Continuously Operating Reference Stations Research Articles

GDDS: Python software for GNSS data download

With the rapid development of global navigation satellite system (GNSS), GNSS data products have been widely used for high-precision positioning and navigation applications. They are typically downloaded from the international GNSS service (IGS) analysis centers and continuously operating reference stations (CORS). However, the conventional GNSS data download method is cumbersome, repetitive, and time-consuming, and it is challenging to meet the demands for rapid acquisition of multi-source data products. Therefore, we have developed a GNSS data download software with Python, which provides an interactive interface for the Windows or Linux operating system to realize the efficient and stable download for a large amount of GNSS data. The software includes five main function modules: Global IGS Data, Post-Processing Product, Regional CORS Data, Custom Download, and Data Decompression. It has the characteristics of diverse data products, map interaction support, and station information retrieval, which can meet the needs of different users.

Inversion of Regional Groundwater Storage Changes Based on the Fusion of GNSS and GRACE Data: A Case Study of Shaanxi–Gansu–Ningxia

This paper aims to address the limitations of the distribution number and uniformity of Continuously Operating Reference Stations (CORS) and their impact on the reliability of inverting regional groundwater storage (GWS) based on Green’s function method and using global navigation satellite system (GNSS) data. A fusion method on the inversion of regional GWS changes from GNSS and the Gravity Recovery and Climate Experiment (GRACE) was proposed in this paper. Taking the Shaanxi–Gansu–Ningxia (SGN) region as an example, the in situ groundwater level data from ten CORS stations and eight wells were used for test analyses. In this paper, an atmospheric pressure model from the European Centre for Medium-Range Weather Forecasts (ECMWF), a global land data assimilation system (GLDAS), a WaterGAP global hydrology model (WGHM), and mean sea level anomaly (MSLA) data were used to quantitatively monitor the influence of vertical deformation caused by non-tidal environmental load. After deducing these loading deformations from the filtered time series of non-linear monthly geodetic height from the GNSS, the GWS changes in the SGN region from 2011 to 2014 were inverted. Meanwhile, the change in surface water storage from the GLDAS and WGHM models were removed from the terrestrial water storage (TWS) changes derived from GRACE. On this basis, the remove–restore theory in the Earth’s gravity field was introduced to both fuse the inversion results and obtain the regional GWS changes based on the fusion method. The results showed the following: (1) The local characteristics from the fusion results were more prominent than those of GRACE on the spatial scale, such as in the southwest and northeast in the study area. In addition, the fusion results were more uniform than those from GNSS, especially for the sparse and missing areas in which CORS stations were located, and the local effect was weakened. (2) On the time scale, compared with GRACE, the trends in GWS changes obtained from the fusion method and from GNSS inversion were roughly the same as the in situ groundwater level changes. (3) For the in situ groundwater wells “6105010031” and “6101260010”, the correlation coefficients of the fusion result were 0.53 and 0.56, respectively. The accuracy of the fusion method was slightly higher than that from GNSS, which indicates that the fusion method may be more effective for areas where CORS stations are missing or sparsely distributed. The methods in this paper can provide significant reference material for hydrodynamic research, sustainable management of water resources, and the dynamic maintenance of height data.

Utilization of iPad Pro LiDAR and Low-Cost GNSS Ublox F9R for Data Collection of Road Assets in the Form of 3D Models

