Kinematic Mode Research Articles

Improving the Stochastic Model of Ionospheric Delays for BDS Long-Range Real-Time Kinematic Positioning

Although ionosphere-free (IF) combination is usually employed in long-range precise positioning, in order to employ the knowledge of the spatiotemporal ionospheric delays variations and avoid the difficulty in choosing the IF combinations in case of triple-frequency data processing, using uncombined observations with proper ionospheric constraints is more beneficial. Yet, determining the appropriate power spectral density (PSD) of ionospheric delays is one of the most important issues in the uncombined processing, as the empirical methods cannot consider the actual ionosphere activities. The ionospheric delays derived from actual dual-frequency phase observations contain not only the real-time ionospheric delays variations, but also the observation noise which could be much larger than ionospheric delays changes over a very short time interval, so that the statistics of the ionospheric delays cannot be retrieved properly. Fortunately, the ionospheric delays variations and the observation noise behave in different ways, i.e., can be represented by random-walk and white noise process, respectively, so that they can be separated statistically. In this paper, we proposed an approach to determine the PSD of ionospheric delays for each satellite in real-time by denoising the ionospheric delay observations. Based on the relationship between the PSD, observation noise and the ionospheric observations, several aspects impacting the PSD calculation are investigated numerically and the optimal values are suggested. The proposed approach with the suggested optimal parameters is applied to the processing of three long-range baselines of 103 km, 175 km and 200 km with triple-frequency BDS data in both static and kinematic mode. The improvement in the first ambiguity fixing time (FAFT), the positioning accuracy and the estimated ionospheric delays are analysed and compared with that using empirical PSD. The results show that the FAFT can be shortened by at least 8% compared with using a unique empirical PSD for all satellites although it is even fine-tuned according to the actual observations and improved by 34% compared with that using PSD derived from ionospheric delay observations without denoising. Finally, the positioning performance of BDS three-frequency observations shows that the averaged FAFT is 226 s and 270 s, and the positioning accuracies after ambiguity fixing are 1 cm, 1 cm and 3 cm in the East, North and Up directions for static and 3 cm, 3 cm and 6 cm for kinematic mode, respectively.

MATHEMATICAL SIMULATION OF THE MOVEMENT OF GRAIN MATERIAL ON THE SURFACE OF THE SPREADER UNDER ITS INTRODUCTION INTO THE ASPIRATION CHANNEL OF THE SEPARATOR

Develop a mathematical model and calculated analytical dependences to determine the trajectories and parameters of grain movement on the surface of the vibrating feeder under the conditions of its introduction into the aspiration channel of the separator. They are based on the methods of mathematical modeling and theoretical mechanics with the application of the equations of motion of a material point under the variable action of vibrations. Theoretical research was conducted using mathematical analysis and modeling theory. The research results are processed using elements of probability theory and mathematical statistics using application packages. A mathematical description of the movement of grains of grain material components (GMC) on the surface of the vibrating feeder under the conditions of its introduction into the aspiration channel of the separator under the conditions of vibration on the GMC. The trajectories of grains on the surface of the vibrating feeder with different size are obtained. The obtained equation of motion of the particle under the action of vibrations allows to determine the dependence of the velocity of the material in the vibrated fluidized bed on a number of factors: geometrical parameters of the vibrating feeder, feed angle, initial kinematic mode of grain material, kinematic mode of the vibrating feeder and friction coefficient. The process of grain material movement on the flat surface of the vibrating feeder is described, which allows to determine the rational parameters of material introduction into the aspiration channel of the separator for its further fractionation. The dependence for the function of the grain flow rate on the flat surface of the vibrating feeder is obtained, which allows to determine the parameters of the grain material distribution by the cross-sectional area of the aspiration channel of the separator. The velocity of grain material on the flat surface of the vibrating feeder is estimated on the basis of a mathematical model constructed by hydrodynamic analogy, which in turn determines the analysis of grain recombination by the thickness of the vibrated liquid layer of grain material.

The effect of function-based and voxel-based tropospheric tomography techniques on the GNSS positioning accuracy

Tropospheric wet delay, the main source of which is water vapor, is one of the major factors affecting the accuracy of positioning techniques using microwave. Tropospheric tomography is a powerful method to reconstruct the water vapor content in four-dimensional (4D) space. This paper studies the effect of using function-based and voxel-based tropospheric tomography methods on the positioning accuracy. This examination is performed on the static and kinematic positioning modes using Global Navigation Satellite Systems (GNSS) stations under different weather conditions. After validating the results of tomography methods using radiosonde observations, the tomography-based positioning solutions, including function-based and voxel-based approaches, are compared with the positions obtained using tropospheric models. The results of two GPS stations show that the accuracy increases when applying tomography approaches. The function-based tomography is able to increase the accuracy of the up component of the static and kinematic modes by about 0.42 and 0.79 cm, respectively, compared to the voxel-based method. In addition, the use of the function-based tropospheric tomography can decrease the convergence time of the kinematic Precise Point Positioning (PPP) solution.

Study On Parameters and Operating Modes of the Device for Deseeding Flax in the Field

The authors showed that the main technological process in the combined and separate methods of fiber flax harvesting is deseeding or separating the seed part of the crop from the stems. It was confirmed that there is a direct impact of this process success on seed and straw losses, the fiber yield and quality, the heap composition, the labor intensity and energy consumption of flax drying and processing. (Research purpose) To develop a technology for stripping fiber flax with a comb deseeder during harvesting, to study the deseeder’s specifications and operating modes. (Materials and methods) The authors studied the technological process of stripping flax with a comb deseeder. An experimental plant of a comb deseeder was designed. A model of theoretical calculation was proposed based on the physical and mechanical properties of fiber flax and agrotechnical requirements for its harvesting. (Results and discussion) The authors theoretically determined the comb deseeder’s optimal height, operation kinematic mode, stripping cleanliness, the radius of the stripper drum. Laboratory studies were conducted. It was shown that threshing seeds in the field will reduce the loss of flax seeds by 10 per cent and the stem waste due to tangling during the harvesting process – by 18 per cent. It will also reduce the number of harvesting vehicles, personnel, and the cost of product. The authors identified an opportunity to increase productivity by increasing the width of the header grip: for example, the width of a grain harvester header is about 4 meters, and the width of a flax harvester header is 1.52 meters, that is, the productivity of flax harvesting will increase 2.6 times at the same speed, and 3 times at a higher speed. It was possible to eliminate one piece of equipment – a heap separating machine, since the technological operation of heap processing is carried out by a grain harvester. (Conclusions) The authors presented a theoretical substantiation of the comb deseeder’s operating parameters and modes for stripping fiber flax in the field. The authors proposed a model to determine them based on the physical and mechanical properties of flax and agrotechnical requirements for its harvesting.

Inter-satellite link augmented BeiDou-3 orbit determination for precise point positioning

Precise Point Positioning (PPP) requires precise products, including high-accuracy satellite orbit and clock parameters. It is impossible to obtain an orbit solution that is sufficiently accurate for PPP services with a regional tracking network; therefore, satellite orbits are usually estimated by a global tracking network with a large number of ground stations. However, it is expensive to build globally distributed stations. Fortunately, BeiDou-3 satellites carry an Inter-Satellite Link (ISL) payload, which can track the whole arc of the BeiDou-3 satellites and enhance the orbit determination accuracy with regional ground stations. In this contribution, a novel orbit determination strategy for BeiDou-3 PPP is proposed, in which the BeiDou-3 satellite orbits are enhanced by the ISL. First, the generation of precise satellite products is demonstrated in detail. In addition, the products are assessed by Satellite Laser Ranging (SLR) residuals and overlap comparisons. Moreover, the products are used for receivers in mainland China to carry out the static and kinematic modes to research the PPP performance of BeiDou-3′s 3IGSO/24MEO constellation. The SLR validations of the satellite orbits demonstrate an accuracy better than 0.1 m in the radial component, and the orbit overlap comparisons show accuracies of 0.016 m in the radial component, 0.088 m in the along-track component and 0.087 m in the cross-track component. The Standard Deviation (STD) in the differences in overlapping arcs for the estimated satellite clocks is approximately 0.10 ns. The static PPP results demonstrate that the error in both the horizontal and vertical components is smaller than 10 cm after 30 minutes of convergence. After 24 hours of convergence, the errors are 0.70 cm, 0.63 cm and 1.99 cm for the north, east and up components, respectively. The kinematic PPP experiment illustrates that the Root Mean Square (RMS) position errors in the north, east and up components are approximately 3.23 cm, 5.27 cm and 8.64 cm, respectively, after convergence. The obtainable positioning and convergence performances are comparable to those using products generated by global tracking networks.

Enabling ambiguity resolution in CSRS‐PPP

<h3>Abstract</h3> Precise point positioning (PPP) uses precise satellite orbits, clock corrections and biases derived from a global network of reference stations to enable accurate positioning worldwide. Natural Resources Canada’s Canadian Spatial Reference System (CSRS) PPP is a free Web service offering automated PPP processing. A critical factor limiting the adoption of PPP in many applications is the convergence time needed to reach centimeter-level accuracies. To address this issue, CSRS-PPP now implements PPP with ambiguity resolution (PPP-AR). This feature required the development of new algorithms, such as sequential normal stacking for least-squares filtering/smoothing, and the weighted integer decision concept for ambiguity validation. New satellite product lines (ultra-rapid, rapid, final) also have been deployed to enable PPP-AR processing with various latencies. This analysis demonstrates that sub-centimeter horizontal accuracies can be obtained in less than one hour for both static and kinematic modes. Using product lines with longer latencies is beneficial, although improvements are typically within the reported uncertainties.

An uncombined triple-frequency user implementation of the decoupled clock model for PPP-AR

Precise point positioning (PPP) has proved its capacity to provide centimetre-level position solutions in open sky environments. However, the technique still suffers from relatively long initial convergence times. Research has proved the potential of ambiguity resolution (AR) to reduce the convergence time and three main methods are used to perform AR: the fractional cycle bias method, the decoupled clock model (DCM) and the integer recovery clock method. This paper focuses on the DCM and expands it at the user side to better fit the current context. Seeing as multi-frequency processing is proving to improve PPP performance, the classical DCM model is extended from a combined dual-frequency model to an uncombined triple-frequency one. The user implementation is tested on 1400, 3-h-long datasets from global IGS stations for 1 week with the Galileo constellation in both static and kinematic modes. First, some of the model-specific parameters are plotted and the estimated receiver biases are visualized. Then, dual- and triple-frequency PPP-AR results are shown. In both frequency modes, the convergence time and accuracy of the float solutions are improved with AR. In the dual-frequency case, the 100-percentile mean convergence time reduces from 19 min for the float solution to 14 min for the fixed solution, and the horizontal root mean square error improves 2.7 to 1.1 cm. In the triple-frequency case, the convergence time reduces from 17.5 min for the float solution to 9.5 min for the fixed solution, and the accuracy improves from 2.6 to 1.0 cm. These results show a minimal improvement in the accuracy between the dual-frequency and triple-frequency AR solutions, and a significant 40–50% improvement in the convergence time. Future work includes applying these developments to multi-constellation PPP-AR, which would further reduce the convergence time.

O‘ZBEKISTON SHAROITIDA SABZI KOVLAGICH ELEVATORI ISHCHI ORGANLARINING PARAMETRLARINI ASOSLASH

Studies show that due to variability of physical and mechanical properties of the soil, hard lumps are formed when carrots are harvested by diggers and remain inseparable from the tubers complicating the sifting process, which leads to overloading of machines. A lattice loosening working part that improves the separating ability of the digger elevator has been developed. The research objective is to seek rationale for the parameters of the lattice ripper of the carrot digger, which ensures a uniform distribution of the soil pile along the width of the elevator and improves complete separation of impurities with minimal damage to root crops. (Materials and methods) The study looked into the geometrical, kinematic parameters of the lattice ripper of the carrot digger. After investigating the physical and mechanical properties of the carrot bed, the research could provide theoretical rationale for the design parameters of the mechanism and its kinematic indicators. (The research results and analysis) It has been found that when the lattice cultivator interacts with the soil layers on the elevator, soil clods get destroyed and the soil gets loosened at the following parameters: the radius of the cultivator - at least 9.5 centimeters, the height of the shaft - 20 centimeters, the loaded part of the foot of the cultivator - 6 centimeters, the width of the grid ripper - 47 centimeters. (Conclusion) It has been revealed that lattice rippers help separate carrot root crops quickly from the soil layer without any damage or loss. It appears that the rotation speed of the grid ripper should not exceed 2.5 meters/second, the kinematic mode of the intensification agent of separation - 2.5, and the radius of the ripper should be at least 9.5 centimeters.

