Vertical gradient and datum height corrections to absolute gravimeter data and the effect of structured fringe residuals
| Autor: | K Charles, R Hipkin |
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| Rok vydání: | 1995 |
| Předmět: | |
| Zdroj: | Metrologia. 32:193-200 |
| ISSN: | 1681-7575 0026-1394 |
| Popis: | Data from FG5 absolute gravimeters have been analysed using processing software developed by Edinburgh University. The work aims to understand apparent inconsistencies between relative and absolute observations and the variation of absolute gravity estimates outside the 10 nm s-2 to 20 nm s-2 (10 nm s-2 = 1 μGal) range expected for FG5 instruments. Data from FG5-103 at Edinburgh, Birkenhead, Teddington and Taunton, FG5-107 at Taunton, FG5-105 at Teddington and FG5-101 at Onsala, Sweden, have been reprocessed. Fitting time-distance pairs to an equation of motion without a vertical gradient of gravity gives an estimate for g at some fraction of the way down the drop. None of the current theories correctly predicts the observed fraction of 0,43, so accurate results can only be found by including the vertical gradient terms to obtain a value of gravity at the top of the drop. Observations of the vertical gradient at some absolute sites have shown it to be nonlinear, so that using the same value in the equation of motion as for datum corrections can lead to significant errors. Solving the full equation of motion should give a constant estimate of gravity for all lengths or starting positions of the drop. This is rarely the case in the samples analysed here and the estimates may vary by up to 250 nm s-2. Systematic site- and instrument-dependent structure in the time-position residuals biases the solution. Removing the stacked residuals produces gravity estimates which are constant and independent of the drop length or starting position. In order to find the gravity offset caused by the system response, the residuals are modelled by a small number of damped sinusoids. |
| Databáze: | OpenAIRE |
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