The development of mapping survey equipment technology products is growing very rapidly. These products include Global Navigation Satellite System (GNSS) and Light Detection and Ranging (LiDAR) technology. The current development of GNSS receivers can be seen in terms of accuracy and price. The GNSS receiver has very high accuracy, especially with the integration with the inertial measurement unit (IMU). This integration system can provide benefits such as estimation of GNSS position data and GNSS data stability. One of the GNSS receiver products that has been integrated with IMU, has an accuracy below 1 meter, and at an economical price is the low-cost GNSS receiver U-blox F9R series. This receiver has a positional accuracy of 0.01 + 1 ppm. LiDAR products are commonly used for the manufacture of 3D objects and distance determination on Autonomous Vehicles, however, in 2020 the company Apple inc. has made a smartphone device that is integrated with LiDAR technology. One of the goals of using this integration system is to visualize 2D objects into 3D Augmented Reality (AR). In this study, iPad Pro LiDAR technology was used to create a 3D road model. This activity continues from previous studies that have used the iPad Pro LiDAR for making 3D buildings and measuring tree diameters. In research related to the manufacture of 3D buildings, the iPad Pro LiDAR has been analyzed and it is stated that it has an accuracy of 2 cm. However, this observation using the iPad Pro LiDAR still does not provide actual position information. One way to get the true position value is to use position data from the GNSS receiver. In this study, the GNSS observation method receiver used is Real Time Kinematic Networked Transported of RTCM via Internet Protocol (RTK-NTRIP). This method utilizes the Global System for Mobile Communications (GSM) network to transmit corrections from several nearby Continuously Operating Reference Stations (CORS) in Radio Technical Commission for Maritime Services (RTCM) format to the user’s receiver. This activity aims to create a database of road assets in 3D with real positions by utilizing the integration between GNSS, IMU, and iPad Pro LiDAR. From this study, it was found that the volume measurement data using GNSS data has a value of 4,930 m3. Meanwhile, processing using 3D model data from the iPad Pro 2020 resulted in 4,422 m3. The results of the two data have a volume difference of 0.5 m3 or 10% of the validation data.

An Efficient Deep Learning-Based Troposphere ZTD Dataset Generation Method for Massive GNSS CORS Stations

Nowadays, a huge amount of GNSS continuously operating reference stations (CORS) have been established around the world, which have already been and will continue providing massive troposphere zenith total delay (ZTD) data. This paper proposes an efficient deep learning-based troposphere ZTD dataset generation method including ZTD series segmentation, addictive and innovational outlier detection, and missing data imputation. The overall standard deviation of first-order ZTD difference series between adjacent epochs of the selected CORS station in January 2018 is reduced from 0.84 to 0.26 mm with the 3-sigma rule and the wavelet decomposition strategy for outlier elimination. A dense neural network (DNN) is subsequently designed to impute missing ZTD data. Only 3.4 minutes are required for the DNN training using a NVIDIA GeForce RTX 3090Ti GPU. The complete ZTD series with missing ZTD data imputed by the well-trained DNN model has a good agreement with the ZTD series before the data imputation in terms of mean value (-0.0184 vs -0.0187 mm) and standard deviation (5.43 vs 5.26 mm). Complete ZTD series of 120 CORS stations are generated to further evaluate the computational efficiency of the proposed method. An average of 2.56/5.38/5.77/4.33 hours are necessary to generate the ZTD dataset for January/April/July/October in 2018, respectively. Our study confirms that the proposed method can efficiently generate CORS-based ZTD dataset, which could be extended to applications including troposphere temporal-spatial pattern exploration and ZTD augmentation on high-precision GNSS positioning.

Основные направления развития государственной координатной основы в Афганистане

The review of the current state of the Afghanistan state coordinate framework, created by both ground and satellite methods, is carried out. It is outlined that when developing the geodetic network of Afghanistan, it is useful to use the experience existing in other countries, but taking into account the territorial characteristics of the state. The basic development directions of the state coordinate framework are formulated: the choice of the state coordinate system and its implementation, the creation of geodynamic polygons, the installation of continuously operating reference stations (CORS) of GNSS. It is recommended to use high-precision differential correction services in inaccessible areas to determine coordinates using GNSS methods. Based on the proposals formulated, it will be possible to create a highly accurate sustainable and developing state geodetic network on the territory of Afghanistan to perform topographic and geodetic works for various purposes, geospatial monitoring, mapping, geodynamic research.

