Station Coordinates Research Articles

Factors to be considered in establishing a scanning laboratory for testing the accuracy of terrestrial laser scanning technologies

Laser scanning is a 21st century mapping technique that is used to generate high density point cloud data in three dimensions (3D). The 3D scans can be used for surveying, mapping and monitoring of rock mass movement in mining. For high precision and reliable work, the instrument must be used correctly, regularly calibrated and checked to ensure that it constantly performs according to manufacturer's specifications. In this study, a Leica Total Station TCR 1201+ and a Trimble S6 Total Station were used to establish accurate coordinates for a control beacon and scanning targets. Thereafter, the scanning of the targets was carried out using a FARO Focus XD 130 terrestrial laser scanner. A comparison was conducted using the coordinates from the terrestrial laser scanner and total station to examine the point accuracy of the FARO scanner. The result from the comparison between the laser scanners coordinates and the total station coordinates showed that the FARO Focus is capable of producing accurate point cloud data that can be used for the purpose of monitoring underground rock mass movements. Lessons learnt during the development of the short-range scanning laboratory are summarised as factors to be considered when establishing such a laboratory. These include, operator knowledge, skill and work flow, robust target design, scanning geometry, full target visibility during scanning, calibration of instruments, laser scanner field of view and application of systematic error propagation during measurements.

ВЛИЯНИЕ АТМОСФЕРНЫХ НАГРУЗОК НА РЕЗУЛЬТАТЫ СПУТНИКОВОГО МОНИТОРИНГА ЗДАНИЯ СТАНЦИОННОГО УЗЛА ЗАГОРСКОЙ ГАЭС-2 МЕТОДОМ PPP

The possibility of using the Precise Point Positioning (PPP) method in the system of integrated monitoring of hydraulic structures is study. Example of measurements in the system of monitoring the Zagorskaya PSPP-2 is shown. The absolute values of the coordinates of monitoring points determined by the PPP method are quite strongly affected by atmospheric loads arising from changes in atmospheric pressure. According to theoretical studies, vertical displacements due to this effect can be up to 25 mm, horizontal up to 1/3 of this value. The results of comparative analysis are obtained and the conclusions are done. The average daily values of the PS34 monitoring station coordinates calculated by the PPP method in the TropoGNSS software product are highly correlate with the series of crustal deformations in the area of Zagorskaya PSPP-2, calculated using the International Mass Loading Service online service, and the vertical coordinate is more correlated with the model data than the horizontal coordinates. Variations in the average daily values of the coordinates of the monitoring station allow us to identify crustal deformations of the order of 5 mm. This indicates a relatively high accuracy of the results of the PPP method and the need to apply external models of atmospheric loads. The use of external models of atmospheric loads can to ensure the required accuracy of observations of vertical and horizontal displacements of concrete dams by the PPP method.

Improved Antenna Phase Center Offsets for BDS-2 IGSO/MEO Satellites Based on MGEX Long-Term Observations

For the purpose of further improving the solution accuracies of the orbital and geodetic parameters for BDS (BeiDou Navigation Satellite System) precise applications, this paper focuses on the enhancements of antenna phase center offsets (PCOs) for BDS-2 IGSOs (Inclined Geosynchronous Satellite Orbits) and MEOs (Medium Earth Orbits) through processing observations from a global tracking network. The daily estimated horizontal and vertical PCO time series of nearly three years from DOY (Day of Year) 001 in 2018 to DOY 180 in 2020 are obtained using the PANDA (Position And Navigation Data Analysis) software. The long-term PCO time series have seasonal variations and systematic effects along with the elevation angle of the Sun with respect to the orbital plane. Then, type-specific x-offsets and y-offsets of IGSOs and MEOs are comprehensively available considering the good consistency for the same satellite type. And a set of satellite-specific vertical offsets are recommended to BDS-2 IGSOs and MEOs since the low coherence of these satellites with the same type. Validation experiments are carried out for comparison between the original MGEX (Multi-GNSS Experiment) PCOs and the newly improved values (iMGEX PCOs for short), including the Precise Orbit Determination (POD) and Precise Point Positioning (PPP). Based on the orbital overlap analysis, the qualities of BDS-2 orbits show great enhancements in the along-track, cross-track and radial components, when the iMGEX PCOs are employed. Results of the independent assessment using SLR (Satellite Laser Ranging) also indicate the improvements on the radial component for C08, C10 and C11 satellites, and most of the orbit RMSs (Root Mean Squares) of iMGEX results decreased by 40.5% on average compared with the MGEX values. Additionally, the experimental station coordinates by static PPP achieve improvements at the rate of 27.1%, 32.6% and 28.4% in the east, north, and up component, respectively, in which more than a half stations realize sub-centimeter positioning accuracy in the north component using the iMGEX PCOs.

