GNSS Measurements Research Articles

An empirical model of ionospheric total electron content (TEC) near the crest of the equatorial ionization anomaly (EIA)

We present a geomagnetic quiet time (Dst > −50 nT) empirical model of ionospheric total electron content (TEC) for the northern equatorial ionization anomaly (EIA) crest over Calcutta, India. The model is based on the 1980–1990 TEC measurements from the geostationary Engineering Test Satellite-2 (ETS-2) at the Haringhata (University of Calcutta, India: 22.58° N, 88.38° E geographic; 12.09° N, 160.46° E geomagnetic) ionospheric field station using the technique of Faraday rotation of plane polarized VHF (136.11 MHz) signals. The ground station is situated virtually underneath the northern EIA crest. The monthly mean TEC increases linearly with F10.7 solar ionizing flux, with a significantly high correlation coefficient (r = 0.89–0.99) between the two. For the same solar flux level, the TEC values are found to be significantly different between the descending and ascending phases of the solar cycle. This ionospheric hysteresis effect depends on the local time as well as on the solar flux level. On an annual scale, TEC exhibits semiannual variations with maximum TEC values occurring during the two equinoxes and minimum at summer solstice. The semiannual variation is strongest during local noon with a summer-to-equinox variability of ~50–100 TEC units. The diurnal pattern of TEC is characterized by a pre-sunrise (0400–0500 LT) minimum and near-noon (1300–1400 LT) maximum. Equatorial electrodynamics is dominated by the equatorial electrojet which in turn controls the daytime TEC variation and its maximum. We combine these long-term analyses to develop an empirical model of monthly mean TEC. The model is validated using both ETS-2 measurements and recent GNSS measurements. It is found that the present model efficiently estimates the TEC values within a 1-σ range from the observed mean values.

Research on GPS Receiver Autonomous Integrity Monitoring Algorithm In the Occurrence of Two-satellite Faults

Reliability is an essential factor for GPS navigation system. Therefore, an integrity monitoring is considered as one of the most important parts for a navigation system. GPS receiver autonomous integrity monitoring (RAIM) technique can detect and isolate fault satellite. Based on particle filter, a novel RAIM method was proposed to detect two-satellite faults of the GPS signal by using hierarchical particle filter. It can deal with any system nonlinear and any noise distributions. Because GNSS measurement noise does not follow the Gaussian distribution perfectly, the particle filter can estimate the posterior distribution more accurately. In order to detect fault, the consistency test statistics is established through cumulative log-likelihood ratio (LLR) between the main and auxiliary particle filters (PFs).Specifically, an approach combining PF with the hierarchical filter is used in the process of two-satellite faults. Through GPS real measurement, the performance of the proposed GPS two-satellite faults detection algorithm was illustrated. Some simulation results are given to evaluate integrity monitoring performance of the algorithm. Validated by the real measurement data, the results show that the proposed algorithm can successfully detect and isolate the faulty satellite in the case of non-Gaussian measurement noise.

AN ALGORITHM FOR NETWORK REAL TIME KINEMATIC PROCESSING

Abstract. NRTK1 is an efficient method to achieve precise real time positioning from GNSS measurements. In this paper we attempt to improve NRTK algorithm by introducing a new strategy. In this strategy a precise relocation of master station observations is performed using Sagnac effect. After processing the double differences, the tropospheric and ionospheric errors of each baseline can be estimated separately. The next step is interpolation of these errors for the atmospheric errors mitigation of desired baseline. Linear and kriging interpolation methods are implemented in this study. In the new strategy the RINEX2 data of the master station is re-located and is converted to the desired virtual observations. Then the interpolated corrections are applied to the virtual observations. The results are compared by the classical method of VRS generation. 1 Network Real Time Kinematic 2 Receiver Independent Exchange Format

Derivation of 3-D surface deformation from an integration of InSAR and GNSS measurements based on Akaike's Bayesian Information Criterion

Derivation of 3-D surface deformation from an integration of InSAR and GNSS measurements based on Akaike's Bayesian Information Criterion

Extraction of geoid heights from shipborne GNSS measurements along the Weser River in northern Germany

