Papers by Demitris Delikaraoglou
This paper reports on recent results of simulations carried out for the purpose of evaluating the... more This paper reports on recent results of simulations carried out for the purpose of evaluating the likely geometric advantages from a future Global Navigation Flower Constellation (GNFC) through comparisons of its performance with that of the conventionally designed constellations of GPS and GALILEO satellite systems. The evaluation of all three satellite systems is performed on the basis of the spatially varying Geometric Dilution of Precision (GDOP) scalar indicator which, at each earth location, reflects at a time instance the contribution of the satellite-receiver geometry which, in turn, affects the resulting accuracy of the navigation solution. The area of interest for the simulations was essentially global, although confined to the zone with latitude bounds -60 deg to +70 deg. The main design concepts and the advantages of the Flower Constellations with respect to the conventional GNSS orbits are discussed. Simulation results are presented in detail which shows that the tested GNFC constellation yields improved navigation performance in terms of GDOP values worldwide, except for a few small areas along the equator and mostly at oceanic regions where, by comparison, the current GPS and GALILEO constellations show slightly better geometric performance.
Samarina. An assessment is also provided of the first results obtained from the repeated observat... more Samarina. An assessment is also provided of the first results obtained from the repeated observations and their combined adjustment, followed by a discussion on their reliability. The reported analysis focuses on the following crucial aspects: the accuracy and the stability of georeferencing, which is fundamental to make comparisons between different multi-temporal measurements; and the computation of deformation based on the survey observations between the established control points. Emphasis is given to the presentation of the results using a detailed 3D model of the church, created from terrestrial laser scanner point clouds. The methodology applied involves the analytical combination of multi-source measurements, i.e. GPS observations and classical surveying observations using appropriate high-end theodolites and total stations, in order to achieve the highest possible accuracy. The use of a time-of-flight laser scanner provided data for the 3D model creation. From the re-measuring of this network four times during a five month period and by comparing and analyzing the results of all measurements, it was possible to detect and obtain crucial information about the building's structural behaviour and the surrounding terrain's displacements and deformations. The results show a tendency of the surrounding ground to slide towards the northeast direction in a very slow tempo. However the observed displacements between characteristic control points on the building itself tend to demonstrate a slow varying periodic effect. The internal accuracy achieved in absolute positioning of the network points is of the order of ±2-3 millimeters.
In this paper we form relations for the determination of the elements of the E\"otv\"os matrix of... more In this paper we form relations for the determination of the elements of the E\"otv\"os matrix of the Earth's normal gravity field. In addition a relation between the Gauss curvature of the normal equipotential surface and the Gauss curvature of the actual equipotential surface both passing through the point P is presented. For this purpose we use a global Cartesian system (X, Y, Z) and use the variables X, and Y to form a local parameterization a normal equipotential surface to describe its fundamental forms and the plumbline curvature. The first and second order partial derivatives of the normal potential can be determined from suitable matrix transformations between the global Cartesian coordinates and the ellipsoidal coordinates. Due to the symmetry of the field the directions of the local system (x, y, z) are principal directions hence the first two diagonal elements of the E\"otv\"os matrix with the measure of the normal gravity vector are sufficient to describe the Gauss curvature of the normal equipotential surface and this aspect gives us the opportunity to insert into the elements of the E\"otv\"os matrix the Gauss curvature.
Canada) Incorporated; and the UNB Department of Surveying Engineering. The goal of this larger pr... more Canada) Incorporated; and the UNB Department of Surveying Engineering. The goal of this larger project is the development of an operational GPS capability for use in hydrographic surveys of Baffin Bay, starting during the 1983 field season. As the results in this report show, within the limitations of the GPS receiver so far available and of the present GPS constellation, this goal has been achieved. The expected launch of an additional GPS satellite and the expected delivery to Nortech of more advanced GPS receivers have the potential to enhance GPS performance in achieving this goal.