Ultra-Dense Networks: A Holistic Analysis of Multi-Piece Path Loss, Antenna Heights, Finite Users and BS Idle Modes

We discover a new capacity scaling law in ultra-dense networks under practical system assumptions, such as a general multi-piece path loss model, a non-zero base station to user equipment antenna height difference, and a finite user equipment density. The intuition and implication of this new capacity scaling law are completely different from those found in the year 2011. That law indicated that the increase of the interference power caused by a denser network would be exactly compensated by the increase of the signal power due to the reduced distance between transmitters and receivers, and thus, network capacity should grow linearly with network densification. However, we find that both the signal and interference powers become bounded in practical ultra-dense networks, which leads to a constant capacity scaling law. Moreover, our new discovery on the constant capacity scaling law indicates three network optimization problems respectively for base station deployment, user equipment scheduling and base station coordination. These three optimization problems are justified and solved in this paper, shedding new light on the deployment and optimization of ultra-dense networks.

Tidal Parameters as a Tool for the Determination of the Coordinates of the SLR Stations

Abstract One of the primary objectives of satellite geodesy is the determination of coordinates of the satellite laser ranging (SLR) stations. This task is conducted by using laser ranging techniques. The main goal of the current study was to assess the influence of using varied values of the tidal parameters (Love h 2 and Shida l 2 numbers) on the determination of the positions of chosen SLR stations. The obtained results are presented for coordinates determination conducted for six SLR stations: Mt Stromlo (no. 7825, Australia), Matera (no. 7941, Italy), Grasse (no. 7845, France), McDonald (no. 7080, USA), Arequipa (no. 7403, Peru) and Beijing (no. 7249, China). The analysis covers SLR data for 2 satellites (LAGEOS1 and LAGEOS2), which were observed for 10 consecutive years (from 2008 to 2018). The analysis was performed using the ITRF2014 reference frame in two scenarios of calculations. In scenario 1, the SLR stations coordinates were calculated using the nominal values as per the International Earth Rotation and Reference System Service (IERS) standards recommendation of the Love/Shida numbers: h 2 = 0.6078, l 2 = 0.0847. In scenario 2, the coordinates were estimated using the harnessing values of the Love/Shida numbers (h 2 = 0.6140 and l 2 = 0.0876), which were proposed by authors in a previous publication. The effect of the application of different values of the Love/Shida numbers for the determination of SLR stations coordinates was scrutinized.

Locational Analysis of Police Stations In Bauchi Metropolis Using GIS Systems

Given the security problem in Nigeria particularly in the North, the need for geospatial analysis of security in Bauchi metropolis in relation to police stations cannot be overemphasized. Apart from the prevalence of security problem in the area current analyses are inadequate, almost non-existent. To tackle this problem, Global Positioning System (GPS) was used to take the coordinates of the police stations in the study area, while the attribute data relating to the number of police personnel in each station were collected using interview and documented data. The data were analysed using simple ratio. Also ArcGIS (Version 10.0) software was used to show the map of the distribution. A nearest neighbourhood analysis has shown that the distribution of stations is random in the area. One and two kilometre buffer zones were generated and the result shows that the old city of Bauchi and the eastern part of the metropolis were fully served while the western and southern parts were underserved. The ratio of population in the area to a police is 898:1 which is far below the United Nation recommended figure of 450:1. The work recommends that there is need for population consideration in citing police stations in the area as well as increasing the work force as means for achieving a holistic security for the metropolis.

