Geodesy Review PDF
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This document provides an overview of geodesy, discussing its definition, branches (geometric, physical, and satellite geodesy), and introduction to satellite geodesy, including methods and applications. It also covers historical milestones and key concepts.
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1. Overview of Geodesy Definition: Geodesy is the science of measuring and mapping the Earth’s surface. o Origin: The word geodesy comes from Greek: Geo meaning "Earth" and Daiein meaning "to divide." o Purpose: Determine the Earth's shape, gravity field, an...
1. Overview of Geodesy Definition: Geodesy is the science of measuring and mapping the Earth’s surface. o Origin: The word geodesy comes from Greek: Geo meaning "Earth" and Daiein meaning "to divide." o Purpose: Determine the Earth's shape, gravity field, and precise location of points on its surface. 2. Branches of Geodesy 1. Geometric Geodesy: o Focuses on determining the Earth’s size and shape using geometry, particularly the ellipsoid of revolution. 2. Physical Geodesy: o Studies the Earth's gravity field to define its size and shape more accurately. 3. Satellite Geodesy: o Utilizes satellite systems (e.g., GPS, GLONASS) to measure Earth's geometry and gravitational field. Satellites are used for precise positioning and understanding the Earth's form. 4. Geodetic Astronomy (Astro-Geodesy): o Involves determining positions using measurements of celestial bodies. 5. Integrated Geodesy: o A relatively new branch, combining aspects of both geometric and physical geodesy. 3. Introduction to Satellite Geodesy Definition: The branch of geodesy that uses artificial satellites to measure and monitor the Earth's size, shape, and gravity field. Main Goals: o Determine Earth’s figure (shape and dimensions). o Measure the geoid (gravity field model) and its temporal variations. o Study geodynamic phenomena (e.g., crustal deformation, polar motion). Historical Milestones: o Sputnik-1 (1957): First artificial satellite launched by the Soviet Union, marking the beginning of satellite geodesy. o Explorer 1 (1958): First U.S. satellite, helped discover the Van Allen radiation belts. o GRACE (2002-2017): Measured Earth's gravity field anomalies, providing insight into mass distribution changes on Earth. 4. Methods in Satellite Geodesy 1. Geometrical Method: o Definition: A direct method where satellites are treated as high-altitude targets visible over large distances. o Application: Used to establish 3D global networks by positioning satellites as "fixed" control points visible from ground stations. 2. Dynamical Method: o Definition: An indirect method that uses the satellite's orbital behavior to infer Earth's gravity field. o Application: Used to observe deviations in satellite orbits caused by gravitational forces, allowing scientists to model the Earth's gravity field. 3. Types of Observation Platforms: o Earth to Space Methods: Observing satellites from Earth (e.g., GPS, Satellite Laser Ranging). o Space to Earth Methods: Using space-based instruments to observe Earth's surface (e.g., radar altimetry). o Space to Space Methods: Tracking one satellite from another (e.g., satellite-to-satellite tracking). 5. Key Satellites in Geodesy Sputnik-1: The first artificial satellite launched in 1957, signaling the start of satellite geodesy. GRACE (Gravity Recovery and Climate Experiment): o Twin satellites used to map Earth's gravity field by tracking changes in distance between them. o Provided data on mass distribution changes related to water storage, ice sheets, and sea level. GOCE (Gravity Field and Steady-State Ocean Circulation Explorer): o Launched by the European Space Agency to map Earth's gravity field with high precision, aiding in oceanography and climate studies. CHAMP (Challenging Minisatellite Payload): o A German satellite used for atmospheric, ionospheric, and geoscientific research, including GPS radio occultation. 6. Applications of Satellite Geodesy 1. Global Geodesy: o Establishing global reference frames. o Determining Earth's ellipsoid dimensions and gravity field. o Connecting national geodetic datums. 2. Geodetic Control: o Setting up geodetic networks for large-scale surveys. o Connecting remote islands with mainland geodetic networks. 3. Geodynamics: o Monitoring crustal movement and tectonic activity. o Measuring polar motion, Earth’s rotation, and Earth tides. 4. Navigation and Marine Geodesy: o Precise navigation for air, sea, and land vehicles. o Marine mapping and oceanographic studies using satellite technology. 5. Applied and Plane Geodesy: o Applications in urban planning, boundary demarcation, and Geographic Information Systems (GIS). o Engineering surveys for construction and land-use projects. 7. Historical Developments in Satellite Geodesy Phases: o 1957-1970: Development of basic methods and satellite orbits. o 1970-1980: Improved accuracy in geodynamical studies (e.g., crustal movements, Earth rotation). o 1980-1990: Operational use of satellite technology in geodesy and surveying. o 1990-2000: Further refinement of global observation systems (e.g., GPS, ITRF). o 2000-Present: Advances in satellite systems (e.g., CHAMP, GRACE, GOCE) and global navigation systems (GNSS). Key Concepts to Remember Geoid: The hypothetical surface representing the global mean sea level, shaped by Earth's gravity field. Ellipsoid: A mathematically defined surface approximating the shape of Earth, used in geodesy for measurements. Gravity Anomalies: Variations in Earth's gravity field due to mass distribution, which can be measured by satellites like GRACE. Reference Frame: A coordinate system used for geodetic measurements (e.g., International Terrestrial Reference Frame - ITRF).