Abstract In-land geoid models rely on several measuring techniques. The quality of those models is directly related to the spatial resolution of the measurement data. Occasionally, a local geoid model does not cover the coastal area at all and a local marine geoid simply does not exist. ShipborneGNSS measurementsmay provide away of overcoming this problem in coastal areas. However, several corrections to the raw measurements must be applied in order to account for systematic effects induced by ship dynamics and other static and dynamic impacts from tides, atmospheric pressure or wind stress. This paper presents the theoretical background for the method and the results of a case study in the estuary of the Weser River in Germany. A series of GNSS measurements were carried out aboard a ship and the approximate geoid height along the river was derived. For accuracy assessments of this method, the resultswere compared to the German Combined QuasiGeoid 2011 (GCG2011). The results are very promising and indicate the ability to extract geoid heights from shipborne GNSS measurements.

Development of the One Centimeter Accuracy Geoid Model of Latvia for GNSS Measurements

There is an urgent necessity for a highly accurate and reliable geoid model to enable prompt determination of normal height with the use of GNSS coordinate determination due to the high precision requirements in geodesy, building and high precision road construction development. Additionally, the Latvian height system is in the process of transition from BAS- 77 (Baltic Height System) to EVRS2007 system. The accuracy of the geoid model must approach the precision of about ∼1 cm looking forward to the Baltic Rail and other big projects. The use of all the available and verified data sources is planned, including the use of enlarged set of GNSS/levelling data, gravimetric measurement data and, additionally, the vertical deflection measurements over the territory of Latvia. The work is going ahead stepwise. Just the issue of GNSS reference network stability is discussed. In order to achieve the ∼1 cm precision geoid, it is required to have a homogeneous high precision GNSS network as a basis for ellipsoidal height determination for GNSS/levelling points. Both the LatPos and EUPOS® - Riga network have been examined in this article.

Estimation of small surface displacements in the Upper Rhine Graben area from a combined analysis of PS-InSAR, levelling and GNSS data

The intra-plate deformation of the Upper Rhine Graben (URG) located in Central Europe is investigated using geodetic measurement techniques. We present a new approach to calculate a combined velocity field from InSAR, levelling and GNSS measurements. As the expected tectonic movements in the URG area are small (less than 1mma−1), the best possible solutions for linear velocity rates from single-technique analyses are estimated in a first step. Second, we combine the velocity rates obtained from InSAR (line of sight velocity rates in ascending and descending image geometries), levelling (vertical velocity rates) and GNSS (horizontal velocity rates) using least-squares adjustment (LSA). Focusing on the Northern URG area, we analyse SAR data on four different image stacks (ERS ascending, ERS descending, Envisat ascending, Envisat descending) using the Persistent Scatterer (PS) approach. The linear velocity rates in ascending and descending image geometries, respectively, are estimated in an LSA from joint time-series analysis of ERS and Envisat data. Vertical velocity rates from levelling are obtained from a consistent adjustment of more than 40 000 measured height differences using a kinematic displacement model. Horizontal velocity rates in east and north direction are calculated from a time-series analysis of daily coordinate estimates at 76 permanently operating GNSS sites in the URG region. As the locations, at which the measurement data of PS-InSAR, levelling and GNSS reside, do not coincide, spatial interpolation is needed during several steps of the rigorous processing. We use Ordinary Kriging to interpolate from a given set of data points to the locations of interest with a special focus on the modeling and propagation of errors. The final 3-D velocity field is calculated at a 200 m grid, which carries values only close to the location of PS points, resulting in a mean horizontal and vertical precision of 0.30 and 0.13 mm a−1, respectively. The vertical component of the combined velocity field shows a significant subsidence of about 0.5 mm a−1 in the northern part of the graben coinciding with a well-known quaternary basin structure. Horizontal displacement rates of up to 0.8 mm a−1 in southeast direction are observed outside the graben, in reasonable alignment with the average direction of maximum horizontal stress. Within the graben, the velocity directions rotate toward east in the non-subsiding part, while an opposite trend is observed in the subsiding part of the graben. The complexities of the observed velocity field are compatible to the geomechanical situation in our investigation area which is characterized by a transition from a restraining to a releasing bend setting. Glacial isostatic adjustment is another potential source influencing the observed velocity field, as well as anthropogenic signals due to mining, oil exploration and groundwater usage that have been identified in some places.

