Crustal motion at the permanent GPS station SVEA, Antarctica
Walyeldeen Hassan Edres
Master’s of Science Thesis in Geodesy No. 3119 TRITA-GIT EX 09-017
Division of Geodesy Royal Institute of Technology (KTH) 100 44 Stockholm, Sweden
August 2009
Crustal motion at the permanent GPS station SVEA, Antarctica
Author: W. Hassan
Supervisor: Dr. M. Horemuž
Examiner: professor. L. E. Sjöberg
Acknowledgements
First and foremost, I would like to take this opportunity to present my sincere gratitude and all kinds of respect to my Supervisor Dr. Milan Horemuž for his advice and guidance during this thesis work. I wish also to give my sincere thankfulness to Professor Lars Sjöberg for his guidance during the master courses as well as for his researches to help us to understand and solve many problems in Geodesy field. I would like to thank Mr. Erick Asenjo for his information about the SVEA station. My deepest gratitude also to Dr. Huaan Fan.
I would like to express my deepest appreciation and my respect to Sweden's country and especially to The Royal Institute of Technology for giving me the opportunity to study this master program.
I wish to express my gratitude to University of Khartoum for the scholarship, and also the teacher’s encouragement during my studies.
Many thanks with respect and love to my friends Faisal .A, Abdalla .A, Mokashfi .S, Abdalmajed .Y, khatim .S, Sedahmed .A, and his wife for all helps and the greatest time during my study. I would like to express my gratitude and all respect to Elbasher Mohammed and Osama Adam for their greatly supports, advises and helps.
I would like to thank my colleagues at the Geodesy and Geoinformatics master program for their kind friendship during my study.
I would like to express my sincere gratitude to my parents and my brother Anwar and my sisters for their encouragement and support in my whole life.
Finally, I also wish to thank everybody who has given me any kind of help to be successful in my life.
WalyEldeen Hassan Stockholm, May, 2009
I
Abstract
Since the last two decades, the Global Positioning System (GPS) has played a special role in Antarctica in the study of crustal motion. The permanent GPS station SVEA was installed in Antarctica by the division of geodesy at KTH. In November 14, 2004 the station became operational and provides continuous GPS data.
The objective of this study is to estimate the crustal motion at SVEA. The GPS data of the first five days of January, years 2005, 2006, 2007 and 2008 of station SVEA and six IGS reference stations have been processed using the Bernese GPS Software 0.5. Two methods (regression analysis and the Bernese software) were used to estimate the velocity at SVEA. In addition, horizontal velocities have been calculated from the plate motion calculator. A student’s t‐test has been used to judge whether the estimated motions are significant or not at risk level 5%.
The estimated velocity components (in mm/year) are 8.0±1.9 North, 1.0 ± 0.5 East and 0.1 ± 0.9 Up in linear regression analysis and 8.4 ±1.9 North, 1.1 ± 0.5 East and 0.2 ± 0.9 Up in the Bernese GPS Software. From the statistical test, the estimated velocity in the North component is significant in the Bernese GPS Software at risk level 5%. For the rest of the components, the estimated velocities are not significant for any method. The estimated horizontal velocities are mostly consistent with plate motion models. In order to estimate reliable and accurate crustal motion in the Up component, the time span should be longer than four years.
Keywords: Antarctica, Campaign, GPS, IGS, processing, session, SVEA, velocity.
