Geodesy Review PDF

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).