Continuously Operating Reference Stations Research Articles

Establishment and Validation of Continuously Operating Reference Stations Geosystems Network on Static and Real-Time Kinematic in Benin City, Nigeria

An infrastructure highly treasured by Geomatics Engineers is the continuously operating reference stations (CORS). CORS technology is a complete paradigm shift from the previously known ground control system to a virtual control system. In this paper, we present the steps taken to install CORS Geosystems in Benin City and further test its efficacy by observing fifteen existing control points located far and near using two Tersus GNSS receivers (A&B) concurrently. We perform statistical adjustment using Trimble Business Center software. Successful adjustment took two (2) iterations with Chi square test at (95%) precision confidence level and degree of freedom being nine (9) showed that the result of the adjustment was reliable. Means of 0.007m, 0.003m 0.000m for Easting, Northings and Heights were obtained while the standard errors (σ) in E, N and H are 0.003m, 0.007m and 0.000m respectively. The achieved RMS errors obtained from the attempted validation confirmed further that the newly installed CORS is capable of providing reliable 3D geo-spatial data for prospective authorized users to proffer solutions to engineering, scientific, environmental and research driven challenges.

Regional Ionospheric Corrections for High Accuracy GNSS Positioning

Centimetre-level accurate ionospheric corrections are required for a high accuracy and rapid convergence of Precise Point Positioning (PPP) GNSS positioning solutions. This research aims to evaluate the accuracy of a local/regional ionospheric delay model using a linear interpolation method across Australia. The accuracy of the ionospheric corrections is assessed as a function of both different latitudinal regions and the number and spatial density of GNSS Continuously Operating Reference Stations (CORSs). Our research shows that, for a local region of 5° latitude ×10° longitude in mid-latitude regions of Australia (~30° to 40°S) with approximately 15 CORS stations, ionospheric corrections with an accuracy of 5 cm can be obtained. In Victoria and New South Wales, where dense CORS networks exist (nominal spacing of ~100 km), the average ionospheric corrections accuracy can reach 2 cm. For sparse networks (nominal spacing of >200 km) at lower latitudes, the average accuracy of the ionospheric corrections is within the range of 8 to 15 cm; significant variations in the ionospheric errors of some specific satellite observations during certain periods were also found. In some regions such as Central Australia, where there are a limited number of CORSs, this model was impossible to use. On average, centimetre-level accurate ionospheric corrections can be achieved if there are sufficiently dense (i.e., nominal spacing of approximately 200 km) GNSS CORS networks in the region of interest. Based on the current availability of GNSS stations across Australia, we propose a set of 15 regions of different ionospheric delay accuracies with extents of 5° latitude ×10° longitude covering continental Australia.

Development of continuously operating reference stations in mountainous areas

The purpose of the study is to provide general information on the design, creation and installation of continuously operating reference station (CORS) in mountainous areas (hardware components and CORS configuration, station specifications, design features and creation of a CORS network). The paper lists the main issues that must be taken into account when creating, installing and developing CORS in the mountains - the closure of the radio horizon, multipath, changes in the troposphere at short distances, local geodynamics, problems of receiving and transmitting differential corrections. It is noted that in mountain gorges, canyons, where it is difficult to receive radio signals from GNSS satellites and exchange information between the CORS GNSS receiver and the rover, it is optimal to develop passive geodetic networks using terrestrial methods (polygonometry, trilateration) based on CORS networks.

ASSESSING QUALITY OF CORSNET-NSW INFRASTRUCTURE FOR USE IN REGIONAL NEW SOUTH WALES, AUSTRALIA

Abstract. CORSnet-NSW is a network of Global Navigation Satellite System (GNSS) Continuously Operating Reference Stations (CORS) covering the state of NSW and providing centimetre-level real-time positioning. This research paper aims to determine the level of accuracy and precision of CORSnet-NSW in regional parts of the network and compare them to that of traditional RTK under identical conditions. It investigates what effects satellite geometry and proximity to a CORS station have on NRTK measurements. It also verifies the CORSnet-NSW claim of network wide 2cm accuracy. The claim was found to be true at the 68% Confidence Interval. Changes in satellite geometry were not found to affect the results for the most part. It was also found that CORSnet-NSW precision was affected by the proximity of the rover to the base/calibration points more than its proximity to a CORSnet-NSW station. However, even though the CORSnet-NSW results were better than expected, traditional RTK remains the most precise and consistent method. This research paper provides GNSS users in regional NSW with the evidence they need to make informed decisions regarding which type of RTK method is fit for their purposes.

