GNSS Receiver Data Research Articles

GRIMS: global and regional ionosphere monitoring system

The ionosphere shows regular changes such as daily, 27 days, seasonal, semi-annual, annual, and 11 years. These changes can be modeled and their effects largely determined. However, in addition to regular changes, irregular changes occur in the ionosphere due to space weather conditions, natural disasters, and human-induced irregularities. GNSS is one of the instruments along with many others that can give a piece of information on the ionospheric state. Various indices/parameters are used to determine the effect of space weather conditions. The well-known ones are solar activity indices, geomagnetic storm indices, magnetic field components, proton density, and proton flux parameters. It is important to take all of these indices into consideration when investigating the source of the anomaly. Considering only some of them may lead to incorrect inferences about the source of possible anomalies. To carry out comprehensive research in this field, it is necessary to analyze a very large data set. This indicates the requirement for an automatic system. With the Global and Regional Ionosphere Monitoring System (GRIMS) designed within the scope of this study, the ionosphere can be monitored globally and regionally. The GRIMS is online at https://www.online-grims.com/. By using Global ionospheric maps and GNSS receiver data, global, regional, and station-specific anomalies can be detected regularly through methods such as HDI (Highest Density Interval) and ARIMA (Autoregressive Integrated Moving Average). GRIMS gathers space weather-related parameters from ionospheric data centers to help users interpret the situation, and it allows users to download the results and request data for specific days. The details of the experimental results and output products of the system designed during the geomagnetic active days of March 17, 18, 2015 are given in this paper. Moreover, geomagnetic active days that occurred between 2000 and 2023 are given in the GRIMS.

ВЫБОР МЕТОДА ОБРАБОТКИ ДАННЫХ И ПОЛУЧЕНИЯ ПРОДОЛЬНОГО ПРОФИЛЯ ДОРОГИ, РЕЖИМА ДВИЖЕНИЯ АВТОМОБИЛЯ С ПОМОЩЬЮ GPS (GNSS-ПРИЕМНИКА)

The existing methods are analyzed for receiving and processing data from a GNSS receiver obtained on a moving car in the form of messages in degrees of latitude and longitude and converting them into meters. An accuracy assessment was carried out to determine the location and movement of machinery using various methods. The method is proposed for data processing and obtaining the longitudinal profile of the road, the car velocity (mode) using a GNSS receiver (according to the parameters of the velocity and altitude of a moving object on the surface of the Earth). It is revealed that the considered foreign methods of location determination in relation to the CIS give significant discrepancies (up to 2 times), which is associated with the use of various systems of reference points in the CIS and abroad, including in cartography, electronic maps. It is established that when estimating the distance covered by the difference in the displacements of two points of the positioning projections and their summation for small quantization increments (8–20 m, depending on velocity and frequency), the considered methods can lead to a discrepancy of up to 30–47 %. It is proposed to use the simplified linear formula lat_m = 112297,6196∙Ddec lat, lon_m = 63215,444 Ddec lon in the territory of the Republic of Belarus when determining relative distances and linking to maps. It has been found that to obtain a longitudinal profile of the road, depending on the distance covered, the mode of movement of vehicles, military machinery, unmanned aerial vehicles, it is more correct to use GNSS receiver data on velocity and altitude, providing a minimum error (0.15 %), which is confirmed by the nature of the change h = f(l), υa = f(l) and indicates the correctness of the proposed method. Also, when modelling the car movement, it is necessary to take into account road factors affecting the driving mode.

On the quality of tropospheric estimates from low-cost GNSS receiver data processing

The goal of this study is to verify whether the low-cost GNSS receivers may provide the tropospheric parameters with accuracy close to that of high-grade ones. In this way, we address a scientific question on the potential usability of low-cost receivers for climate monitoring. We assess zenith tropospheric delays (ZTD) and, for the first time, horizontal gradients derived from Precise Point Positioning with low-cost receivers. ZTD estimates are also validated against ERA5, which is the fifth generation reanalysis for the global climate and weather produced by the European Centre for Medium-Range Weather Forecasts. We proved that low-cost equipment has the potential to provide tropospheric estimates with comparable accuracy to high-grade receivers. We also reveal a high agreement between GNSS ZTDs and these of ERA5 reanalysis. Finally, we show that applying a surveying-grade antenna to a low-cost receiver may enhance the accuracy of the tropospheric estimates derived from mass-market receivers.

