Differential GPS Research Articles

Assessment of the Positioning Accuracy of DGPS and EGNOS Systems in the Bay of Gdansk using Maritime Dynamic Measurements

Differential Global Positioning Systems (DGPS) and the European Geostationary Navigation Overlay Service (EGNOS) are included in a group of supporting systems (Ground-Based Augmentation System (GBAS)/Space-Based Augmentation System (SBAS)) for the American GPS. Their main task is to ensure better positioning characteristics (accuracy, reliability, continuity and availability) compared to GPS. Therefore, they are widely applied wherever GPS failures affect human safety, mainly in aviation, land and marine navigation. The aim of this paper is to assess the predictable positioning accuracy of DGPS and EGNOS receivers using a vessel manoeuvring in the Bay of Gdansk. Two receivers were used in the study: a Simrad MXB5 (DGPS) and a Trimble GA530 (EGNOS), which were simultaneously recording their coordinates. The obtained values were compared with the trajectory computed using a geodetic Global Navigation Satellite System (GNSS) receiver (Trimble R10) connected to a GNSS network, ensuring an accuracy of 2–3 cm (p = 0·95). During a four-hour measurement session, the accuracy statistics of these systems were determined based on around 11,500 positionings. Studies have shown that both positioning systems ensure a similar level of accuracy of their positioning services (approximately 0·5–2 m) and they meet the accuracy requirements set in published standards.

Effects of Site-Dependent Errors on the Accuracy of C/A Code DGPS Positioning

Several differential GPS processing techniques can be used; for instance, single differencing and double differencing, which are popular in practice. Irrespective of the DGPS processing technique used, the ultimate accuracy of the user-location depends on the existence of non-common or site-dependent errors, which occur at the points of observation and the reference. Of these, the most common and dominant site-dependent error is the multipath. Therefore, this research evaluates the effects of site-dependent errors on C/A code differential GPS correction accuracies by providing special emphasis on the multipath error. For the analyses, four segments of about 24-hour continuous static C/A code based DGPS observations were conducted at three precisely known ground stations and four different multipath environments were introduced by placing three different types of artificial signal reflectors at one of the observation stations. By using the known GPS receiver-reflector configuration, pseudo-range multipath was precisely calculated for each observation segment. C/A code DGPS positioning accuracies before and after multipath mitigation were presented by evaluating the effect of the most dominant site-dependent error, i.e., multipath, on C/A code DGPS correction accuracies.

A CORS-Based Differential Correction Approach for AIS Mobile Stations.

In order to remedy the inadequacy of the sources of differential corrections in current automatic identification system (AIS) and to improve the positioning accuracy of AIS mobile stations using single-point positioning, a differential correction approach for AIS mobile stations based on the continuously operating reference station (CORS) network is proposed. In the approach, AIS server derives real-time pseudo-range differential corrections from each reference station in CORS network and generates the corrections for AIS mobile stations. Then AIS base stations transmit these differential corrections to mobile stations using broadcast or addressed binary messages for positioning. Load analysis and testing show that this approach can effectively meet the need for differential corrections for most AIS mobile stations under the condition that the occupancy rate of the AIS channel is less than 1% when using broadcast binary messages. In addition, since this method is based on the existing CORS network, it is straightforward to implement in engineering projects and does not require additional hardware upgrades to the existing differential global positioning system (DGPS) and AIS infrastructure.

Monitoring of large-scale deformation in mining areas using sub-band InSAR and the probability integral fusion method