Real-Time Single-Frequency Precise Point Positioning for Connected Autonomous Vehicles: A Case Study over Brazilian Territory

Intelligent Transportation Systems (ITS) and Connected Autonomous Vehicles (CAV) are extremely active areas of research, which have attracted the attention of users, companies, and development agencies worldwide. The Global Navigation Satellite System (GNSS) is a main enabling technology, as ITS/CAV applications are fundamentally dependent on precise positioning systems. Among the recent GNSS technology advances that have allowed high accuracy to be achieved is Real-Time Precise Point Positioning (RT-PPP). Even though the Real-Time Service (RTS) of the International GNSS Service (IGS) provides various correction streams for RT-PPP deployment, some of them (e.g., those associated with ionospheric delays) still have limited accuracy. This has motivated local organizations and research institutes to deploy their own RT-PPP products, based on a denser regional network of GNSS Continuously Operating Reference Stations (CORS). The purpose of this work is to evaluate the performance of a recently established regional ionosphere RT-PPP product, from the Argentine University of La Plata (UNLP), which serves all of South America, with extensions to the Caribbean and Antarctica Peninsula. The main contributions of the work are: we show that RT-PPP using UNLP products outperforms RT-PPP using products exclusively from IGS-RTS; we benchmark positioning strategies, such as Post-Processed PPP (PP-PPP) and Relative Global Positioning System (RGPS); and, demonstrate the ability of Brazilian RT-PPP users employing Single-Frequency (SF) GPS code measurements and UNLP ionosphere products to achieve the CAV lane-level specification (i.e., 1-meter horizontal positioning accuracy at 95% probability). The article includes results from both static and moving experimental tests.

Regional Ionosphere Delay Models Based on CORS Data and Machine Learning

<h3>Abstract</h3> The ionospheric refraction of GNSS signals can have an impact on positioning accuracy, especially in cases of single-frequency observations. Ionosphere models that are broadcasted by the satellite systems (e.g., Klobuchar, NeQuick-G) do not include enough details to permit them to correct single-frequency observations with sufficient accuracy. To address this issue, regional ionosphere models (RIMs) have been developed in several countries in the western Balkans based on dense Continuous Operating Reference Stations (CORS) observations. Subsequently, a RIM for the western Balkans was built using an artificial neural network that combined regional ionosphere parameters estimated from the CORS data with spatiotemporal (latitude, longitude, hour of day), solar (F10.7) and geomagnetic (Kp, Dst) parameters. The RIMs were tested at the solar maximum (March 2014), a geomagnetic storm (March 2015), and the solar minimum (March 2018). The new RIMs mimic the integrated electron density much more effectively than the Klobuchar model. Furthermore, RIMs significantly reduce the ionospheric effects on single-frequency positioning, indicating their necessity for use in positioning applications.

Determination of position coordinates of the new active CORS in Ghana

Global Navigation Satellite System (GNSS) technologies provide services and applications in a wide range of areas, including survey and mapping, transportation, precision agriculture, urban planning, smart mobility and smart city management, to name a few. Most of these applications rely on real-time kinematic (RTK) technology, which is typically supported by a network of continuously operating reference stations (CORS). In order to improve GNSS applications in Ghana, eight new CORS were established by the Licensed Surveyors Association of Ghana (LiSAG) in 2019 known as LiSAGNet. Accurate and precise positions of the LiSAGNet are, however, very critical for GNSS applications. Thus, the aim of this study is to determine accurate three-dimensional (3D) coordinates of the LiSAGNet using Network-based and Precise Point Positioning (PPP) techniques based on the International Terrestrial Reference Frame (ITRF). Positions of the new CORS were computed from data for 11 consecutive days using gLAB software v5.4.1 in PPP mode and the Canadian Spatial Reference System PPP (CSRS-PPP) online services as a check. Position solutions from both gLAB and CSRS-PPP were compared, which yielded coordinates variability of 0.001 m, 0.003 m and 0.029 m in the northings (N), eastings (E) and up (U) directions respectively and were therefore accepted as the final coordinates of the LiSAGNet. Positions from the PPP and Network-based techniques were also compared to determine consistencies or otherwise in the coordinates of the LiSAGNet. The study concluded that positions of LiSAGNet showed more consistency when determined by Network-based technique than when determined by PPP technique.

