Man has been interested in learning about the size and shape of the Earth for many centuries. Early Chinese imagined that the univers was an egg and the Earth the yolk inside. In early greece, some speculated that the Earth was a flat disc but a spherical shape was the most widely accepted idea during the Greek era. The Greeks made efforts to determaine the size of the Earth. The most famous of these ancient measurments was done by Eratosthenes in a well of Syene, an accomplishment for which he is called the founder of geodesy. The telescope, logarithmic tables, and the method of triangulation developed in the seventeenth century contributed greatly to the foundation of geodetic science. The measurments of geodetic arc by the French Academy of Sciences in 1735 to determine the length of a meridian degree conclusively proved the Earth to be flattened ellipsoid, one of the milestones in the history of geodesy. In the eighteenth century, many famous scientists made important contributions to geodesy. Gauss invented the least squares method and defined the geoid. He laid the theretical foundations of geodesy and ushered it into its mature age. Laplace devoted himself to celestrial mechanics and tidal theory. Bessel made the first accurate determination of the Earth's flattening.

In its early stage, geodesy was basically geometrical by nature, involving measurement of geometric quantities (angle and length) and employing geometric and trigonometric methods to study the geometric properties of the Earth (size, shape, and position) . Phisical geodesy came into being rather than later, although it developed much faster.

The advent of modern computers, coupled with the developement of space technology in the last three decades, has produced major breakthroughs in both geometric and physical geodesy.

Literally, geodesy means " dividing the Earth ." The measurement and description of the Earth's surface was the province of classical geodesy as defined by Helmert 1880. That definition no longer fully reflects the role of present-day geodesy. The scope of present-day geodesy may be seen in the structure of the International Association of Geodesy (IAG), with its fine section and various commissions and special study groups. For the period 1983-1987, the sections of IAG included: positioning, advanced space tecnology (used geodesy), determination of the gravity field, general theory and methodology, and geodynamics.

Regions of geodetic research which are introduced by IAG (International Association of Geodesy) are as follows :

• Positioning
• Advanced Space Technology
• Determination of the Gravity Field
• General Theory and Methodology
• Geodynamics

Within these subjects, we are interested in and study about ...

• determining the gravity field of the Earth and inferring underground density structure,
• observing the Earth tide and inferring the structure of the Earth's interior and
• observing the crustal deformation and inferring the mechanism of it.