Construction of nominal ionospheric gradient using satellite pair based on GNSS CORS observation in Indonesia

Ground-Based Augmentation System (GBAS) is a GNSS augmentation system that meets International Civil Aviation Organization (ICAO) requirements to support precision approach and landing. GBAS is based on local differential GNSS technique with reference stations located around an airport to provide necessary integrity and accuracy. The performance of the GBAS system can be affected by gradient in the ionospheric delay between aircraft and reference stations. A nominal ionospheric gradient, which is bounded by a conservative error bound, is represented by a parameter σvig. The parameter σvig is commonly determined using station pair to GNSS Continuous Operating Reference Station (CORS) data. The station-pair method is susceptible to doubling of the estimation error of receiver inter-frequency bias (IFB) and is not suitable with the CORS conditions in Indonesia. We propose a satellite-pair method that is found to be more suitable for the CORS network over Indonesia which is centered in Java and Sumatra islands. An overall value of σvig (5.21 mm/km) was obtained using this method along with preliminary results of a comparison of σvig from Java and Sumatra islands.Graphical

Ambiguity Resolution for Long Baseline in a Network with BDS-3 Quad-Frequency Ionosphere-Weighted Model

For long baseline in a network, the traditional combined ionosphere-free (IF) + wide-lane (WL) strategy is commonly used, but the residual tropospheric delays and larger noise hamper the basic ambiguity resolution (AR). With the completion of the BeiDou global navigation satellite system (BDS-3) and the quad-frequency signals provided by BDS-3 satellites, we can construct more combinations that are conducive to ambiguity resolution. Compared with ionosphere-free linear combinations, we estimated ionospheric delay using three independent WL observations, and formed an ionosphere-weighted model using uncombined code and phase observations, which proved to be quite effective. Based on the real quad-frequency BDS-3 observations of two CORS (Continuously Operating Reference Stations) and two user stations, we processed eight days of data to study the formal and empirical ambiguity success rates and user positioning errors. The rounding success rate of WL ambiguity was significantly improved with ionospheric correction. The success rate of the basic ambiguity increased from 94.4 and 96.1% to 98.0% using the quad-frequency ionosphere-weighted (QFIW) model compared with the double-frequency ionosphere-free (DFIF) model and the triple-frequency geometry-based (TFGB) model. Furthermore, the user E/N/U positioning accuracy improved by 20.6/31.5/13.1% and 6.3/22.9/5.8%, respectively.

Некоторые особенности выполнения кадастровых работ с использованием постоянно действующих базовых станций

The authors consider the features of cadastral works using continuously operating reference stations (CORS). One of the key parameters affecting the determining the coordinates of the base station accuracy is its distance from the original CORS, which must be confirmed at the stage of satellite equipment certification. Reliable and effective control of the exactness of satellite positioning is the discrepancy of the measured line length between the base stations being determined and the same length calculated from the coordinates of the base stations obtained as a result of satellite positioning. If this criterion is met, it can be argued that the base stations whose coordinates are determined relative to the original CORS can be the starting points for determining the location of real estate objects. Based on these conceptual provisions, experimental work was carried out in the territory of the Altai Republic to determine the coordinates of the base stations being computed relative to the three CORS with subsequent processing using the criteria proposed in the article. The results of the performed studies enable