Multi-Epoch 3D-Mapping-Aided Positioning using Bayesian Filtering Techniques

<h3>Summary</h3> The performance of different filtering algorithms combined with 3D mapping-aided (3DMA) techniques is investigated in this paper. Several single- and multi-epoch filtering algorithms were implemented and then tested on static pedestrian navigation data collected in the City of London using a u-blox EVK M8T GNSS receiver and vehicle navigation data collected in Canary Wharf, London, by a trial van with a Racelogic Labsat 3 GNSS front-end. The results show that filtering has a greater impact on mobile positioning than static positioning, while 3DMA GNSS brings more significant improvements to positioning accuracy in denser environments than in more open areas. Thus, multi-epoch 3DMA GNSS filtering should bring the maximum benefit to mobile positioning in dense environments. In vehicle tests at Canary Wharf, 3DMA GNSS filtering reduced the RMS horizontal position error by approximately 68% and 57% compared to the single-epoch 3DMA GNSS and filtered conventional GNSS, respectively.

Использование БПЛА Geoscan 201 для съемки линейного объекта трассы Хива–Ургенч

The aim of this work is to perform a linear aerial survey of the Khiva–Urgench highway using the Geoscan 210 UAV, the results of which will create orthophotomaps at a scale of 1:1 000, which are necessary for designing bicycle and sidewalk paths along this route. Surveyors of the Applied Geodesy Department of UZGASHKLITI performed a field planned-altitude reference at this object. 48 control points were determined. Characteristic solid contours along the route were chosen as reference points. The binding of control points was carried out from the starting points of the State Geodetic Networks, using satellite receivers (SN 5242498595, 5243499034, 4827155394) in the RTK mode in a radial way, by the calibration method on the ground. The coverage area was 17.4 sq. km. Aerial photography was carried out at a height of 211 m by a Geoscan 201 unmanned aerial vehicle at a scale of 1:500 with a DSC RXIR digital camera with a focal length of 35 mm. Forward overlap of aerial photographs was 70 %, and lateral—50 %. 4 aerial routes were made at this facility, the photography basis was 42 m. The number of aerial photographs at the facility was 3 868 pieces, and the coverage of aerial photography was 300 m. The images and their EXIF files were georeferenced by performing field processing using the Geoscan Planner program. Before the start of field work, the GNSS receiver (Trimble R6) was installed at a known point on the ground and started in static mode (10 Hz). The aircraft has a GNSS receiver (Topcon) operating in fast static mode (10 Hz). The GNSS data on the ground and on board the aircraft are balanced. Image center coordinates are calculated from the base station GNSS receiver data using MAGNET Tools software. Then the data is imported into Agisoft Metashape software for automatic processing. In this case, the coordinates of the image centers were recalculated from the WGS-84 system into the SK-42 (Pulkovo 1942) system adopted in our country. The process of optimization and alignment of aerial photographs was carried out. After that, in order to obtain a high image quality, the orthophoto map was built using a height map built on the basis of a dense point cloud. The result of the work performed are orthophoto maps for the Khiva–Urgench highway, which will be used to design the location of bicycle and sidewalk paths.

Using KNN Algorithm Predictor for Data Synchronization of Ultra-Tight GNSS/INS Integration

The INS system’s update rate is faster than that of the GNSS receiver. Additionally, GNSS receiver data may suffer from blocking for a few seconds for different reasons, affecting architecture integrations between GNSS and INS. This paper proposes a novel GNSS data prediction method using the k nearest neighbor (KNN) predictor algorithm to treat data synchronization between the INS sensors and GNSS receiver and overcome those GNSS receiver’s blocking, which may occur for a few seconds. The experimental work was conducted on a flying drone over a minor Hungarian (Mátyásföld, 47.4992 N, 19.1977 E) model airfield. The GNSS data are predicted by four different scenarios: the first is no blocking of data, and the other three have blocking periods of 1, 4, and 8 s, respectively. Ultra-tight architecture integration is used to perform the GNSS/INS integration to deal with the INS sensors’ inaccuracy and their divergence throughout the operation. The results show that using the GNSS/INS integration system yields better positioning data (in three axes (X, Y, and Z)) than using a stand-alone INS system or GNSS without a predictor.

