at least twice for geodetic networks. The univariate case is simpler than the multivariate case, and if the repetitive observations may be analyzed as a univariate case, more reliable results can be obtained for outlier detection. In this study, the univariate analysis method was proposed for repetitive geodetic observations. The reliability of the univariate method was measured based on its mean success rate compared with the mean success rates of classical methods. The leveling network was simulated, and analyses were carried out. The results obtained from the univariate case are more reliable than those obtained from classical ones. [ABSTRACT FROM AUTHOR]

The deflection of the vertical is an important parameter that combines both physical (astronomic) and geometric (geodetic) determined quantities. This paper introduces an alternative didactic approach based on rotations of three-dimensional right-handed local frames that simplifies such concepts as the derivation of Laplace's equation and facilitates understanding of vertical deflection components and their transformations under different assumptions. Variations in deflections of the vertical as a consequence of geometric changes introduced by the future replacement of the North American Datum of 1983 (NAD 83) are also investigated. [ABSTRACT FROM AUTHOR]

Global Navigation Satellite System (GNSS) surveys performed in critical environments (e.g., urban canyons, mountainous areas, or areas of dense vegetation) usually suffer from a lack of satellite coverage as a result of obstacles such as buildings and vegetation. GNSS mission-planning software provides an estimate of satellite visibility and dilution-of-precision (DOP) values along a planned trajectory to establish the best time frame over which to perform the survey. However, such an estimate is not reliable in a complex scenario because the surrounding environmental morphology is not considered. This paper introduces a new method to improve the prediction of GNSS satellite visibility. This method involves computing GNSS satellites position by means of the orbital parameters, as well as using three-dimensional digital surface models (DSMs) to develop a more reliable mission plan. The time evolution of key parameters describing the GNSS constellation is computed by means of a visibility georeferenced map for both dynamic and static surveys. [ABSTRACT FROM AUTHOR]

The so-called -rule is a simple and widely used heuristic for outlier detection. This term is a generic term of some statistical hypothesis tests whose test statistics are known as normalized or studentized residuals. The conditions, under which this rule is statistically substantiated, were analyzed, and the extent it applies to geodetic least-squares adjustment was investigated. Then, the efficiency or nonefficiency of this method was analyzed and demonstrated on the example of repeated observations. [ABSTRACT FROM AUTHOR]

This paper presents a method for the surveying and reliable processing of Global Navigation Satellite System (GNSS) observations in rapid and ultrarapid static surveying for determination of control-point coordinates. The presented technique allows for reliable determination of coordinates, even in the case of highly difficult observation conditions (e.g., for control points situated along forest edges or entirely in the forest, near buildings, or in the vicinity of power-transmission lines). The paper also analyzes different projects of the global positioning system (GPS/GLONASS) networks from the perspective of their credibility and reliability. The control-point coordinates are determined by three GNSS receivers positioned in line on a special base, providing a credible control of GNSS baselines during rapid and ultrarapid static surveys. The GNSS receivers are separated by the distance of 0.5 m. Given the gross errors in baseline coordinates determined that happen in practice, simultaneous use of three receivers for position determination of a control point allows reliable determination of the coordinates even under significantly obstructed access to satellites. The practical surveys were conducted using Topcon and Trimble receivers using real and virtual reference stations. The presented survey and GNSS data-processing methodology allow obtaining centimeter-level accuracy in a few minutes of GPS/GLONASS observations for control points located in obstructed conditions. [ABSTRACT FROM AUTHOR]

Geodetic network design and optimization is a very well-known concept in geodesy. However, in many cases, the available geodetic network configuration with respect to the estimation model is insufficient because of the physical and financial limitations. For the case of estimating the datum transformation parameters between two datums, the colocated points are only an unevenly and inhomogenously distributed subset of the available national/regional networks. Because the transformation parameters are defined with respect to an earth-centered, earth-fixed (ECEF) frame, very limited geographic coverage of the national/regional networks often leads to a weakly multicollinear estimation problem. Such limited geographical coverage is often coupled with the intrinsic geometrical distortions as well as the relatively lower precision of the observations, in particular, when transforming a terrestrial network into a space-based network. In such cases, the individual parameters become highly correlated and oversensitive to the network configuration, and the individual transformation parameters cannot be estimated reliably. In this study, the concept of an idealized three-dimensional (3D) regional network geometry is introduced, its inverse cofactor matrix is analytically derived, and a regularized estimation method based on the inverse cofactor matrix of an ideal network distribution is presented to deal with the weakly multicollinear datum transformation problem. The efficiency of the proposed method is shown in three realistically simulated networks. The proposed method outperforms the standard least squares in terms of mean square error (MSE) and reduces the correlations among the parameters. [ABSTRACT FROM AUTHOR]