Overview of 3D Documentation Data and Tools available for Archaeological Researches: case study of the Romanesque Church of Dugny-sur-Meuse (France)

Abstract. In this paper, the 3D documentation of the full structure of the Romanesque church of Dugny-sur-Meuse is discussed. In 2012 and 2013, a 3D recording project was carried out under the supervision of the Photogrammetry and Geomatics Research Group from INSA Strasbourg (France) in cooperation with C. Kraemer, archaeologist from Nancy (France). The goal of the project was on one hand to propose new solutions and tools to the archaeologists in charge of the project especially for stone by stone measurements. On the other hand, a simplified 3D model was required by the local authorities for communication purposes. To achieve these goals several techniques were applied namely GNSS measurements and accurate traverse networks, photogrammetric recordings and terrestrial laser scanning acquisitions. The various acquired data are presented in this paper. Based on these data, several deliverables are also proposed. The generation of orthoimages from plane as well as cylindrical surfaces is considered. Moreover, the workflow for the creation of a 3D simplified model is also presented.

The management of scarce water resources using GNSS, InSAR and in-situ micro gravity measurements as monitoring tools

South Africa is a water scarce country hence the careful monitoring and management of available water resources is critical for the wellbeing of the citizens of the country. A high percentage of the Earth’s water supply is stored underground which can be extracted either through pumping or using artesian pressure. This paper describes the application of GNSS, InSAR and In-Situ Micro Gravity measurements for the monitoring of an artesian wellfield in the Oudtshoorn District in the Western Cape province of South Africa. GNSS receivers were run continuously for a period of 133 days between March and August 2014 to detect possible surface subsidence during pumping and artesian free flow extraction of water in the wellfield. Two InSAR scenes were processed, one during the peak period of water extraction from the wellfield and the other approximately 4 months after all boreholes were closed and pumps switched off. A micro-gravity campaign was conducted over two days in the wellfield with the gravity meter co-located at one borehole which was opened on the second day of the campaign. The results from the GNSS monitoring showed a subsidence of approximately 15 to 20 mm at the peak of the free flow and pump while those from the InSAR and microgravity measurements were largely inconclusive.

A novel guidance and navigation system for MAVs capable of autonomous collision-free entering of buildings

Micro Aerial Vehicles for autonomous explorations of hazardous areas are predestined to support emergency and rescue forces. Especially the autonomous access to buildings is highly demanding due to insufficient GNSS reception in urban terrain and narrow passageways into buildings. Thus, this paper presents a complete flight system, consisting of guidance, navigation and control subsystems. All these elements are designed to enable safe flights into buildings. The guidance subsystem is divided into two parts. The vision based guidance part is manoeuvring the MAV on an intermediate position in front of the building. The potential field based guidance part enables the MAV to fly inside the buildings without having any collisions. For that, neither any prior knowledge about the building structure, nor any maps are necessary. To provide the flight guidance with information about the actual kinematic state of the MAV an accurate and robust navigation system not depending on GNSS measurements is used. The complete system is evaluated using simulated flight data.

Socio-educational and Scientific-technical Aspects of the Architectural Presentation of Spaces Intended for Religious Act in Romania

Resection is one of the most used methods that provides undeniable accuracy within topo-geodetic measurements using optical stations. The particularity of this method consists in setting up the total station above the new point (the point to be determined) and sighting the old fixed points. When the topo-geodetic measurements are performed using optical stations, usually some of the old fixed points sighted consist in the crosses that are located on the Tower of the churches in that locality. Although, worldwide the trend is to proceed to the GNSS measurements, at universities the courses contain a history of the topo-geodetic measurements for the students to be informed and learn about the classic methods and optical measuring methods. Getting through all stages characteristic to topo-geodetic measurements from simple to complex and presentation of the methods developed since the most ancient times up to the most modern and sophisticated used at the present time, are designed to provide to the students the necessary information for a better perception and comparative use of knowledge. Resection's features will be presented in this paper also highlighting the teaching methods, presentation of the Church as an institution and its social role in topo-geodetic measurements.

