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Basics of Space Geodesy  Basics of Geodesy Geodesy is the science of accurately measuring and understanding three fundamental properties of the Earth: its geometric shape , its orientation in space, and its gravity field— as well as the changes of these properties with tim...

Basics of Space Geodesy  Basics of Geodesy Geodesy is the science of accurately measuring and understanding three fundamental properties of the Earth: its geometric shape , its orientation in space, and its gravity field— as well as the changes of these properties with time. Geodesy has 3 main pillars Geokinematics – concerned with the geometric aspect of the earth (size and shape) and movements e.g., crustal deformation Earth Rotation and Orientation Gravity Field These three pillars are unified by Reference Frames 2  What is Geodesy Geodesy is the scientific discipline that deals with the measurement and understanding of Earth's shape, orientation, gravity field, and their variations over time. Geodesy is the science of accurately measuring and understanding three It involves precise measurements and fundamental properties of the Earth: its geometric shape, its orientation calculations to determine the size, in space, and its gravity field— as shape, and position of points on well as the changes of these properties with time. Earth's surface and to study the dynamic processes occurring within the Earth.  Geodesy provides a fundamental framework for various applications, including mapping, navigation, land surveying, and understanding Earth's geophysical phenomena.  Key Components of Geodesy Earth's Shape: Geodesy aims to define and understand the shape of the Earth. It involves modeling the Earth as an oblate spheroid or ellipsoid, which approximates the Earth's shape accurately. Earth's Orientation: Geodesy determines the orientation of Earth in space, including its rotation axis and how it changes over time. Gravity Field: Geodesy studies Earth's gravitational field, including its strength and variations in space and time. Understanding the gravity field provides insights into mass distribution and geodynamic processes. These three pillars are unified by Reference Frames Three Pillars of Geodesy  Importance of Geodesy Mapping and Cartography: Geodesy forms the foundation of accurate mapping and cartographic representations, enabling the creation of detailed maps and spatial data. Navigation and Positioning: Geodesy plays a crucial role in navigation systems, such as GPS and GNSS, enabling precise positioning and tracking worldwide. Earth Sciences: Geodesy provides critical data for understanding Earth's processes, including tectonic plate movements, sea-level changes, and deformation monitoring.  Infrastructure Development: Geodesy is essential for infrastructure projects like construction, land management, and urban planning, ensuring accurate positioning and alignment. Climate Studies: Geodesy contributes to climate studies by monitoring changes in sea level, ice masses, and land movements, providing valuable data for climate modeling and predictions.  Branches of Geodesy Geodetic Surveying: Geodetic surveying involves the collection of precise measurements on the Earth's surface to establish geodetic control networks. It includes techniques such as triangulation, trilateration, leveling, and GPS/GNSS observations. Geodetic surveying is essential for accurate positioning, mapping, and land surveying. Physical Geodesy: Physical geodesy deals with the study of Earth's gravity field and its variations. It involves the measurement and analysis of gravity data to understand the distribution of mass within the Earth. Physical geodesy contributes to understanding Earth's interior structure, tectonic processes, and geodynamic phenomena. Satellite Geodesy: Satellite geodesy focuses on utilizing data from satellite-based positioning and Earth observation systems for geodetic purposes. It includes techniques such as GPS/GNSS positioning, satellite altimetry, satellite gravimetry, and SAR interferometry. Satellite geodesy enables precise positioning, deformation monitoring, gravity field determination, and mapping applications.  Geodetic Datum and Reference Frames: Geodetic datums and reference frames define the coordinate systems and reference points used for geodetic measurements and mapping. This branch of geodesy is concerned with establishing and maintaining consistent and accurate reference systems to ensure compatibility and interoperability of geodetic data across different regions and time. Geodetic Geophysics: Geodetic geophysics combines geodetic techniques with geophysical principles to study Earth's internal structure and processes. It involves using gravity, GPS/GNSS, and other geodetic measurements to understand phenomena such as plate tectonics, crustal deformation, and earthquakes. Geodetic Cartography: Geodetic cartography focuses on the accurate representation of geographic information on maps. It includes techniques for map projection, coordinate transformations, and spatial data management to ensure precise and consistent cartographic products.  Geodetic Geodynamics: Geodetic geodynamics studies Earth's dynamic processes and movements using geodetic measurements. It involves monitoring plate tectonics, crustal deformations, sea-level changes, and other geophysical phenomena using techniques such as GPS/GNSS, InSAR, and gravity measurements. Geodetic Time and Precision Timing: Geodetic time and precision timing deal with the accurate measurement and synchronization of time using satellite-based timing systems such as GPS/GNSS. It has applications in telecommunications, navigation, financial transactions, and scientific experiments Geodesy and Allied Fields  Introduction to Satellite Geodesy Satellite geodesy is the science of measuring and understanding Earth's shape, orientation, and gravitational field using artificial satellites. It plays a crucial role in various applications, including positioning, height determination, gravity field studies, deformation monitoring, and time synchronization.  Historical Overview of Space Geodesy Space geodesy represents a significant milestone in geodetic measurements, utilizing artificial satellites to revolutionize the field. Early Developments: Geodesy traces its roots back to ancient civilizations, with early attempts to measure Earth's shape and size. Ground-based techniques like triangulation and astronomical observations were used to establish reference points and measurements.  Birth of Satellite Geodesy: The launch of the first artificial satellite, Sputnik 1, by the Soviet Union in 1957 marked the beginning of satellite geodesy. Sputnik 1 provided the opportunity to measure precise orbits and study the Earth's gravity field. Key Milestones: In 1960, the launch of the Transit satellite system by the U.S. Navy allowed accurate positioning through the Doppler effect. The development of the Global Positioning System (GPS) in the 1970s revolutionized navigation and precise positioning worldwide. The launch of other global navigation satellite systems like GLONASS, Galileo, and BeiDou expanded the capabilities of satellite geodesy.  Basic Geodetic Problems 1) determination of precise global, regional and local three-dimensional positions (e.g. the establishment of geodetic control); 2) to study the variations in the intensity and direction of gravity over the earth's surface, hence to determine the form of the geoid and the earth's external equipotential surfaces; 3) to study satellite orbits to obtain the same earth's external equipotential surfaces and 4) the measurements and modelling of geodynamical phenomena (e.g. polar motion, 17 Earth rotation, mass re-distribution, crustal deformation).  Solutions to these problems aide in: computation of geodetic prediction of satellite orbits, networks, shape of the earth, determination of etc. assisting geophysicists with earth theories and prospecting determining secular and periodic vertical and horizontal land movements. monitoring hydrological cycle, etc. 18 18  Measurements in Geodesy 1) Measurements in Geodesy 2) Gravity Measurements Astronomic Measurements Absolute Gravity Measurements Coordinate Systems of Spherical Relative Gravity Measurements Astronomy Gravity Measurements on the Ocean and Variation of Stellar Coordinates, Star in the Air Catalogues Time varying gravity Time Systems Gravity Reference Systems Astronomic Positions and Azimuth Determination of the Gravity Gradient Measurement of Earth Tides 9  Measurements in Geodesy 3) Terrestrial Geodetic 4) Satellite Observations Measurements The Unperturbed Motion of a Satellite Horizontal Angle Measurements The Perturbed Motion of the Satellite Distance Measurements Artificial Earth Satellites, Time Zenith Angle Measurements Measuring Systems Levelling Laser Distance Measurements Doppler Frequency Shift Measurements GNS S Very Long Baseline Interferometry Satellite Altimetry Interferometric synthetic aperture radar 10  To determine global positions and to measure long baselines you need: more accurate observing instruments than those surveyin - used for g although frequently surveyors measurements and geodesists of the gravity field use the same instruments. complicated mathematical techniques to take into account things like the earth's curvature and, especially, the gravity field The effects of the gravity field are especially difficult to deal with. For example, when geodesists or surveyors say a surface is horizontal, what they really mean is that it is a surface of constant gravitational potential. 21 21 Why Satellite Geodesy... ??? 