Reliability of CSRS-PPP for Validating the Egyptian Geodetic Cors Networks

Abstract The development, utilization, and maintenance of continuously operating reference stations (CORS) network are vital in many areas of surveying and geodesy, such as controlling geodetic networks, developing local ionospheric models, and estimating the tectonic plate movements. Accordingly, the Egyptian Surveying Authority (ESA) established a CORS network consisting of 40 stations covering the Nile valley and its delta in 2011. CORS collect global navigation satellite system (GNSS) data. Recently, Egypt has witnessed rapid growth in many infrastructure projects and the development of new cities on a national scale. Therefore, there is an urgent need to investigate the ESA-CORS accuracy; the quality of data from the ESA-CORS must be considered for monitoring continuous tectonic motion, coordinating changes, and for Egypt’s development plan. Contemporary research worldwide identified considerable benefits of the precise point positioning (PPP) solution of dual- or single-frequency GNSS data. This study investigates the reliability of using the CSRS-PPP service for three consecutive observation days of 32 ESA-CORS networks in Egypt and the surrounding six international GNSS services (IGS)-CORS. For ESA-CORS, the PPP solution showed a root mean square error (RMSE) value of 6 mm (standard deviation [SD] = 3–4 mm) in east and north; for the height direction, the solution indicated an RMSE value of 22 mm (SD was about 14 mm). At a confidence level of 95%, this study revealed that SD95% was 2 mm in east and north directions and 6–7 mm for the height direction. This study shows that the PPP solution shown from the ESA-CORS stations is associated with two times better for horizontal and four times for the height direction than the delivered form ESA-CORS stations.

Considerations and Multi-Criteria Decision Analysis for the Installation of Collocated Permanent GNSS and SAR Infrastructures for Continuous Space-Based Monitoring of Natural Hazards

Over the past few decades, the global population and the built environment’s vulnerability to natural hazards have risen dramatically. As a result, decisive actions, such as the SENDAI framework, have emerged to foster a global culture of successful disaster risk reduction policies, including actions to mitigate the social and economic impact of geohazards. The effective study of natural disasters requires meticulous and precise monitoring of their triggering factors, with ground- and space-based techniques. The integration of GNSS and SAR observations through the establishment of permanent infrastructures, i.e., Continuously Operating Reference Stations (CORS) networks and arrays of Corner Reflectors (CRs), may form a seamless ground displacement monitoring system. The current research literature provides fragmented guidelines, regarding the co-location of SAR and GNSS permanent infrastructures. Furthermore, there exist no guidelines for the determination of the most suitable locations using a holistic approach, in terms of criteria and required data. The purpose of this paper is to present a semi-automatic multicriteria site suitability analysis and evaluation of candidate sites for the installation of a permanent CORS and two CRs; one for each pass, taking into account various parameters and criteria. The first results demonstrate that the collocation of SAR and GNSS permanent infrastructures, utilizing a holistic criteria-based approach, is successful and complies with all the literature’s requirements.

Quality assessment of Continuous Operating Reference Stations (CORS) - GPS stations in Mexico

The present analysis provided the quality assessment of 65 Continuous Operating Reference Stations (CORS) situated in and around Mexico using the data of about ten years (January 2010 to January 2020). To accomplish the assessment, we considered 4 quality indexes for performing the quality check, incluing the multipath effect on L1 and L2 bands, signal-to-noise ratio in both bands, cycle slips, and integrity. Meanwhile, a new reference parameter named regional values for Mexico (RVM) was calculated for the stations situated in Mexico. Additionally, an exhaustive analysis of the quality indicators in the worst and best cases was performed. The signal degradation was proved by a long-term time series and crustal deformation analysis in GAMIT/GLOBK platform. The results showed a strong correlation between integrity, cycle slips and daily observations time, and the multipath effect is strong in the case of outdated systems. The study indicates that the estimated quality indexes and values could be the basis for establishing new CORS in Mexico, and the errors corrections which cannot be mitigated in the post-processing stage would greatly help utilize the data for different scientific applications. The results were supported by deformation analysis in part of Baja California Peninsula in Mexico indicating northern and eastern velocity vector of −3.08 ± 0.02 mm/yr, −7.85 ± 0.02 mm/yr and −0.07 ± 0.03 mm/yr, −9.33 ± 0.02 mm/yr respectively at MPR1 and INEG stations.

