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![Space Geodetic Techniques
• ITRS Combination Centers
• Institute Géographique National (IGN), Paris France
• Jet Propulsion Laboratory, USA
• DGFI TUM – Techniques are combined based on
combination of NEQs of Gauss- Markov Model
• DTRF 2014
• Station coordinates
• Full set of EOP
[Bloßfeld, 2015]](https://image.slidesharecdn.com/itrfslideshare-190528090522/75/International-Terrestrial-Reference-Frame-11-2048.jpg)
![Space Geodetic Techniques – Colocation Sites
• Colocation Sites – Measurements between technique reference
points are necessary to combine station. These are called local
ties(Differential coordinates)
[Seitz, 2012]](https://image.slidesharecdn.com/itrfslideshare-190528090522/75/International-Terrestrial-Reference-Frame-12-2048.jpg)
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International Terrestrial Reference Frame
The document discusses the International Terrestrial Reference Frame (ITRF) and its fundamental role in geosciences. It explains that ITRF is crucial for monitoring Earth's motions and positions relative to space, and provides a realization of the International Terrestrial Reference System (ITRS) through 3D coordinates of points on Earth's surface. It then outlines the space geodetic techniques that provide input data to define ITRF, applications of ITRF in geosciences, current inconsistencies and limitations, and improvements and alternative reference frames being developed.
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International Terrestrial Reference Frame
- 1. INTERNATIONAL TERRESTIAL REFERENCEFRAME (ITRF) AND ITS FUNDAMENTAL ROLE FOR GEOSCIENCES Er. Dipesh Suwal Geomatics Engineer and Survey Officer ESPACE Student dipeshsuwal@gmail.com Blosfeld, 2017
- 2. Presentation Outlines • Motivation– Why do we need ITRF in Geoscience ? • What is ITRS and ITRF ? • Input Data - Space Geodetic Techniques • Role of ITRF in Geosciences • Current Inconsistencies and Limitations • Improvement and Alternative Reference Frames
- 3. Motivation – Whydo we need Reference Frames in Geoscience ? Pearlman Pearlman
- 4. Motivation – Whydo we need Reference Frames in Geoscience ? Monitoring The Earth System Pearlman
- 5. Motivation – Whydo we need Reference Frames in Geoscience ? EVERYTHING IS MOVING ! • Earth, along with all celestial bodies are not static, they rotate, revolve or undergo deformations. • Some of the examples are : • Plate motions • Polar motion • Earth’s rotation in motion • Loading effects on Earth’s crust due to ice, ocean, atmosphere • Horizontal Deformations due to Earthquakes • Vertical Deformation due to Glacial Isostatic Adjustment • Continuous monitoring is absolutely crucial. • Motions and positions are relative concepts and are described with respect to some reference.
- 6. ITRS and ITRF •ITRS is a world spatial reference system co-rotating with the Earth in space ITRS ITRF International Terrestrial Reference System International Terrestrial Reference Frame Conceptual or Theoretical Definition Realization of ITRS – Quantitatively describe positions and motions on the Earth’s crust Concept is ideal reference system Realization is based on parameters chosen. Not unique. Other Reference System : ICRS Other Frames : ICRF
- 7. International Terrestrial ReferenceSystem • ITRS is defined as specific GTRS defined within IUGG Resolution 2, 2007 • Origin : coincides with geocentre or CM of the Earth • Orientation : is equatorial and equal to orientation initially given by BIH at epoch 1984 • Scale : is consistent with TCG time coordinate for geocentric local frame Note: GTRS- Geocentric Terrestial Reference System, BIH : Bureau Intenational de I’Heure, TCG –Temps-coordonnée géocentrique, IUGG – International Union of Geodesy and Geophysics Royal Observatory of Belgium
- 8. International Terrestrial ReferenceFrame (ITRF) • Datum definition of ITRF • Reference ellipsoid : Geodetic Reference System 1980 (GRS 80) • Origin : realized through SLR • Scale: weighted mean average of VLBI and SLR • Orientation: orientation initially given by BIH at epoch 1984 • ITRS’s time evolution of orientation is ensured by No-Net rotation condition w.r.t horizontal tectonic motions • ITRS is realized and defined by IERS • through 3D coordinates and velocities of points fixed to the Earth's crust Note: IERS- International Earth rotation and Reference Systems Service
- 9. ITRF Input Data- Space Geodetic Techniques Very Long Baseline Interferometry Satellite Laser Ranging Doppler Orbitography and Radio positioning Integrated By Satellite ( DORIS) Global Navigation Satellite System (GNSS)