1) determination of precise global, regional and local three-dimensional positions (e.g. the establishment of geodetic control); 2) to study the variations in the intensity and direction of gravity over the earth's surface, hence to determine the form of the geoid and the earth's external equipotential surfaces; 3) to study satellite orbits to obtain the same earth's external equipotential surfaces and 22 4) the measurements and modelling of geodynamical phenomena (e.g. polar  Space/Satellite Geodesy Geodesy provides a foundation for all Earth observations Space geodesy is the use of precise measurements between space objects (e.g., orbiting satellites) to determine Positions of points on the Earth Position of the Earth’s pole Earth’s gravity field and geoid  Without Satellite Geodesy, we could not have been to … Navigate and survey across ocean, land and air seamlessly Determine the actual shape of the earth Remotely monitor tectonic movements  Why Satellite Geodesy 1) The requirement for improved geodetic information came with the rapid increase as major surveys and positioning techniques were still laborious, difficult and can be very dangerous in certain circumstances. 2) There was a need for integration of surveys on a worldwide basis to relate all the major datums of different continents. 25  "Satellite" simply refers to an object that moves around another body in space. The curved path taken by the said object in motion around a point in space is the orbit. The computation and prediction of precise satellite orbits, together with appropriate observations and adjustment techniques is the most essential task in satellite geodesy. 26 26  Precise time-dependent satellite positions in a suitable reference frame are required for nearly all tasks in satellite geodesy. For better appreciation of satellite methods in geodesy, students and practitioners must have a basic knowledge of satellite orbital motion, including the major perturbations, in order to assess the appropriate requirements for orbit determinations. 27 27  Data from space geodesy measurements archive are utilized for direct science observations and geodetic studies, e.g., plate motion, gravity field, earthquake displacements, Earth orientation, atmospheric angular momentum, etc. Data also contribute to the determination of the Terrestrial Reference Frame, an accurate set of positions and velocities TRF provides the essential stable coordinate system that allows measurements to be linked over space and time; independent of the technology used to define it  Space geodetic networks (GNSS, SLR, VLBI, DORIS) provide the critical infrastructure necessary to develop and maintain the TRF Data used for Precise Orbit Determination (POD) SLR and DORIS data used to calculate and verify precise orbits for Earth observation missions (e.g., ERS-1/2, ALOS, Jason-1/2, Envisat, TOPEX, etc.) SLR data and GPS flight receiver data also utilized for POD efforts for other geophysical missions (e.g., GFO-1, CHAMP, GRACE, ICESat, GOCE, etc.) Additional products include atmosphere measurements to aid in weather forecasting, etc  Two-body Problem Considering artificial satellites the mass of the smaller body (the satellite) usually can be neglected compared with the mass of the central body (Earth). The two-body problem is to determine the motion of two point particles that interact only with each other. Eg include a satellite orbiting a planet, a planet orbiting a star, two stars orbiting each other (a binary star). Under the assumption that the bodies are homogeneous and thus generate the gravitational field of a point mass the orbital motion in the two-body problem can be described empirically by Kepler’s laws. 30  Keplerian Laws of planetary motion 1) The orbit of each planet is an ellipse with the Sun at one of the foci. 2) Each planet revolves so that the line joining it to the Sun sweeps out equal areas in equal intervals of time. 3) The squares of the periods of any two planets are in the same proportion as the cubes of their mean distances to the Sun. 31  Semi-major axis, a, of the ellipse defining the size Keplerian Elements of the orbit. Inclination, i, of the orbital plane with respect to the equatorial plane Numerical eccentricity, e, of the ellipse describing the shape of the orbit. Argument of perigee, ω, the angle (in the orbital plane) between the ascending node and the perigee (measured in the direction of the motion of the satellite). Right ascension, Ω, of the ascending node. i.e. the angle between the direction to the vernal equinox and the intersection line of the satellite‘s orbital plane with the equatorial plane. Perigee passing time, Tp, the time when the satellite 33 33 passes through the point nearest to the Earth  Forces Acting on Satellites Two-Body Term of Earth's Gravity Field Oblateness of Earth Lunar Gravitational Attraction Solar Gravitational Attraction Other Terms of Earth's Gravity Field Radiation Pressure (direct) Solid Earth Tides Ocean Tides Earth Albedo Relativictic Effects 34 34 Thank You 35