Low Cost GNSS Trimble BD982 and U-blox Performance Test Analysis F9 Series for Several Measurement Methods (Case Study: Sidoarjo Regency)

Global Navigation Satellite System (GNSS) is a tool that can assist community activities, especially in navigation and positioning for mapping surveys. This tool has an accuracy of up to millimeters for determining the position of latitude and longitude, but to get this accuracy requires an expensive cost, which is more than 200 million rupiah. Currently the development of GNSS receivers is very rapid, one of which is a low-cost GNSS product. The advantages of this receiver are that it has a low cost, light weight and an accuracy of up to centimeters for determining latitude and longitude positions. In this study, we have conducted trials using a low-cost GNSS receiver from several products such as U-blox, Trimble, and Comnav. For products from U-blox in this study, the F9P and F9R series were used. The F9R series is one of the receivers that has been integrated with the inertial measurement unit (IMU)/inertial navigation system (INS), the benefit of this integration is to improve position accuracy when data collection using the kinematic method. Products from U-blox have position accuracy below 1 meter. Meanwhile, the series used in Trimble and Comnav products are Trimble BD982 and Comnav Oem Board K708 which have accuracy below 1 centimeter. The purpose of this activity is to compare all these receivers by using Comnav OEM Board K708 data as validation data. Several parameters in this study will be analyzed such as the number of satellites obtained by the receiver, position accuracy and various other analyzes. The measurement methods that will be carried out in this study are static differential and Real Time Kinematic (RTK) measurements that utilize direct corrections from Continuously Operating Reference Stations (CORS) and deformation observations. The results of the first analysis obtained in this activity are the number of satellites obtained by the U-blox F9 series receiver which is more stable to receive satellites, namely as many as 24-29 satellites, then Trimble BD982 as many as 2-32 satellites, and Comnav K708 receivers as many as 3-28 satellites. Meanwhile, the Dilution Of Precision (DOP) values for 4 receivers, namely K708, F9P, and F9R, have stable values ranging from 0.5-1 compared to the BD982 receiver which fluctuated in several observation epochs, especially in the last observation epoch. In observations using the static differential method, using corrections from CORS for positioning this receiver can be used because the difference in position data is in the range of 0.009 m - 0.040 m from reference data (receiver K708). Meanwhile, the data receiver that has been integrated with IMU/INS (F9R) kinematic method has the smallest position difference value (K708) compared to other receivers, which is from 0.001 m - 8.091 m. In testing for deformation measurements, further research needs to be done because the data obtained is still in the form of a simulation.

Effects of the Continuously Operating Reference Station (CORS) network on the accuracy, precision, and Time to Fix Ambiguity (TTFA) performance

The geometric design of the Continuously Operating Reference Station (CORS) network is one of the most critical factors that impact accuracy, precision, and Time to Fix Ambiguity (TTFA) performance. In this study, the authors investigate the subject of geometric design by using both local ISKI CORS and national CORS-Turkey (CORS-TR) networks, and they redesign the ISKI CORS network by increasing interstation distances. For three systems, real-time Virtual Reference Station (VRS) solutions have been obtained and tested with Analysis of Variance (ANOVA). As a result, the 8-station ISKI CORS provides the most accurate results in the vertical component. In contrast, for TTFA performance, the CORS-TR network shows worse outcomes than the others. Due to the increase in the interstation distances, the increase in the base length caused worse results in FIX solution ratios for redesigned ISKI CORS. In summary, the authors have stated that the 8-station ISKI CORS network performs better, especially regarding vertical accuracy. Furthermore, the authors state that the TTFA performance and FIX solution ratios are high, and the ISKI CORS geometric design is optimal.