- 10. Space Geodetic Techniques TechnologyPros Cons VLBI Determine Earth Orientation parameters (EOP) Determine scale with high accuracy Only Few observing stations all over the world SLR Determine CM of Earth with high accuracy Determine scale with high accuracy Only Few observing stations all over the world GNSS Large number of distribution, high accuracy of adjusted parameters Complicated modelling of perturbation DORIS Large number of ground beacons homogenously distributed (no internet is required) Less accurate compared to other
- 11. Space Geodetic Techniques •ITRS Combination Centers • Institute Géographique National (IGN), Paris France • Jet Propulsion Laboratory, USA • DGFI TUM – Techniques are combined based on combination of NEQs of Gauss- Markov Model • DTRF 2014 • Station coordinates • Full set of EOP [Bloßfeld, 2015]
- 12. Space Geodetic Techniques– Colocation Sites • Colocation Sites – Measurements between technique reference points are necessary to combine station. These are called local ties(Differential coordinates) [Seitz, 2012]
- 13. Space Geodetic Techniques- Core Sites Blosfeld, M. , 2017 Fig. Core Site at Wetzell, Germany with all four Space Geodetic Technique in site
- 14. Role of ITRFin Geoscience? • Design Fault at bridge Construction in Laufenburg (2003), based on different reference frames
- 15. Role of ITRFin Geosciences DGFI-TUM realization of the International Terrestrial Reference System: DTRF2014
- 16. Role of ITRFin Geosciences Hanse, 2008
- 17. Role of ITRFin Geoscience? • Describe shape of the Earth and its orientation • Surveying - Positioning and Navigation • Modelling of post-seismic deformations e.g. earthquake • Monitoring of global sea level variations in space and time • Monitoring of displacements induced by postglacial rebound or ice melting • Georeferencing diverse data related to earth and environment Pearson, 2015
- 18. Current Inconsistencies andLimitations Mathis Blosfeld • ITRF is realized considering linear station motion only thus the obtained coordinates are only geocentric in a sense of mean • CM determined by SLR and not using • GNSS – high earth orbiting • DORIS – difficult modelling, complex structure of satellite • ITRF orientation is realized by NNR condition based on selected station network • which is not uniquely defined, depend on individual ITRS CC • Scale is realized as weighted mean scale of VLBI and SLR measurements • Not GNSS and DORIS scale
- 19. Current Inconsistencies andLimitations • Limitations due to no consideration of Non Linear station motions model • All Residual deformations which are modelled using piece-wise linear functions of time which is not enough. (except solid Earth tides, pole and atmospheric tides – Geophysical Model) • Other Limitations – • frequency of ITRF realizations every 3 – 5 years, • non-availability of ITRF coordinates after huge seismic activities • Japan after 2010 earthquake can’t use ITRF 2008 to relocate positions • inhomogeneous distribution of stations Khan et al., 2010
- 20. Improvement and AlternativeReference Frames • Alternatives - Epoch Reference Frames • Modelling of non linear station motion Pearson, 2015 • Realization of regional reference frames as densification of ITRF. Example European Terrestrial Reference System ( ETRF 89), NAD83, SIRGAS. Nepal National Deformation Model (Nepal NDM)
- 21. Summary • Why dowe need ITRF in Geoscience ? • What is ITRS and ITRF ? • Input Data from Space Geodetic Techniques • Role of ITRF in Geosciences – Some Applications • Current Inconsistencies and Limitations • Improvement and Alternative Reference Frames
- 22. References • Pearson, C.(2017) Progress on the development of a modernized geodetic datum for Nepal following the April 25, 2015 Mw7.8 Gorkha earthquake for Survey Department,Nepal. • Altamimi, Z., Metivier, L. & Collilieux, X., 2012. ITRF2008 plate motion model, J. geophys. Res., 117, doi:10.1029/2011JB008930. • Altamimi, Z., Boucher, C., Drewes, H., Ferland, R., Larson, K., Ray, J. & Rothacher, M., Combination of station positions and velocities, IERS Workshop on combination research and global geophysical fluids, 2002. • Altamimi, Z., Rebischung, P., Métivier, L. & Collilieux, X. (2016), ITRF2014: A new release of the International Terrestrial Reference Frame modeling nonlinear station motions, J. Geophys. Res. Solid Earth, 121, 6109– 6131, doi:10.1002/2016JB013098. • Altamimi, Z., ITRF and Co-location Sites, ENSG/LAREG, 6-8 Avenue Blaise Pascal, 77455 Marne-La-Vallee Cedex 2, France • Angermann, D., Blosfeld, M. & Seitz, M., Why do we need epoch reference frames ? • Kreemer, C., Blewitt, G. & Klein, E.C., 2014. A geodetic plate motion and Global Strain Rate Model, Geochem. Geophys. Geosyst., 15, 3849–3889. • Pearman, M., Global Geodetic Observing Systems and Core sites • Drewes, H. & Blosfeld, M., How to fix the geodetic datum for reference frames in geosciences applications • Drewes, H., Frequent epoch reference frame instead of instant station positions and constant velocities • Metivier, L., Collilieux, X., Alamimi, Z. & Lercier, D., The ITRF and its Scientific applications