ABSTRACTThe large-scale and rapid land subsidence that occurs in mining areas often leads to problems, such as densely spaced interference fringes and the temporal decorrelation of interferometric synthetic aperture radar (InSAR) interferograms. To solve these problems, sub-band InSAR is applied to monitor the large-scale deformation that occurs in mining areas. First of all, four different bandwidth images with three sub-band bandwidth parameters are used to extract simulated mining-induced subsidence with seven different deformation magnitudes. The results of the simulation experiment suggest the following conclusions. In monitoring subsidence with different deformation magnitudes using images with different bandwidths, an optimal monitoring value exists; wider image bandwidths lead to smaller optimal monitoring values and higher monitoring accuracies. Therefore, an appropriate sub-band bandwidth should be selected that depends upon the image bandwidth and the subsidence level to achieve optimal monitoring. The optimal sub-band bandwidth for monitoring subsidence of different magnitudes in mining areas is determined through simulation experiments, and these conclusions can provide a technical basis for selecting the appropriate sub-band bandwidth for the monitoring of subsidence in mining areas. Although sub-band InSAR can reduce the number of interference fringes and the difficulty of unwrapping, the simultaneous introduction of large amounts of noise leads to reduced monitoring precision, and the application of the probability integral method in the prediction of mine subsidence is more mature. Therefore, the combined use of sub-band InSAR and the probability integral fusion method to monitor mining-induced deformation is proposed in this paper. The probability integral method is used to perform noise peeling on the interferometric phases of the sub-bands to improve the monitoring accuracy of sub-band interferometry. Then, according to the results of the simulation experiment, the fusion method with the appropriate sub-band bandwidth parameters is applied to monitor the surface deformation associated with working face 52,304 from 2 December 2012 to 13 December 2012. Finally, the monitoring results are compared with the results of monitoring using conventional differential interferometric synthetic aperture radar (D-InSAR) and global positioning system (GPS) field survey data. The results show that the reliability and accuracy of the fusion method are much better than those of conventional D-InSAR in monitoring the large-scale deformation that occurs at the edges of subsidence basins.

Calibration of a three-dimensional laser Doppler velocimeter in a land integrated navigation system.

In the land navigation field, a laser Doppler velocimeter (LDV), which is able to measure the speed of a carrier, can be combined with a strapdown inertial navigation system (SINS) to form an integrated navigation system. To realize the integrated navigation positioning of a free motion carrier on the ground accurately, this paper introduces a split-reuse three-dimensional (3D) LDV. For the error parameters during application, a Kalman filtering calibration method with the assistance of a differential global positioning system (DGPS) is put forward in this paper. Two groups of integrated navigation experiments are designed to validate the effectiveness of this method and the universality of the obtained parameters. The experimental results show that the calibration method proposed in this paper is effective and the 3D LDV after compensation can greatly improve the positioning accuracy of the integrated navigation. The maximum horizontal position errors of the two experiments calculated by the dead reckoning of the 3D LDV and the gyroscopes are 4.2m and 2.9m, and the maximum altitude errors are 0.8m and 0.9m, respectively.

Performance Assessment of Multi-GNSS Precise Velocity and Acceleration Determination over Antarctica

A conventional Differential GPS (DGPS) techniques-based velocity and acceleration method (named here as ‘DVA’) may be difficult to implement in the Antarctic as there is a sparse distribution of reference stations over Antarctica. Thus, in order to overcome the baseline limitations and to obtain highly accurate and reliable velocity and acceleration estimates for airborne gravimetry, a network-based velocity and acceleration determination approach (named here as ‘NVA’), which introduces a wide network of stations and is independent of precise clock information, is applied. Here its performance for velocity and acceleration determination is fully exploited by using Global Positioning System (GPS), GLONASS, Galileo and BeiDou observations. Additionally, a standalone receiver-based method named ‘SVA’, which requires precise clock information, is also implemented for comparison. During static tests and a flight experiment over Antarctica, it was found that the NVA method yields more robust results than the SVA and DVA methods when applied to a wide area network. Moreover, the addition of GLONASS, Galileo and BeiDou systems can increase the accuracy of velocity and acceleration estimates by 39% and 43% with NVA compared to a GPS-only solution.