A Comparative Study of BDS Triple-Frequency Ambiguity Fixing Approaches for RTK Positioning.

Concerning the triple-frequency ambiguity resolution, in principle there are three different realizations. The first one is to fix all the ambiguities of the original frequencies together. However, it is also believed that fixing the combined integer ambiguities with longer wavelength, such as extra-wide-lane (EWL), wide-lane (WL), should be advantageous. Also, it is demonstrated that fixing sequentially EWL, WL and one type of original ambiguities provides better results, as the previously fixed ambiguities increase parameters’ precision for later fixings. In this paper, we undertake a comparative study of the three fixing approaches by means of experimental validation. In order to realize the three fixing approaches from the same information in terms of adjustment, we developed a processing strategy to provide fully consistent normal equations. We first generate the normal equation with the original undifferentiated carrier phase ambiguities, then map it into that with the combined and double-differenced ambiguities required by the individual approach for fixing. Four baselines of 258 m, 22 km, 47 km and 53 km are selected and processed in both static and kinematic mode using the three ambiguity-fixing approaches. Indicators including time of first fixed solution (TFFS), the correct fixing rate, positioning accuracy and RATIO are used to evaluate and investigate results. We also made a preliminary theoretical explanation of the results by looking into the decorrelation procedure of the ambiguity searching algorithm and the intermediate results. As conclusions, integrated searching of original ambiguities or combined ambiguities has almost the same fixing performance, whereas the sequential fixing of EWL, WL and B1 ambiguities overperforms the integrated searching. By the way, the third-frequency data can shorten the TFFS significantly but can hardly improve the positioning.

Single-epoch RTK performance assessment of tightly combined BDS-2 and newly complete BDS-3

The BeiDou global navigation satellite system (BDS-3) constellation deployment has been completed on June 23, 2020, with a full constellation comprising 30 satellites. In this study, we present the performance assessment of single-epoch Real-Time Kinematic (RTK) positioning with tightly combined BeiDou regional navigation satellite system (BDS-2) and BDS-3. We first investigate whether code and phase Differential Inter-System Biases (DISBs) exist between the legacy B1I/B3I signals of BDS-3/BDS-2. It is discovered that the DISBs are in fact about zero for the baselines with the same or different receiver types at their endpoints. These results imply that BDS-3 and BDS-2 are fully interoperable and can be regarded as one constellation without additional DISBs when the legacy B1I/B3I signals are used for precise relative positioning. Then we preliminarily evaluate the single-epoch short baseline RTK performance of tightly combined BDS-2 and the newly completed BDS-3. The performance is evaluated through ambiguity resolution success rate, ambiguity dilution of precision, as well as positioning accuracy in kinematic and static modes using the datasets collected in Wuhan. Experimental results demonstrate that the current BDS-3 only solutions can deliver comparable ambiguity resolution performance and much better positioning accuracy with respect to BDS-2 only solutions. Moreover, the RTK performance is much improved with tightly combined BDS-3/BDS-2, particularly in challenging or harsh conditions. The single-frequency single-epoch tightly combined BDS-3/BDS-2 solution could deliver an ambiguity resolution success rate of 96.9% even with an elevation cut-off angle of 40°, indicating that the tightly combined BDS-3/BDS-2 could achieve superior RTK positioning performance in the Asia–Pacific region. Meanwhile, the three-dimensional (East/North/Up) positioning accuracy of BDS-3 only solution (0.52 cm/0.39 cm/2.14 cm) in the kinematic test is significantly better than that of the BDS-2 only solution (0.85 cm/1.02 cm/3.01 cm) due to the better geometry of the current BDS-3 constellation. The tightly combined BDS-3/BDS-2 solution can provide the positioning accuracy of 0.52 cm, 0.22 cm, and 1.80 cm, respectively.