II
Abbreviation
CODE Center for Orbit Determination in Europe
CIO Conventional International Origin
DoD Department of Defense
GNSS Global Navigation Satellite System
GPS Global Positioning System
LEO Low Earth Orbit
ICRF International Celestial Reference Frame
ICRS International Celestial Reference System
IGS International GNSS Service
IRM IERS Reference Meridian
IRP IERS Reference Pole
ITRF International Terrestrial Reference Frame
ITRS International Terrestrial Reference System
NAVSTAR Navigation System with Time and Ranging
NNR No Net Rotation
NNSS Navy Navigation Satellite System
QIF Quasi Ionosphere‐Free
RINEX Receiver Independent Exchange Format
RMS Root Mean Square
RTK Real Time Kinematic
SCAR Scientific Committee on Antarctic Research
SLR Satellite Laser Ranging
VLBI Very Long Baseline Interferomety
III
Contents
Acknowledgements ………………...……………………………………………………………...... I
Abstract ………………...…………………………..………………………………………………...... II
Abbreviation………………...……………………………………………………………………...... III
List of Figures………………...………….………………………………………………………...... IV
List of Tables ………………...………….………………………………………………………...... IIV
1 Introduction ...... 1 1.1 Background ...... 1 1.2 Thesis Motivation and Objectives ...... 2 1.3 Thesis Outline ...... 5 2 Concepts of the global positioning system (GPS) ...... 7 2.1 Geodetic Reference System ...... 7 2.1.1 International Celestial Reference System...... 7 2.1.2 International Terrestrial Reference System...... 7 2.2 GPS Overview ...... 9 2.3 GPS observables ...... 10 2.4 The code observation ...... 10 2.4.1 The phase observation ...... 10 2.5 GPS differencing ...... 11 2.5.1 The single difference ...... 11 2.5.2 The double difference ...... 11 2.5.3 The triple difference...... 12 2.6 The error sources in GPS...... 12 2.6.1 Satellite and Receiver clock error ...... 12 2.6.2 The Ephemeris error ...... 12 2.6.3 The atmosphere effect’s ...... 13 2.6.4 Multipath ...... 14 2.6.5 Antenna phase center ...... 14
3 Data Processing ...... 15 3.1 GPS Data ...... 15 3.2 Overview of the Bernese GPS Software Version 0.5 ...... 16 3.3 The Processing Steps ...... 17 3.3.1 Orbit Generation ...... 17 3.3.2 Receiver Clock Synchronization ...... 18 3.3.3 Baselines ...... 18 3.3.4 Preprocessing Phase Observations ...... 19 3.3.5 Screening of Post‐Fit Residuals ...... 19 3.3.6 First Network Solution ...... 20 3.3.7 Ambiguity Resolution ...... 20 3.3.8 Final network Solution...... 20 3.3.9 Flow Diagram for the Processing Steps ...... 21 4 The SVEA GPS Station Coordinates ...... 23 4.1 Combination of Solutions ...... 23 4.2 Stability of the Session Solution ...... 28 5 Velocity Estimation and Analysis ...... 31 5.1 Velocity estimation using Linear Regression Analysis ...... 31 5.2 Velocity Estimation using the Bernese GPS software ...... 33 5.3 The horizontal displacement of station SVEA ...... 34 5.4 Analysis of the Estimated Velocity ...... 36 5.5 The Horizontal Velocity from the Plate Motion Calculator ...... 37 6 Conclusions and Recommendations ...... 39 References ...... 41 Appendix ...... 43
List of Figures
Figure 1.1: The permanent GPS station SVEA ….……………..………………..…………………. 4
Figure 1.2: The Antarctica Map, the location of the reference IGS stations and station SVEA……………………………………………………………………………………..…………………………. 4
Figure 3.1: The baselines between SVEA station and the IGS stations …………… ..…..18
Figure 3.2: The flow diagram shows a summery of the processing strategy (for each session) by using Bernese GPS software……………………………….…………………….…… 21
Figure 4.1 The temporal coordinate change of station SVEA in the X coordinate …24
Figure 4.2: The temporal coordinate change of station SVEA in the Y coordinate …25
Figure 4.3: The temporal coordinate change of station SVEA in the Z coordinate …25
Figure 4.4: The temporal coordinate change of station SVEA in the North component ………………………………………………………………………………………………..…27
Figure 4.5: The temporal coordinate change of station SVEA in the East component…………………………………………………………………………………………………. 27
Figure 4.6: The temporal coordinate change of station SVEA in the UP component ………………………………………………………………………………………………… 28
Figure 5.1: The estimated horizontal velocity (mm/yr) using Linear Regression Analysis (black) is 8.1 ± 1.9 at azimuth 7.46 0.06°, and Bernese software (red) is 8.5 ± 1.9 at azimuth 7.12 0.06° …….…………………………………………………………… 35
Figure 5.2: The estimated velocity using Bernese GPS software and Linear Regression versus the calculated velocity from plate motion models in the North component ……………………………………………………………………………………………… 38
Figure 5.3: The estimated velocity using Bernese GPS software and Linear Regression versus the calculated velocity from plate motion models in the East component ……………………………………………………………………………………………… 38
IV
List of Tables
Table 1.1: The general information of the reference IGS stations (DAV1, OHI2, SYOG, MAW1, MCM4 and VESL) as well as SVEA GPS station………………………………. 3
Table 1.2: The approximate distance from station SVEA to thhe reference IGS stations …………………………………………………………………………………………………………… 3
Table 3.1: The campaigns and sessions that have been used for processing. The cross mark (X) refers to the observation data that are not available for some IGS stations while the right mark ( ) refers to the observation data that are available for all IGS stations………………………………………………………………………………………………16