This contribution reviews a few basic concepts of optimization and design of a geodetic network. Proper assessment and analysis of networks is an important task in many geodetic-surveying projects. Appropriate quality-control measures should be defined, and an optimal design should be sought. The quality of a geodetic network is characterized by precision, reliability, and cost. The aim is to present a few case studies that have been designed to meet optimal precision and reliability criteria. Though the case studies may be of interest to the geodetic community in their own right, the aim is to gain insight into the general optimization problem of a geodetic network. This is also potentially of interest for educational purposes. The case studies include a zeroth-order design to improve the precision of the network points in a traverse network and a first-order design to meet the high reliability and maximum precision criteria in a geodetic network. It is shown that not only the configuration of the network but also the type of the observations used can affect the design criteria. For example, the case studies presented show that the optimal shape of the trilateration network (intersection with distances) can result in a weak network in the sense of reliability and precision if the observations are replaced by angles rather than distances (triangulation network). In close relation to the optimization problem of a geodetic network, the global positioning system satellite configuration is also optimized for a particular case that provides the minimum value of the geometric dilution of precision. [ABSTRACT FROM AUTHOR]

In 1986, Canada, Greenland, and the United States adopted the North American Datum of 1983 (NAD 83) to replace the North American Datum of 1927 as their official spatial reference system for geometric positioning. The rigor of the original NAD 83 realization benefited from the extensive use of electronic distance measuring instrumentation and from the use of both TRANSIT Doppler observations and very long baseline interferometry observations. However, the original NAD 83 realization predated the widespread use of the global positioning system and the use of continuously operating reference stations. Consequently, NAD 83 has evolved significantly in the United States since 1986 to embrace these technological advances, as well as to accommodate improvements in the understanding of crustal motion. This paper traces this evolution from what started as essentially a two-dimensional (2D) reference frame and has been progressing toward a four-dimensional (4D) frame. In anticipation of future geodetic advances, the U.S. National Geodetic Survey is planning to replace NAD 83 about a decade from now with a newer, more geocentric spatial reference system for geometric positioning. [ABSTRACT FROM AUTHOR]

The subtle curves of the masterpiece of ancient Greece, the Athenian Parthenon, have been the object of many investigations of scientists of various disciplines. A lot of discussion has centered on the shape of the monument's curved stylobate surface and the kind of mathematical curve that best describes it. This paper presents a new approximation of the stylobate's curves using the Parthenon's transverse and longitudinal inclinations estimated from the measured uneven heights of the lowermost drums of its peristasis columns. This study uses least squares techniques and their appropriateness checked through their correlation coefficients to estimate two kinds of conic sections: a circle and a parabolic curve. Finally, the minimum detectable constructional inaccuracy is estimated. [ABSTRACT FROM AUTHOR]

The number of global positioning system (GPS) tracking stations is increasing, primarily because the stations are multifunctional. In civil engineering, they can be used for precision positioning; in the earth sciences, they can be used to monitor faults and earthquakes; and in the atmospheric sciences, they can be applied to predict perceptible water vapor. Currently, there are more than 400 GPS stations in Taiwan; however, the data obtained through such stations are not being assessed carefully. Experienced scientists and engineers examine the data in advance to see if they qualify for research purposes, but inexperienced users can adopt poor quality data that eventually lead to inaccurate research results. Of the observation stations with receivers that were renewed between 2006 and 2008 in the International GNSS Service Network, four stations (ZIMM, BOR1, NRC1, and NICO) were selected to be the subjects of this research. Six indexes of data quality were observed to calculate the quality of data obtained before and after receiver renewal. Then, analyses were conducted to understand the relationship between the quality indexes and positioning precision. The results showed that after receiver renewal, the positioning precision of the four stations was improved by 1-19%. Therefore, positioning precision is positively affected by the six data quality indexes. It was also discovered that receiver clock error was the most critical factor among the six indexes. In conclusion, if data quality control can be applied to GPS tracking stations, the data obtained will be more reliable for research purposes, and the accuracy of subsequent engineering and science measurements will be improved. [ABSTRACT FROM AUTHOR]