Editor's Notes
- #4 The rotation is measured with respect to a frame tied to stellar objects called ICRF
- #5 Quantifying plate motion is essential to understand the mechanism of plate tectonics and its implications for geologic processes at plate boundaries, including how these processes relate to earthquakes and volcanic activity. Example is : NA12 reference frame developed by Blewitt et al. (2013) for crustal deformation studies in North America,
- #7 ITRF is a set of physical points with precisely determined coordinates in cartesian or geographic systems tied to ITRS ITRF provides stable coordinate system that allows us to measure change over space and time The (ITRF), based on a combination of station positions and velocities provided by space geodetic techniques (VLBI, SLR, GNSS and DORIS), permits the determination of precise absolute and relative motions of major tectonic plates.
- #8 (GTRS) is trihedron, whose basic vectors span a 3-dimensional, orthogonal and right-handed Euclidean vector space. Geocentric space-time coordinates within the framework of Special and General Relativity. It co-rotates with the Earth and is related to the GCRS through spatial rotations using the (EOP). EOP connects ICRF and ITRF. (TCG -) is a coordinate time standard intended to be for all calculations pertaining to precession, nutation, the Moon, and artificial satellites of the Earth. It is equivalent to the proper time experienced by a clock at rest in a coordinate frame co-moving with the center of the Earth: that is, a clock that performs exactly the same movements as the Earth but is outside the Earth's gravity well. It is therefore not influenced by the gravitational time dilation The scale is dependent on the modelling of some physical parameters,
- #9 and the absolute TRF orientation (unobservable by any technique) is arbitrary or conventionally defined through specific constraints. Earth orientation parameters measure the orientation of Earth with respect to inertial space (which is required for satellite orbit determination and spacecraft navigation) and to the TRF, which is precondition for long-term monitoring. Polar motion and UT1 track changes in angular momentum in the fluid and solid components of the Earth Intersection of axes of SLR antennae VLBI reference point GNSS reference point DORIS reference point
- #10 VLBI is a geometric technique: it measures the time difference between the arrival at two Earth-based antennas of a radio wavefront emitted by a distant quasar. 2. Satellite Laser Ranging (SLR) and Lunar Laser Ranging (LLR) use short-pulse lasers and state-of-the-art optical receivers and timing electronics to measure the two-way time of flight (and hence distance) from ground stations to retroreflector arrays on Earth orbiting satellites and the Moon. 4. or, in French, Détermination d'Orbite et Radiopositionnement Intégré par Satellite (in both case yielding the acronym DORIS) is a French satellite system used for the determination of satellite orbits (e.g. TOPEX/Poseidon) and for positioning.
- #11 pro: spherical (perturbations can be modeled accurately) and Low Earth Orbiting (LEO, high sensitivity w.r.t. Earth’s gravitational field) satellites allow to determine the Center of Mass of the Earth with very high accuracy. Precision, accuracy, long-term stability and reliability of the products can be improved by the combination of different observation techniques, which provide an individual sensitivity with respect to several parameters. The estimation of geodetic parameters from observations is mostly done by least squares adjustment within a Gauß-Markov model. The combination of different techniques can be done at three different levels: at the level of observations, at the level of normal equations and at the level of parameters
- #12 The activities like observations, data flow, data analysis and provision of results are coordinated by the international services of the IAG, e.g. IERS, IVS (International VLBI Service), ILRS (International Laser Ranging Service), IGS (International GNSS Service) and IDS (International DORIS Service).
