Low-cost Single-frequency GPS Research Articles

Real-Time Implementation of Relative Positioning Approaches Using Low-Cost Single-Frequency GPS Receivers and Raspberry Pi Platform for Agriculture Applications

Real-Time Implementation of Relative Positioning Approaches Using Low-Cost Single-Frequency GPS Receivers and Raspberry Pi Platform for Agriculture Applications

Investigation of a L1-optimized choke ring ground plane for a low-cost GPS receiver-system

AbstractBesides the geodetic dual-frequency GNSS receivers-systems (receiver and antenna), there are also low-cost single-frequency GPS receiver-systems.The multipath effect is a limiting factor of accuracy for both geodetic dual-frequency and low-cost single-frequency GPS receivers. And the multipath effect is for the short baselines dominating error (typical for the monitoring in Engineering Geodesy). So accuracy and reliability of GPS measurement for monitoring can be improved by reducing the multipath signal.In this paper, the self-constructed L1-optimized choke ring ground plane (CR-GP) is applied to reduce the multipath signal. Its design will be described and its performance will be investigated.The results show that the introduced low-cost single-frequency GPS receiver-system, which contains the Ublox LEA-6T single-frequency GPS receiver and Trimble Bullet III antenna with a self-constructed L1-optimized CR-GP, can reach standard deviations of 3 mm in east, 5 mm in north and 9 mm in height in the test field which has many reflectors. This accuracy is comparable with the geodetic dual-frequency GNSS receiver-system. The improvement of the standard deviation of the measurement using the CR-GP is about 50 % and 35 % compared to the used antenna without shielding and with flat ground plane respectively.

PERFORMANCE ANALYSIS OF LOW-COST SINGLE-FREQUENCY GPS RECEIVERS IN HYDROGRAPHIC SURVEYING

Abstract. The International Hydrographic Organization (IHO) has issued standards that provide the minimum requirements for different types of hydrographic surveys execution to collect data to be used to compile navigational charts. Such standards are usually updated from time to time to reflect new survey techniques and practices and must be achieved to assure both surface navigation safety and marine environment protection. Hydrographic surveys can be classified to four orders namely, special order, order 1a, order 1b, and order 2. The order of hydrographic surveys to use should be determined in accordance with the importance to the safety of navigation in the surveyed area. Typically, geodetic-grade dual-frequency GPS receivers are utilized for position determination during data collection in hydrographic surveys. However, with the evolution of high-sensitivity low-cost single-frequency receivers, it is very important to evaluate the performance of such receivers. This paper investigates the performance of low-cost single-frequency GPS receivers in hydrographic surveying applications. The main objective is to examine whether low-cost single-frequency receivers fulfil the IHO standards for hydrographic surveys. It is shown that the low-cost single-frequency receivers meet the IHO horizontal accuracy for all hydrographic surveys orders at any depth. However, the single-frequency receivers meet only order 2 requirements for vertical accuracy at depth more than or equal 100 m.

Improving the Quality of Low-Cost GPS Receiver Data for Monitoring Using Spatial Correlations

Abstract The investigations on low-cost single frequency GPS receivers at the Institute of Engineering Geodesy (IIGS) show that u-blox LEA-6T GPS receivers combined with Trimble Bullet III GPS antennas containing self-constructed L1-optimized choke rings can already obtain an accuracy in the range of millimeters which meets the requirements of geodetic precise monitoring applications (see [27]). However, the quality (accuracy and reliability) of low-cost GPS receiver data, particularly in shadowing environment, should still be improved, since the multipath effects are the major error for the short baselines. For this purpose, several adjoined stations with low-cost GPS receivers and antennas were set up next to the metal wall on the roof of the IIGS building and measured statically for several days. The time series of three-dimensional coordinates of the GPS receivers were analyzed. Spatial correlations between the adjoined stations, possibly caused by multipath effect, will be taken into account. The coordinates of one station can be corrected using the spatial correlations of the adjoined stations, so that the quality of the GPS measurements is improved. The developed algorithms are based on the coordinates and the results will be delivered in near-real-time (in about 30 minutes), so that they are suitable for structural health monitoring applications.

