Untersuchungen zur Modellbildung bei der Auswertung absoluter Schweremessung

An important task in absolute gravimetry is the establishment of high-precision gravity control networks for geodynamics research. Vertical crustal movements and subsurface mass shifts can be monitored by gravity observations contributing to the understanding and modelling of the underlying geophysical processes. The manufacturer of the new FG5 absolute gravity meter claims an instrumental precision of a few #+-#0.01 #mu#ms"-"2. In this thesis it is investigated whether the data processing of absolute gravity measurements matches this accuracy. With JILA and FG5 type absolute gravimeters free-fall experiments (drops) are performed to derive a gravity value g from the acceleration of the test mass. Introducing the vertical gravity gradient (determined by relative gravity measurements) in the data processing, the reference height for g is defined as the height of the test mass at rest, prior to the start of the drop. In this thesis a new, gradient independent solution is developed to calculate the reference height precisely (#+-#0.3 mm triple bond #+-#1 nms"-"2). Using the same approach a formula is derived which describes the effect of non-linearities in the vertical gradient. The LOMB-SCARGLE periodogram analysis allows to process time series with unequally spaced observations. Applying this method, periodical signals were found in the adjustment residuals. These are induced by instrumental vibrations and cause a systematic shift in the resulting gravity value. The amplitudes and phases of dominant frequencies are determined in a common adjustment with g using the periodogram results as a-priori information. A very critical frequency range was found between 1 and 10 Hz. Frequencies in this range may bias g extremely (> 0.1 #mu#ms"-"2) and cannot be separated accuratly enough from the gravity signal. Investigations dealing with natural gravity changing phenomena (tides, groundwater and air pressure variations, polar motion) show that a total reduction accuracy of #+-#20 to #+-#30 nms"-"2 is achievable, while maximum uncertainties can exceed #+-#100 nms"-"2. In mountain areas, however, the accuracy can improve to #+-#10 to #+-#20 nms"-"2, if the stations are set up at appropriate locations (i.e. stations based on bedrock). The increase is mainly due to the exclusion of hydrological effects. (orig.)SIGLEAvailable from TIB Hannover: ZS 299A(204)+a+b / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman