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e-magazine article

2013

Β Γκίκας, Ε Παπατζίκου, Δ Κάτσιος (2013) Ολοκληρωμένη Επιθεώρηση Ασφάλειας Οδικών Υποδομών με Χρήση Συστήματος Κινηματικής Χαρτογράφησης. Τεύχος 2013_10, Γεωδαισίας Δείγματα και Παραδείγματα, e-Περιοδικό Εργαστηρίου Ανώτερης Γεωδαισίας, Σχολή Αγρονόμων Τοπογράφων Μηχανικών, Εθνικό Μετσόβιο Πολυτεχνείο. [e-magazine article]

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2012

Ν Καλαμπόγιας, Μ Καμποσούλη, Γ Μπουμπάκης, Σ Φαχουρίδη και Δ Δεληκαράογλου (2012) Χαρτογραφώντας το πεδίο βαρύτητας της Γης ... σε High Definition: Η δορυφορική αποστολή GOCE Τεύχος 2012_08, Γεωδαισίας Δείγματα και Παραδείγματα, e-Περιοδικό Εργαστηρίου Ανώτερης Γεωδαισίας, Σχολή Αγρονόμων Τοπογράφων Μηχανικών, Εθνικό Μετσόβιο Πολυτεχνείο [e-magazine article]

Abstract: Nowadays, the problems caused in the environment by the human activities on earth have multiplied to such an extent that their impact is constantly getting worse. For this reason, international efforts have begun in order to deal with this problem in the best way possible. Exactly in this direction moves and the European Space Agency's (European Space Agency, ESA) "Living Planet Programme". This effort is focused around several Earth observation satellite missions, smaller in scope than in the past, but with specific goals and objectives. The ultimate goal is to better understand and gain more detailed knowledge of the natural forces and the various processes of the Earth and the Earth's environment in general, so that to be able to protect the Earth itself, and organize in a better way our lives on it. This effort is to include a total of nine satellite missions, the so-called "Earth Explorers". Two of these missions, were selected in 1999 to mark the beginning of this long-term programme - respectively, the so-called GOCE (Gravity Field and steady-state Ocean Circulation Explorer) and the ADM- Aeolus missions, which have as their main objective, the first to study of Earth's gravity field and the steady-state of the oceans and the other to study the forces occurring in the atmosphere. GOCE is the first among a series of the first six missions already defined by ESA which has the main aim of collecting highly accurate data about the Earth's gravitational field that will help us increase the level our knowledge on various physical phenomena such as earthquakes, internal processes that exist on Earth, activities of volcanoes, the ocean circulation which plays an important role in the energy transported to the whole world, as well as changes in the sea surface and in many other applications. The main product of the mission is expected to be a detailed model of the Earth's geoid which will be calculated with great accuracy (about 1 mgal or 10-5 m/s2 for gravity anomalies and 1-2 cm in the geoid heights) and high spatial resolution (around 100 km or less on a global scale). The previous article presented an overview of the technology, the technical data and the scientific achievements of the two preceding gravity missions, CHAMP and GRACE, which were to study the temporal changes of Earth's gravity field on a global scale and demonstrete how their data would relate to the physical processes occurring inside and at the surface of the planet. In this issue, the discussion is extended further to describe the ongoing mission of the GOCE satellite and outline some of its important results to date. Specifically, the innovative measuring technique being used, the so-called gravity gradiometry will be presented, together with the new images of the Earth's gravitational field that have already been computed from the satellite's data, thus showing, among many other applications, how the accurate recording of the gravity signals is emerging as the key element for tracking and estimating the direction of motion of the ocean currents.

2011

Δ Δεληκαράογλου (2011) Δοκιμάζοντας επιτυχημένες γεωδαιτικές τεχνικές ... στη Σελήνη Τεύχος 2011_06, Γεωδαισίας Δείγματα και Παραδείγματα, e-Περιοδικό Εργαστηρίου Ανώτερης Γεωδαισίας, Σχολή Αγρονόμων Τοπογράφων Μηχανικών, Εθνικό Μετσόβιο Πολυτεχνείο [e-magazine article]