Stochastic Analysis of Low-Cost Single-Frequency GPS Receivers

Typically, dual-frequency geodetic grade GNSS receivers are utilized for positioning applications that require high accuracy. Single-frequency high grade receivers can be used to minimize the expenses of such dual-frequency receivers. However, user has to consider the resultant positioning accuracy. Since the evolution of low-cost single-frequency (LCSF) receivers is typically cheaper than single-frequency high grade receivers, it is possible to obtain comparable positioning accuracy if the corresponding observables are accurately modelled. In this paper, two LCSF GPS receivers are used to form short baseline. Raw GPS measurements are recorded for several consecutive days. The collected data are used to develop the stochastic model of GPS observables from such receivers. Different functions are tested to determine the best fitting model which is found to be 3 parameters exponential decay function. The new developed model is used to process different data sets and the results are compared against the traditional model. Both results from the newly developed and the traditional models are compared with the reference solution obtained from dual-frequency receiver. It is shown that the newly developed model improves the root-mean-square of the estimated horizontal coordinates by about 10% and improves the root-mean-square of the up component by about 39%.

DEVELOPMENT AND EVALUATION OF A UAV BASED MAPPING SYSTEM FOR REMOTE SENSING AND SURVEYING APPLICATIONS

Abstract. In recent years, unmanned aerial vehicles (UAVs) have increasingly been used in various application areas, such as in the remote sensing or surveying. For these applications the UAV has to be equipped with a mapping sensor, which is mostly a camera. Furthermore, a georeferencing of the UAV platform and/or the acquired mapping data is required. The most efficient way to realize this georeferencing is the direct georeferencing, which is based on an onboard multi-sensor system. In recent decades, direct georeferencing systems have been researched and used extensively in airborne, ship and land vehicle applications. However, these systems cannot easily be adapted to UAV platforms, which is mainly due to weight and size limitations. In this paper a direct georeferencing system for micro- and mini-sized UAVs is presented, which consists of a dual-frequency geodetic grade OEM GPS board, a low-cost single-frequency GPS chip, a tactical grade IMU and a magnetometer. To allow for cm-level position and sub-degree attitude accuracies, RTK GPS (real-time kinematic) and GPS attitude (GPS compass) determination algorithms are running on this system, as well as a GPS/IMU integration. Beside the direct georeferencing, also the precise time synchronization of the camera, which acts as the main sensor for mobile mapping applications, and the calibration of the lever arm between the camera reference point and the direct georeferencing reference point are explained in this paper. Especially the high accurate time synchronization of the camera is very important, to still allow for high surveying accuracies, when the images are taken during the motion of the UAV. Results of flight tests demonstrate that the developed system, the camera synchronization and the lever arm calibration make directly georeferenced UAV based single point measurements possible, which have cm-level accuracies on the ground.

Embedded Linux 기반 무인비행로봇의 저가 고정밀 위치 모니터링 시스템 구현 연구

Abstract: Recently, UFRs (Unmanned Flying Robots) have begun to be utilized in various areas for civilian and military applications. Due to this increased utilization, accidents involving UFRsare also increasing. To prevent or monitor accidents caused by UFRs, high-accuracy positioning information is one of the most important technical elements. This paper proposes an efficient UFR monitoring system which provides accurate UFR positioning information with low-cost onboard elements; a small ARM module based on an embedded Linux operating system, a low-cost single frequency GPS receiver with a cheap patch antenna, and a versatile wireless network interface module. The ground monitoring system employs a dual frequency GPS receiver to generate exact UFR coordinates with cm-level accuracy. By processing the UFR measurements based on the Inverse RTK (Real Time Kinematic) method, the ground monitoring system determines the cm-level accurate coordinates of the UFR. The feasibility of the proposed UFR monitoring system was evaluated by three experiments in terms of data loss and accuracy.Keywords: URF, embedded linux, GPS, inverse RTK, monitoring system

MONITORING OF LANDSLIDES WITH MASS MARKET GPS: AN ALTERNATIVE LOW COST SOLUTION

Abstract. The territory of Italy is seriously afflicted by hydrological risk, with 82% of its area affected by this phenomenon. In recent years, technologies and advanced research have played an important role in realizing complex automatic systems devoted to landslide monitoring and to alerting the population. Sometimes, the cost of these systems (communications network, sensors, software, technologies) prevents their use, and in particular the cost of sensors has a large impact on the final investment. For example, geodetic GNSS receivers are usually employed to conduct landslide monitoring, but they are costly. Nowadays, new technologies make it possible to use small and efficient low cost single frequency GPS receivers, which are able to achieve a centimetric or better level of accuracy, in static positioning. The rapid development and diffusion of the GNSS network to provide a positioning service has made it possible to use single frequency receivers, thanks to the use of virtual RINEX. This product is generated by a network of permanent stations. In this research, the actual performance of a mass market GPS receiver was tested, with the purpose of verifying if these sensors can be used for landslide monitoring. A special slide was realized, in order to conduct a dedicated test of the detection of displacements. Tests were carried out considering two factors: acquisition time and distance from the Virtual Station. The accuracy and precision of movement determination were evaluated and compared, for each test, considering the different factors. The tests and results are described in this contribution.