SAEnet: an application for adjustment of horizontal network using particle swarm optimization algorithm

The horizontal network of control stations plays an important role in geometric measurement activities, such as determining positions of point, distance, area, or even volume. One of the methods of determining horizontal network values is the least squares method. The method of least squares is one of the most frequently used methods to obtain unique estimates for a set of redundant measurements. The equations that are used in the horizontal network surveys are the nonlinear equations so it must be linearized in order to be computed using least squares method. The problem that arises when linearizing the nonlinear observation equation is the approximate coordinates of the network stations are needed for its computations. In order to handle this problem, the Particle Swarm Optimization (PSO) algorithm is applied as an algorithm for determining the approximate coordinate values of the network stations. The algorithm of PSO is a heuristic function that optimizes a problem by iteratively trying to improve a candidate solution toward the best solutions. The advantages of PSO are that PSO is designed for solving a problem more quickly when classic methods are too slow and finding an approximate solution when classic methods fail to find any exact solution. This paper presents the design of an application for horizontal network adjustment using PSO algorithm, namely SAEnet. The Algorithm was written in Matlab which is very effective in matrix manipulation and has been widely used in various fields of numerical computations. The computation of horizontal network adjustment using SAEnet application consists of determination of initial approximation values using PSO and the adjustment computation using the least squares method. SAEnet is also equipped with save menu to Microsoft Excel format and load menu from Microsoft Excel format. The test shows that the input and output of the program can run as expected. The results are then compared to other program, like STAR*NET, using a variety of data sets. The results of both computations show the maximum difference between both programs is 0.000040 while the average difference is 0.000020. The test shows that there is no significant difference between the results of the SAEnet and STAR*NET computation. Hence, SAEnet can be used for horizontal network adjustment computation.

Multi-Cell Interference Exploitation: Enhancing the Power Efficiency in Cell Coordination

In this paper, we propose a series of novel coordination schemes for multi-cell downlink communication. Starting from full base station (BS) coordination, we first propose a fully-coordinated scheme to exploit beneficial effects of both inter-cell and intra-cell interference, based on sharing both channel state information (CSI) and data among the BSs. To reduce the coordination overhead, we then propose a partially-coordinated scheme where only intra-cell interference is designed to be constructive while inter-cell is jointly suppressed by the coordinated BSs. Accordingly, the coordination only involves CSI exchange and the need for sharing data is eliminated. To further reduce the coordination overhead, a third scheme is proposed, which only requires the knowledge of statistical inter-cell channels, at the cost of a slight increase on the transmission power. For all the proposed schemes, imperfect CSI is considered. We minimize the total transmission power in terms of probabilistic and deterministic optimizations. Explicitly, the former statistically satisfies the users’ signal-to-interference-plus-noise ratio (SINR) while the latter guarantees the SINR requirements in the worst case CSI uncertainties. Simulation verifies that our schemes consume much lower power compared to the existing benchmarks, i.e., coordinated multi-point (CoMP) and coordinated-beamforming (CBF) systems, opening a new dimension on multi-cell coordination.

A combined EMD and MSSA model for the extraction of gravity tide correction from relative gravimetric data

A combined empirical mode decomposition (EMD) and multichannel singular spectrum analysis (MSSA) model (EMD–MSSA model) was used for extraction of the gravity tide correction without a priori information (e.g., station coordinates) from static relative gravimetric data. Static observational data acquired using a CG-5 relative gravimeter over 16 days were used to investigate the feasibility and reliability of the proposed method. The singular spectrum analysis (SSA) method and empirical mode decomposition (EMD)–independent component analysis (ICA) method were also adopted for comparison. Experimental results show that the time series of the gravity tide correction estimated using EMD–MSSA, SSA and EMD–ICA methods are consistent with a theoretical reference (the Longman formula). The gravity tide correction estimated using the EMD–MSSA method is closer to the theoretical model than other methods, the root-mean-square difference of the residuals between estimated values and theoretical values are smallest, and the accuracy of the gravity tide correction time series derived using the EMD–MSSA method is thus highest. The correlation coefficient of extraction results and GT is highest for the results extracted using the EMD–MSSA method. The experimental results show that using the EMD–MSSA model, which combines the advantages of the MSSA and EMD signal processing methods, improves the extraction estimation accuracy and reliability of the gravity tide correction from relative gravimetric data.

Impact of network constraining on the terrestrial reference frame realization based on SLR observations to LAGEOS

The Satellite Laser Ranging (SLR) network struggles with some major limitations including an inhomogeneous global station distribution and uneven performance of SLR sites. The International Laser Ranging Service (ILRS) prepares the time-variable list of the most well-performing stations denoted as ‘core sites’ and recommends using them for the terrestrial reference frame (TRF) datum realization in SLR processing. Here, we check how different approaches of the TRF datum realization using minimum constraint conditions (MCs) and the selection of datum-defining stations affect the estimated SLR station coordinates, the terrestrial scale, Earth rotation parameters (ERPs), and geocenter coordinates (GCC). The analyses are based on the processing of the SLR observations to LAGEOS-1/-2 collected between 2010 and 2018. We show that it is essential to reject outlying stations from the reference frame realization to maintain a high quality of SLR-based products. We test station selection criteria based on the Helmert transformation of the network w.r.t. the a priori SLRF2014 coordinates to reject misbehaving stations from the list of datum-defining stations. The 25 mm threshold is optimal to eliminate the epoch-wise temporal deviations and to provide a proper number of datum-defining stations. According to the station selection algorithm, we found that some of the stations that are not included in the list of ILRS core sites could be taken into account as potential core stations in the TRF datum realization. When using a robust station selection for the datum definition, we can improve the station coordinate repeatability by 8%, 4%, and 6%, for the North, East and Up components, respectively. The global distribution of datum-defining stations is also crucial for the estimation of ERPs and GCC. When excluding just two core stations from the SLR network, the amplitude of the annual signal in the GCC estimates is changed by up to 2.2 mm, and the noise of the estimated pole coordinates is substantially increased.

A new 3D laser-scanning and GPS combined measurement system

Terrestrial laser scanning (TLS) is widely used because of its ability to quickly acquire high-density and high-precision 3D image and topographic data. However, it can only acquire independent coordinate system points, which restricts its application in large-scale deformation monitoring. In this study, we constructed a measurement system to acquire global coordinate point cloud data by combining TLS and GPS (Global Positioning System). The coordinate values of retro-reflective targets could be acquired in different coordinate systems, the GPS coordinate and the TLS station coordinate, synchronously. Our experiments showed that, after registration with the homonymy points acquired by 30-min short-baseline differential GPS using the ICP algorithm, the positional accuracy of the TLS retro-reflective target center in the global coordinate was better than 10 mm. This high precision meets, for instance, the requirements of coal mining subsidence monitoring. We used our new combined measurement system to acquire and process the point cloud data of a frame structure. The measurements demonstrated the practicability and robustness of the new measurement system.

ADJUSTMENT OF CADASTRAL NETWORK USING LEAST-SQUARES VARIANCE COMPONENT ESTIMATION

Abstract. The role of the stochastic model very important in data processing of geodetic network since it describes the accuracy of the measurements and their correlation with each other. Knowledge of weights of the observables is required to provide a better understanding of the sources of errors and to model the error, hence the weights need to be determined correctly. This study concentrates on the estimation of variance components from different types of instruments used in the cadastral survey. The ideas are to combine the conventional and advanced instruments in a traverse network to enhance the estimated variance component in the stochastic model. Thus, Least Squares Variance Component Estimation (LS-VCE) method was used in this study because the method is simple, flexible and attractive due to the precision of variance estimators that can be directly obtained. Observation data come with several types of instruments such as chain measurement, Electronic Distance Measurement and total station were utilized. The findings showed that LS-VCE method was very reliable in cadastral network application. Besides, the results revealed that the estimated variance components for distance scale error, σp seem to become unrealistic for each data tested. It was found that the traverse network which included chain survey, showed the insignificant result to the precision of station coordinates when the measurements were combined.