Reducing multipath effect of low-cost GNSS receivers for monitoring by considering temporal correlations

Abstract The investigations on low-cost single frequency GNSS receivers at the Institute of Engineering Geodesy (IIGS) show that u-blox GNSS receivers combined with low-cost antennas and self-constructed L1-optimized choke rings can reach an accuracy which almost meets the requirements of geodetic applications (see Zhang and Schwieger [25]). However, the quality (accuracy and reliability) of low-cost GNSS receiver data should still be improved, particularly in environments with obstructions. The multipath effects are a major error source for the short baselines. The ground plate or the choke ring ground plane can reduce the multipath signals from the horizontal reflector (e. g. ground). However, the shieldings cannot reduce the multipath signals from the vertical reflectors (e. g. walls). Because multipath effects are spatially and temporally correlated, an algorithm is developed for reducing the multipath effect by considering the spatial correlations of the adjoined stations (see Zhang and Schwieger [24]). In this paper, an algorithm based on the temporal correlations will be introduced. The developed algorithm is based on the periodic behavior of the estimated coordinates and not on carrier phase raw data, which is easy to use. Because, for the users, coordinates are more accessible than the raw data. The multipath effect can cause periodic oscillations but the periods change over time. Besides this, the multipath effect’s influence on the coordinates is a mixture of different multipath signals from different satellites and different reflectors. These two properties will be used to reduce the multipath effect. The algorithm runs in two steps and iteratively. Test measurements were carried out in a multipath intensive environment; the accuracies of the measurements are improved by about 50 % and the results can be delivered in near-real-time (in ca. 30 minutes), therefore the algorithm is suitable for structural health monitoring applications.

GPS‐based satellite formation flight simulation and applications to ionospheric remote sensing

The Virginia Tech Formation Flying Testbed (VTFFTB), a GNSS-based hardware-in-the-loop (HIL) simulation testbed for spacecraft formation flight, is developed and applied to ionospheric remote sensing. The current VTFFTB consists of GNSS RF hardware signal simulators, multi-constellation multifrequency GNSS receivers, a navigation and control system, an STK visualization system, and an ionospheric remote sensing system. GPS signals are emulated using GNSS simulator scenarios that include ionospheric phenomena. A formation of two spacecraft (“chief” and “deputy”) is considered. GNSS receiver data are used to produce space-based Total Electron Content (TEC) and scintillation measurements. A reference low Earth orbit (LEO) scenario is benchmarked with past simulation results to validate functionality. A LEO formation flying mission is designed to probe two Equatorial Spread F (ESF) scenarios with plasma bubbles. The results investigate the structure of ionospheric irregularities and demonstrate that the GPS-based satellite formation is able to measure vertical electron density by differencing 1D GPS vertical TEC.

A Design for a Trusted Community Bathymetry System

Marine Volunteered Geographic Information (informally “crowdsourced bathymetry”) has raised much interest within the authoritative hydrographic community as a means to cheaply gather information to satisfy chart updating requirements. So far, however, a routine path to the official chart has been rare, mainly due to lack of calibration and other metadata that would satisfy liability concerns. As an alternative to these ideas, a data collection system is proposed which, by design, can auto-calibrate and provide other data quality guarantees, and thereby generate data that by construction should be qualified for hydrographic use. This idea is termed here Trusted Community Bathymetry (TCB). A design for such a system is outlined, and its performance demonstrated experimentally through a prototype system based on a low-cost, post-processed GNSS receiver and NMEA data logger. By comparison against NGS control and survey-grade GNSS equipment, it is shown that the TCB system achieves centimeter to decimeter-level positioning in 3D, auto-calibrates vertical offsets to the sonar transducer within a decimeter, and provides realtime uncertainty estimates for ellipsoid-referenced soundings. Additionally, in an underway field trial, the total vertical uncertainty of the soundings is shown to be within the limits required for IHO Order 1b (S.44, 5 Ed.) surveys.

Autonomous Dam Surveillance Robot System Based on Multi-Sensor Fusion.

Dams are important engineering facilities in the water conservancy industry. They have many functions, such as flood control, electric power generation, irrigation, water supply, shipping, etc. Therefore, their long-term safety is crucial to operational stability. Because of the complexity of the dam environment, robots with various kinds of sensors are a good choice to replace humans to perform a surveillance job. In this paper, an autonomous system design is proposed for dam ground surveillance robots, which includes general solution, electromechanical layout, sensors scheme, and navigation method. A strong and agile skid-steered mobile robot body platform is designed and created, which can be controlled accurately based on an MCU and an onboard IMU. A novel low-cost LiDAR is adopted for odometry estimation. To realize more robust localization results, two Kalman filter loops are used with the robot kinematic model to fuse wheel encoder, IMU, LiDAR odometry, and a low-cost GNSS receiver data. Besides, a recognition network based on YOLO v3 is deployed to realize real-time recognition of cracks and people during surveillance. As a system, by connecting the robot, the cloud server and the users with IOT technology, the proposed solution could be more robust and practical.

