Dual-Frequency Static PPP Over Fixing Time Using Final-Product Free Online Services: CSRS-PPP Vs. PPP-WIZARD Vs. APPS

The currently available triple-frequency signals give rise to new prospects for precise point positioning (PPP). However, they also bring new bias, such as time-varying parts of the phase bias in the hardware of receivers and satellites due to the fact that dual-frequency precise clock products cannot be directly applied to triple-frequency observation. These parameters generate phase-based inter-frequency clock bias (PIFCB), which impacts the PPP. However, the PIFCBs of satellites are not present in all GNSSs. In this paper, various IF1213 PPP models are constructed for these parts, namely, the triple-frequency PIFCB (TF-C) model with PIFCB estimation, the TF inter-frequency bias (IFB) (TF-F) model ignoring the PIFCB, and the TF-PIFCB-IFB (TF-CF) model with one system PIFCB estimation. Additionally, this study compares these IF1213 PPP models with the dual-frequency ionosphere-free (DF) model. We conducted single system static PPP, dual-system static and kinematic PPP experiments based on BDS/GPS observation data. The GPS static PPP experiment demonstrates the reliability of the TF-C model, as well as the non-negligibility of the GPS PIFCB. The BDS static PPP experiment demonstrates the reliability of the TF-F and TF-CF models, and that the influence of the BDS-2 PIFCB can be neglected in BDS. The BDS/GPS PPP experimental results show that the third frequency does not significantly improve the positioning accuracy but shortens the convergence time. The positioning accuracy of TF-C and TF-CF for static PPP is better than 1.0 cm, while that for kinematic PPP is better than 2.0 cm and 4.0 cm in the horizontal and vertical components, respectively. Compared with the DF model, the convergence time of the TF-C and TF-CF models for static PPP is improved by approximately 23.5%/18.1%, 13.6%/9.7%, and 19.8%/12.1%, while that for kinematic PPP is improved by approximately 46.2%/49.6%, 33.5%/32.4%, and 35.1%/36.1% in the E, N and U directions, respectively. For dual-system PPP based on BDS/GPS observations, the TF-C model is recommended.

In precise point positioning (PPP) solutions, stochastic modeling of the receiver clock parameter affects solution stability, especially the station up component. This study analyzes GPS + Galileo static and kinematic PPP solutions for 14 GNSS stations equipped with ultra-stable hydrogen masers, utilizing real-time orbit and clock products, such as HAS, IGS, and CNES, as well as final products from CODE. The solution with modeling of the receiver clock parameter enhances stability and precision compared to the reference solution, in which the receiver clocks are estimated independently for each epoch. In static PPP solutions, receiver clock modeling reduces spikes in the clock parameter and improves short-term stability. The most notable improvement of the station up component reaches up to 59, 21, 25, and 38% for HAS, IGS, CNES, and CODE, respectively, in terms of the interquartile range (IQR) of the estimated parameter during the first three processing hours. For kinematic PPP solutions, the maximum reduction of the up component standard deviation is 38, 50, 18, and 26% for HAS, IGS, CNES, and CODE, respectively across all analyzed GNSS stations. Additionally, the IQR analysis of epoch-wise differences in the station up component indicates even greater enhancements, with reductions reaching up to 63, 70, 52, and 83% for HAS, IGS, CNES, and CODE, respectively. Epoch-wise differences indicate short-term stability. The proposed clock modeling improves both the common clock parameter and the vertical component, enhancing PPP solution by increasing stability (reduced variability) and precision (reduced dispersion) across real-time and post-processed GNSS products.