Prediction of CORS Water Vapor Values Based on the CEEMDAN and ARIMA-LSTM Combination Model

By relying on the advantages of a uniform site distribution and continuous observation of the Continuously Operating Reference Stations (CORS) system, real-time high-precision Global Navigation Satellite System/Precipitable Water Vapor (GNSS/PWV) data interpretation can be carried out to achieve accurate monitoring of regional water vapor changes. The study of the atmospheric water vapor content and distribution changes is the basis for the realization of rainfall forecasting and water vapor circulation research. Such research can provide data support for the effective forecasting of regional precipitation in megacities and the construction of a more sensitive flood prevention and warning system. Nowadays, a single model is often adopted for GNSS/PWV time series. This makes it challenging to match the high randomness characteristic of water vapor change. This study proposes a hybrid model that takes into account the linear and nonlinear aspects of water vapor data by using complete empirical mode decomposition (CEEMDAN) of adaptive noise, differential autoregressive integrated moving average (ARIMA), and the long-short-term memory network (LSTM). The CEEMDAN is used to decompose the water vapor data series. Then, the high- and low-frequency data are modeled separately, reducing the sequence’s complexity and non-stationarity. In selecting the prediction model, we use the ARIMA model for the high-frequency series and the ARIMA–GWO–LSTM ensemble model for the low-frequency sub-series and residual series. The model is verified using GNSS/PWV time series data collected at the Hong Kong CORS station in July 2021. The results show the following: (1) The LSTM model optimized by the grey wolf optimization algorithm (GWO) is comparable with the single LSTM model in the low-frequency sequence prediction process, and the error items are reduced by 30% after calculation. (2) During the process from CEEMDAN decomposition to the use of the combination model for prediction, the accuracy evaluation indexes of the station increase by more than 20%. The interpolation method can accurately determine the regional water vapor spatial variation, which is of practical significance for local rainfall forecasting. High-frequency data obtained by CEEMDAN decomposition demonstrate the dramatic changes in water vapor before and after the rainfall, which can provide ideas for improving the accuracy of rainfall forecasting.

Pseudorange multipath at Zomba geodynamics Continuously Operating Reference Station (CORS) in Malawi

Multipath effects are mostly regarded as a nuisance in Global Navigation Satellite System (GNSS) receiver measurements and it is of utmost relevance to expose the magnitude this error has on observations. The impact of multipath is characterized in the context of a given environment and application. In Malawi, Zomba geodynamics Continuously Operating Reference Station (CORS) is in a multipath prone environment. The GNSS observations for this station have been used in geodynamics studies in Malawi without an understanding of multipath affecting the positioning accuracy. Taking this as an advantage, this paper evaluated pseudorange multipath (MP) and signal noise ratio (SNR) on both L1 (MP1 and SNR1) and L2 (MP2 and SNR2) for the station. This was specifically addressed by computing the elevation mask with minimum and maximum multipath effects. In addition, the number of satellite vehicles (SVs) and their associated Geometric Dilution of Precision (GDOP) are also determined to define their relationship with respect to elevation angles. One week GNSS observations spanning a twenty-four hour interval for DOY 001 to DOY 007 in January 2018 were analysed in Translation Editing and Quality Check (TEQC) software at four (10º, 15º, 20º and 25º) cut-off angles. Results indicate high multipath effects for both MP1 and MP2 at 10º elevation mask among the four elevation masks. The least MP1 and MP2 multipath effects were detected at an elevation angle of 25º. In addition, MP1 multipath was worse than MP2 all the angles. Moreover, statistical results demonstrated an increase in both SNR1 and SNR2 with respect to elevation angle. For these days, L2 signal was more affected by noise than L1. Further to this, an assessment of SVs and GDOP for the CORS show that at least ten (10) satellites were observed in each day at 10º and 15º elevation cut-off. The number of satellites dropped to five (5) at the elevation angle of 25º resulting into a larger GDOP value of 4.5 (a decrease by about 38% from 1.7 at 10º and 15º elevation cut-off angles). Therefore, to increase both the number of satellites and precision, Zomba CORS may be upgraded to a multi-constellation CORS by including other navigation systems such as GLONASS, Galileo and BeiDou. While it is possible to reject GNSS satellite observations below the horizon, it is recommended that post-processing of GNSS data for Zomba geodynamics CORS be done at elevation masks above 15º. Considering that multipath repeats itself every sidereal day, it is thus recommended to model or remove multipath affecting Zomba geodynamics CORS. In addition, the study also recommends that trees very close to Zomba CORS antenna be removed to reduce signal scattering.