- #13 Core Sites: Metsahovi, Hertebeesthoek, Washington, Yarragaddee Colocation Sites: Given the precision increase of the measurement of the space geodesy techniques and modelling, 1 mm precision or better should be the goal of all new local tie surveys. Without colocation sites, an inter technique combined TRF could not exist RFI issues influence the relative placement of instruments in core sites Geographical location, communication, weather, local infrastructure, site security We have NEQ of diff technology, NEQ of all technologies fro EOP are constrained, staion coordinates are not same thus to strengthen the network, additional constrain needed to introduced.
- #15 Design error at bridge construction in Laufenburg (2003): During the construction of the bridge across the Rhine river in Laufenburg, a control showed that a height difference of 54 centimeters exists between the bridge built from the Swiss side and the roadway of the German side. Reason of the error is the fact that the horizons of the German and Swiss side are based on different reference frames. Germany refers to the sea level of the North Sea, Switzerland to the Mediterranean. Courtesy of Hermann Drewes/DGFI
- #16 Horizontal station velocity field of DTRF 2014 time-dependent coordinates on the Earth’s surface is fundamental for many Earth observation applications. these coordinates need to be monitored to account all geophysical changes affecting the Earth’s surface. Earth observation, georeferencing applications, depend on being able to determine positions to mm level precision. Point positions, to be meaningful, have to be determined and expressed in a well-defined reference frame. All current global and regional reference frames rely on the availability of the International Terrestrial Reference Frame (ITRF)
- #17 ITRF is used as the standard in national and continental reference frame implementation where the rotation pole of a given plate is often part of their definitions. 2. Both ITRS and WGS84 are global systems. As a consequence, due to plate tectonic motions, the coordinates in the different continents move with respect to each other. 3. ITRF2005, the coordinates of Brussels change by about 2.5 cm/year. This time evolution makes these unsuitable for practical cartographic applications of centimeter-precision. 4. To remedy to this problem, defined the ETRS89 to be used in Europe. The ETRS89 ~ ITRS at the epoch 1989.0 and fixed to the stable part of the Eurasian Plate. the station positions expressed in ETRS89 are almost constant. 5. (ETRS89~ITRF by a transformation formula.
- #18 Sea level rise estimations, global plate tectonics, co/post-seismic deformation studies or the interpretation of displacements induced by postglacial rebound or recent ice melting all require an accurate reference frame/ accurate time dependent coordinates to points on Earth’s crust Quantifying plate motion is essential to understanding the mechanism of plate tectonics and its implications for geologic processes at plate boundaries, including how these processes relate to earthquakes and volcanic activity. e.g. NA12 reference frame developed by Blewitt et al. (2013) for crustal deformation studies in North America, 4. It provides the foundation for much of the space-based and ground-based Observations in Earth science and global change 5. A precise TRF is also essential for interplanetary navigation, astronomy, and astrodynamics.
- #19 1. Removable Discrepancies in Realization of ITRS Relativistic scale Permanent Tide SLR only because of spherical satellites, small area to mass ratio, low altitudes 2. Satellites rotate around the CM but are observed from stations at the Earth’s crust (ITRF). This means, theoretically, that the space geodetic techniques can determine the translation between the CF-frame and the CM-frame. 3. Same reson, perturbation model, phase offsets of GNSS
- #20 The largest non-linear motions that can be observed in geodetic time series are abrupt discontinuities. They are typically due to equipment changes or earthquake ruptures. For instance, it appears that co-seismic deformations and In addition, after a great earthquake, some of the geodetic stations impacted by the earthquake show non-linear relaxation motions during a few years due to post-seismic deformations. This non-linear behavior is today modeled in reference frame constructions as a piece-wise linear function, which is not accurate enough. Not only eq, but also activities like ice melting A major challenge will be to incorporate those non-linearity behaviors in the ITRF model for the time evolution of station coordinates and/or frame parameters. Last one : station distribution for monitoring the deformations is very inhomogeneous (bulk in North America and Europe)
- #21 1.ERF: frequent weekly estimation of station and positions and EOP from combination of four techniques 2.Instead of irregular “new solutions” at discontinuities we can introduce frequent regular epochs (every week, month, …) and quit the velocities. 3. due to plate tectonic motions, the coordinates in the different continents move with respect to each other. in the ITRF2005, the coordinates of Brussels change by about 2.5 cm/year. This time evolution makes them unsuitable for practical cartographic applications of cm preciosion. 4.SIRGAS identical to the (ITRS). Its realization is a regional densification of the global (ITRF) in Latin America and the Caribbean. The reference station positions are associated to a specific (reference) epoch and their variation with time is taken into account by discrete station velocities or by a continuous velocity model, which comprises tectonic plate movements and crustal deformations of the region .