The GNSS precise point positioning (PPP) technique has been extensively covered in recent research. In this study, six International global navigation satellite system (GNSS) Service (IGS) stations defined by 4-digits code in Africa were selected to be processed. The stations cover different climates in Africa. HARB, SUTH and WIND stations cover the mid-latitude area and NKLG, NURK and MAL2 are located in the equatorial region. Two data sessions were selected in processing to cover the winter and summer seasons: the first session of 3 days [01–03 January 2013 (DOY: 001–003/2013)] and the second session of 3 days [01–03 July 2013 (DOY: 182–184/2013)]. This paper aims to evaluate the accuracy of static PPP coordinate solution in Africa for different convergence times using free online services: Canadian Spatial Reference System (CSRS)-PPP, Automatic Precise Point Service (APPS)-PPP and GPS Analysis and Positioning Software (GAPS)-PPP. The stations’ observation times were divided into different observation times (1, 2, 4, 8, 12, and 24 h).The PPP coordinate solution was compared to the reference solution of those stations. The investigation is continued by estimating the PPP total tropospheric zenith delay (TZD) parameters, which were obtained by the different online services. These parameters were compared to the published parameters from IGS. The comparison between the different online services shows that the CSRS-PPP provides the best solution after 4 and 8 h. The APPS-PPP and CSRS-PPP provides the same solution in millimeters level after 12 h. In the equatorial region, the PPP coordinate solution is significantly improved between 12 and 24 h. Moreover, GAPS-PPP is not recommended to be used in the equatorial stations, where it shows a high error compared to CSRS-PPP and APPS-PPP even after 24 h. The mid-latitude stations show a better PPP coordinate solution in the winter than in the summer, but the equatorial stations present a low accuracy for the two sessions. Regarding the PPP tropospheric delay estimation, an additional station (HNUS) is used in the mid-latitude area, which has a low ellipsoidal height. APPS-PPP shows the best solution in the TZD estimation. The GAPS-PPP online service shows a systemic error in estimation and a high RMS relative to the TZD values known from IGS. The ellipsoidal height for antenna indicates a negative correlation to the estimated tropospheric values, but there is no effect for the variation of the ellipsoidal height in the estimated RMS. The estimated tropospheric parameters are correlated with the PPP coordinate estimation, where the GAPS-PPP service provides the worst PPP coordinate solution and at the same time, it shows the worst accuracy for tropospheric parameters estimation. Moreover, the estimated tropospheric parameters for the mid-latitude stations in the summer season show a higher RMS than in the winter season, which matches the same sequence of the PPP coordinates. The NKLG and NURK stations present a low accuracy for the tropospheric estimation, which is matching to the low accuracy of the PPP coordinates obtained from the different online services.

Recent progress in integer ambiguity resolution at a single station has made it possible to achieve high positioning accuracy in static precise point positioning (PPP) using a short period of observations. In this paper, 12 stations across Europe are used to conduct short-period (i.e. one, two, three and four hours) static PPP with ambiguity resolution from Day 245 to 251 in 2007. It is demonstrated that, when over three hours of observations are used, PPP can achieve a success rate of 100% for ambiguity resolution, a 3D positioning accuracy of about 1.0 cm and an occurrence of less than 1.0% for degraded solutions. Moreover, for the fixed solutions, increasing the observation period hardly improves the horizontal positioning accuracy while still improving the vertical one. Therefore, it is proposed that at least three hours of observations should be used in the ambiguity-fixed static PPP if a reliable millimetre positioning accuracy is required in the engineering applications.

In addition to GPS and GLONASS constellation, the number of (Global Navigation Satellite System) GNSS satellites are increasing, it is now possible to evaluate and analyze the position accuracy with multi GNSS constellation. In this paper, statistical assessment of static Precise Point Positioning (PPP) using GPS, GLONASS, dual system GPS/GLONASS, three system GPS/GLONASS/Galileo, GPS/GLONASS/BeiDou and multi system GPS/GLONASS/Galileo/BeiDou PPP combinations is evaluated. Observation data of seven whole days from seven IGS multi GNSS experiment (MGEX) stations is used for analysis. Position accuracy and convergence time is analyzed. Results show that the GPS/GLONASS positioning accuracy increases over GPS PPP. Standard deviations (STDs) of position errors for GPS PPP are 4.63, 3.00 and 6.96 cm in east, north and up components while STDs for GPS/GLONASS PPP are 4.10, 3.42 and 6.50 cm respectively. Root mean square for three dimension (RMS3D) for GPS/GLONASS PPP solution is 8.96 cm. With the addition of Galileo and BeiDou to the combined GPS/GLONASS further enhances the positioning accuracy. Root mean square for horizontal component reach to 5.35 cm of GPS/GLONASS/Galileo/BeiDou PPP solutions. Results analysis of GPS/GLONASS/Galileo PPP solutions show an improvement of convergence time by only 3.81% to achieve accuracy level of 3.0 cm over GPS/GLONASS/BeiDou PPP mode. Results also demonstrate that position accuracy improvement after adding BeiDou observations to the GPS/GLONASS PPP mode is not significant.

