New era of geodesy

The 20th century opened a new era for geodesy. It had to do so because geodesy faced new problems which the classic methods were not able to solve. In earlier times most countries were satisfied to have their own geodetic control point system. For that purpose even poor dimensions of the earth and the classic arc measuring method were sufficient. It did not matter how much the control point systems of various countries differed from one another. During the last century, however, geodesists had to join not only to the geodetic systems of various countries but of different continents as well.

Geodesy today is the science which carries out measurements with the accuracy that is beyond the reach of other branches of science. In order to do this we must know the accuracy of the dimensions of the earth as well as its detailed shape. In other words, we must know the dimensions of the earth ellipsoid along which we carry out the computations of the control points in different parts of the world, as well as the distances of the geoid from the earth ellipsoid and its inclination as referred to the ellipsoid.

Evidences of this new era are the celestial methods, the electronic measurement methods and the gravimetric methods, as well as the new types of measuring instruments and computing machines which were brought to science last century. All geodetic instruments are being continually developed and improved. New types of geodetic measuring instruments are lighter, smaller and more convenient to use than the old-fashioned instruments and they make observations two to three times faster.

Cylindrical axes, glass circles, focusing lenses, coincidence spirit levels, optical micrometers, and particularly the possibility of reading directly the mean of two diametrically opposite points of circles, are the most striking features of these new instruments.

The Vening Meinesz pendulum apparatus for gravity measurements at sea, the underwater gravimeter and other types of gravimeteres developed in the mid-20th century have brought a new epoch in the gravity survey of the globe. These new instruments permit the gravity survey of the oceans and seas, constituting 70 per cent of the whole area of the globe, which was in earlier times gravimetrically "terra incognita”.

With the appearance of artificial earth satellites new era has begun in measuring techniques. The use of unreliable stars (seen only in clear nights) has been replaced by the use of artificial satellites which are available 24 hours a day and are located to our needs. Today we have Global Positioning System which is in general use and. is available on the whole earth 24 hours a day. This system is useful in many branches from navigation to the most accurate measurements in geodesy and geodynamics.

Дата добавления: 2015-07-19