Georeferencing kinematic modeling and error correction of terrestrial laser scanner for 3D scene reconstruction

Georeferencing means to transform the point cloud data collected by the terrestrial laser scanner (TLS) into a global coordinate system for three-dimensional (3D) scene reconstruction. However, the current georeferencing methods are mainly applicable for the TLS operating in the static mode; when the TLS is moving (i.e., in the kinematic working mode) during the 3D scene reconstruction, severe georeferencing error will be generated due to the kinematic measurement noise and geometric falsification offsets. To bridge this research gap, a new method based on the kinemics state constraints converted measuring Kalman Filter (KSC-CMKF) and the Levenberg Marquardt Wavelet neural network (LM-WNN) is proposed to correct the TLS georeferencing error in the kinematic operating mode (i.e., TLS kinematic georeferencing error). This new method can automatically correct the georeferencing error and simultaneously reduce the TLS systematic bias to save time and cost for the kinematic georeferencing. In order to achieve the georeferencing error correction, two kinematic models are established to respectively address the straight-line movement and turn movement scenarios. Then, the LM-WNN algorithm is used to estimate the uncertain propagation of the TLS kinemics error model to optimize the kinematic parameters. Subsequently, the KSC-CMKF algorithm is applied to correcting the coordinate transformation error between the TLS spherical coordinate and the global Cartesian coordinate. Lastly, the pre-survey signalized spherical targets are adopted as the ground control points to evaluate the performance of the TLS kinematic georeferencing. Experimental results demonstrate that the overall accuracy of the proposed TLS kinematic georeferencing method for the 3D scene reconstruction is significantly improved and is superior to that of two existing popular methods.

Comparative analysis of four different single-frequency PPP models on positioning performance and atmosphere delay retrieval

Single-frequency precise point positioning (SF-PPP) has attracted increasing attention due to its high precision and cost effectiveness. With various strategies to handle the dominant error, i.e., ionosphere delay, the ionosphere-float (IF), ionosphere-free-half (IFH), ionosphere-corrected (IC), and ionosphere-weighted (IW) SF-PPP models are certain to possess different characteristics and performance levels. This study is dedicated to assessing and comparing the four models from model characteristics, positioning performance, and atmosphere delay retrieval. The model comparison shows that IC and IW models are full-rank while IF and IFH models have a rank deficiency of size one that will result in biased estimations, which means the better solvability of IC and IW models. The experiments are carried out based on the 7-day Global Positioning System (GPS) observations collected at 57 global Multi-GNSS Experiment (MGEX) stations and Global Ionosphere Map (GIM) products. The results indicate that the IW model can accelerate SF-PPP convergence and achieve higher positioning accuracy compared to the other three SF-PPP models, especially in kinematic mode. With convergence criteria of 0.25 m in horizontal and 0.5 m in vertical, the east/north/up convergence times of IW model are 0.5/15.0/25.0 min and 0.5/16.0/36.5 min for static and kinematic modes, respectively. The IW model is able to achieve an instantaneous positioning accuracy of 0.28/0.35/0.75 m. In addition, a real kinematic test also demonstrates the best positioning solutions of IW model. Regarding troposphere delay retrieval, the IF, IFH, and IW models obtain a comparable daily accuracy of 3.0 cm on average, while the IC model achieves the worst accuracy of 8.0 cm. For precise ionosphere delay estimation, IW model only needs an average initialization time of 34.3 min, but a longer initialization time of 51.6 min is required for IF model. The daily precision of ionosphere delay estimation for IW model can reach up to 10.8 cm. At the present accuracy of GIM products, it is suggested that the IW model should be adopted for SF-PPP first due to its superior performance in positioning and atmosphere delay retrieval.