The BeiDou Navigation Satellite System (BDS) offers orbit and clock corrections through the B2b signal, enabling Precise Point Positioning (PPP) without relying on ground communication networks. This capability supports applications such as aerial and maritime mapping. However, achieving high precision during the convergence period remains challenging, particularly for missions with short observation durations. To address this, we analyze the performance of PPP over short periods using PPP-B2b products and propose using the backward smoothing method to enhance the accuracy during the convergence period. Evaluation of the accuracy of PPP-B2b products shows that the orbit and clock accuracy of the BDS surpass those of GPS. Specifically, the BDS achieves orbit accuracies of 0.059 m, 0.178 m, and 0.186 m in the radial, along-track, and cross-track components, respectively, with a clock accuracy within 0.13 ns. The hourly static PPP achieves 0.5 m and 0.1 m accuracies with convergence times of 4.5 and 25 min at a 50% proportion, respectively. Nonetheless, 7.07% to 23.79% of sessions fail to converge to 0.1 m due to the limited availability of GPS and BDS corrections at certain stations. Simulated kinematic PPP requires an additional 1–4 min to reach the same accuracy as the static PPP. Using the backward smoothing method significantly enhances accuracy, achieving 0.024 m, 0.046 m, and 0.053 m in the north, east, and up directions, respectively. For vehicle-based positioning, forward PPP can achieve a horizontal accuracy better than 0.5 m within 4 min; however, during the convergence period, positioning errors may exceed 1.5 m and 3.0 m in the east and up direction. By applying the smoothing method, horizontal accuracy can reach better than 0.2 m, while the vertical accuracy can improve to better than 0.3 m.

Precise Point Positioning (PPP) algorithms have been widely used in the Global Positioning System (GPS)-based applications. A PPP technique with a single receiver provides effective solutions where accurate absolute positioning is required. This paper provides the performance assessment of GPS PPP for detecting the displacements caused by an earthquake. For this purpose, the earthquake that occurred on 21 July 2017 at Kos-Bodrum with the impact of Mw 6.6 was investigated by analyzing the data of the permanent GPS stations located around the related region with the PPP technique. The location distances of these GPS stations range from 10 to 89 km to the epicenter of this earthquake. GPS data provided from seven permanent stations from the Continuously Operating Reference Stations-Turkey (CORS-TR) and local Bodrum CORS networks were processed to determine the co-seismic displacements during the earthquake. The data of these stations for days of year (DOYs) 200, 201, 202, and 203 were analyzed with post-process static PPP and kinematic PPP methods. GIPSY-OASIS II v6.4 was used for processing the data and all of the solutions were performed in the ITRF2008 reference frame. Two strategies were followed on the post-process static solutions. In the first strategy, 4-day data with 24-h observations were separately analyzed day by day. In the second strategy, the 24-h data were divided into 3-h duration, which is the minimum duration for optimum PPP solutions, and then the analyses were performed. When the displacements between DOYs 200 and 203 are considered in the 24-h data analysis, significant displacements have been observed through northwest direction in the northern stations whereas MUG1 is excluded. Moreover, there is significant displacement through the southeast direction in the station DATC located in the south of the epicenter. When the 3-h solutions are examined, displacements, especially on n and e directions, are observed starting from the solutions, which include Mw 6.6 earthquake. According to the kinematic PPP solutions, the effects of the Mw 6.6 earthquake can be seen clearly in the stations DATC, ORTA, TRKB, and YALI. Considering all outcomes, the PPP technique with both static and kinematic solutions provides effective results for detecting the displacements during the earthquake.

In recent decades, Precise Point Positioning (PPP) has become a well-established GNSS positioning method that is used in various applications. PPP is characterized by the use of precise satellite products (satellite orbits, clocks, and biases) combined with the accurate modeling of various error sources and elaborate algorithms. This way, PPP allows us to achieve position accuracies at the centimeter or even millimeter level. Nowadays, several institutions provide high-quality multi-GNSS satellite products through the International GNSS Service (IGS). These modern satellite products enable, for example, integer ambiguity fixing and incorporating observations from multiple GNSS in the PPP solution, typically enhancing the PPP performance.In this contribution, we provide an overview of the currently available multi-GNSS satellite products and discuss their potential benefits of using 2+ frequencies and alternatives to the ionosphere-free linear combination. These methods are considered advantageous for improving PPP performance, particularly regarding convergence time. We present PPP results using GPS, GLONASS, Galileo, and BeiDou observations and satellite products from different institutions, focusing on integer ambiguity resolution (PPP-AR). Additionally, we test the combined multi-GNSS product developed by the GNSS Research Center at Wuhan University as part of the IGS PPP-AR Pilot Project. We evaluate the resulting coordinate accuracy, convergence behavior, and ambiguity fixing rates. The PPP investigations are conducted with the open-source raPPPid, part of the Vienna VLBI and Satellite Software (VieVS PPP). 