Redundancy and lack of information in specific problems of GNSS measurement processing

The paper focuses on four problems of GNSS measurement processing. The difficulty of problems lies in large volume of available data and limited resources of onboard equipment (phase measurement ambiguity resolution, fault detection and isolation); or in insufficient volume and fragmentarity of data (multiantenna heading determination in constrained conditions, navigation of geostationary satellites). Theoretical foundations of proposed solutions are given. Experimental results are provided.

Modern geodetic methods for high-accuracy survey coordination on the example of magnetic exploration

The purposes and problems of the international network of geomagnetic observatories INTERMAGNET are briefly described in the work. The importance of the development of the Russian segment of the network as a part of a system for monitoring and estimating geomagnetic conditions on the Russian territory is emphasized. An example of the use of modern high-precision geodetic equipment for coor-dinate referencing of field geophysical observation is described. Factors that distort the referencing of field observations in problems of survey, engineering, and technical geophysics are listed, as well as those related to detail and high-resolution geophysical surveying and those that require a corresponding accuracy of observation point coordination. The magnetic exploration at the site of the Yamal INTERMAGNET-standard observatory serves an example to describe a technique for geodetic provision of a detailed geophysical survey by means of joint use of differential GNSS measurements and electronic tacheometry. The main advantages and disadvantages of the technique suggested are listed.

Assessment of high-rate GPS using a single-axis shake table

The developments in GNSS receiver and antenna technologies, especially the increased sampling rate up to 100 sps, open up the possibility to measure high-rate earthquake ground motions with GNSS. In this paper we focus on the GPS errors in the frequency band above 1 Hz. The dominant error sources are mainly the carrier phase jitter caused by thermal noise and the stress error caused by the dynamics, e.g. antenna motions. To generate a large set of different motions, we used a single-axis shake table, where a GNSS antenna and a strong motion seismometer were mounted with a well-known ground truth. The generated motions were recorded with three different GNSS receivers with sampling rates up to 100 sps and different receiver baseband parameters. The baseband parameters directly dictate the carrier phase jitter and the correlations between subsequent epochs. A narrow loop filter bandwidth keeps the carrier phase jitter on a low level, but has an extreme impact on the receiver response for motions above 1 Hz. The amplitudes above 3 Hz are overestimated up to 50 % or reduced by well over half. The corresponding phase errors are between 30 and 90 degrees. Compared to the GNSS receiver response, the strong motion seismometer measurements do not show any amplitude or phase variations for the frequency range from 1 to 20 Hz. Due to the large errors for dynamic GNSS measurements, it is essential to account for the baseband parameters of the GNSS receivers if high-rate GNSS is to become a valuable tool for seismic displacement measurements above 1 Hz. Fortunately, the receiver response can be corrected by an inverse filter if the baseband parameters are known.

Navigation solution for a geostationary satellite based on its dynamic equations and occasional GNSS measurements

The paper offers solution to the problem of geostationary spacecraft navigation by navigation satellite signal measurements using nonlinear dynamic equations, which include perturbing factors such as non-sphericity of the gravitational field of the Earth, gravitational attraction of the Moon and the Sun, and direct solar radiation pressure. This solution uses the iterative Kalman filter based on UD-decomposition and is focused on the onboard implementation with limited computing resources. The estimates of current coordinates and velocity components obtained with the Kalman filter are taken into account when integrating nonlinear equations of a spacecraft motion up to the next solution time moment. With undetermined solar radiation pressure coefficient, the proposed solution proved efficient in terms of accuracy requirements for the spaceborne satellite navigation receiver. The tests were conducted using a GPS signal simulator and a receiver.

The role of GNSS in the navigation strategies of cost-effective agricultural robots

