Tutorial De Geodesia

University of New Brunswick
GeodesyGroup, http://einstein.gge.unb.ca
An Online Tutorial in

GEODESY
by
©AcademicPress 2001, published with permission, for personal use only

Note: this article is to appear in the upcoming (2001) edition of the AP Encyclopedia of Science and Technology. The author hereby thanks the Academic Press for their kind permission to publish this onlinepresentation, as well as to Professor D.E. Wells, Professor R.B. Langley, and Dr. Juraj Janak for their comments and suggestions on the previous version of the text.

Outline:

What is geodesy? Geodesy is a science, the oldest earth (geo-) science, in fact. It was born of fear and curiosity, driven by a desire to predict natural happenings and calls for the understanding of these happenings. Theclassical definition, according to one of the "fathers of geodesy" reads: "Geodesy is the science of measuring and portraying the earth’s surface" [Helmert, 1880, p.3]. Nowadays, we understand the scope of geodesy to be somewhat wider. It is captured by the following definition [Vanícek and Krakiwsky, 1986, p.45]: "Geodesy is the discipline that deals with the measurement and representation of the earth,including its gravity field, in a threedimensional time varying space." (Note that the contemporary definition includes the study of the earth gravity field – see section III – as well as studies of temporal changes in positions and in the gravity field – see section IV.)

I. ning II. III. IV. V.

IntroductionPositio Earth gravity field Geo-kinematics Satellite techniques

I. IntroductionI.A. Brief history of geodesy Little documentation of the geodetic accomplishments of the oldest civilizations, the Sumerian, Egyptian, Chinese and Indian, has survived. The first firmly documented ideas about geodesy go back to Thales of Miletus (c.625–c.547 BC), Anaximander of Miletus (c.611–c.545 BC) and the school of Pythagoras (c.580–c.500 BC). The Greek students of geodesy included Aristotle(384–322 BC), Eratosthenes (276–194 BC) – the first reasonably accurate determination of the size of the earth, but not taken seriously until 17 centuries later – and Ptolemy (c.75–151 AD). In the Middle Ages, the lack of knowledge of the real size of the earth led Toscanelli (1397-1482) to his famous misinterpretation of the world (Figure 1) which allegedly lured Columbus to his first voyagewest.

Figure 1 – Toscanelli’s view of the Western Hemisphere Soon after, the golden age of exploration got under way and with it the use of position determination by astronomical means. The real extent of the world was revealed, to have been close to Eratosthenes’s prediction, and people started looking for further quantitative improvements of their conceptual model of the earth. This led to newmeasurements on the surface of the earth by a Dutchman Snellius (in 1610’s) and a Frenchman Picard (in 1670’s), and the first improvement on Eratosthenes’s results. Interested reader can find fascinating details about the oldest geodetic events in [Berthon and Robinson, 1991]. At about the same time, the notion of the earth gravity started forming up through the efforts of a Dutchman Stevin(1548-1620), Italians Galileo (1564-1642) and Borelli (1608-1679), an Englishman Horrox (1619-1641), culminating in Newton’s (1642-1727) theory of gravitation. Newton’s theory predicted that the earth’s globe should be slightly oblate due to the spinning of the earth around

its polar axis. A Frenchman Cassini (1625-1712) disputed this prediction; consequently, the French Academy of Science organizedtwo expeditions, to Peru and to Lapland, under the leadership of Bouguer and Maupertuis, to measure two meridian arcs. The results confirmed the validity of Newton’s prediction. In addition, these measurements gave us the first definition of a metre, as one ten-millionth part of the earth quadrant. For two hundred years, from about mid-eighteenth century on, geodesy saw an unprecedented growth in...