Abstract: On September 10, 2011, onboard a Delta II rocket, NASA launched, after a one-day delay, the twin satellites of the much awaited satellite mission GRAIL (Gravity Recovery and Interior Laboratory). This mission signals once again the presence of man on the Moon, with the main objective to study the internal structure and gravitational field of the nearest planetary companion of the Earth, to renew the human imagination and to inspire the new generation of research scientists toward the implications of the new lunar exploration efforts. The information from the measurements of the Moon's gravity field from the two satellites will be used like X-rays to map the Moon's interior, from crust to core, so that to reveal the moon's subsurface structures and, indirectly, its thermal history. The mission also will answer longstanding questions about Earth's moon and provide scientists a better understanding of how Earth and other rocky planets in the solar system formed. The measurement technique to be used by GRAIL was pioneered by the joint U.S.-German Earth observing Gravity Recovery and Climate Experiment, or GRACE, mission launched in 2002. The Grace satellites measure gravity changes related to the movement of mass within Earth, such as the melting of ice at the poles and changes in ocean circulation.

Δ Κιτσάκης, Μ Βακαλοπούλου και Δ Δεληκαράογλου (2011) Χαρτογραφώντας το πεδίο βαρύτητας της Γης ... σε High Definition: Η δορυφορική αποστολή GRACE ΤΕΥΧΟΣ 7 - ΟΚΤΩΒΡΙΟΣ/ΝΟΕΜΒΡΙΟΣ 2011, [e-magazine article]

Abstract: From the start of the gravity mission GRACE (Gravity Recovery and Climate Experiment) in 2002, three strong earthquakes made their presence felt in the satellites: the Sumatra earthquake in 2004 which after Christmas day had caused the large tsunami in the Indian Ocean, the earthquake in Chile in 2010 (magnitude 8.8) and the Japan earthquake of magnitude 8.9 in March 2011, with the great death toll and damage caused by the huge tsunami that followed and the strong aftershock that caused the nuclear accident in Fukushima. The twin GRACE satellites, are part of a series of sophisticated geodetic satellites whose main objective is to map the Earth's gravitational field with unprecedented accuracy, global coverage and resolution. Prior to these two satellites, in 2000, the (CHAllenging Mini-Satellite Payload) or CHAMP opened the way and it was followed in 2009 by a new, more sophisticated mission aimed at more precise mapping of the gravitational field of the planet with the satellite GOCE (Gravity Field and Steady-State Ocean Circulation Explorer). The gravitational field of Earth is not static. Any redistribution of the mass of the planet - which may be caused by rain, floods, melting glaciers and earthquakes - lead to such change. The twin satellites in the GRACE mission, which are known among scientists with the nicknames "Tom" and "Jerry", have confirmed this with their measurements which showed that such changes affected their orbital motion, and hence giving scientists the opportunity to detect them by "monitoring" the changes in the distance-in-space between the two spacecraft. This article presents an overview of the new technology, the technical characteristics and the scientific achievements of the GRACE mission, and briefly also of the CHAMP mission, and how they allowed us to study the temporal changes in the gravitational field of Earth on a global scale and how these relate to natural the processes taking place in the interior and the surface of the planet. In the next issue, this overview will be extended to describe the ongoing GOCE mission, the innovative sensor fusion techniques being used to produce the new views of the gravitational field of Earth based on the first two years data and how, among many other applications, the satellite is showing that the precise mapping of the gravity field is emerging as a key element for monitoring the progress and direction of movement of ocean currents. It is shown briefly that the key factors which contributed to the significant progress made since the second half of the last century were due to the advancement of observing techniques for forecasting the behavior of the seas which increased our capability to collect continuous observations of the ocean (and atmosphere), especially after the development of advance geodetic satellite technologies, such as satellite altimetry, and how these data led to the understanding of the dynamics of the ocean.

Β Γκίκας (2011) Παρακολούθηση της δυναμικής συμπεριφοράς μεταλλικών κατασκευών με χρήση ρομποτικού γεωδαιτικού σταθμού (RTS) Τεύχος 2011_05, Γεωδαισίας Δείγματα και Παραδείγματα, e-Περιοδικό Εργαστηρίου Ανώτερης Γεωδαισίας, Σχολή Αγρονόμων Τοπογράφων Μηχανικών, Εθνικό Μετσόβιο Πολυτεχνείο [e-magazine article]

Abstract: The systematic monitoring and analysis of the dynamic behavior of metallic structures against seismic action, alternating loads of wind, snow and temperature variations of the environment is a key factor for their safe operation. Traditionally, determination of the kinematic characteristics of a structure is achieved indirectly by using various sensors such as accelerometers and gradiometers. In recent years the application of positioning systems like GPS (Global Positioning System) have demonstrated the capabilities and contributions of geodetic methods to monitor the dynamic behavior of metallic structures and other infrastructure works. Furthermore, recent developments in the technology of modern geodetic stations with automatic target recognition and tracking (Tracking Total Stations) make conventional surveying methods to be a reliable, alternative method for recording the kinematic characteristics of such structures.

