Published by De Gruyter

Volume 9 Issue 1

Issue of Journal of Applied Geodesy

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Contents
Journal Overview

Publicly Available March 14, 2015

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Page range: I-IV

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Research Articles

March 14, 2015

Improved area-based deformation analysis of a radio telescope’s main reflector based on terrestrial laser scanning

Christoph Holst, Axel Nothnagel, Martin Blome, Philip Becker, Malwin Eichborn, Heiner Kuhlmann

Page range: 1-14

Abstract

The main reflectors of radio telescopes deform due to gravitation when changing their elevation angle. This can be analyzed by scanning the paraboloid surface with a terrestrial laser scanner and by determining focal length variations and local deformations from best-fit approximations. For the Effelsberg radio telescope, both groups of deformations are estimated from seven points clouds measured at different elevation angles of the telescope: the focal length decreases by 22.7 mm when tilting the telescope from 90 deg to 7.5 deg elevation angle. Variable deformations of ± 2 mm are detected as well at certain areas. Furthermore, a few surface panels seem to be misaligned. Apart from these results, the present study highlights the need for an appropriate measurement concept and for preprocessing stepswhen using laser scanners for area-based deformation analyses. Especially, data reduction, object segmentation and laser scanner calibration are discussed in more detail. An omission of these steps would significantly degrade the deformation analysis and the significance of its results. This holds for all sorts of laser scanner based analyses.

March 14, 2015

Precise Point Positioning using Multi-Constellation GNSS Observations for Kinematic Applications

Mahmoud Abd Rabbou, Ahmed El-Rabbany

Page range: 15-26

Abstract

Traditional precise point positioning (PPP) is commonly based on un-differenced ionosphere-free linear combination of Global Positioning System (GPS) observations. Unfortunately, for kinematic applications, GPS often experiences poor satellite visibility or weak satellite geometry in urban areas. To overcome this limitation, we developed a PPP model, which combines the observations of three global navigation satellite systems (GNSS), namely GPS, GLONASS and Galileo. Both un-differenced and between-satellite single-difference (BSSD) ionosphere-free linear combinations of pseudorange and carrier phase GNSS measurements are processed. The performance of the combined GNSS PPP solution is compared with the GPS-only PPP solution using a real test scenario in downtown Kingston, Ontario. Inter-system biases between GPS and the other two systems are also studied and obtained as a byproduct of the PPP solution. It is shown that the addition of GLONASS observations improves the kinematic PPP solution accuracy in comparison with that of GPS-only solution. However, the contribution of adding Galileo observations is not significant due to the limited number of Galileo satellites launched up to date. In addition, BSSD solution is found to be superior to that of traditional un-differenced model.

March 14, 2015

An Innovative Dual Frequency PPP Model for Combined GPS/Galileo Observations

Akram Afifi, Ahmed El-Rabbany

Page range: 27-34

Abstract

This paper develops a new dual-frequency precise point positioning model, which combines GPS and Galileo observables. The addition of Galileo satellite system offers more visible satellites to the user, which is expected to enhance the satellite geometry and the overall PPP solution in comparison with GPS-only PPP solution. However, combining GPS and Galileo observables introduces additional biases, which require rigorous modelling, including the GPS to Galileo time offset, and Galileo satellite hardware delay. In this research, a GPS/Galileo ionosphere-free linear combination PPP model is developed. The additional biases of the GPS/Galileo combination are lumped and accounted for through the introduction of a new unknown parameter, inter-systems bias, in the PPP mathematical model. It is shown that a subdecimeter positioning accuracy level and 25% reduction in the solution convergence time can be achieved with the developed GPS/Galileo PPP model.