Correcting surface loading at the observation level: impact on global GNSS and VLBI station networks

Time-dependent mass variations of the near-surface geophysical fluids in atmosphere, oceans and the continental hydrosphere lead to systematic and significant load-induced deformations of the Earth’s crust. The Earth System Modeling group of Deutsches GeoForschungsZentrum (ESMGFZ) provides vertical and horizontal surface deformations based on numerical models of the global geophysical fluids in atmosphere, oceans and the continental hydrosphere with a spatial resolution of $$0.5^\circ $$ and a temporal sampling of down to 3 h (Dill and Dobslaw in J Geophys Res 118(9):5008–5017, 2013. https://doi.org/10.1002/jgrb.50353). The assessment of conventionally—i.e. without consideration of non-tidal loading models—processed global GNSS datasets reveals that large parts of the residual station coordinates are indeed related to surface loading effects. Residuals explained by the models often have a pronounced annual component, but variability at other periodicities also contributes to generally high correlations for 7-day averages. More than 10 years of observations from about 400 GNSS and 33 VLBI stations were specifically reprocessed for this study to incorporate non-tidal loading correction models at the observation level. Comparisons with the corresponding conventional processing schemes indicate that the coordinate repeatabilities and residual annual amplitudes decrease by up to 13 mm and 7 mm, respectively, when ESMGFZ’s loading models are applied. In addition, the standard deviation of the daily estimated vertical coordinate is reduced by up to 6.8 mm. The network solutions also allow for an assessment of surface loading effects on GNSS satellite orbits, resulting in radial translations of up to 4 mm and Earth orientation parameters (EOP). In particular, the VLBI-based EOP estimates are critically susceptible to surface loading effects, with root-mean-squared differences reaching of up to 0.2 mas for polar motion, and 10 µs for UT1-UTC.

Comparative analysis of modern deformation and the newest motions of the Earth surface in the territory of Ukraine

Currently, the data of the Global Navigation Satellite Systems (GNSS) are widely used in the field of navigation, geodesy, cartography and regional geodynamic studies, in particular, in monitoring the movement of lithospheric plates, etc. Further development and creation of local GNSS networks, as well as the long-term replenishment of databases regarding the determination of the coordinates of individual stations and the speeds of their movement allows obtaining reliable more detailed information on the current deformation of the Earth's surface. The article discusses the current deformation of the Earth’s surface based on the analysis of the Global Navigation Satellite Systems data from the GAO NAS of Ukraine in comparison with the heights of the UGK2012 quasi-geoid and the latest lineament zones and faults, as well as with the late Pliocene-Quaternary vertical movements of the Earth’s crust. According to the results of the analysis of high-precision coordinates of displacement vectors of permanent GNSS stations in the territory of Ukraine, deformation parameters of the Earth’s surface were obtained, areas of prevailing compression values — tension and left-right-side rotation of the Earth’s surface were identified, the boundaries between which can be drawn along the latest lineament zones and faults. The areas of the predominant stretching of the Earth’s surface correspond to the zones of the newest tectonic uplifts (Volyn-Podolsk and Periazov hills) and maximum amplitudes of the Pliocene-Quaternary movements and positive geoid anomalies, and the areas of prevailing compression are zones of tectonic descents (Polissian and Peridnieper lowland), minimal amplitudes of Pliocene-Quarternary movements and minor heights of the geoid. Four large modern geoblocks have been identified: North-West and North-East, which rotate clockwise, and South-West and South-East rotating counterclockwise. At a qualitative level, the mechanism of interconnection of modern and newest movements of the Earth’s crust, namely, the presence of the latest tectonic zones of uplifting and lowering with corresponding tensions and movements of its surface, on which modern tensions (and corresponding movements) are imposed that are associated with the tectonic movement of the Eurasian Plate in northeastern direction and the irregular rotation of the Earth.