Table 4.1: The residuals in (mm) between the combined solution and the session solution and the RMS in (mm) campaign 2005….………………………………………………… 28
Table 4.2: The residuals in (mm) between the combined solution and the session solution and the RMS in (mm) campaign 2006………………………………………………… 29
Table 4.3: The residuals in (mm) between the combined solution and the session solution and the RMS in (mm) campaign 2007…..…………………………………………… 29
Table 4.4: The residuals in (mm) between the combined solution and the session solution and the RMS in (mm) campaign 2008………………………………………………… 29
Table 5.1: The estimated velocity (mm⁄yr) and its standard error (± mm), using the Bernese GPS software……………….. ………………………………………………………….….. 32
Table 5.2: The residual errors in (mm) between the computed coordinates and the predicted coordinates, using Linear Regression Analysis...... …... 32
Table 5.3: The estimated velocity (mm⁄yr) and its standard error (± mm), using the Bernese GPS software ………..………………………………………………………………….. 33
Table 5.4: The residual errors in (mm) between the computed coordinates and the predicted coordinates, using the Bernese GPS software ………………….………………. 33
Table 5.5: The results of the statistical student’s t‐ test of the estimated velocities, using the Linear Regression Analysis and the Bernese GPS software ……………….. 36
Table 5.6: The calculated horizontal velocity from the Plate Motion Calculator….. 37
IIV
Chapter 1
1 Introduction
1.1 Background
In many applications of engineering, deformation measurement is a very important field, especially in geodesy to study the crustal motion and other geodynamic phenomena. In general there are two reasons for deformation studies: practical reasons and scientific reasons. Practical reasons include checking the stability of a structure and detecting the precursors of earthquakes; scientific reasons include understanding the mechanism of deformation [CHEN, 1983].
The methods for deformation monitoring can be divided into geodetic and non‐ geodetic methods [Horemuž, 2004]. In geodetic methods, the geodetic concepts and precise geodetic instruments were used to detect the deformation. This method has a wide application in global deformation such as landslides, tectonic and continental motion by using the geodetic space technique such as the global positioning system (GPS), Very Long Baseline Interferometry (VLBI) and satellite laser ranging (SLR). The geodetic methods were used in local deformation studies such as in dams, mining and structures (VASA ship) by using highly accurate instruments such as
Precise Level, Precise Theodolite, and Precise Total Station.
Usually, the geodetic deformation methods make use of the deformation network. The deformation network can be either a reference (absolute) network or a relative network. In absolute deformation networks, some of the network points (stations) are regarded as fixed points, which are placed outside the deformable body so that the deformation can be explained as absolute displacement of the object points. In the relative deformation network, all points (stations) are regarded as a subject of deformation, or in other words, all points are located inside the deformable body. The relative deformation networks are more complicated than the absolute ones due to the relative deformation (rotation and displacement) between the deformation network points [Caspary, 1988].
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1. Introduction
1.2 Thesis Motivation and Objectives
Since the mid 19th century, several researches in the geodesy field have been conducted in Antarctica using the photogrammetrical and astronomical techniques. In the last couple of decades, the Global Positioning System (GPS) has become a very important geodetic technique for monitoring deformation networks due to its high accuracy to detect the crustal motion and realize the Terrestrial Reference System in Antarctica [Dietrich, et al., 1998; Reinhard, et al., 2008].
In this thesis, we are going to use the permanent GPS station SVEA. It is installed in a rock area in Heimefrontfjella, Antarctica by the division of geodesy at the Royal Institute of Technology, Stockholm, Sweden, under the supervision of Professor Lars Sjöberg and Mr. Erick Asenjo. This station is equipped with a Trimble R7 GPS receiver with consumption 1.8‐2.3 W, antenna type ASHTECH with Radome code SNOW (ASH701945E_M SNOW) and steel tripod (see figure.1.1). The R7 GPS receiver is a dual frequency system with L C capability and the operating temperature of this receiver goes down to 40° C. Data are logged in a 1 GB Compact Flash memory; this memory can work down to 40° C. The data are collected annually by manually changing the memory card during the summer expeditions. At this time, the automatic transfer of data via satellite communication is not possible. The receiver is powered from six 12 V batteries, with a capacity of 600 Ah. The batteries are charged through solar panels until the sun is above the horizon and by wind generators during the period of winter darkness. This station has been in operation since the 1st of December 2004 and provides daily observation and navigation data of continuous measurements with a recording dual frequency (phase and code observations) in an interval sampling rate of 15 seconds. In addition, Real Time Kinematic (RTK) service will be available when station SVEA is open [Sjöberg, et al., 2006].