Monitoring the response of engineering structures, such as tall buildings, tower and large-scale bridges, under severe loading conditions, such as strong earthquake or wind storm, is an important requirement to verify their design and construction and to evaluate structural condition and reliability. In the last two decades, high-rate real-time or post-processed kinematic differential Global Positioning System (DGPS) has been widely used in dynamic displacement measurements of civil engineering structures. In recent years, interest has increased for Precise Point Positioning (PPP) due to its capability to generate positioning solutions as accurate as DGPS. In this study, the potential of post-processed kinematic PPP in terms of monitoring dynamic displacement response of a structure has been explored based on free damped oscillation events obtained from a model structure, which is able to vibrate in the fundamental and higher modes of vibration. A number of experiments have been carried out and five events, each of which is different character, have been selected to compare PPP results with DPGS results in the time and frequency domain. The results clearly demonstrate that the PPP method, like the DGPS method, offers great potential for the measurement of horizontal and vertical dynamic movement of structures. The impact of a short period (one minute) of observation length on the result of the kinematic PPP method was also investigated in terms of sensing the dynamic movement of a structure. Twenty selected one-minute data-sets extracted from a one-hour original data-set were processed by Canadian spatial reference system PPP and each one-minute PPP solution was compared with the corresponding segment obtained from the one-hour PPP solution. The results show that the one-minute PPP solution is able to extract the fundamental natural frequency of the oscillation in the horizontal and vertical component just like the one-hour PPP solution after the offset is removed and the lower frequency trend component is filtered out.

PPP-based UAV modeling using Galileo HAS orbit/clock products and RTS smoother

Although there are already several real-time precise positioning service providers, unfortunately, not all users can use the correction information due to either cost of the service and limitation of their equipment or out of the service coverage. An alternative way is to enhance the accuracy of the predicted satellite clocks for precise real-time positioning. Based on the study of existing prediction models, an improved model combing the spectrum analysis (SA) and the generalized regression neural network (GRNN) model is proposed especially for BeiDou satellite navigation system (BDS)-2 satellites. The periodic terms and GRNN-related parameters including length and interval of sample data, as well as a smooth factor, are optimized satellite by satellite to consider satellite-specific characteristics for all the fourteen BDS-2 satellites. The improved model is validated by comparing the predicted clocks of existing models and the improved model with precisely estimated ones. The bias of the predicted clock is within ±0.5 ns over three hours and better than that of the other models and can be used for several real-time precise applications. The clock prediction is further evaluated by applying clock corrections to precise point positioning (PPP) in both static and kinematic mode for eight IGS (International GNSS Service) MGEX (Multi-GNSS Experiment) stations in the Asia-Pacific region. In the static PPP, the improved model is validated to be effective, and position accuracies of some IGS MGEX stations achieve more than 30.0% improvements on average for each component, which enables us to obtain sub-decimeter positioning. In the kinematic PPP, the improved model performs much better than the others in terms of both the convergence time and the position accuracy. The convergence time can be shortened from 1–2 h to 0.5–1 h, while the position accuracy is enhanced by 15.4%, 21.6% and 19.3% on average in east, north and up component, respectively.