Determination of the local tidal parameters for the Borowiec station using Satellite Laser Ranging data

The values of regional tidal parameters h2, l2 associated with the tidal variations of ground stations were estimated for the Polish Satellite Laser Ranging (SLR) station Borowiec using SLR data. The study is based on satellite observations taken by the global network of ground stations during the period from January 1, 1999 until January 1, 2019 for monthly orbital arcs of the satellites LAGEOS-1 and LAGEOS-2. The adjusted regional values for h2 equalling 0.7308 ± 0.0008 and l2 equalling 0.1226 ± 0.0003 are discussed and compared with the nominal values of h2 and l2 given in the the International Earth Rotation and Reference Systems Service (IERS) standards and with other estimations of these parameters. Furthermore, the influence of the tidal parameters changes on estimation of the Borowiec station coordinates in the ITRF2014 reference frame was investigated. The analysis was carried out in two variants. The first one consisted in the determination of the Borowiec station coordinates with the use of the nominal values of the tidal parameters: h2 = 0.6078 and l2 = 0.0847 (IERS recommended values). In the second one, the Borowiec station coordinates were determined using the local tidal parameters estimated in this paper (h2 = 0.7308 ± 0.0008 and l2 = 0.1226 ± 0.0003). The differences between X, Y ,Z for Variant 1 and Variant 2 are −3.5, 3.3 and 4.2 mm, respectively.

Influence of Geophysical Signals on Coordinate Variations GNSS Permanent Stations in Central Europe

Abstract This article presents an analysis of the extent of the impact of deformations of the earth’s crust resulting from geophysical models on changes in the coordinates of Global Navigation Satellite System (GNSS) stations. The author presents the results of analyses of the spatial correlation coefficient of deformation components for the non-tidal atmospheric loading (NTAL), non-tidal ocean loading (NTOL) and hydrological loading (HYDRO) models of geophysical deformation. In addition, the author calculated the correlation coefficients between station’s coordinate series to determine whether the deformations of the earth’s crust have a more global, large-area (regional scale) or local-range (local scale) impact, limited to the nearest of stations. In addition to correlation coefficients, the author analysed the similarity in periodic components between station coordinates by calculating the coherence between them. The results of the analysis showed that for the height components (Up), we observe the global range of deformation models, and the NTAL deformation has the greatest influence on the change in them. The lack of correlation between coordinate signals for horizontal components may result from specific local conditions in the place of the station, low-resolution of geophysical models and small amplitudes of these signals in relation to noise. An analysis of the coherence coefficients showed that each station coordinates shows completely different periodic components in the North, East and Up directions.

Troposphere delay modeling with horizontal gradients for satellite laser ranging

Satellite laser ranging (SLR) constitutes a fundamental space geodetic technique providing global geodetic parameters, such as geocenter coordinates, Earth rotation parameters, and low-degree gravity field coefficients. The tropospheric delay correction is one of the crucial corrections that have to be taken into account when processing SLR data. Current conventional models of the troposphere delays assume a full symmetry of the atmosphere above SLR stations. Neglecting horizontal gradients in SLR solutions introduces a systematic error in SLR products, especially for the observations at low elevation angles, and leads to a deterioration of the consistency between SLR and other space geodetic techniques, such as global navigational satellite systems and very-long-baseline interferometry. We derive new mapping function coefficients, as well as first- and second-order horizontal gradients, all of which are based on numerical weather models, in order to properly consider the azimuthal asymmetry in SLR solutions. We test the enhanced mapping function and horizontal gradients on the solutions based on 11 years of SLR observations to LAGEOS-1/2 satellites and 1 year of SLR observations to Sentinel-3A. The consideration of azimuthal asymmetry of the atmosphere above the SLR stations has a systematic effect on SLR-derived products, such as station and geocenter coordinates and pole coordinates. Horizontal gradients in SLR solutions improve the consistency between SLR-derived pole coordinates and the combined IERS-C04 series by means of reducing the offset for the X and Y pole coordinates by 20 {upmu }mathrm{as}. The second-order horizontal gradients are negligible in SLR solutions; thus, including first-order gradients is sufficient for SLR solutions.