Manifestation of earthquake preparation zone in the ionosphere before 2021 Sonitpur, Assam earthquake revealed by GPS-TEC data

Global Positioning System (GPS) Continuously Operating Reference Station (CORS) data analysis shows that the ionosphere's electron density variability is linked to the deformation and stress accumulation in the Earth's crust. Anomalies in ionosphere total electron content (TEC) variability before 2021 M6.4 Sonitpur, Assam earthquake were detected using L1 and L2 GPS frequencies that showed three distinct abnormalities on April 3, 9, 10, 2021. Pearson's correlation coefficient (r) of TEC decreases in the CORS that lies away from the earthquake epicenter, indicating the possibilities of a positive relationship between TEC variability and earthquake epicenter. TEC concentration also decreases towards the epicenter within the earthquake preparation zone (EPZ). It is also observed that the Pearson's correlation coefficient (r) of TEC decreases linearly near the EPZ. The study demonstrates the possibilities of determining the TEC anomalous zone in the ionosphere that coincides with the EPZ in the crustal rocks. The research indicated the possibilities of magnitude estimation of an impending earthquake based on the TEC anomalous zone in the ionosphere using closely spaced dense CORS network data.

A Modelling Study by Factorial Design on GNSS Positioning

Although researchers have widely studied the analysis and modelling of error sources on Global Navigation Satellite Systems positioning, some of these errors have not been eliminated significantly and only some of the Global Navigation Satellite System’s data are modelled. The present work was undertaken to determine the effect of different variables, namely: season, the number of visible satellites, and dilution of precision on the efficiency of horizontal and vertical CORS (Continuously Operating Reference Stations) positioning. For this aim, the CORS data was collected at 14 different test points during 600 epochs with 1-second intervals. Factorial designs supply an efficient solution to understand the impact of several factors on a response variable. A full factorial design with three factors at two levels was applied for these purposes. According to the results of the full factorial design, all factors significantly affected the response variable. Also, the interaction effects of factors were analysed on the CORS horizontal and vertical positioning. The regression equations were obtained for all situations.

PERFORMANCE OF BURSA-WOLF MODEL FOR DEFORMING REGION: CASE STUDY IN MALAYSIA

Abstract. Bursa-Wolf model is a common mathematical approach for coordinate transformation practice between two reference frames. For the case of deforming region, the existing reference frame has been experiencing a non-linear shifting over the time due to co-seismic and post seismic occurrences. Imprecise coordinate in the reference frame definition could degrading critical positioning, surveying, and navigation activities. This require a new realization of reference frame and the coordinate transformation linkage is suggested to be developed in relating the new and existing reference frame. This study provides performance of Bursa-Wolf model as coordinate transformation approach for a deforming region that is experiencing non-linear shifting due to the co-seismic and post-seismic events. The Bursa-Wolf were generated from 32 dependent Global Positioning System (GPS) Continuously Operating Reference Stations (CORS) in Malaysia meanwhile another 20 independent neighbouring stations were utilized for assessment purposes. Seven parameters (7p) of Bursa-Wolf were estimated with RMS at ±4.5mm, ±9.2mm and ±2.1mm respectively. The independent stations were classified as internal and external assessment station and the root mean square (RMS) were found at less than 10mm. The internal station has depicted a better RMS in each component which are ±5.1mm, ±6.5mm and ±1.5mm respectively. Meanwhile for external stations RMS in each component are ±6.1mm, ±8.7mm and ±3.5mm respectively. The result shows that Bursa-Wolf model is sufficient to be used as coordinate transformation approach for deforming region.

Optimising the Use of National CORS Data in the Context of Thailand

This dissertation concerns the optimisation of the use of spatial data from the National Continuously Operating Reference Stations (NCORS) in Thailand. Thailand, among many countries, has established NCORS to observe and process the Global Navigation Satellite System (GNSS) signals into spatial data to improve the positional accuracy in spatially related activities. Despite many potential user groups, only some of them appeared actually to use NCORS data. In order to investigate and recommend policy venues to encourage the use of NCORS data, this research formulates an NCORS data ecosystem concept, applies the concept to identify the gaps in NCORS data use in Thailand, and examines the policies to address the identified gaps. The research shows that Open Data is a prerequisite to make data available to the maximum extent, but not a guarantee that the data also will be used. Next to Open Data, also users, including Open Data intermediaries, must be empowered. The facilitating conditions should be satisfied to enable users to use the data. These conditions require time to take effect. Only then will the spatial data not be kept away in hidden places but will become accessible and usable for as many users as possible in Thailand and deliver social and economic benefits reported in other countries.