Θ ΑΓΑΠΗΤΟΣ, Ε ΑΘΑΝΑΣΟΠΟΥΛΟΥ, Χ ΑΛΕΥΡΑΣ, Γ ΓΕΩΡΓΙΛΑΚΗΣ, Σ ΓΕΩΡΓΟΠΟΥΛΟΣ, Δ ΔΗΜΗΤΡΙΟΥ, Μ ΔΗΜΟΥ, Χ -Μ ΚΟΓΕΩΡΓΟΣ, Θ ΜΕΞΗΣ, Θ ΜΠΙΡΗΣ, Ε ΜΠΟΥΣΙΑΣ-ΑΛΕΞΑΚΗΣ, Κ ΝΤΑΛΟΥΚΑ, Ε ΠΑΣΧΑΛΙΔΟΥ, Π ΠΟΥΛΙΔΗΣ, Λ ΣΠΥΡΟΥ, Β ΣΤΟΥΡΝΑΡΑΣ, Μ -Α ΤΖΑΡΙΑ, Ε ΤΣΙΛΙΑΚΟΥ, ΦΙΛΛΙΠΑΣ, κ α ι Δ Δεληκαράογλου (2011) Δορυφόροι αλτιμετρίας εντοπίζουν "Hotspots" για την πιθανή εκμετάλλευση της κυματικής ενέργειας Τεύχος 2011_02, Γεωδαισίας Δείγματα και Παραδείγματα, e-Περιοδικό Εργαστηρίου Ανώτερης Γεωδαισίας, Σχολή Αγρονόμων Τοπογράφων Μηχανικών, Εθνικό Μετσόβιο Πολυτεχνείο [e-magazine article]

Abstract: The technique of satellite altimetry is used as a geodetic tool mainly for the systematic study of the dynamic state of the sea surface (e.g., tides, currents, waves), as well as to determine the marine geoid in the oceanic and open seas areas. The students of the Higher Geodesy Laboratory of the Department of Surveying Engineering, National Technical University of Athens, as part of the requirements for the course "Introduction to Earth's Gravity Field", during the fall semester of the academic year 2010-11, studied the role of satellite altimetry in a different application: that is, how to use it as a diagnostic tool to identify marine areas with the potential for the exploitation of wave energy in the Greek seas. Their tests with weekly samples of satellite altimetry data showed that it is possible to identify and propose areas where appropriate installation of wave energy harvesting facilities. The need for more extensive such studies, is readily understood if one considers the importance of utilizing more renewable energy resources today. The wave energy together with other clean energey resources such as wind, solar, geothermal, etc. form an inexhaustible renewable energy resource which is very friendly to the environment. If we consider our country's efforts to enter the global energy saving networks, and the fact that Greece is surrounded by extensive coastlines and a large marine space we can easily understand the economic, social and political importance of exploiting this abundant energy resource. A summary of the most representative results of the student's quick evaluations reveal how the altimetry carrying satellites "detect" wave energy hotspots in the Greek seas are presented in the following pages.

Γεωργία Κατσιγιάννη (2011) Διαφαινόμενες νέες προοπτικές από τη συνδυασμένη χρήση των επερχόμενων συστημάτων GNSS για κινηματικές εφαρμογές στον ελληνικό χώρο Τεύχος 2011_03, Γεωδαισίας Δείγματα και Παραδείγματα, e-Περιοδικό Εργαστηρίου Ανώτερης Γεωδαισίας, Σχολή Αγρονόμων Τοπογράφων Μηχανικών, Εθνικό Μετσόβιο Πολυτεχνείο [e-magazine article]

Abstract: The purpose of this thesis is the study and comparison of present and future Global Navigation Satellite Systems (GNSS). More specifically, the study is focused on the GPS (Global Navigation Satellite System), Galileo and EGNOS (European Geostationary Navigation Overlay System) systems which are compared in terms of their performance with respect to the conditions of satellite visibility, the dilution of precision (DOP), the level of Navigation System Precision (NSP) and system integrity. For this purpose several tracks of kinematic users were studied, using different means of transportation over the territory of Greece.

