عنوان مقاله [English]
نویسنده [English]چکیده [English]
Today, despite the emergence of precise surveying devices for ranging, including its more advanced type, namely GPS, the question still remains about the accuracy of such machines. Possibly accurate measurement is not necessary in many ordinary surveying works, but in fine works it is necessary that the accuracy of spacer be controlled and determined. One of the most important surveying operations which needs great precision is microgeodesy. This operation has applications in measuring dams’ displacement, earth’s tectonic movements, landslides and even predicting earthquake and rise or fall of sea levels, installing an important piece in giant factories and measuring its movements, etc. In such operations, the spacer is used after determining its precision. Despite rapid advancement of GPS receivers in surveying operations, they are still not used singly in microgeodetic works, because their relative precision is not suitable for such operations, especially in short distances. Consequently it is used merely as a complementary. Electronic spacers have the highest precision in short and long distances. If we take a look at the precision of spacers in various distances, we notice that up to five kilometers the electronic spacers, especially those working based on two-color method are of high accuracy. From eight to thirty kilometers the single-frequency GPS systems, from thirty to eighty up to a hundred kilometers the two-frequency GPS systems, and in higher distances ranging by the SLR and V.L.B.I methods are of great precision.