The objectives of future GPS-based geodetic systems have often been summarized as being twiforld:... more The objectives of future GPS-based geodetic systems have often been summarized as being twiforld: (a) to provide accurate positions (up tp 100s of kilometers with sub-decimeter accuracy, and at 10s of kilometers to less than 1-3 cm level) for the thousands of horizontal and vertical control points that comprise the current national geodetic databases in support of topographic mapping efforts and the growing need for better geodetic control for multipurpose cadastre systems; and (b) to measure vector baselines up to intercontinental distances with an accuracy better than 0.01 part per million and to apply this capability to the study of tectonic and crustal deformations. A conceivable strategy to meet such diverse needs mest be essentially tree-tiered: first, the higher level being the optimazation of methodologies and strategies for high precision orbit and positioning determinations of GPS-based geodetic measurements, including the optimal configurations for unified determination o...
We consider some theoretical and practical problems in establishing 3-D multi-station, geodetic c... more We consider some theoretical and practical problems in establishing 3-D multi-station, geodetic control networks using interferometric type observations of the Global Positioning System collected with Texas Instruments TI-4100 GPS receivers. The Canadian Geodetic Survey has established a precise calbration network in the Ottawa area where baselines ranging from 13 to 102 km were observed in 1984 with Ti-4100 GPS receivers. Six of these baselines were previously measured using the Macrometer V-1000 Interferometric Surveyor which provides an extra comparison with the TI-4100 results. Results of the Ti-4100 campaign are presented with emphasis on the associated analysis techniques and the comparison of the horizontal and vertical accuracies against independent terrestrial observations. ΠΕΡΙΛΗΨΗ Στο άρθρο αυτό γίνεται επισκόπηση συγκεκριμένων θεωρητικών και πρακτικών προβλημάτων, που προέκυψαν κατά την εγκατάσταση γεωδαιτικών δικτύων ελέγχου αποτελούμενων από πολλούς σταθμούς για τρισδι...
During the summer of 1983 the Earth Physics Branch (EPB) and the Canadian Geodetic Survey (CGS) o... more During the summer of 1983 the Earth Physics Branch (EPB) and the Canadian Geodetic Survey (CGS) of the Federal Department of Energy, Mines and Resources leased two Macrometer V-1000 GPS receivers in order to ecaluate this latest surveying technology and test various independent sets of processing software. The reults of this campaign on a precise GPS test network in the Ottawa area led CGS to use, in a subsequent campaign, four Macrometer receivers simultaneously, to survey a 22-station network in the province of Manitoba during the summer of 1984. This paper summarizes the results obtained during this campaign, with emphasis on the surveying logistics and the practical apsects of surveying with the Macrometer V-1000 receiver, data processing approaches and adjustment methods of the data. ΠΕΡΙΛΗΨΗ Κατά τη διάρκεια του καλοκαιριού του 1983 το Τμήμα Γεωφυσικής (Earth Physics Branch, EPB) και η Καναδική Γεωδαιτική Υπηρεσία (Canadian Geodetic Survey, CGS), του Υπουργείου Ενέργειας, Ορυκ...
At the invitation of Geodetic Survey, ISTAC, Inc. of Pasadena, California and Sunrise Internation... more At the invitation of Geodetic Survey, ISTAC, Inc. of Pasadena, California and Sunrise International of Mesa, Arizona, personnel of the Canadian Geodetic Survey (CGS) Division of the Department of Energy, Mines and Resources conducted a series of tests of the ISTAC-SERIES GPS Positioner Model 2002 and associated post-processing software. During a two-day period, 2-3 Apri I, 1986, four ISTAC-Model 2002 GPS receivers occupied eight stations on the Ottawa 3-D GPS Test Network. The baseline lengths between these stations ranged from some 2.2 to 222.3 km. From the simultaneous GPS observations, relative positions between stations of the test network were determined by processing the observations with the ISTAC-2002 data processor. The evaluation and analysis focused on the operation of the receivers and the accuracy of the relative position determinations. Baseline and network solutions were analyzed by comparison with coordinates previously determined by CGS from Texas Instruments 4100 a...