Calibration Method for Angular Positioning Deviation of a High-Precision Rotary Table Based on the Laser Tracer Multi-Station Measurement System

This paper proposes a calibration method for angular positioning deviation of a high-precision rotary table based on the laser tracer multi-station measurement system. The algorithm error of the calibration method for angular positioning deviation of a high-precision rotary table based on the laser tracer multi-station measurement system was mainly discussed. During the experiments, the laser tracer was fixed on the work surface of the rotary table, and the rotary was fixed on the work surface of the coordinate measurement machine (CMM). The rotary table was rotated with the same angular interval. In this case, an optimization method for calculating the coordinates of a laser tracer station by using Levenberg–Marquardt algorithm and singular value decomposition transform was proposed. Then, the angular positioning deviation of the rotary table was calibrated by an established geometric relationship model between the coordinates of laser tracer stations and the rotation angle of the rotary table. The angular positioning deviation of the high-precision rotary table was as low as ±0.9″, and the error of the calibration method was ±0.4″. The experimental results proved the feasibility of the proposed calibration method. The calibration method proposed in this paper is suitable for the case that the rotary table is not linked with the CMM, especially for large high-precision rotary tables.

Computationally efficient dual-frequency uncombined precise orbit determination based on IGS clock datum

Using uncombined (UC) or undifferenced original observations has become a research topic in the global navigation satellite system (GNSS) community. This far, precise orbit determination (POD) with ionospheric-free (IF) observation combination has been favored. Using the uncombined strategy, i.e., using the raw observations to perform POD, the slant ionospheric delay is regarded as an unknown epoch parameter. We assume that the slant ionospheric delay depends on the frequency having the same magnitude for pseudoranges and carrier phases but opposite sign. Since there are, at each station and each epoch, as many ionospheric delay parameters as the observed satellites, a large number of ionospheric parameters need to be estimated for uncombined POD. The usual approch is that, when the observations at an epoch are accumulated, the epoch parameters consisting of clock and ionospheric parameters are eliminated simultaneously, which results in low computational efficiency. We develop a high-efficiency method by eliminating ionospheric parameters one by one, where each of them is eliminated when the observations of a station and a satellite are accumulated and no matrix inversion is required. In this uncombined POD algorithm, the IF-combined clock datum adopted by the international GNSS service (IGS) clock products is used to keep compatibility with existing IGS products by using the re-parameterized observation equations. We deduce the ambiguity resolution strategy for uncombined POD. In the experimental part, the modified parameter elimination method is first validated. With GPS observations from 58 global IGS stations, the first iteration processing time of parameter estimation for IF POD, UC POD and modified UC POD are 3.6, 62.5 and 9.2 min, respectively. The computational efficiency of modified UC POD strategy is greatly improved compared to UC POD. Then, the IF POD and the improved UC POD strategies with ambiguity float and fixed solutions are analyzed by comparing orbits, clocks, station coordinates and tropospheric delays with respect to IGS products. Results show that the accuracy of UC and IF solutions is comparable. Afterward, the repeatability of station coordinates is analyzed. With the solutions of 13 POD arcs, the repeatability over 13 days is consistent for UC and IF strategy. In addition, the ambiguity fixing rate, data usage rate, as well as residuals of code and phase observations, is analyzed. It is concluded that the slight difference between UC and IF strategy may be related to the data usage rate.

ANALYSIS OF COMMON QUALITY PROBLEMS IN COORDINATE TRANSFORMATION BETWEEN REFERENCE COORDINATE SYSTEM AND GEOCENTRIC COORDINATE SYSTEM

Abstract. In the working of the existing reference coordinate system transformed into the coordinate system of the geocentric coordinate system, many experts and scholars have in-depth research on the transformation methods such as geodetic control point results (including GNSS base station coordinates, GNSS control point coordinates, triangle point coordinates), basic geographic information data results (including DLG, DOM, DEM, DRG, DSM, etc.) and other spatial information data. On the basis of these studies, many provinces and cities have completed the coordinate system transformation of surveying and mapping results in China. This paper expounds the method of transforming the existing reference coordinate system into the geocentric coordinate system, summarizes and sorts out the common quality problems in the process of different data and different methods, and analyses the causes of the problems and the impact on the transforming results. Based on the above work, The paper provides reference and suggestions for the transforming work, which is aimed to improve the transformation quality in the future.