Improved precision levelling for deriving significant vertical movements of the earth's crust

Abstract The accuracy and reliability of determinations of recent vertical crustal movements are determined by the quality of precise elevation measurements, by the knowledge of the effects of errors that are unavoidable in the measuring set-ups and their propagation, and by the methods of error analysis and of evaluation of measurements. The accuracy of precise levelling techniques is essentially defined by • -the performance of the equipment, • -effects such as the sinking in of levelling rods, rod graduation errors and asymmetric refraction which cannot be completely avoided in measurement set-ups, • -movements of control points during the period of measurement. Measures for increasing the accuracy of levellings for the derivation of crustal movements are • -to garantee the reliability of data acquisition using automatic data recording, • -metrological determination of external influences on the measuring system, such as sinking in of levelling rods and asymmetric refraction, • -further acceleration of the measuring process.