ΠΕΡΙΛΗΨΗ Η εν λόγω εργασία αποτελεί μέρος διδακτικού υλικού μιας σειράς σεμιναρίων GPS, που δόθηκ... more ΠΕΡΙΛΗΨΗ Η εν λόγω εργασία αποτελεί μέρος διδακτικού υλικού μιας σειράς σεμιναρίων GPS, που δόθηκαν το 1985, για το Καναδικό Ινστιτούτο Τοπογραφίας, σε τρια τοπικά τεχνικά επιμελητήρια Τοπογράφων Μηχανικών. Παρουσιάζεται μια λεπτομερή ανασκόπηση των μαθηματικών μοντέλων, που χρησιμοποιούνται για την ανάλυση των μετρησεων φάσης του φέροντος κύματος του GPS για γεωδαιτικές εφαρμογές. Εξετάζονται αρχικά τα χαρακτηριστικά του ραδιοσήματος, που εκπέμπουν οι δορυφόροι GPS, και αναλύονται οι διαφορές μεταξύ των μετρήσεων του κώδικα και των μετρήσεων της φάσης του φέροντος κύματος GPS. Περαιτέρω αναλύονται οι κύριες πηγές σφαλμάτων των εν λόγω μετρήσεων, των επιδράσεων τους στο σήμα GPS και τα τυπικά μεγέθη τους, και επεξηγείται η μορφή των αντιστοίχων μοντέλων, που ελαχιστοποιούν ή εξαλείφουν τα εν λόγω σφάλματα. Τέλος αναφέρονται οι τεχνικές που αφορούν την αντιμετώπιση του ιδιαίτερου προβλήματος της «ολίσθησης» των ακεραίων κύκλων φάσης, που παρουσιάζεται σε περιπτώσεις που διακόπτεται γ...
There currently exist unanswered questions regarding the effects of increased ionospheric variabi... more There currently exist unanswered questions regarding the effects of increased ionospheric variability on Global Positioning System (GPS) carrier phase signals at the northern geomagnetic latitudes. The paper describes the experience gained while processing GPS carrier phase observations collected in the Canadian aurora region. In order to gain a better insight into the behaviour of the ionosphere and to enhance the modelling of the ionospheric delays experienced by the GPS carrier signals in these high latitude regions, we have tested the use of an autoregressive process (AR) model to approximate the observed ionospheric delays over typical GPS sessions (3-5 hours) and over short (<20 km) to medium lengh (<75 km) baselines. Numerical results using dual frequency TI-4100 observations from a three-day dataset show that an AR model generally of order 2 to 5 would reproduce the L1/L2 ionospheric delays observed at a station to an rms level of 4 cm or better under unusually adverse...
The Canadian Geodetic Survey has recently initiated a study aimed at examining various candidate ... more The Canadian Geodetic Survey has recently initiated a study aimed at examining various candidate near-future scenarios for the combined application of Very Long Baseline Interferometry (VLBI), the Global Positionig System (GPS) and communication technoilogies in Canada. One such system, based upon selected VLBI and GPS stations and a number of automatic, active control GPS sites (ACS) appears extremely attractive. Each site will house a GPS receiver controlled by an inexpensive microcomputer housed in an enviromentally-controlled shelter which is to be operating automatically and continuously. This system should be capable of positioning both satellites and ground receivers to the decimeter or sub-decimeter level at a reasonable cost. Activities and plans for the implementation of the network of Active Control Points will be presented. ΠΕΡΙΛΗΨΗ Η Καναδική Γεωδαιτική Υπηρεσία (Canadian Geodetic Survey) πρόσφατα ξεκίνησε μια έρευνα με στόχο να εξετασθούν για το άμεσο μέλλον διάφορα σε...