Observation data sets from three different periods and 23 International GNSS Service (IGS) stations spread over the world were processed in static mode using four online free precise point positioning (PPP) services: Automatic Precise Positioning Service (APPS), GPS Analysis and Positioning Software, Canadian Spatial Reference System precise point positioning service, and Magic-PPP. The estimated positions of the 23 IGS stations were compared with the published values. The estimated zenith tropospheric delays (ZTDs) at these stations were compared with the corresponding IGS troposphere products published on the IGS Web site. Furthermore, in order to analyze PPP precision for short observation periods, GPS observation data sets with a sampling rate of 1 s collected by one CORS station were also processed by the four online PPP services. Calculation shows that the precision of daily solutions for north and east (N/E) components estimated by the four online PPP services can reach millimeter level, the precision of ellipsoid elevation (H) can reach 1---2 cm, and precision of ZTDs estimation results is approximately 1---2 cm. Compared with the corresponding values published on the IGS Web site, the precision of ZTDs estimated by APPS is higher than those estimated by the other three PPP online services; the differences between ZTDs by APPS and IGS values are mostly within ±1 cm. For PPP with short observation periods, the precision of N/E components within 2, 1, and 0.5 h observation periods can reach about 2---3, 2---7, and 3---8 cm, respectively, while the precision of H components is about 3---5, 5---12, and 10---18 cm, respectively.

Since Global Positioning System (GPS) has been routinely conducted in many engineering projects, it is also effectively applied to the assessment and preventing of forest and natural resources. Depending on the GPS survey method preferred in the applications performed around the forest environments, different level point positioning accuracy can be achieved. Traditionally, for many precise positioning applications, relative static positioning has been used. The data obtained have been analyzed with high-cost scientific and commercial software, which are required a good knowledge of processing procedures. However, in recent years, web based online services that use Precise Point Positioning (PPP) technique, developed as a special type of relative positioning, that enables to process and analyze the static data easily, have become a significant alternative for users. These developments on GPS based surveyings that significantly make contributions to the studies applied around the forest environment, in terms of time, cost, accuracy and labour are preferred in many engineering facilities. In this study, it is aimed to research performance of GPS PPP technique and web based online services in positioning applications especially performed around the forest environments. For this purpose, two test stations have been established in different locations around the forest area, located in Campus of Davutpasa, Yildiz Technical University, Istanbul, and stations have been observed repeatedly in static GPS surveying mode for 3 days and per day with 3-hours observation duration. The observations have been computed by commercial software as using final GPS ephemerides products so called TopconTools v8.2 and also by web based online services namely OPUS, AUSPOS, CSRS-PPP, GAPS and APPS. From the results, when 3D positioning differences have been examined, it is seen that the positional accuracy is range from 0.024 m to 0.251 m for TP01 and from 0.078 m to 1.033 m for TP02 with respect to both relative solution and PPP solution, which is used by web based online services. When the results have been examined for only CSRS-PPP, APPS and GAPS services, which are used PPP solution, it is seen that the positional accuracy for 3D positioning differences is range from 0.024 m to 0.251 m for TP01 and from 0.078 m to 0.859 m for TP02. The results show that since the static GPS data is collected for duration of 3-hours and more, PPP technique and the web based online services using this technique for precise positioning applications around the forest environment give effective solutions to the users and at the same time decrease the survey cost with respect to equipment and software.

In recent years, in addition to the GPS constellation, the ability to utilise extra satellites available in the GLONASS system enhanced the capabilities and possible applications of precise point positioning (PPP) method. However, the intrinsic differences between GPS and GLONASS and the lack of a fully tested global tracking network of multi-GNSS systems necessitate the evaluation of their combined use. This paper offers a comprehensive statistical assessment of static PPP using GPS-only, GLONASS-only and GPS/GLONASS combined data. Data analysis is performed in a short (hourly to daily) and a long (several weeks) term, spanning observations from eleven IGS stations. Evaluation of the results reveals insignificant differences in the accuracy and repeatability among the three satellite constellation solutions for long (8 h, 24 h) observation times. The superiority of the combined GPS/GLONASS solution is apparent for short (1 h, 2 h) observation periods, whereas analysis confirms the stability of PPP solutions for the very long (several weeks) observation periods irrespectively of the satellite constellation used.

BeiDou navigation satellite system(BDS)has opened service in most of the Asia-Pacific region,it offers the possibility to break the technological monopoly of GPS in the field of high-precision applications,so its performance of precise point positioning(PPP)has been a great concern.Firstly,the constellation of BeiDou regional navigation system and BDS/GPS tracking network is introduced.Secondly,the precise ephemeris and clock offset accuracy of BeiDou satellite based on domestic tracking network is analyzed.Finally,the static and kinematic PPP accuracy is studied,and compared with the GPS.The actual measured numerical example shows that the static and kinematic PPP based on BDS can achieve centimeter-level and decimeter-level respectively,reaching the current level of GPS precise point positioning.