The idea of integrated measurements, combining classic field observations and satellite observations, has recently been applied in geodetic work with increasing frequency. To draw an entire set of such observations numerically, it is necessary to reduce them to a common mathematical space (e.g., onto the surface of an ellipsoid WGS84). This paper presents a proposed adjustment of GPS observations in a local reference system without the necessity of transforming and mapping them. The adjustment process is carried out after a GPS vector network is transformed into a spatial angular-distance network. This allows an easy integration with classical observations (joint adjustment of all observations). Detailed formulas are provided and used to develop a mathematical adjustment model. The computational algorithm is verified in practice. [ABSTRACT FROM AUTHOR]

The least-squares estimation exhibits a poor performance in the presence of gross errors. One of the typical approaches to control the influence of outliers is to use robust estimation techniques. The well-established geodetic reliability theory is comprised of two main components: internal and external reliability. Both reliability measures are important diagnostic tools for inferring the strength of the model validation. To gain further insight into robust M-estimation performance, the variation characteristics of internal and external reliability measures are addressed for a particular robust estimator. Theoretical analyses show that, during the iterative reweighting procedure for uncorrelated observations, the internal reliability measures as represented by minimal detectable bias become larger and larger. For purpose of illustration, a numerical example associated with a simulated geodetic leveling network is provided. As expected, for the outlying observations, their corresponding external reliability measures get smaller and smaller when the iteratively reweighted least-squares method is implemented. [ABSTRACT FROM AUTHOR]

A new geodetic method for accurate determination of nearshore wave characteristics is proposed. This method is based on a robotic total station set on stable position on the coast and aiming at a passive reflector mounted on a buoy, usually at a distance of a few hundred meters. This method permits the identification of the changing three-dimensional coordinates of the reflector/buoy in a selected, fixed coordinate system independent of the buoy with centimeter accuracy, and a rate of up to 6 Hz, and it can even determine very precisely waveforms, including those with steep sides. The effectiveness of the method is demonstrated on the basis of results of two cases studies. While this method provides exceptional quality results for small waves, it can also be used for large waves as well, and especially to calibrate other wave measurement techniques. Techniques to avoid clipping effects usually affecting the wave measurements and the possibility to measure the wave and current direction are also discussed. [ABSTRACT FROM AUTHOR]

A linear transformation, including a similarity model and an affine model, plays an important role in reference frame transformation problems. It establishes geometric relations between different reference frames by adopting physically interpretable parameters, and allows one to integrate positional coordinates across various systems. In this study, an analytical noniterative approach for solving the indirect problem (i.e., parameter estimation) of a linear transformation model is proposed. It gives a closed-form solution for the transformation without any prerequisite on the magnitude of parameters. Consequently, neither good initial values nor iterations are required during the parameter estimation process. Through numerical examples, it is illustrated that the proposed approach is capable of giving accurate parameter estimates as a classic least-squares technique does, but with much higher computational efficiency. In a reference frame transformation problem of 1,000 control points, the proposed approach takes less than 0.1 s to produce an accurate solution, while an ordinary least-squares approach takes 10-17 s to finish the same analysis. With the above advantages, this approach would especially benefit the cases in which a real-time application or large network is involved in an analysis. [ABSTRACT FROM AUTHOR]

This article deals with the characteristics of deformation of a body or a figure represented by discrete points of geodetic network. In each point of geodetic network kinematic quantities are considered normal strain, shear strain, and rotation. They are computed from strain and rotation tensors represented by displacement gradient matrix on the basis of known point displacement vector. Deformation analysis requires the appropriate treatment of kinematic quantities. Thus statistical properties of each quantity in a single point of geodetic network have to be known. Empirical results have shown that statistical properties are strongly related to the orientation in single point and local geometry of the geodetic network. Based on the known probability distribution of kinematic quantities the confidence areas for each quantity in a certain point can be defined. Based on this we can carry out appropriate statistical testing and decide whether the deformation of network in each point is statistically significant or not. On the other hand, we are able to ascertain the quality of the geometry of the geodetic network. The known characteristics of the probability distributions of two strain parameters and rotation in each point can serve as useful tools in the procedures of optimizing the geometry of the geodetic networks. [ABSTRACT FROM AUTHOR]

