Introduction to Geodesy Flashcards
Geodesy in the Geodetic Glossary (NGS 2009)
“The science concerned with determining the size and shape of the Earth” or “The science that locates positions on the Earth and determines the Earth’s gravity field.”
Fundamental Properties of the Earth (3)
(1) its geometric shape,
(2) its orientation in space, and
(3) its gravity field as well as the changes of these properties with time.
Geodesy from the Greek words
“geo” and “desa” means “earth” and “to divide”.
Webster’s definition of Geodesy
That branch of applied mathematics which determines by observation and measurement the exact positions of points and the figure and areas of large portion of the earth’s surface, the size and shape of the earth, and the variations in the terrestrial gravity
Classical definition by F. R. Helmert, 1880
“the science of measuring and portraying the Earth’s surface”
Contemporary definition by Vanicek & Krakiwsky, 1986
“the discipline that deals with the measurement and representation of the Earth’s surface, including its gravity field, in a three-dimensional time varying space”
General ideas or concepts of Geodesy (3)
(1) the size and shape of the earth
(2) the gravity field of the earth
(3) the positioning of points on the surface of the earth
Modern definition of Geodesy (2)
(1) measurement and modeling of the geodynamic
(2) phenomena such as polar motion, Earth rotation and crustal deformation
Branches of Geodesy (4)
(1) Physical Geodesy
(2) Geometric Geodesy
(3) Geodetic Astronomy
(4) Satellite Geodesy
Geodesy Subdivisions (3)
(1) Geometrical geodesy
(2) Physical geodesy
(3) Satellite geodesy
Concerned with describing locations in terms of geometry.
Geometrical Geodesy
One of the primary products of geometrical geodesy.
Coordinate Systems
Concerned with determining the Earth’s gravity field, which is necessary for establishing heights.
Physical Geodesy
Concerned with using orbiting satellites to obtain data for geodetic purposes.
Satellite Geodesy
Homer: 9th Century B.C.
Earth was a flat disk supporting a hemispherical sky.
Pythagoras: 6th Century B.C (2)
(1) Suggested that the earth was spherical in shape
(2) Made on the basis that a sphere was considered a perfect form, and not by deduction from observations
Aristotle: 4th Century B.C. (3)
The earth must be spherical in shape;
(1) Changing horizon as one travels in various directions,
(2) Round shadow of the earth that was observed in lunar eclipses; and
(3) Observation of a ship at sea where m ore (or less) of the ship is seen as the sheep approaches (or goes away)
To settle the issue, they sent out an expedition to confirm the correctness of the claims. The measurements of the expedition in Peru conclusively proved the earth to be flattened.
French Academy of Sciences in 1735
Geoid Development in 1872-1873
Listing introduced the concept of the geoid as the surface of the undisturbed seas and its continuation into the continents. Theellipsoid of previous studies now became an approximation of the earth.
Geoid Development in 1884
Helmert defined more precisely the geoid identifying it with an ocean with no disturbances such as would be caused by tides, winds, waves, temperature, pressure and salinity differences. Etc. This geoid was considered to be an equipotential surface of the earth’s gravity field.
Everyday Geodesy (3)
(1) GNSS navigation system
(2) Web-based mapping services
(3) Ships and aircraft
Why learn about Geodesy? (2)
(1) The need for flatness
(2) Round realities
Units in Geodesy (2)
(1) Angular Units
(2) Linear Units
Angular Units (6)
(1) Degrees, minutes and seconds
(2) Radians
(3) Circles and Semicircles
(4) Grade/grad/gon
(5) Mil
(6) Milli-arc second (mas)