The Research Activities of the Main Astronomical Observatory of the National Academy of Sciences of Ukraine on the Use of GNSS Technology

The current state of the research activities of the Main Astronomical Observatory of the National Academy of Sciences of Ukraine (MAO NASU) on the use of GNSS technology is presented. Today, MAO operates a permanent GNSS network consisting of five stations (two stations are temporarily inactive). All stations are included in EPN and the EPOS network, GLSV, KHAR, and UZHL stations are also integrated to the IGS network. MAO Operational Centre also provides automatic data transfer from 12 stations installed by other Ukrainian organizations included in the international networks. Data from approximately 300 Ukrainian permanent GNSS stations are stored in the MAO Local Data Centre. The MAO Local Analysis Centre uses Bernese GNSS Software for different types of data processing of GNSS observations. Rapid processing is performed on a daily basis for monitoring the stability of the permanent stations from some Ukrainian RTK networks. All available observations data from the Ukrainian stations for the period from December 7, 1997, to January 28, 2017, were processed according EPN standards during the MAO’s second reprocessing campaign and regular processing. As a result, the coordinates in the IGb08 reference frame and tropospheric zenith delays for 233 permanent stations (202 of them are the Ukrainian stations), as well as the velocities for the 128 stations that have observation period more than 3 years, were estimated. The creation and development of local GNSS networks, as well as the long-term filling of databases with high-precision coordinate solutions and estimates of the displacement velocities of GNSS stations, made possible to conduct geodynamic studies at the local level. The strain ellipses and rotation were found based on estimated coordinates and velocities of the GNSS stations. In 2016–2019, Kharkiv National University of Radio Electronics, in cooperation with MAO NASU, performed a number of studies on high-precision GNSS positioning and navigation. New implementations of modern methods and algorithms for the PPP positioning were created and experimentally tested. The errors of the daily floating PPP solutions were 5…8 mm (with a probability of P ≈ 95%) for static mode and 5…8 cm (P ≈ 68%) for kinematic mode. The decimeter/centimeter error of determining the coordinates of current satellites with low Earth orbits (LEO) in the implementation of kinematic floating and fixed PPP solutions was proven. The development of a high-accuracy multiposition phase system of trajectory measurements for field tests of high dynamic aircrafts (HDA) were proposed. The estimated values of the root-mean-square error (RMSE) in determining the HDA motion variables were in the range from 0.05 to 0.40 m for coordinates and from 0.5 to 1.6 cm/s for the velocity vector components.

An Investigation of Precise Orbit and Clock Products for BDS-3 from Different Analysis Centers.

A quality evaluation of precise products for BDS-3 constellations is presented for the first time in this contribution. Then, the tropospheric delay retrieval and positioning performance of BDS-3 precise point positioning (PPP) solutions using the precise products (gbm, wum, iac, sha, cnt) with observations from 24 stations from DOY 280 to 317 in 2020 was comprehensively investigated. The orbit comparisons present consistencies of 0.09–0.22 m for the C19–C37 satellites and of 0.5–1.2 m for the C38–C46 satellites among the final products. The standard deviation (STD) values of the clock differences of iac showed the best agreement with those of gbm, followed by wum, sha. The clock differences performance of cnt was the worst. For BDS-3 PPP solutions with five Analysis centers (ACs) products, the median convergence times of static PPP mode incorporating the gbm, wum, iac, sha, and cnt products were 31.0, 33.5, 34.5, 37.8, and 72.0 min, respectively; the median convergence times of kinematic PPP model incorporating the same products were 40.5, 41.0, 50.5, 55.0, and 94.0 min, respectively. The positioning accuracies in the static and kinematic modes were approximately 1–4 cm, 2–6 cm in the horizontal and vertical components, respectively. With the final products in kinematic mode, the performance of PPP with real-time products (cnt) is poorer than all PPP with final products. The median of ZTD accuracies of the five products gbm, wum, iac, sha, and cnt were 7.84, 7.58, 7.04, 7.19, and 10.1 mm, respectively, and the accuracy differences were very small among five AC products (gbm, wum, iac, sha).