NOAA’s National Geodetic Survey has developed the horizontal time-dependent positioning (HTDP) software to provide a way for its users to estimate the coordinate changes associated with horizontal crustal motion in the United States. HTDP contains a model for estimating horizontal crustal velocities and separate models for estimating the displacements associated with 29 earthquakes (two in Alaska and 27 in California). This software is updated periodically to provide more accurate estimates for crustal velocities and earthquake displacements, as well as to include models for additional earthquakes. In June 2008, NGS released version 3.0 of HTDP (HTDP 3.0) that introduces an improved capability for predicting crustal velocities, based on a tectonic block model of the western contiguous United States (CONUS), that is, from the Rockies to the Pacific coast. Values for the model parameters that predict the velocity at any point within the domain were estimated from 4,890 horizontal velocity vectors (derived from repeated geodetic observations), 170 fault slip rates, and 258 fault slip vector azimuths. Extensive testing indicates that this model can predict velocities within CONUS with a standard error of less than 2 mm/year in both the north and east components. HTDP 3.0 also introduces a model for the combined coseismic and postseismic displacements associated with the magnitude 7.9 Denali earthquake that occurred in central Alaska on November 3, 2002. [ABSTRACT FROM AUTHOR]

This study selected five indexes to determine the relationship between data quality and positioning precision. These indexes are multipath on L1, multipath on L2, observations by cycle slips, clock offset, and clock stability. To reduce the number of common errors, six types of global positioning system (GPS) receivers are selected and set up in an Ultra-Short Distance Network at the National Measurement Laboratory, Taiwan, for 3 days. The first three indicators are calculated with the Teqc software, and the last two indicators are computed using the Bernese software. Moreover, the observations from three GPS tracking stations, namely, short baseline (about 25 km), middle baseline (about 150 km), and long baseline (around 2000 km), were downloaded from the Internet and processed using Bernese software. Analytical results indicate that clock stability and observations divided by cycle slips are found to be very important positioning factors. Clock offset and multipath effects do not significantly affect the GPS results. [ABSTRACT FROM AUTHOR]

The performance of the new EGM2008 global geopotential model (GGM), over the northern Nile valley and delta in Egypt, has been evaluated. Over 305 global positioning system (GPS)/levelling stations, the standard deviation of the undulation differences has been estimated to be 0.23 m. Thus, it can be concluded that the EGM2008 is superior to earlier GGMs over the northern area of Egypt by a factor of 1.6. Moreover, four mathematical models have been investigated in order to incorporate local data sets with the EGM2008, leading to the conclusion that the first-order polynomial is the optimum one. An improvement of about 26% has been obtained after applying that regression model, and the standard deviation has been decreased to 0.17 m. As a result, the EGM2008 produces a crucial influence on integrated GPS surveys where the orthometric heights can be obtained without any additional costs. Such a practice presents a suitable alternative, from an economical point of view, to substitute the expensive traditional levelling technique particularly for topographic mapping. [ABSTRACT FROM AUTHOR]

At the beginning of the 21st century, a significant technological change took place in geodetic astronomy. In Zurich and Hannover, digital zenith camera systems were developed based on digital imaging sensors (charge-coupled device) that strongly improved the degree of automation, efficiency, and accuracy of the observation of the direction of the plumb line and its vertical deflection. This paper describes the instrumental design of the new digital zenith camera systems and gives an overview of the data processing with focus on the models used for astrometric data reduction and tilt correction. Results of frequently repeated observations of vertical deflections and comparison measurements show an accuracy of vertical deflection measurements of better than 0.1 arc sec. Application examples for vertical deflection data from zenith camera observations, such as the high-precision local gravity field determination in engineering projects and gravity field validation are summarized. [ABSTRACT FROM AUTHOR]

Surveying technology as regards total stations (TS) has changed in the last fifty years. The original idea of measuring and storing polar coordinates has been progressively revolutionized by means of reflectorless distance measuring capabilities, as well as steer measurements, robotic, camera, and scanning functions. This enables the so-called intelligent tacheometry which is explained in detail herein, relying on the instruments capability to react autonomously on the object due to the reflectorless measuring device and eventually with image assistance and in interaction with the robotic drive. This paper revises thoroughly the evolution of conventional TS as figured out in the sixties until the promising image assisted scanning total station that are starting to come out with many surveying capabilities, but half way of what it might be an image assisted photogrammetric scanning TS (IAPSTS) with full photogrammetric functionalities. Following the writers’ opinions, the IAPSTS might surprisingly change the way both field surveying and processing are carried out in scenarios such as documentation of cultural heritage and industrial factory measurements. [ABSTRACT FROM AUTHOR]