Performance Evaluation of USTEC Product for Single-Frequency Precise Point Positioning

Geodetic-grade dual-frequency GPS receivers are typically used for precise point positioning (PPP). Unfortunately, these receiver systems are expensive and may not provide a cost-effective solution in many instances. The use of low-cost single-frequency GPS receivers, on the other hand, are limited by the effect of ionospheric delay. A number of mitigation techniques have been proposed to account for the effect of ionospheric delay for single-frequency GPS users. Unfortunately, however, those mitigation techniques are not suitable for PPP. More recently, the U.S. Total Electron Content (USTEC) product has been developed by the National Oceanic and Atmospheric Administration (NOAA), which describes the ionospheric total electron content in high resolution over most of North America. This paper investigates the performance of USTEC and studies its effect on single-frequency PPP solution. A performance comparison with two widely-used ionospheric mitigation models is also presented.

GoGPS: open source software for enhancing the accuracy of low-cost receivers by single-frequency relative kinematic positioning

goGPS is a free and open source satellite positioning software package aiming to provide a collaborative platform for research and teaching purposes. It was first published in 2009 and since then several related projects are on-going. Its objective is the investigation of strategies for enhancing the accuracy of low-cost single-frequency GPS receivers, mainly by relative positioning with respect to a base station and by a tailored extended Kalman filter working directly on code and phase observations. In this paper, the positioning algorithms implemented in goGPS are presented, emphasizing the modularity of the software design; two specific strategies to support the navigation with low-cost receivers are also proposed and discussed, namely an empirical observation weighting function calibrated on the receiver signal-to-noise ratio and the inclusion of height information from a digital terrain model as an additional observation in the Kalman filter. The former is crucial when working with high-sensitivity receivers, while the latter can significantly improve the positioning in the vertical direction. The overall goGPS positioning accuracy is assessed by comparison with a dual-frequency receiver and with the positioning computed by a standard low-cost receiver. The benefits of the calibrated weighting function and the digital terrain model are investigated by an experiment in a dense urban environment. It comes out that the use of goGPS and low-cost receivers leads to results comparable with those obtained by higher level receivers; goGPS has good performances also in a dense urban environment, where its additional features play an important role.

Cycle slips detection algorithm for low cost single frequency GPS RTK positioning

Conventionally, cycle slips are detected by combining phase observations or phase/code observations. However, this is unsuitable for single frequency receivers in real time kinematic (RTK) positioning. Therefore, this study introduces an algorithm based on outlier detection concept to the detection and repair of cycle slip during GPS RTK positioning. The efficacy of the algorithm was verified on a low cost single frequency GPS receiver. To investigate the ability of the algorithm to detect error within a single cycle, minimum detectable bias (MDB) of less than one cycle was used as the index of success. Experiments verified the availability of the algorithm up to 96·12% (10° mask angle). The algorithm was able to accurately detect the time when cycle slips occur and precisely estimate their size in various simulated scenarios. Finally, tests were performed based on real data, and the results confirm that the proposed algorithm is applicable for single frequency RTK positioning.

Precise GPS Positioning with Low-Cost Single-Frequency System in Multipath Environment

Low-cost, single-frequency GPS systems provide economical positioning solutions to many geomatics applications, including GIS and low-accuracy surveying applications. Unfortunately however, the positioning accuracy obtained with those systems is not sufficient for many surveying applications. This is mainly due to the presence of ionospheric delay and multipath. In this research ionospheric delay is accounted for using regional high-resolution ionospheric maps produced by the US National Oceanic and Atmospheric Administration (NOAA). The major remaining constraint and challenging problem is multipath. This is because multipath is environmentally-dependent, difficult to model mathematically and cannot be reduced through differential positioning. This research proposes a new approach to identify multipath-contaminated L1 measurements through wavelet analysis. First, the difference between the code and carrier-phase measurements is estimated, leaving essentially twice the ionospheric delay, multipath and system noise. The ionospheric delay is largely removed by using high-resolution ionospheric delay maps produced by NOAA. The remaining residuals contain mainly low-frequency multipath, if it exists, and high-frequency system noise, which are decomposed using Daubechies family wavelets (db8). A satellite signal is identified as contaminated by multipath based on the standard deviation of the low-frequency part of the residual component. The L1 measurements obtained from the satellites with the lowest multipath are used to compute the final positions using two software packages, namely Trimble Total Control (TTC) and Bernese scientific processing software. The Magellan AC12 low-cost single-frequency GPS receiver was extensively tested in static mode. It is shown that accuracies within 5 cm are routinely obtained for baselines up to 65 km under various multipath environments.