Comparative evaluation and analysis of different tropospheric delay models in Ghana

Tropospheric delay prediction models have become increasingly important in Global Navigation Satellite System (GNSS) as they play a critical role in GNSS positioning applications. Due to the different atmospheric conditions over the earth regions, tropospheric effect on GNSS signals also differs, influencing the performance of these prediction models. Thus, the choice of a particular prediction model can significantly degrade the positioning accuracy especially when the model does not suit the user’s environs. Therefore, a performance assessment of existing prediction models in various regions for a suitable one is very imperative. This paper evaluates and analyses seven commonly used tropospheric delay models in Ghana in terms of performances in Zenith Tropospheric Delay (ZTD) estimation and baseline positional accuracies using data from six selected Continuously Operating Reference Stations (CORS). The 1˚x1˚ gridded Vienna Mapping Functions 3 (VMF3) ZTD product and coordinates solutions from the CSRS-PPP positioning service were respectively used as references. The results show that the Black model performed better in estimating the ZTD, followed by Askne and Nordius model. The Saastamoinen, Marini and Murray, Niell, Goads and Goodman and Hopfield models respectively performed poorly. However, the result of the baseline solutions did not show much variation in the coordinate difference provided by the use of the prediction models, nonetheless, the Black and Askne and Nordius models continue to dominate the other models. Of all the models evaluated, either Black or Askne and Nordius model is recommended for use to mitigate the ZTD in the study area, however, the choice of the Black model will be more desirable.

Applying Malawi Continuously Operating Reference Stations (CORS) in GNSS Meteorology

Global Navigation Satellite System (GNSS) signals in the L-band are affected by the non-dispersive neutral atmosphere. Regardless of their center frequency, the L-band code and phase observations are affected by the same measure of delay. GNSS receivers play a significant role in quantifying the zenith tropospheric delay (ZTD) from satellite signals. Malawi has a Continuously Operating Reference Stations (CORS) network which was established to support research in geophysical geodesy and geodynamics. However, the quality of the observations tracked by the CORS has never been tested in terms of its meteorological application. In this paper, the ZTD estimation approach and the evaluation of results from the Global Positioning System (GPS) measurements are presented. The optimal approach of precise point positioning (PPP) was used to estimate ZTD from one-week datasets which were collected from six CORS monuments distributed in the northern and southern regions of Malawi. In addition, the zenith wet delay (ZWD) and zenith hydrostatic delay (ZHD) were also estimated to determine their respective contributions to the total delay in all the stations. Alongside the meteorological parameters, the positioning repeatabilities were also established for all stations. Results indicate that the averaged ZTD, ZWD and ZHD can reach as high as 247mm, 47 mm, and 199 mm, respectively. The minimum ZTD, ZWD, and ZHD for the stations can drop to as low as 220 mm, 24 mm, and 181 mm, respectively. This indicates that the ZHD contributes to more than 90% of the total delay at the stations. For the positioning performance, there was no obvious disparity in the latitude (less than 0.5 cm), longitude (less than 1 cm), and ellipsoidal height repeatabilities (less than 1.5 cm). Thus, the results clearly demonstrate that the Malawi CORS network may be used for GNSS-based meteorological applications using the available geodetic receivers. However, for high precision meteorological applications, Malawi may consider densifying the available network with geodetic grade receivers.&#x0D;

Congruence through repeatability of position solutions by different GNSS survey techniques

