As children, when we learn that there was a time that people thought that Earth was flat, we laugh. But in actuality, we've only known that for a few hundred years, a very short amount of time compared to the age of the Earth and the age of humanity. In the 21st century, the field of geodesy, is still a growing because humans continue to develop new ways of evaluating the size and shape of the Earth. Additionally, the shape of the surface is constantly changing. Mountains grow taller, oceans recede, islands are formed, and craters can be made.
The main way that researchers presently study the shape of the Earth is from space by using satellites and other reference objects such as quasars or the Moon. Despite measuring from so far away, "early space geodetic measurements ... had accuracy levels between 5 and 10 centimeters". Today, satellites have the capability of measuring minute surface changes on both solid and liquid surfaces as well as differences in both the atmosphere and the ionosphere.There are actually four different geodetic techniques that can be used from space: positioning, altimetry, InSAR (interferometric synthetic aperture radar), and gravity studies. By using these techniques, precise positioning can be achieved over large distances. And since they operate in space, the rotation of the earth allows for repetitive data collection of each portion of the earth.
Not only are these techniques important for geodesy, but they are also important in determining weather conditions, natural disasters, glacier movement, and sea level change. They can also be used to view tectonic plate movements, which in turn can cause earthquakes and volcanic eruptions. On a more long term scale, these technologies are especially helpful when looking at phenomenons such as climate change, because very accurate, consistent data is taken for the entire planet and patterns can be more easily studied.
Geodesy first strove to define to the shape and size of the Earth but now, technology has caused geodesy to leech into many other disciplines, propelling scientific studies forward and improving quality of life on the planet.
Wdowinski, S., & Eriksson, S. (2009). Geodesy in the 21st Century. Eos, Transactions American Geophysical Union, 90(18), 153-155.