Characteristics of phase bias from CNES and its application in multi-frequency and multi-GNSS precise point positioning with ambiguity resolution

While precise point positioning ambiguity resolution (PPP AR) is a valuable tool of the multi-constellation global navigation satellite system (multi-GNSS), phase biases are critical to implement PPP AR. Multi-frequency phase biases and satellite attitude files are provided freely by Centre National d’Etudes Spatiales (CNES), which are estimated based on GeoForschungs Zentrum (GFZ) satellite rapid orbit and clock products. However, the temporal characteristics of these phase biases and their positioning performance in the multi-frequency and multi-GNSS PPP AR have not been investigated yet, especially in the low sun elevation and satellite maneuver period. We introduce the transformation between multi-frequency phase biases and integer recovery clock model. In this transformation, inter-frequency clock biases (IFCBs) and inconsistencies in satellite attitude model errors between GFZ and CNES products are well considered. Experiments with GPS/Galileo/BeiDou observations from 34 stations were performed in static and kinematic modes, and the multi-frequency phase residuals were analyzed in the low sun elevation. Our results show that the impact of IFCBs and inconsistencies in satellite attitude errors could be mitigated at the user ends by using phase biases and satellite attitude files. Under the condition of satellite reverse yaw maneuvers, the performance of kinematic PPP without phase biases or deleting maneuvering satellites would be degraded significantly until the end of satellite observation arc or the next reverse yaw maneuver occurs. By applying phase biases with PPP AR, the positioning accuracy could be improved by 34.4%, 23.1%, and 37.4% in the east (E), north (N), and up (U) directions, respectively. Therefore, we suggested that PPP users should apply phase biases and satellite attitude files when using the GFZ rapid orbit and clock products, especially for satellite maneuvers and low sun elevation.

Real‐time and dynamic time transfer method based on double‐differenced real‐time kinematic mode

In this study, a real-time and dynamic time transfer method based on double-differenced (DD) real-time kinematic (RTK) mode is proposed. First, the method forms the DD observations of Global Navigation Satellite System (GNSS) to fix the DD ambiguity, and then, all of the fixed single-differenced (SD) ambiguities are recovered while defining the SD ambiguity datum; finally, the method uses the SD observations to realise the time transfer by using the fixed SD ambiguities. Five different baseline links were used for the validations. The results demonstrated that the DD-RTK method can be used for both kinematic positioning and precise time transfers, and it provides for much better accuracy and stability than the un-differenced precise point positioning method because it is operated by the broadcast ephemeris, which is more convenient for real-time applications.

Analysis of real-time multi-GNSS satellite products of Wuhan University for rapid response of precise positioning

When users need to quickly process GNSS data, they often need the satellite orbit and clock products with the minimum latency and the highest precision, and it is a good solution to receive the real-time satellite RTCM SSR correction stream to recover the precise satellite orbit and clock products in real time and then store them in an offline repository for rapid response of precise positioning. In this paper, the real-time multi-GNSS orbit and clock RTCM SSR correction stream broadcast by SSRC00WHU0 mountpoint of Wuhan University is used to recover precise satellite orbit and clock products in real time. First, the seven-day orbit files and clock files were obtained and stored locally, and compared with the final MGEX precise satellite orbit and clock products. The results show that the real-time orbit and clock products of GPS and Galileo satellites have the best accuracy, followed by GLONASS satellites and BDS satellites. The real-time orbit products can reach the accuracy level of 5 cm for GPS satellites, 8 cm for Galileo satellites, 15 cm for GLONASS satellites and 16 cm for BDS-3 satellites, and the real-time clock products can reach the accuracy level of 0.43 ns for GPS satellites, 0.44 ns for Galileo satellites, 0.91 ns for GLONASS satellites and 3.14 ns for BDS satellites. Then, the observation data of 20 IGS stations randomly distributed around the world from DOY 150 to 156 in 2021 were processed by static precise point positioning (PPP) mode using the recovered real-time products. The results show that the average positioning accuracy can reach 1.57 cm, 0.76 cm and 1.67 cm in east, north and up direction for static PPP, respectively. Finally, using the recovered real-time products and the final products, the GPS observation data collected in aviation were processed in pseudo real-time in a kinematic mode. The results show that the RMSs of positioning errors are 8.5 cm, 2.4 cm and 16.5 cm in the east, north and up direction, respectively. In addition, one-day multi-GNSS observation data at 20 IGS stations were processed in a kinematic PPP mode, and the results show that the average positioning accuracy is 3.11 cm, 2.04 cm and 4.94 cm in east, north and up directions.