In this study, we determined three-dimensional (3D) position coordinates for eight new Continuous Operating Reference Stations (CORS) in Ghana through three different GNSS positioning techniques. The three GNSS positioning techniques whereby the network of CORS was tied to ITRF14 and War Office 1926 datums included:1) Precise Point Positioning (PPP); 2) Precise Differential GNSS (PDGNSS), using reference stations based on ITRF14; and 3) PDGNSS, using reference stations based on War Office. The PPP solutions were computed using the Canadian Spatial Reference System Precise Point Positioning software (CSRS-PPP), available online and as an open source GNSS laboratory tool software (gLAB). The PDGNSS solutions were obtained from OPUS and AUSPOS online services, as well as from self-post-processing using Topcon Tools software v8.2.3. All solutions were computed using 24-hour data for twelve consecutive days in the month of October 2018 (GPS DoY 284 to GPS DoY 295). The quality, reliability, and acceptability of position solutions were measured by computing the average positioning error, the rate of ambiguity resolution and the repeatability ratios of the solutions. The variability of coordinate differences for each pair of different positioning techniques was computed to determine their solution congruences. Ultimately, , the average positioning errors in northing, easting, and height were 0.003m, 0.005m and 0.009m, respectively. The rate of ambiguity resolution was between 75.3% and 90.3%. Repeatability ratios ranged between 1: 68,500,000 and 1: 411,100,000. Finally, the minimum and maximum range of variability in coordinate differences for each pair of positioning techniques was 1mm to 16mm for horizontal positions and 2mm to 137mm for vertical positions.

Recovering Regional Groundwater Storage Anomalies by Combining GNSS and Surface Mass Load Data: A Case Study in Western Yunnan

The redistribution of surface mass (e.g., atmosphere, soil water, oceans, and groundwater) can cause load responses, resulting in vertical deformations of the crust. Indeed, the global navigation satellite system (GNSS)-based continuously operating reference stations (CORS) are able to accurately measure the vertical deformation caused by surface mass loads. In this study, the CORS was used to invert groundwater storage anomalies (GWSA), represented by the equivalent water height (EWH), after removing the effect of the non-groundwater surface mass load (atmospheric, groundwater, and non-tidal oceanic loads) from the vertical deformation monitored by CORS. In addition, the global and regional high-resolution surface mass models were combined to calculate the high-precision load deformation field in in western Yunnan using the remove–restore method, thereby obtaining more accurate surface mass load data and improving the accuracy of the inverted GWSA results. In order to assess the feasibility of the CORS inversion for the GWSA used, 66 CORS stations in western Yunnan Province were considered, presenting weekly GWSA data from 10 January 2018 to 31 December 2020. The results revealed significant seasonal variation in GWSA in the study area, showing an amplitude range of −200–200 mm. This approach is based on the already-established CORS network without requiring additional set-up costs. In addition, the reliability of CORS inverse results was assessed using Gravity Recovery and Climate Experiment (GRACE) inverse results and actual groundwater monitoring data. According to the obtained results, GWSA can be monitored by both CORS and GRACE data; however, CORS provided a more effective spatiotemporal resolution of GWSA. Therefore, the CORS network combined with surface mass load data is able to effectively monitor the spatiotemporal dynamics of GWSA in small-scale areas and provides important references for the study of hydrology.

Single-Epoch Ambiguity Resolution of a Large-Scale CORS Network with Multi-Frequency and Multi-Constellation GNSS

Ambiguity resolution at Continuously Operating Reference Station (CORS) network sites is the key step in the whole processing chain of Network Real Time Kinematic (NRTK). An appropriate ambiguity-resolution speed is important, and single-epoch ambiguity resolution has not been realized yet, especially for large-scale CORS. We attempt to realize single-epoch ambiguity resolution for a large-scale CORS network by neglecting tropospheric delay through forming difference between satellites with close mapping functions whether they belong to the same or different GNSSs. As only two frequency bands are shared among GPS, Galileo and BeiDou, the biggest challenge is how to get this single-epoch ambiguity solution for wide-lane combinations of L1 and L5 when the difference is formed between satellites of different GNSSs. The proposed method includes five steps for ambiguity resolution for different combinations: extra wide-lane, wide-lane, inter-GNSS wide-lane, subset narrow-lane and narrow-lane. The single-epoch ambiguity-resolution performance is assessed based on GNSS observations from two long-distance baselines formed with IGS stations, BRUX-REDU and BAUT-LEIJ, separated by distances of approximately 104 km and 151 km, respectively. The numerical results show that the fixing rate of the single-epoch ambiguity resolution can reach more than 90%, so for a large-scale CORS network, single-epoch ambiguity resolution is feasible and can be realized in the future.