March 14, 2015

Performance Analysis of Fault Detection and Identification for Multiple Faults in GNSS and GNSS/INS Integration

Muwaffaq Alqurashi, Jinling Wang

Page range: 35-48

Abstract

For positioning, navigation and timing (PNT) purposes, GNSS or GNSS/INS integration is utilised to provide real-time solutions. However, any potential sensor failures or faulty measurements due to malfunctions of sensor components or harsh operating environments may cause unsatisfactory estimation for PNT parameters. The inability for immediate detecting faulty measurements or sensor component failures will reduce the overall performance of the system. So, real time detection and identification of faulty measurements is required to make the system more accurate and reliable for different applications that need real time solutions such as real time mapping for safety or emergency purposes. Consequently, it is necessary to implement an online fault detection and isolation (FDI) algorithm which is a statistic-based approach to detect and identify multiple faults.However, further investigations on the performance of the FDI for multiple fault scenarios is still required. In this paper, the performance of the FDI method under multiple fault scenarios is evaluated, e.g., for two, three and four faults in the GNSS and GNSS/INS measurements under different conditions of visible satellites and satellites geometry. Besides, the reliability (e.g., MDB) and separability (correlation coefficients between faults detection statistics) measures are also investigated to measure the capability of the FDI method. A performance analysis of the FDI method is conducted under the geometric constraints, to show the importance of the FDI method in terms of fault detectability and separability for robust positioning and navigation for real time applications.

March 14, 2015

Analytic Error Assessment of Gyro-Free INS

Itzik Klein

Page range: 49-62

Abstract

Agyro-free INS consists of at least six distributed accelerometers capable of obtaining linear and angular acceleration and thereby capable of functioning as a conventional INS. Most of the research in the gyro-free field focused on seeking optimal accelerometer configurations and less attention was given to deriving appropriate statespace models and analytical error assessment as in a conventional INS. In this paper, we aim to fill this gap by contributing to three aspects of gyro-free theory. Firstly, practical gyrofree kinematic equations of motion and corresponding error-state models fitting to any set of accelerometers configuration are derived. Secondly, an analytic error assessment of the North Channel dynamics is provided enabling insight on the parameters affecting the gyro-free INS position error. Thirdly, a comparison between INS and gyrofree INS is performed, based on the derived analytical expressions.

March 14, 2015

A mascon adjustment of the Earth’s gravity field using GOCE gradiometer data

Eirik Mysen

Page range: 63-72

Abstract

We have subtracted known contributions from the GOCE gradiometer data that forms the basis of the fourth generation time-wise gravity field solution (TIM4), and mapped the residuals onto a local mascon model covering the south of Norway. Quasigeoids derived from combinations of the mascon adjusted TIM4 solution and EGM08 were then compared to height anomalies of a precise and dense GPS/levelling network. It was found that a mascon adjustment of TIM4 based on the first satellite cycle could improve the consistency between the corresponding quasigeoid and the network by about 0.5 cm. If the data foundation of the mascon solution was expanded to include also the next two-three satellite cycles then an improved consistency between the corresponding quasigeoid and the network height anomalies appeared on all spatial scales.

About this journal

Objective
The Journal of Applied Geodesy (JAG) is a forum for peer-reviewed research articles in the area of application of geodesy to engineering and other natural sciences. It publishes innovative contributions on sensor developments, multi-sensor systems and sensor data fusion focusing on the capture of georeferenced data. Hence topics related to navigation and mobile mapping will also be covered by JAG. The scope includes optical and microwave 3-D measurement techniques and other sensors for geotechnical measurements. Furthermore, applied geodesy articles from all areas of satellite-based geodetic networks, deformation measurements, deformation analysis, modelling of local geodynamic processes and the development of intelligent alert systems, measurement techniques for large construction sites and mechanical engineering will be presented. With increased use of the tools of Artificial Intelligence for sensor control, sensor fusion and data analysis, manuscripts on these topics with a strong emphasis on applied geodesy will also be published.

Topics

Navigation and mobile mapping
Optical and microwave 3-D measurement techniques
Satellite-based geodetic networks
Deformation measurements
Deformation analysis
Modelling of local geodynamic processes
Intelligent alert systems
Measurement techniques for large construction sites
Mechanical engineering
Sensor control
Sensor fusion

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Research articles

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