The observations of geodetic very long baseline interferometry (VLBI) measurements refer to an invariant point of the radio telescope. This point is often called the reference point. For the interpretation of VLBI results it is necessary to know the position of this invariant point and its possible variation with time. Only the knowledge of the reference point makes it possible to combine VLBI results with results from other colocated techniques and in the framework of the global geodetic observing system (GGOS). Within the GGOS an automated monitoring of the reference points and therefore of the local-tie vectors at colocation stations is discussed earlier in other studies. In this paper a new mathematical model is described to allow such an automated monitoring of the reference point of an azimuth-elevation type radio telescope. [ABSTRACT FROM AUTHOR]

In the network-based real-time kinematic (RTK) global positioning system approach, the rover positioning accuracy and reliability depends on the quality of the atmospheric corrections, which is largely a function of spatial and temporal variability of ionospheric and tropospheric parameters. The location of the rover receiver with respect to the reference network receivers is also a very important factor, especially for applications such as off-shore navigation, where favorable geometry cannot always be assured. The primary goal of this paper is to describe tests of the speed and reliability of the ambiguity resolution and the ultimate accuracy of kinematic positioning for two representative reference receiver geometries: (1) pentagonal reference receiver geometry, with network-rover separation up to 131 km, which represents a typical reference scenario where the rover is located inside the reference network; and (2) irregular geometry, simulating a shore-bound scenario where the reference network can support only extrapolation of the atmospheric corrections to an off-shore rover (outside the reference network), with network–rover separation up to 200 km. The latter scenario is of special interest here, as the objective is to investigate the maximum acceptable separation of the rover receiver from the shore-bound reference stations. The Ohio Continuously Operating Reference Stations (CORS) network is used to simulate both scenarios, and the MPGPS software developed at The Ohio State University Satellite Positioning and Inertial Navigation Laboratory is used to carry out the analyses over a 24-h period of varying ionospheric activity. As a result of this study, the error budget associated with both network geometries is obtained, and the limitations of the network approach as a function of the network-rover geometry can be ascertained. [ABSTRACT FROM AUTHOR]

This paper presents the performance of the real-time kinematic (RTK) technique in very severe conditions. The measurements were conducted in forest conditions during two different experiments. Two Global Positioning System receivers were used: an Ashtech Z-Surveyor and a Z-Xtreme. Radiomodems were used for transmitting RTK corrections from a reference station to a rover. The RTK measurements were performed during quite good satellite configuration. The use of RTK technology, based on the Ashtech Z-Xtreme receiver as a rover in forest terrain, allowed centimeter accuracy to be obtained. However, practical experiments showed that there is a need for redundant independent RTK solutions based on repeated independent ambiguity reinitializations. Although gross errors might occur, the RTK technique can be very helpful technology for centimeter positioning in woodland areas. [ABSTRACT FROM AUTHOR]

The detection of the discordant points, i.e., outliers, in linear regression models is a problem, which has been studied extensively. Huber’s M-estimation is recommended not only for robust regression but also for detecting outliers. However, M-estimation does not show high performance in detecting outliers for some cases. The aim of this paper is to propose a new method for improving the ability of M-estimation in outlier detection. It consists of the iterative combination of the M-estimator along with a scheme of reducing weights in some observations at random. The theorems proving contribution of the proposed algorithms have also been included. A series of Monte Carlo simulation experiments show that the performance of the new algorithm in the presence of outliers is better than M-estimation alone. By using the new method, the results, on average, improved by about 7%. [ABSTRACT FROM AUTHOR]

In global positioning system (GPS) positioning, the tropospheric delay is a systematic error. Mismodeling of the tropospheric delay results in a degradation of the estimated height component, and thus constitutes a limitation to high-accuracy GPS applications. As such, it is obvious that the tropospheric delay should be modeled as accurately as possible. Modeling the tropospheric delay for some applications, such as precise airborne kinematic differential positioning, is further complicated due to the large altitude difference between the ground-based receiver and the airborne roving receiver. This study tests and analyzes three methods for modeling the tropospheric delay, in an attempt to improve the accuracy of the height component for airborne GPS kinematic positioning. As there are several other error sources in GPS, the test and evaluation have to be carefully designed, as any improvements in accuracy due to the use of any tropospheric modeling approaches could be masked by other effects, such as residual orbit errors and ionospheric delays. The analysis is performed for real airborne GPS data and data from a multiple-base station network, and model performance evaluation is based on an independently well-determined aircraft trajectory. Test results show that the estimation of residual tropospheric zenith delay simultaneously with the position parameters after applying the tropospheric delay corrections derived from a network of GPS receivers is seen as the best option with an additional 62% improvement for the height component in terms of standard deviation when compared with results from using a UNB3 tropospheric model only. [ABSTRACT FROM AUTHOR]