Activities and plans for the implementation of a Canadian network of Active Control' GPS Poin... more Activities and plans for the implementation of a Canadian network of Active Control' GPS Points (ACP) are described. Each site will house a GPS satellite receiver controlled by a microcomputer monitoring the tracking of all visible satellites which is to operate automatically and continuously. The resulting Active Control System LACS) would act as both a GPS satellite tracking network for regional orbi t improvement over Canada, and as IIbase stati ons II fo r user differential positioning. Current plans call for the implementation of two to five such ACP sites as a prototype system. The design of the stations and of the central control facility are also described. ΠΕΡΙΛΗΨΗ Στο παρόν άρθρο περιγράφονται οι δραστηριότητες και ο σχεδιασμός για την εγκατάσταση, στον Καναδά, ενός Συστήματος Ενεργών Γεωδαιτικών Δικτύων από σημεία GPS (Active Control GPS Points - ACP). Σε κάθε σταθμό του εν λόγω δικτύου θα είναι εγκατεστημένος ένας δέκτης GPS, ο οποίος θα ελέγχεται πλήρως από ένα μικρ...
Canada's Pacific coast, an area of interplate deformation, and the Hudson Bay and its surroun... more Canada's Pacific coast, an area of interplate deformation, and the Hudson Bay and its surrounding region where postglacial rebound rates are high, offer a unique geodynamic and geographic environment for utilizing the capabilities of the Geodynamics Laser Ranging System (GLRS) and its associated laser altimeter for the measurement of large-scale crustal movements and the mapping of the heights of ocean, terrain and ice surfaces. The proposed investigations would exploit the synergistic use of GLRS , the Canadian networks for the monitoring of crustal movements and gravity change in these regions and the Canadian network of GPS Active Control Stations currently under implementation. The specific objectives would be threefold: (1) to demonstrate through simulations and experimental data collection _and analysis , the usefulness of GLRS ranging to passive reflectors as a technique of augmenting current GPS/VLBI monitoring operations for the study of (i) plate interactions at the we...
The theorcticul and practical aspects of the gravitational covariance functions are the subject o... more The theorcticul and practical aspects of the gravitational covariance functions are the subject of this work. The method of least squares collocation, as it introduced in Physical Geodesy for a theoretically exact combination of different data to a consistent anomalous gravity field, requires the knowledge of the covariances of the various gravitational quantities which are usually considered in a standard gravitational field estimation. These quantities are interelated through the field structure by linear operations. If the covariance of one of these quantities specified, that of the others can be computed. Thereby the application of least squares collocation can be established. Though the variations of the earth's gravity field can be represented by any of these quantities, there are certain purposes which impose the choice of either the covariance function of the gravity anomalies or the covariance function of of the disturbing potential as the basic covariance function of t...
A software package (In FOOTRAN 77) for the analysis of differential GPS observations is presented... more A software package (In FOOTRAN 77) for the analysis of differential GPS observations is presented for use in experiment planning, simulation studies and optimal design problems. The geodetic parameters include station coordinates, receiver clock error parameters and satellite orbit error parameters. A discussIon of the mathematIcal models on which the program is based provides an overview of the modes of differential GPS operations and the determination of station coordinates from simultaneous observatIons from a network of stations. ΠΕΡΙΛΗΨΗ Η εν λόγω εργασία περιγράφει αναλυτικά τα μαθηματικά μοντέλα, που χρησιμοποιούνται στο λογισμικό πακέτο VECA (VECtor Adjustment), που αναπτύχθηκε για την ανάλυση μετρήσεων διαφορικού GPS, για το σχετικό εντοπισμό σημείων. Οι γεωδαιτικοί παράμετροι, που υπολογίζονται, συμπεριλαμβάνουν τις συνταγμένες σταθμών, τις παραμέτρους που περιγράφουν τα σφάλματα των χρονομέτρων των δεκτών GPS, καθώς και παραμέτρους, που περιγράφουν τα σφάλματα των τροχιακ...