Shipborne GNSS acquisition of sea surface heights in the Baltic Sea

Abstract For determining precise sea surface heights, six marine GNSS (global navigation satellite system) survey campaigns were performed in the eastern Baltic Sea in 2021. Four GNSS antennas were installed on the vessel, the coordinates of which were computed relative to GNSS–CORS (continuously operating reference stations). The GNSS–CORS results are compared to the PPP (precise point positioning)-based results. Better accuracy is associated with the GNSS–CORS postprocessed points; however, the PPP approach provided more accurate results for longer than 40 km baselines. For instance, the a priori vertical accuracy of the PPP solution is, on average, 0.050 ± 0.006 m and more stable along the entire vessel’s survey route. Conversely, the accuracy of CORS-based solutions decreases significantly when the distances from the GNSS–CORS exceed 40 km, whereas the standard deviation between the CORS and PPP-based solutions is up to 0.075 m in these sections. Note that in the harbor (about 4 km from the nearest GNSS–CORS), the standard deviation of vertical differences between the two solutions remains between 0.013 and 0.024 m. In addition, the GNSS antennas situated in different positions on the vessel indicated different measurement accuracies. It is suggested for further studies that at least one GNSS antenna should be mounted above the mass center of the vessel to reduce the effects of the dominating pitch motion during the surveys.

Comparison of Deformation Vectors Due to Earthquake in Subduction Zone and Sumatran Fault for Each Phase of Earthquake Cycle

This study compares the deformation in West Sumatra due to the earthquakes in the subduction zone and the Sumatran Fault. The Mw6.0 Mentawai earthquake 2019 with a thrust fault mechanism and the Mw5.4 South Solok earthquake 2019 with a strike-slip fault mechanism were used as case studies for the subduction zone and Sumatran Fault, respectively. The deformation was observed using 12 SuGAr (Sumatra GPS Array) and 8 InaCORS (Indonesian Continuously Operating Reference Station) stations, which were processed using GAMIT/GLOBK software. There are differences in the deformation vectors of the two earthquakes. The Mentawai earthquake experienced larger energy accumulation than the South Solok earthquake. The coseismic phase of the Mentawai earthquake experienced the largest horizontal shift at the SLBU station, which was 15.48 mm in the direction of S29.96W, while the South Solok earthquake is found to horizontally shift the CSDH station at the size of 5.75 mm towards S11.45E. The postseismic phase of the Mentawai earthquake lasted 60 days, longer than the South Solok earthquake (20 days). The difference in deformation characteristic between these two earthquakes found in this study will be valuable information in modeling earthquakes in Sumatra.

Experimental Analysis of GPS L2C Signal Quality under Various Observational Conditions

To appropriately handle the GPS L2C signal for the future development of positioning algorithms, this contribution has endeavoured to figure out its features by computing some quality measures of all the modernised satellites (i.e., twenty-three as of January 2022) and comparing them with those of the C/A and P2(Y) code. A series of quality analyses have been carried out to GPS measurements at twenty-four continuously operating reference stations (CORS) equipped with eight receiver models. In addition, experimental data acquired by a combination of high-end and cost-effective receivers have been intensively assessed to characterise the relative signal quality of the L2C to the legacy codes. The observational conditions considered in this study include different multipath environments and receiver dynamics. The results of the analyses, in general, indicate that the quality of the L2C-derived measurements is equivalent to the legacy civilian code (i.e., C/A) but superior to the encrypted military signal (P2(Y)). Hence, it is expected that the new civilian GPS signal enhances the positioning performance of dual-frequency measurements with both high-end and cost-effective receivers.