Kinematic GNSS positioning results compared against Agisoft Metashape and Pix4dmapper results produced in the San Joaquin experimental range in Fresno County, California

Abstract RTKLIB which is an open source Global Navigation Satellite Systems (GNSS) software has gained rapid acceptance among Surveying professionals thanks to recent developments in UAS (Unmanned Aerial System) technology. RTKLIB enables standard and precise point positioning (PPP) in real-time and post-processing modes to be performed. As such, UAS users utilize this software to analyze GNSS data collected by GNSS systems on UAS. By being versatile and free, RTKLIB is commonly used by many; however, it is not the only freely available GNSS software. There are also freely available online GNSS data processing software running on servers. These online GNSS data processing services provide data processing in static, kinematic and rapid static modes. Because UAS collect data in kinematic mode, in this study, kinematic data processing by aforementioned software (CSRS-PPP, GAPS and APPS) is analyzed. The results coming from these software are compared against the results produced by photogrammetric software (Agisoft Metashape and Pix4Dmapper). The aim of this practical project is to produce generalizable knowledge about the performance of these software. It is found out that RTKLIB and CSRS-PPP achieved cm-level precision. Yet, GAPS and APPS achieved dm-level precision both for horizontal and vertical coordinates. This study demonstrates the precision and accuracy expected from these software if they are used for kinematic GNSS data processing.

Assessment and Analysis of the Four-Satellite QZSS Precise Point Positioning and the Integrated Data Processing With GPS

The Quasi-Zenith Satellite System (QZSS), which serves Japan and its surrounding areas, is a regional navigation satellite system developed by Japan Aerospace Exploration Agency. The system is now in a four-satellite constellation with preliminary standalone navigation and positioning capabilities. In this paper, the performance of QZSS-only precise point positioning (PPP) in both static and kinematic modes is initially evaluated using the datasets spanning 11 days from 11 tracking stations in Asia-Pacific regions and the final precise orbit and clock products from the analysis centers GFZ and WUM. For completeness, the GPS/QZSS integrated data processing with GFZ and WUM final products as well as the L6E real-time orbit and clock corrections is also analyzed. The results indicate that the static positioning accuracy of QZSS-only PPP is approximately 4, 2 and 15 cm in the east, north and up directions, respectively, and the static convergence time of QZSS-only PPP with WUM and GFZ products can be 75.2, 44.3 and 45.6 min, and 153.5, 201.6 and 162.8 min in the three directions, respectively. As for the QZSS-only kinematic PPP solutions, the re-convergence repeatedly occurs due to limited available satellites. To achieve more reliable solutions, the inter-system bias parameter in GPS/QZSS PPP processing is recommended to be estimated as random walk process or white noise process. The improvement of post-processed GPS/QZSS PPP over GPS-only case is marginal on position accuracies, but can be several minutes on convergence time. Compared with post-processed GPS/QZSS PPP, the real-time one achieves worse position accuracies but comparable convergence time.

Experience of determining the parameters of the elastoviscoplastic soil model

Rheological studies of soils were carried out by S.S. Vyalov, M.N. Gol’dshtejn, N.N. Maslov, G.I. Ter-Stepanyan, S.R. Meschyan, A.L. Gol’din, Z.G. Ter-Martirosyan and many others. On the basis of existing rheological soil models, a new universal rheological equation was proposed in Ter-Martirosyan’s dissertation, which allows describing kinematic shear, creep and stress relaxation at the same parameters. Experimental studies of the soil were carried out in a simple shear device in a kinematic loading mode at a shear displacement rate u̇= 0.05 mm/min and at two values of compaction loads (σ1 &lt; σ2). Based on the results of the experimental studies, the parameters of the elastoviscoplastic model were determined and graphs of the dependence of shear stresses on time were plotted, which clearly show the high convergence of the experimental and theoretical curves.