The current state of automation technology has led to a growing interest in the design and development of new use-case agricultural robots that can provide effective solutions to the challenges that agriculture is facing in industrialized countries, especially those derived from labor shortage and ever-increasing production costs. The advent of autonomous moderate-size machines in the field appears as a prospective way of promoting the sustainable production of food in Europe, Japan, and North America. However, there exist important obstacles to the broad expansion of autonomous robots in the field; reliability, safeguarding, system complexity, and cost-efficiency in particular rank high among the impediments to overcome before prototypes move into the production stage. Robot navigation is essential for the successful deployment of autonomous machines in conventional farms, as a minimum level of safety has to be granted at the same time that navigation engines cannot be too sophisticated for solutions to compete with current equipment. In such compromise, global navigation satellite systems play a key role due to its wide range of solutions, and an important number of limitations. In this research, a variety of experiments were conducted to determine the scope of GNSS solutions as a principal component of the navigation system of novel farm robots. Results showed that regardless of the quality of the receiver used, multipath and other uncontrollable errors eventually occur in the field, and therefore signal consistency must be continuously checked by the robot’s navigation engine. Different strategies based on the meticulous analysis of NMEA strings, the optimal combination of GGA and VTG messages, and the trajectory-based redundant estimation of robot planar states are proposed to enhance the integration of GNSS measurements in the navigation engine of agricultural robots.

Integration of Multi-Constellation GNSS Precise Point Positioning and MEMS-Based Inertial Systems Using Tightly Coupled Mechanization

We develop a new integrated navigation system, which integrates multi-constellations GNSS precise point positioning (PPP), including GPS, GLONASS and Galileo, with low-cost micro-electro-mechanical sensor (MEMS) inertial system, for precise positioning applications. To integrate GNSS and the MEMS-based inertial system, the process and measurement models are developed. Tightly coupled mechanism is adopted, which is carried out in the GNSS raw measurements domain. Both un-differenced and between-satellite single-difference (BSSD) ionosphere-free linear combinations of pseudorange and carrier phase GNSS measurements are processed. Rigorous models are employed to correct GNSS errors and biases. The GNSS inter-system biases are considered as additional unknowns in the integrated error state vector. The developed stochastic model for inertial sensors errors and biases are defined based on first order Gaussian Markov process. Extended Kalman filter is developed to integrate GNSS and inertial measurements and estimate inertial measurements biases and errors. Two field experiments are executed, which represent different real-world scenarios in land-based navigation. The data are processed by using our developed Ryerson PPP GNSS/MEMS software. The results indicate that the proposed integrated system achieves decimeter to centimeter level positioning accuracy when the measurement updates from GNSS are available. During complete GNSS outages the developed integrated system continues to achieve decimeter level accuracy for up to 30 seconds while it achieves meter-level accuracy when a 60-second outage is introduced.

Проблемы избытка и недостатка измерений ГНСС в специальных задачах вторичной обработки

Проблемы избытка и недостатка измерений ГНСС в специальных задачах вторичной обработки

Uso de información ionosférica obtenida por GNSS para detectar y medir fulguraciones solares

The Ionosphere, the partially ionized atmospheric region ranging from approximately 60 to +1000 km height, is typically affected by spatial and temporal variations, driven by Local Time (solar illumination), Latitude (magnetic field and solar illumination) and time (space weather, among seasonal and solar cycle dependence). It can be indirectly studied from the dual L-band frequency GNSS measurements by assuming the first order ionospheric delay approximation (the higher order ionospheric effects in GNSS typically constitute less than 0.1% of the overall ionospheric effect and only affects very precise applications). Moreover, the Ionosphere is affected as well by ionospheric waves, ,solar flares and other space weather effects. Recent modeling techniques and corresponding results are going to be summarized regarding to the daylight sudden overionization generated by the radiation associated to Solar Flares facing the Earth, and its measurement by means of Global Navigation Satellite Systems. This approach has already been implemented in real-time by the authors.

Globally exponentially stable attitude and gyro bias estimation with application to GNSS/INS integration

This paper deals with the construction of nonlinear observers for navigation purposes. We first present a globally exponentially stable observer for attitude and gyro bias, based on gyro measurements and two or more pairs of vector measurements. We avoid the well-known topological obstructions to global stability by not confining the attitude estimate to SO(3), but rather estimating a full rotation matrix with nine degrees of freedom. We also show how the attitude can be estimated under a relaxed persistency-of-excitation condition, with a single vector measurement as a special case. Next, we use the attitude observer to construct a globally exponentially stable observer for gnss/ins integration, based on accelerometer, gyro, and magnetometer measurements, as well as gnss measurements of position and (optionally) velocity. We verify the stability properties of the design using experimental data from a light fixed-wing aircraft.