The rapid rate of evolution of space positioning systems such as LBI and GPS is changing the prac... more The rapid rate of evolution of space positioning systems such as LBI and GPS is changing the practice of geodesy as we have known it in the past few decades. There is already strong evidence that these new technologies may ~rovide the means of achieving a long sought goal of geodesists -a unified, worldwide geodetic control network tied to an inertial reference frame. Repeated L~I determinations at regular and frequent intervals will provide a precise record of the dynamic behaviour of Earth on a global scale, as well as changes in the relative position of the antennas on Earth1s surface with accuracies at the 5 to 10 cm level aChievable over observation periods of less than a day. GPS will permit rapid, economical positioning with accuracies of a few centimetres over distances of 20-100 km or more, thus replacing terrestrial methods for most geodetic tasks. In this paper possible scenarios currently under/consideration at the Canadian Geodetic Survey (CGS) for the application of L~...
Data produced by cameras,radiometers and a variety of other airborne sensors are used for remotel... more Data produced by cameras,radiometers and a variety of other airborne sensors are used for remotely scanning the Earth, gathering observations useful in such applications as agricultural development, deforestation and land use or providing a capability of data acquisition at times of such emergencies as flooding, forest flres and oil-spills. Coupling this remotely sensed data with other land-based information using geographical infonnation systems makes it more powerful. Today, the Global Positioning System (GPS) of satellites can provide the necessary georeferencing required for combining these capabilities effectively and accurately. In this paper, the use of kinematic stand-alone GPS or combined Inertial Navigation System (INS) and GPS techniques are reviewed. A widerange of existing and potential applications are discussed. Particularly, practical results showing the degree of consistency of differential GPS when multiple monitor stations are used are presented. Current advances ...
This is an internal Technical Report prepared by GAIA Inc., Memphis, Tennessee (D. Christodoulidi... more This is an internal Technical Report prepared by GAIA Inc., Memphis, Tennessee (D. Christodoulidis) and the Canadian Geodetic Survey, EMR Canada (D. Delikaraoglou) in the context of the Joint USA-Canada Project on the "Development ofa Cryospheric Information System for the Monitoring of Global Climate Change in Canada". It deals with the problem of the radar altimeter functional response over the continental ice sheets, which is considerable more complex than over the oceans. Causal factors identified in this complicated response include sloping surfaces, undulating ice surfaces with characteristic wavelengths at the same spatial scale as the altimeter's beam-limited footprint, and off-track reflections. Retracking methods using the altimeter's return pulse waveforms were applied on available GEOSAT altimeter data and show that the radar altimeter data is a very valuable source of topographic information of the continental ice sheets, including the inland seas (e.g...
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Papers by Demitris Delikaraoglou
BeiDou, offer three or more signal carriers for civilian use and much more redundant observables. The additional
frequencies can significantly improve the capabilities of the traditional geodetic techniques based on GPS signals
at two frequencies, especially with regard to the availability, accuracy, interoperability and integrity of highprecision
GNSS applications. Furthermore, highly redundant measurements can allow for robust simultaneous
estimation of static or mobile user states including more parameters such as real-time tropospheric biases and
more reliable ambiguity resolution estimates.
This paper presents an investigation and analysis of accuracy improvement techniques in the Precise Point
Positioning (PPP) method using signals from the fully operational (GPS and GLONASS), as well as the emerging
(Galileo and BeiDou) GNSS systems. The main aim was to determine the improvement in both the positioning
accuracy achieved and the time convergence it takes to achieve geodetic-level (10 cm or less) accuracy. To this
end, freely available observation data from the recent Multi-GNSS Experiment (MGEX) of the International
GNSS Service, as well as the open source program RTKLIB were used.