Single Epoch Ambiguity Resolution of Small-Scale CORS with Multi-Frequency GNSS

The network real-time kinematic (RTK) technique uses continuously operating reference stations (CORS) within a geographic area to model the distance dependent errors, allowing users in the area to solve ambiguities. A key step in network RTK is to fix ambiguities between multiple reference stations. When a new satellite rises or when maintenance happens, many unknown parameters are involved in the mathematical model, and traditional methods take some time to estimate the integer ambiguities reliably. The purpose of this study is the single-epoch ambiguity resolution on small-scale CORS network with inter-station distance of around 50 km. A new differencing scheme is developed to explore the full potential of multi-frequency Global Navigation Satellite System (GNSS). In this scheme, a differencing operation is formed between satellites with the closest mapping functions. With the new differencing scheme, tropospheric error can be mostly neglected after the correction, as well as the double-differencing operation. Numerical tests based on two baselines of 49 km and 35 km show that the success rate of ambiguity resolution can reach more than 90%. The single-epoch ambiguity resolution for reference stations brings many benefits to the network RTK service, for example, the instantaneous recovery after maintenance or when a new satellite rises.

Evaluation of Network RTK Positioning Performance Based on BDS-3 New Signal System

The BeiDou navigation satellite system (BDS-3) has been deployed and provides positioning, navigation, and timing (PNT) services for users all over the world. On the basis of BDS-2 system signals, BDS-3 adds B1C, B2a, B2b, and other signals to realize compatibility and interoperability with other global navigation satellite systems (GNSS). Network real-time kinematic (RTK) technology is an important real-time regional high-precision GNSS positioning technology. Combined with the network RTK high-precision service platform software developed by the author’s research group and the measured data of a provincial continuously operating reference station (CORS) in Hubei, this paper preliminarily evaluates the network RTK service performance under the new signal system of BDS-3. The results show that single BDS-3 adopts the new signal combination (B1C+B2a) and transition signal combination (B1I+B3I) when providing virtual reference station (VRS) services, the RTK fixation rate of the terminal is above 95%, and the horizontal and elevation accuracies are within 1cm and 2 cm, respectively, which meets the requirements of providing high-precision network RTK services by a single BDS-3 system. In addition, the positioning accuracy of BDS-2 is relatively poor, while the accuracy of BDS-3 is better than global positioning systems (GPS) and BDS-2. The combined processing effect of the B1I+B3I transition signal of BDS-2/3 is optimal, the accuracy of E and N directions is better than 0.5 cm, and the accuracy of U direction is better than 1.5 cm. It can be seen from the atmosphere correction accuracy, regional error modeling accuracy, and network RTK terminal positioning accuracy that the service effect of the B1C+B2a combination is slightly better than that of the B1I+B3I combination. When a single BDS-3 constellation provides network RTK services, it is recommended to use the B1C+B2a combination as the main frequency solution, and when the BDS-2/3 constellation provides service, it is recommended to use the B1I+B3I combination as the main frequency solution.

REVIEW OF INTERNATIONAL GNSS DATA SHARING POLICY FRAMEWORKS AND PRACTICES

Global Navigation Satellite Systems, or GNSS, is a space technology that has become an important component of positioning, navigation, and timing (PNT) in a broad variety of military and civilian applications. Accordingly, the GNSS is being supported with Continuously Operating Reference Station (CORS) networks which are a common type of GNSS ground-based augmentation infrastructure that governments and industry use to distribute centimetre accurate PNT information throughout the nation or region. In Malaysia, there are few CORS networks currently in services. It was difficult to integrate CORS networks even within the country since the CORS operating came from several different organizations. Furthermore, the CORS data sharing between the public and private sectors in providing precise positioning applications also challenging issue due to the fact that the data contains sensitive information. The relevant policy document on data sharing in the country is still vague. This paper review on existing GNSS data sharing policy framework and practice at the international and national levels. A number of countries from each continents were chosen to be studied further in order to identify the requirements that could be considered for adoption. The goal of this study is to create a clear conceptual framework for GNSS data sharing in the country, as well as to resolve some grey areas between public and private GNSS users.

Regional Crustal Vertical Deformation Driven by Terrestrial Water Load Depending on CORS Network and Environmental Loading Data: A Case Study of Southeast Zhejiang.