Κ Ζαφείρης, Γ Σουρής και Δ Δεληκαράογλου (2011) GPS Υπηρεσίες PPP: Ανάλυση μετρήσεων γρήγορα, εύκολα, αξιόπιστα, ΔΩΡΕΑΝ!!! Τεύχος 2011_04, Γεωδαισίας Δείγματα και Παραδείγματα, e-Περιοδικό Εργαστηρίου Ανώτερης Γεωδαισίας, Σχολή Αγρονόμων Τοπογράφων Μηχανικών, Εθνικό Μετσόβιο Πολυτεχνείο [e-magazine article]

Abstract: Establishing geodetic control networks for the purpose of serving various applications has been proven in practice that can be a costly task, even with the use of satellite positioning systems like GPS, EGNOS and GLONASS today or/and GALILEO in the near future. The main reason for the considerable costs is that such tasks require the deployment of multiple receivers in the field, so that to acquire simultaneous satellite measurements at many points which are needed in order to provide high accuracy. Moreover, the field work is followed by lengthy computational procedures which are required for the careful treatment of the collected observations. This computational procedure, in turn, it is necessary to be carried out by experienced personnel in the use of appropriate, usually complex, software which has to be of high standards so that to ensure accuracy and reliability of the results. Even with the use of the various services currently offered by various providers of Virtual Reference Stations networks (VRS Networks), such as the Hellenic Positioning System (HEPOS), while facilitating the necessary computational procedures, the cost can be quite high (e.g. because of subscription charges and service fees for the use of the services offered by the providers of such networks, extra charges associated with the downloading of needed data files from real or virtual network stations, etc.). However, it is now possible to utilize one of the many available nowadays free Online Services providing analysis of GPS measurements. The analyses of GPS data by these online services are based on a technique known as Precise Point Positioning (PPP). These services provide accurate results after processing the available measurements from a single (usually dual frequency) receiver operated by a single person in the field. The analysis of the measurements, in this case, does not require any specialized staff familiar with any special software, but only an internet connection in order to download the GPS measurement files to the Online Service. The only requirement are: the format of the files of the field measurements to be in one of the internationally accepted standards for GPS data exchange, such as the conventional RINEX or the Hatanaka Compact RINEX format, and to have an internet connection in order to upload the GPS measurement files to the Online Service. Typically, the results from the adjustment of the measurements uploaded to the Online Service are sent almost immediately (e.g. within a few minutes, depending on the file size) to the email address specified by the user. In order to demonstrate the ease of use and the capabilities of using the PPP technique through such an Online Service, we have selected a real geodetic network of nine points, which is part of network of permanent GPS stations installed and operated by the Institute of Geodynamics, National Observatory of Athens. The GPS data collected at these stations are available in daily files through NOA's web site at http://www.gein.noa.gr/gps.html. Using data from these stations, from different days and different durations of measurement sessions, we have looked at different aspects related to the PPP results obtained through an Online Service (e.g. solution convergence, repeatability) and came up with valuable conclusions regarding the possibilities and benefits of using these new techniques, which are particularly attractive and beneficial in cases whereby there is a need to establish geodetic networks in areas where there are no available networks of permanent stations GNSS (e.g. in remote areas) or where the existing geodetic infrastructure does not allow the establishment of appropriate reference stations for conducting kinematic RTK or network VRS/RTK surveys.

Δ Δεληκαράογλου (2011) Πως το GPS "είδε" το σεισμό Μ=9 στο Honshu της Ιαπωνίας Τεύχος 2011_01, Γεωδαισίας Δείγματα και Παραδείγματα, e-Περιοδικό Εργαστηρίου Ανώτερης Γεωδαισίας, Σχολή Αγρονόμων Τοπογράφων Μηχανικών, Εθνικό Μετσόβιο Πολυτεχνείο [e-magazine article]

Abstract: In the Higher Geodesy Laboratory of the Department of Surveying Engineering, National Technical University of Athens we have analyzed various data sets from several permanent GPS stations of the active network of the International GNSS Service (IGS, formely the International GPS Service) in the vicinity of the devastating earthquake near the East Coast Of Honshu, Japan, that hit on Friday 11/3/2011, 5:46:23 UTC. It is interesting that the kinematic positioning solutions detection for at least two nearby stations, approximately 140 and 430 km from the epicenter of the earthquake, showed ground movements of up to 3 meters, and also indicate clearly, minutes after the first shock, the intense post-seismic displacement waveforms. A summary of the most significant results of these quick evaluations reveal how GPS "saw" (detected) the big earthquake in Hunshu are presented in the following pages.