The main objectives of this thesis are to process the GPS data of the first five days of January, years (2005, 2006, 2007 and 2008) of the SVEA station using the Bernese GPS software 0.5 with International GNSS Service (IGS) reference stations in Antarctica as a reference (absolute) network, in order to estimate the possible crustal motions and plate motions at station SVEA.
2
1.2 Thesis motivation and objectives
Table 1.1 shows the general information about the reference IGS stations (DAV1, OHI2, SYOG, MAW1, MCM4 and VESL) and station SVEA, these IGS reference stations have been chosen depending on the approximate shortest distance from station SVEA as in Table 1.2. The map of Antarctica and the location of the IGS reference stations, as well as the location of station SVEA, is given in Figure 1.2.
Table 3.1: The general information of the reference IGS stations (DAV1, OHI2, SYOG, MAW1, MCM4 and VESL) as well as SVEA GPS station.
STATION NAME RECEIVER TYPE ANTENNA TYPE Location dav1 66010M001 ASHTECH UZ‐12 AOAD/M_T AUST Davis, Antarctica mcm4 66001M003 ASHTECH Z‐XII3 AOAD/M_T JPLA Ross Island, Antarctica ohi2 66008M005 AOA SNR‐8000 AOAD/M_T DOME O'Higgins, Antarctica maw1 66004M001 LEICA GRX1200 AOAD/M_T AUST Mawson, Antarctica syog 66006S002 TRIMBLE 4000SSI AOAD/M_T DOME East Ongle Island, Antarctica vesl 66009M001 TRIMBLE 4000SSI TRM29659.00 TCWD Vesleskarvet, Antarctica
SVEA TRIMBLE R7 ASH701945E_M SNOW Heimefrontfjella, Antarctica
Table 1.4: The approximate distance from station SVEA to the reference IGS stations.
Base line Distance in km SVEA ⎯ DAV1 2879.1 SVEA ⎯ MAW1 2574.2 SVEA ⎯ MCM4 3050.7 SVEA ⎯ OHI2 2153.9 SVEA ⎯ SYOG 1804.8 SVEA ⎯ VESL 422
3
1. Introduction
Figure 1.1: The permanent GPS station SVEA.
Figure 1.2: The Antarctica Map, the location of the reference IGS stations and station SVEA.
4
1.3 Thesis Outline
1.3 Thesis Outline
The thesis consists of six chapters. The first chapter is an introduction which describes the background of the deformation and the thesis motivation and objectives. Chapter two is oriented to give overview of the most important theory behind the GPS. Chapter three describes the processing strategy in the Bernese GPS software that has been used in this thesis. Chapter four contains the temporal change of SVEA coordinates and the daily repeatability results. Chapter five describes the estimation of the velocity by using two methods and then the statistical analysis of the estimated velocity as well as the calculated horizontal velocity from the plate tectonic motion calculator. The last chapter contains the conclusion of this study and some recommendations for the next work.
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6
Chapter 2
2 Concepts of the global positioning system (GPS)
In order to understand the GPS positioning it is important to understand the basic theories and concepts behind the global positioning system (GPS). This chapter gives an overview and the most important concepts of the GPS System.
2.1 Geodetic Reference System
2.1.1 International Celestial Reference System.
The space fixed inertial system is usually related to extraterrestrial objects like stars, quasars (extragalactic radio sources), planets, or the Moon. They are therefore, also is called the International Celestial Reference System (ICRS) [Seeber .G, 2003]. This system is a very important to describe the dynamic motion of the GPS satellite according to the principles of Newton’s mechanics .The ICRS was defined as the system with origin at the gravity center of earth and the Z axis toward the mean position of the celestial pole that has been defined by the Conventional International Origin (CIO) at epoch J2000.0 (The time epoch, 12 January 1 of year 2000) and the X‐axis is toward the vernal equinox, which is defined by a set of fundamental stars at epoch J2000.0 [Fan, 2007]. In January 1998 the International Earth Rotation Service (IERS) was established the International Celestial Reference Frame ICRF (The realization of ICRS) by using a set of 608 radio star observed by VLBI.
2.1.2 International Terrestrial Reference System.
The position of the points on (or close to) the Earth surface can be defined by the International Terrestrial Reference system (ITRS). This system was defined as the system with origin at the gravity center of Earth and the Z axis toward the mean position of the pole that has been defined by IERS Reference Pole (IRP). The Xaxis is toward the intersection of the Greenwich meridian plane which was defined by IERS Reference Meridian (IRM) in the equatorial plane and Yaxis is perpendicular with the Xaxis in the same equatorial plane [Fan, 2007]. The ITRS was realized by a number of terrestrial sites where the temporal effects (plate tectonic motion, tidal effects) were used to improve the ITRS [Hofmann‐ Wellenhof , et al, 2002], and the result of this realization is the terrestrial reference frame such as the World Global System 1984 (WGS 84) and the International Terrestrial Reference Frame .