The Effect of Multipath on Single Frequency C/A Code Based GPS Positioning

The differential GPS (DGPS) technique is one of the most popular and comparatively accurate techniques available to enhance the positioning accuracy by minimizing most of the common errors. However, the ultimate accuracy of the user location depends on the remaining non-common errors (multipath, receiver clock, and noise), which occur at the points of observation and reference. Out of these errors, multipath is the most dominant and challenging error to predict and minimize. Single frequency C/A code based GPS receivers are popular due to their comparatively low cost compared to dual frequency (L1/L2) GPS receivers. This paper focuses on evaluating the effect of multipath error on single frequency C/A code based GPS positioning. For the analysis, 72,000 continuous GPS observations with one-second interval under four different multipath environments were conducted by utilizing three geodetic GPS units. Accordingly, the observations with more than 5cm on the 2D positional error, created by the effected multipath, were always less than 25%. Here, an average of 16% of observations exceeded 20cm in 2D positional error. Further, it was noted that the presence of multipath introduces significantly higher and comparatively lower 3D positional errors on DGPS observations. This could be due to the compensation of negative and positive effects caused by the multipath and other remaining non-common mode errors at the reference and user stations. In addition, C/A code based single frequency GPS observations were significantly influenced by multipath, not only by the close-by reflectors but also by the ground surface. The effect of multipath was about 50% of the total 3D positional error for the four tested multipath environments.

Accuracy Assessment of Digital Elevation Model Generated by SAR Stereoscopic Technique Using COSMO-Skymed Data

Radargrammetry technique using the stereoscopic synthetic aperture radar (SAR) images is used for the generation of a digital elevation model (DEM) of a region requires only the amplitude images. SAR stereoscopic technique is analogous to the stereo-photogrammetric technique where the optical stereoscopic images are used for DEM generation. While the advantages of the SAR images are their indifference to atmospheric transparency and solar illumination conditions, the side-looking geometry of the SAR increases the complexity in the SAR stereo analysis. The availability of high spatial and temporal resolution SAR data in recent years has facilitated generation of high-resolution DEM with greater vertical accuracy using radargrammetric technique. In the present study, attempt has been made to generate the DEM of Dehra Dun region, India, from the COSMO-Skymed X-band SAR data-pair acquired at 8 days interval through the radargrammetry technique. Here, radargrammetric orientation approach has been adopted to generate the DEM and various issues and processing steps with the radargrammetry technique have been discussed. The DEM was validated with ground measured elevation values using a differential global positioning system and the root-mean-square error of the DEM was found as 7.3 m. The DEM was compared with the reference DEM of the study area generated from the Cartosat-1 stereo data with a model accuracy of 4 m.

Application of Differential Global Positioning System and Path Planning to Robot Outdoor Patrol

Application of Differential Global Positioning System and Path Planning to Robot Outdoor Patrol

GPS Relative Navigation for the CanX-4 and CanX-5 Formation-Flying Nanosatellites

In November 2014 the CanX-4 and CanX-5 spacecraft became the first nanosatellites to demonstrate autonomous formation control with error less than 1 m. This feat was accomplished both in along-track formations at 1000 and 500 m range and projected circular orbit formations at 100 and 50 m. This control performance was enabled through carrier-phase differential GPS navigation techniques, providing online relative state estimates typically accurate to better than 10 cm. It was an important milestone on the road to regular and fully operational formation-flying missions. This paper provides an overview of the relative positioning algorithm design, presents an independent assessment of the receiver performance, and assesses the absolute and relative navigation results. The mission’s on-orbit results are compared with an independently determined orbit solution computed using the GPS High Precision Orbit Determination Software Tools at the German Aerospace Centre.

Vegetation and terrain drivers of infiltration depth along a semiarid hillslope

An improved understanding of the drivers controlling infiltration patterns in semiarid regions is of key importance, as they have important implications for ecosystem productivity, retention of resources and the restoration of degraded areas. The infiltration depth variability (ΔInf) in vegetation patches at the hillslope scale can be driven by different factors along the hillslope. Here we investigate the effects of vegetation and terrain attributes under hypothesis that these attributes exert a major control in ΔInf within the patches. We characterise the ΔInf within vegetation patches at a semiarid hillslope located at the Jornada Experimental Range at dry antecedent conditions preceding two winter frontal rainfall events. We measured these events that are typical during winter conditions, and are characterised by low intensity (0.67 and 4.48 mm h−1) and a total rainfall of 10.4 and 4.6 mm. High precision geo-referenced wetting front depth measurements were taken at various locations within the vegetation patches using differential GPS. Vegetation and terrain attributes were analysed to explain the ΔInf among the vegetation patches. The infiltration depths in the periphery of the patches were in general considerably deeper than those in the centre. The observations suggest that the upslope margin of the patches received additional water in the form of runon from upslope adjacent bare soil. Patch orientation with regard to the slope dictated the effect of the rest of the patch attributes and the distance to the hillslope crest on ΔInf. We found that primarily patch orientation, followed by shape and size modulate lateral surface water transport through their effects on overland flow paths and water retention; something that would be obscured under more simplistic characterisations based on bare versus uniform vegetated soil discrimination.

Coupling terrestrial LiDAR and video imagery to perform 3D intertidal beach topography

This study investigates the possibility of combining two shore-based remote sensing techniques, 2D LiDAR and video imagery, to measure 3D intertidal beach topography. The shoreline elevation, measured on a single cross-shore section of the beach by a 2D LiDAR, was combined with the video-derived shoreline contour to finally obtain intertidal beach topography. Vertical root-mean-square error between differential GPS and remotely-derived intertidal beach profiles had an average value of 0.12 m, with maximum disparities of 0.14 m. Two 3D Digital Elevation Models (DEMs) of the beach produced over two tidal cycles demonstrated the feasibility of shore-based LiDAR-video system of describing in detail the short-term morphological evolution of the intertidal area. Results suggest that the LiDAR-video system can improve the capability of remotely surveying intertidal beach topography providing high quality measurements.

Deep-seated gravitational slope deformations triggered by extreme rainfall and agricultural practices (eastern Michoacan, Mexico)

The study of deep-seated gravitational slope deformations (DSGSD) in Mexico is scarce; therefore, their localization and causes are highly overlooked. The present paper examines the characterization of the DSGSD of Jungapeo and Las Pilas in eastern Michoacan state, currently active and endangering their inhabitants. An integrated study, including detailed lithology, morpho-structural inventories, analysis of land use, and pluviometric regime, was performed and complemented with differential global positioning system monitoring networks. Both landslides developed over highly weathered volcano-sedimentary rocks. On the one hand, the Jungapeo landslide has an estimated volume of 990,455 m3 with steady decreasing velocity rates from 41 to 15 cm/month in the first monitoring period to 13–3 cm/month in the last one. On the other hand, the Las Pilas landslide estimated volume is about 1,082,467 m3 with a stable velocity rate of 1.3 to 0.1 cm/month. Despite the multi-storeyed style of activity, two behaviors of instability were distinguished: slow deformation and secondary landslide stages. The conditioning factors for slow deformation in both DSGSD are the combination of weathered lithology with clay- and sand-rich content, and the shift toward intensive monoculture. The triggering factor is related to excess water produced by an inefficient flood-irrigation system that also generates an atypical acceleration behavior in both landslides during the dry season. The DSGSD activity thus predisposes the generation of tension cracks and secondary scarps from which the collateral landslides are triggered by atypical rainfall, such as that of 2010.

Toward a Definition of Minoan Agro-Pastoral Landscapes: Results of the Survey at Palaikastro (Crete)

Agricultural production and the palatial redistribution of staples have played a key role in the debate concerning the emergence of social complexity in Minoan Crete. However, much of the focus has fallen on major settlements where such products were consumed, rather than on the landscape where agricultural surplus was produced. While there is no shortage of landscape surveys on Crete, their emphasis has typically been on the distribution of rural settlements instead of on identifying landscape structures and arrangements—such as terraces, enclosures, and field systems—that might provide data about a territory's economic focus. A key aim of the new survey at Palaikastro has been to address this bias. By combining extensive archaeological survey with differential GPS (DGPS) measurements, high-resolution aerial photography, and microrelief generation and analysis, the project has identified hundreds of structures, forming an almost continuous fossilized landscape and providing important clues on landscape management practices. The results highlight the importance of pastoral practices, to which a large part of the landscape was dedicated. Agricultural arrangements were also documented in the form of terraced areas adapted for dryland agriculture and reflecting concerns for soil retention. We argue that a highly structured landscape, indicative of pressures in land use, was established during the Middle and Late Minoan periods across Palaikastro's territory. This article is also available as open access on AJA Online.

Late Quaternary tectonic activity and shortening rate of the Beiluntai fault zone in the South Tianshan, Xinjiang, NW China

The Beiluntai fault is a Holocene active fault and is the boundary fault between the South Tianshan and Tarim Basin. Since the Late Quaternary, the continuous activities of the Beiluntai fault have caused dislocation, deformation, and fold uplift of multi-phase alluvial geomorphologic surfaces. Using a high-precision differential global positioning system, we measured the fault scarp morphology of multi-phase geomorphologic surfaces in the Akeaiken and Zhuanchang sections of the Beiluntai fault. Via large-scale active fault mapping, we found that the Akeaiken section is dominated by thrusting, while the Zhuanchang section is dominated by fold uplift. We obtained the ages of the different phases of the geomorphologic surfaces (Fan4, Fan3b, Fan3c, and Fan2) using the optically stimulated luminescence dating method. We found that since the formation of the Fan4 geomorphologic surface, the crustal shortening rate (approximately 2.4 mm/a) of the Akeaiken section has remained basically constant. However, the crustal shortening rate of the Zhuanchang section in the south–north direction (1.43–1.81 mm/a) during the Late Quaternary was significantly less than that in the Akeaiken section, suggesting that the crustal shortening rate in the south–north direction of the Beiluntai fault zone decreases from west to east. A comprehensive comparison of the South Tianshan piedmont thrust-and-fold belt system also showed that the crustal shortening rate decreases from west to east.

Soil Fertility Mapping of Different VDCs of Sunsari District, Nepal Using GIS

Soil fertility degradation has become a major problem for agricultural management in Nepal. A detailed soil fertility status of different VDCs of Sunsari district was investigated during 2015 and soil related crop production constraints were identified for proper utilization of agricultural land. Total 131 numbers of geo-referenced (GPS based) composite surface soil samples (0-15 cm) were collected from eleven Village Development Committees of Sunsari District. The sample points were recorded with a differential global position system and mapped using Geographic Information System (GIS). Soils were analyzed for mechanical composition, pH, organic matter, total nitrogen, available phosphorus, potassium and micronutrients like Boron, Zinc, Copper and Iron. About 38.9% soils were found to be silty clay loam, 20.6% were silty clay, 19.1% were clay loam and 21.4% were of other textural classes. Most of the soils were acidic and only few were neutral and slightly alkaline in nature. Soil Organic matter varies from 3.57% to 0.28% with a mean value of 1.53 %. The mean total nitrogen, available phosphorus, potassium was found to be 0.08%, 44.37 kg/ha and 128.04 kg/ha respectively. The mean hot water extractable Boron, DTPA extractable Copper, Zinc and Iron was found to be 0.14, 0.06, 0.15 and 10.71 mg/kg respectively. Thematic maps were prepared for each soil parameters using ArcGis10.1 software and ordinary Kriging interpolation was used in order to predict values for not sampled locations. The fertility maps provide the readymade source of information about soil fertility status and serve as the decision making tool for successful raising and development of crops. It can be concluded from the above study that GPS and GIS based soil fertility maps helps farmers, scientists, planners and students in providing soil test based fertilizer recommendation for intensive and sustainable site specific crop production.Int. J. Appl. Sci. Biotechnol. Vol 6(2): 142-151

Accurate Three Dimensional Coordinates Measurements Using Differential GPS Real Time Kinematic Mode

The accurate 3-D coordinate's measurements of the global positioning systems are essential in many fields and applications. The GPS has numerous applications such as: Frequency Counters, Geographic Information Systems, Intelligent Vehicle Highway Systems, Car Navigation Systems, Emergency Systems, Aviations, Astronomical Pointing Control, and Atmospheric Sounding using GPS signals, tracking of wild animals, GPS Aid for the Blind, Recorded Position Information, Airborne Gravimetry and other uses. In this paper, the RTK DGPS mode has been used to create precise 3-D coordinates values for four rover stations in Baghdad university camp. The HiPer-II Receiver of global positioning system was used to navigate the coordinate value. The results will be compare with the Google Earth viewer coordinates values, the comparison shows that absolute error was few millimeters between actual and measured coordinate's values.