This paper presents one of the most comprehensive tests conducted about the real-time kinematics (RTK) and continuously operating reference stations (CORS) network using instruments from three global positioning system (GPS) manufacturers (Leica, Topcon, and Trimble). The test was carried out between August and October 2006 in the Marmara Region of Turkey as part of the research project for establishing RTK CORS network covering all of Turkey. Three GPS networks (NET-120, NET-90, and NET-60) were designed, each consisting of six CORS points: with interstation distances of 120, 90, and 60 km, respectively. Leica, Trimble, and Topcon directly participated in the tests, each company contributing a 2 week effort. RTK surveys were compiled at check points (previously known points) and new points were generally selected in built-up areas. Flachen Korrectur parameter—Spatial correction parameters, virtual reference stations, pseudoreference stations, and master auxiliary concept techniques were used for RTK positioning. Postprocessing by network solution software was also used at check points. The results of network-based RTK and postprocessing were found to be successful at each net, the main exception being the difficulties encountered by one of the firms participating at NET-120. Results are discussed in the paper. [ABSTRACT FROM AUTHOR]

Robust estimation of unknown parameters in linear models with only a single error component has been widely investigated. However only a small percentage of literature treats robust estimate of variance components in heteroscedastically mixed models. The correction-based pseudoobservation method, the ρ(x)-function-based robust maximum likelihood estimate (MLE) and restricted maximum likelihood estimate methods, as well as the robust Helmert method are the three kinds of typical robust methods for estimating variance components of linear mixed models. However, they are generally affected by different types of scoring functions and various tuning factors based on M estimate defined by Huber from the maximum likelihood type of estimation. In addition, the pseudoobservation method will encounter risks of incorrect corrections due to the misidentification of gross errors. In this paper, gross errors and random or normal errors are assumed to be occasionally additive, independent, normally distributed with different scales, and all are regarded as missing and/or unobservable data. Together with the observations, they form a complete data problem where the unknown parameters and variance components need to be estimated. The expectation-maximization (EM) algorithm for finding the MLEs is robustified by estimating the variances of gross errors by defining weights and proposing to jointly solve the robust estimation of the unknown parameters and variance components. A numerical example of a global positioning system baseline network shows that the robustified EM algorithm can find a reliable estimate of unknown parameters and variance components, and efficiently separate the gross errors and subrandom effects or errors by computing their respective Bayesian estimate. [ABSTRACT FROM AUTHOR]

By applying integrated least-squares adjustment of multicampaigns geographic positioning system (GPS) measurements, the velocity of any GPS monument can be obtained. The resulting velocities are used to estimate the strain rate tensors and their variances under infinitesimal strain assumption in a discrete triangle. In this paper, the GPS measurements of five campaigns, which were carried out in Shanghai City from 2002 to 2005, are used to determine the velocity of each GPS monument. Then the horizontal strain rate tensors are calculated with the relative velocities of the sites obtained. The analysis of these principal strain rates together with a comparison of the geological information is performed. The patterns of the principal strain rates show a significant northwest to southeast extension zone in the southwestern part of Shanghai, which agrees well with the neo-tectonic activity of an existing geological fault, the so-called “Dachang–Zhoupu” fault. [ABSTRACT FROM AUTHOR]

Online global positioning system (GPS) processing services have provided users with the opportunity to obtain freely high precision coordinates in a recognized datum. However, all services are dependent on the quality of the data and the length of data span supplied to them by the user. This study aims to assess the four globally available online GPS processing services from the point of view of a user wishing to take advantage of such a service for datum realization. Data from eight selected international GNSS service stations have been processed by each service and the results have allowed a statistically significant comparison analysis to be performed. Although users can expect a variability of results from different services when processing identical data, solutions with 24 h data are generally repeatable at the 1–2 cm level and accurate in terms of international terrestrial reference frame coordinate recovery at the 3–4 cm level. Such differences are accentuated as observation time decreases. Finally, postprocessing kinematic data, currently performed by only one online service, is a valid option for users provided they ensure data quality. [ABSTRACT FROM AUTHOR]