Monitoring regional terrestrial water load deformation is of great significance to the dynamic maintenance and hydrodynamic study of the regional benchmark framework. In view of the lack of a spatial interpolation method based on the GNSS (Global Navigation Satellite System) elevation time series for obtaining terrestrial water load deformation information, this paper proposes to employ a CORS (Continuously Operating Reference Stations) network combined with environmental loading data, such as ECMWF (European Centre for Medium-Range Weather Forecasts) atmospheric data, the GLDAS (Global Land Data Assimilation System) hydrological model, and MSLA (Mean Sea Level Anomaly) data. Based on the load deformation theory and spherical harmonic analysis method, we took 38 CORS stations in southeast Zhejiang province as an example and comprehensively determined the vertical deformation of the crust as caused by regional terrestrial water load changes from January 2015 to December 2017, and then compared these data with the GRACE (Gravity Recovery and Climate Experiment) satellite. The results show that the vertical deformation value of the terrestrial water load in southeast Zhejiang, as monitored by the CORS network, can reach a centimeter, and the amplitude changes from −1.8 cm to 2.4 cm. The seasonal change is obvious, and the spatial distribution takes a ladder form from inland to coastal regions. The surface vertical deformation caused by groundwater load changes in the east–west–south–north–central sub-regions show obvious fluctuations from 2015 to 2017, and the trends of the five sub-regions are consistent. The amplitude of surface vertical deformation caused by groundwater load change in the west is higher than that in the east. We tested the use of GRACE for the verification of CORS network monitoring results and found a relatively consistent temporal distribution between both data sets after phase delay correction on GRACE, except for in three months—November in 2015, and January and February in 2016. The results show that the comprehensive solution based on the CORS network can effectively improve the monitoring of crustal vertical deformation during regional terrestrial water load change.

Türkiye’de ulusal ve yerel sürekli gözlem yapan sabit GNSS istasyonları ağlarının mevcut durumu, standartlar ve farklı ağların entegrasyonu

Turkey's National Permanent GNSS Network-Active (TUSAGA-Active) that has been started to use since 2009 is currently the most widely used geodetic infrastructure element in point positioning in Turkey. In addition to this network operating with the network RTK principle, there are also local Continuously Operating Reference Stations (CORS) networks in our country, which are mainly operated by local governments and a small number of private sector organizations. These networks, which are used nationally and locally, are used effectively in scientific studies as well as in basic engineering works. Integration of local networks in the axis of standards to be defined with the national TUSAGA-Active network is an important issue that should be on the agenda of our country's geodesy community. In this study, CORS networks established at national and local levels in different countries, and examples of the developed standards are given, the current situation in Turkey and contribution of local networks to the scientific studies are discussed. The studies conducted for the comparison of national and local CORS networks were examined, emphasizing the importance of distance between stations in determining the positioning. In this context, the contribution of local networks to the national network has been demonstrated. In this framework, it has been evaluated that shortening the baseline lengths as a result of integration and thus increasing the point density may contribute positively to the network solution quality. However, in order to achieve this development, it is recommended that the development of standards for the design and operation of CORS networks established locally in our country should be addressed with priority.

Preliminary Results on Tropospheric ZTD Estimation by Smartphone

The Global Navigation Satellite System (GNSS) receiver is one of the many sensors embedded in smartphones. The early versions of the Android operating system could only access limited information from the GNSS, allowing the related Application Program Interface (API) to obtain only the location. With the development of the Android 7.0 (Nougat) operating system in May 2016, raw measurements from the internal GNSS sensor installed in the smartphone could be accessed. This work aims to show an initial analysis regarding the feasibility of Zenith Total Delay (ZTD) estimation by GNSS measurements extracted from smartphones, evaluating the accuracy of estimation to open a new window on troposphere local monitoring. Two different test sites have been considered, and two different types of software for data processing have been used. ZTDs have been estimated from both a dual-frequency and a multi-constellation receiver embedded in the smartphone, and from a GNSS Continuously Operating Reference Station (CORS). The results have shown interesting performances in terms of ZTD estimation from the smartphone in respect of the estimations obtained with a geodetic receiver.