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2. Concepts of the global positioning System (GPS)
• World Geodetic System 1984 (WGS84) :
The World Geodetic System 1984 (WGS84) is a Conventional Terrestrial Frame, realized by modifying the Navy Navigation Satellite System (NNSS), or TRANSIT. Associated to this frame is a geocentric ellipsoid of which is defined by the semi major axis a, the flattening of the ellipsoid f, the angular velocity of earth
rotation and the geocentric gravitational constant μ (Mass of earth include the atmosphere) .This frame has been used for GPS satellite system since 1987, and the origin and axes of WGS84 defined as [Fan, 2007]:
− The origin at Earth’s centre of mass including the oceans and the atmosphere. − The Z‐Axis from the origin toward the IERS Reference Pole (IRP) which is consistent with the CIO within precision of the realization (0.03 sec). − The X‐Axis at the Intersection of the Greenwich meridian plane with the equatorial plane. − The Y‐Axis is inside the equatorial plane and completes a right‐handed coordinate system (O-XYZ).
− International Terrestrial Reference Frame ITRF :
The International Terrestrial Reference Frame (ITRF) is a Conventional Terrestrial System, realized by a set of control ground points most of them equipped by Satellite Laser Ranging (SLR) or Very Long Base Line Interferometry (VLBI). This frame has been updated and designated
by ITRF , where is the last year in which data were used for the realization, and the origin and axes of (ITRF) defined as [Fan, 2007]:
− The origin at Earth’s centre of mass includes the oceans and the atmosphere. − The Z‐Axis from the origin toward the IERS Reference Pole (IRP) which is consistent with the CIO within precision of the realization (0.03 sec). − The X‐Axis at the Intersection of the Greenwich meridian plane with the equatorial plane. − The Y‐Axis is inside the equatorial plane and completes a right‐handed coordinate system (O-XYZ).
Example of ITRF : ITRF designates the frame of coordinate and velocities constructed in 1998 using all the IERS data available through 1997,
the last ITRF is designated ITRF which is coincided with WGS 84 at 10cm level [Fan, 2007].
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2. 2 GPS Overview
2.2 GPS Overview
In 1973, the US Department of Defense (DoD) commenced the development of NAVSTAR (Navigation System with Time and Ranging) Global Positioning System (GPS), and the first satellites were launched in 1978. The GPS system was controlled and oriented by the DoD but is partially available for civilian and foreign users. In general GPS satellite system consists of three segments (space segment; Control/monitoring segment and the User segment).
− The space segment consists of 28 satellites including spares. The satellites are in 6 orbits, at a height of 20200 km above the Earth. The six orbital planes are equally spaced, and are inclined at 55 degree to the equator. The system has been designed so that at least four to eight satellites will always be available in view at least 15 degree above the horizon, each GPS satellite broadcast L Band carrier frequencies, both frequencies are derived from the fundamental frequency (f =10.23 MHZ) . L1 = 1575.42 MHz (10.23 × 154) and L2 = 1227.6 MHz (10.23 × 120), wave length 19 cm and 24.4 cm respectively. The carriers are phase modulated to carry two codes, known as the P code (precise code) and the C/A code (Course/Acquisition code). In addition the GPS satellite broadcast continues information about the satellite clock, the satellite orbit, the satellite health status, and various other data, which are called GPS navigation message.
− The Control/monitoring segment consists of a master control station located near Colorado Springs, five monitor stations around the equator and three ground control stations. The main task of control/monitoring segment is to update the satellite orbit, satellite clock and the satellite states (health) by tracking the navigation signals by the monitor stations and sends their data back to the master control station, and then the calculated orbit, clock parameters and other parameters are uploaded to the satellite via one of the three ground control stations.
− The User segment consists of the user community and GPS receivers. In general the user community can be divided into two groups’ military users and civilian users. The GPS receiver types can be classified into four groups depends on the used code as the following [Sjöberg L E, 2007]:
i. C/A –code pseudorange receiver. ii. C/A –code carrier phase receiver. iii. P –code carrier phase receiver. iv. Y –code carrier phase receiver.
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2. Concepts of the global positioning System (GPS)
2.3 GPS observables
2.4 The code observation
The code observation is observing the signal traveling time from the satellite to receiver (the difference ∆ between the time of emission on the satellite ( ) and the reception time on the receiver tR )) as the following [Sjöberg, 2007]: