Physical geodesy
Study of Earth's gravity and its potential field for geodesy.
Physical geodesy is the study of the physical properties of Earth's gravity and its potential field (the geopotential), with a view to their application in geodesy. It involves the measurement and analysis of gravity, the geoid, and gravity anomalies to understand Earth's shape and gravitational field.
- field
- Geodesy
- known_for
- Study of Earth's gravity field, geoid determination, gravity anomalies
Lore & Background
Physical geodesy relies on traditional instruments like theodolites, which use the gravity field to orient their vertical axis along the local plumb line via a spirit level. Vertical and horizontal angles are measured relative to this local vertical and the local horizon. Levelling instruments obtain geopotential differences between points, which can be converted to metric height differences.
Reader's Guide
Physical geodesy is significant for defining the geoid, the equipotential surface of Earth's true gravity field that approximates mean sea level. The geoid undulates relative to a reference ellipsoid, with separations of up to 100 metres in some regions. Gravity anomalies, computed as the difference between observed and normal gravity, are used in Stokes' equation and further reduced via Bouguer corrections to account for topography. These concepts underpin vertical datums and height systems, with practical implications for surveying and navigation.
Did You Know?
- Gravity is commonly measured in m·s⁻², and potential in m²·s⁻².
- The geopotential unit (GPU) equals 10 m²·s⁻², roughly corresponding to a 1-metre change in height.
- The geoid can stick out as much as 100 m above the reference ellipsoid west of Ireland.
- Bouguer anomalies are computed by subtracting the attraction of a flat plate of thickness H from free-air anomalies.
Frequently Asked Questions
Who is Physical geodesy?
Physical geodesy is the branch of geodesy devoted to mapping and analyzing Earth's gravitational field and its associated potential-energy surface. It treats gravity itself as the primary subject of investigation within the broader geodesy discipline.
What are Physical geodesy's powers/role?
Its core abilities involve measuring local gravity values, identifying gravity anomalies, and determining the shape of the geoid. Through these tasks it helps scientists characterize the true three-dimensional form of the planet.
How does Physical geodesy's story end?
As a living field of research it has no fixed ending—its ongoing narrative is the continuous refinement of global gravity models and geoid representations. Each new satellite mission or ground survey adds another chapter to that story.
Why is Physical geodesy important?
It supplies the gravitational reference framework that underpins precise positioning, sea-level monitoring, and studies of mass redistribution inside the Earth. Without its data, GPS accuracy and climate-related ocean measurements would lose a critical anchor.
What is Physical geodesy's signature move?
Its signature technique is geoid determination—translating thousands of gravity measurements into a smooth equipotential surface that approximates mean sea level. This single deliverable ties together satellite observations, tidal data, and terrestrial gravity surveys.
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