The Medieval cave village of Casalrotto (Mottola, Apulia): New data on the settlement and its necropolis from archaeological and geophysical measurements

This study concerns the main results of the research activity aimed at a new integrated knowledge of Casalrotto, a Medieval cave village (12th–13th century) near Mottola (Province of Taranto southern Italy). The research was based on archaeological and geophysical surveys performed in 2015. In particular, archaeological investigations have allowed the upgrading of the existing plan of the village through Differential Global Position System (DGPS) topographical surveys, while geophysical measurements, using ground-penetrating radar (GPR) and magnetometry in gradiometry configuration, have allowed a better delimitation of the necropolis and the detection of buried structures.

Extraction and accuracy assessment of DTMs derived from remotely sensed and field surveying approaches in GIS framework

Generating a high precision continuous surface is a key capability required in most geographic information system (GIS) applications. In fact the most commonly used surface type is a digital elevation model (DEM). Recently, there are some sources of remote sensing data that provide DEM information such as; LiDAR, InSAR and ASTER GDEM which ranged from very high to low spatial resolution. However, new methods of topographic field surveying still highly on demand e.g. Differential GPS and Total station devices. In both method of capturing the terrain elevation the post processing need to be applied to create a continuous surface from point clouds. Geostatistical analysis were used to interpolate the taken sample points from site into continuous surface. In current research, we examined the height accuracy of LiDAR point clouds and total station dataset with three non-adoptive interpolation models including, invers distance weightage (IDW), nearest neighbour (NN) and radial basis function (RBF) based on referenced DGPS points. RMSE and R square regression analysis were conducted to reveal the most accurate approaches in pilot study area. The results showed Lidar surveying (less than 0.5 meter RMSE) has higher height accuracy compared to Total station surveying (above 1 meter in RMSE) to extract DTM in flat area; while consumed less computational processing time. Moreover, IDW was the best and accurate interpolation model in both datasets to generate raster cautious terrain model.

Assessment of the position accuracy of a single-frequency GPS receiver designed for electromagnetic induction surveys

In precision agriculture (PA), compact and lightweight electromagnetic induction (EMI) sensors have extensively been used to investigate the spatial variability of soil, to evaluate crop performance, and to identify management zones by mapping soil apparent electrical conductivity (ECa), a surrogate for primary and functional soil properties. As reported in the literature, differential global positioning systems (DGPS) with sub-metre to centimetre accuracy have been almost exclusively used to geo-reference these measurements. However, with the ongoing improvements in Global Navigation Satellite System (GNSS) technology, a single state-of-the-art DGPS receiver is likely to be more expensive than the geophysical sensor itself. In addition, survey costs quickly multiply if advanced real time kinematic correction or a base and rover configuration is used. However, the need for centimetre accuracy for surveys supporting PA is questionable as most PA applications are concerned with soil properties at scales above 1 m. The motivation for this study was to assess the position accuracy of a GNSS receiver especially designed for EMI surveys supporting PA applications. Results show that a robust, low-cost and single-frequency receiver is sufficient to geo-reference ECa measurements at the within-field scale. However, ECa data from a field characterized by a high spatial variability of subsurface properties compared to repeated ECa survey maps and remotely sensed leaf area index indicate that a lack of positioning accuracy can constrain the interpretability of such measurements. It is therefore demonstrated how relative and absolute positioning errors can be quantified and corrected. Finally, a summary of practical implications and considerations for the geo-referencing of ECa data using GNSS sensors are presented.