Exploring GNSS Crowdsourcing Feasibility: Combinations of Measurements for Modeling Smartphone and Higher End GNSS Receiver Performance.

GNSS receiver data crowdsourcing is of interest for multiple applications, e.g., weather monitoring. The bottleneck in this technology is the quality of the GNSS receivers. Therefore, we lay out in an introductory manner the steps to estimate the performance of an arbitrary GNSS receiver via the measurement errors related to its instrumentation. Specifically, we do not need to know the position of the receiver antenna, which allows also for the assessment of smartphone GNSS receivers having integrated antennas. Moreover, the method is independent of atmospheric errors so that no ionospheric or tropospheric correction services provided by base stations are needed. Error models for performance evaluation can be calculated from receiver RINEX (receiver independent exchange format)data using only ephemeris corrections. For the results, we present the quality of different receiver grades through parametrized error models that are likely to be helpful in stochastic modeling, e.g., for Kalman filters, and in assessing GNSS receiver qualities for crowdsourcing applications. Currently, the typical positioning precision for the latest smartphone receivers is around the decimeter level, while for a professional-grade receiver, it is within a few millimeters.

GPS IIR-M L1 Transmit Power Redistribution: Analysis of GNSS Receiver and High-Gain Antenna Data

All seven operational GPS Block IIR-M satellites have been subject to short maintenance periods between February 7 and 8, 2017. With the help of data from several tracking stations of the International GNSS Service (IGS) and high-gain antenna measurements, it could be identified that the satellites’ transmit power of different L1 signal components has been changed during the maintenance. The analysis shows that the total radiated power of the satellites remains constant, but the power of the C/A-code and the P(Y)-code signals are increased whereas the powers of the M-code and the intermodulation product are reduced. A detailed look reveals a more efficient use of the total available power on the spacecraft through the decreased power of the intermodulation product. Thus, in sum more power is available for the three navigation signals on L1. Observations from geodetic GNSS receivers have been analyzed to demonstrate the effect of the change in L1 signal power distribution on the measured C/N0 of the C/A-code and P(Y)-code for different receiver types. High-gain antenna data collected before and after the maintenance periods are used to analyze improved utilization of the available power through the reduction of the losses caused by the intermodulation product.

Kinematic precise point positioning using GPS and GLONASS measurements in marine environments

The Precise Point Positioning (PPP) technique has received increased attention in recent years. When employing PPP, users need only a single GNSS receiver data to obtain a cm to dm accuracy level on a global datum, both in static and kinematic modes. This technique has become more popular due to its easy use, simple field operations, no base station(s) requirement, and provides cost effective high accuracy positioning. In satellite-based positioning, the accuracy and reliability of the positioning results are strongly dependent on the number and geometry of visible satellites, and quality of the observations. This issue is more important when the measurements are conducted in environments where satellite signals are blocked or degraded in some places like narrow channels, ravines, congested harbors, coastal areas with intense urbanization, inland waterways, in waters having severe terrain obstructions or surrounded by high mountains. To overcome this limitation, a combination of GPS and GLONASS measurements are proposed, especially to achieve more reliable and accurate solutions by increasing the number of visible satellites. The additional satellite system’s observations like GLONASS, are expected to enhance the positioning accuracy and solution availability where especially not enough numbers of GPS satellites are visible. As of today, precise orbits and clock data are available not only for GPS but also for GLONASS. This provides an opportunity to apply the PPP technique to GPS and GLONASS observations. In this study, performance of the PPP method is assessed in a dynamic environment using GPS-only and GPS+GLONASS observations. Accordingly, a kinematic test is carried out at the Obruk Lake Dam in the Çorum province, of Turkey. The collected data is processed using a globally popular on-line processing service: the Canadian Spatial Reference System-Precise Point Positioning Service (CSRS-PPP) operated by the Geodetic Survey Division of Natural Resources Canada (NRCan). The results show that the combined GPS+GLONASS data produced almost the same level of accuracy with the GPS-only data if there is a sufficient number of GPS satellites with good geometry. In the extreme cases, such as the elevation of satellites above 40 degrees, the GPS cannot provide a solution. However, when data and both satellites systems are combined, it is then possible to provide the solution. The results also reveal that a dm-level of accuracy can be achieved with the PPP technique in a dynamic environment. This accuracy level largely meets the requirements of many marine applications, including precise hydrographic surveying, marine geodesy, navigation and oceanography.