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Global Geoid Determination
Published in Petr Vaníček, Nikolaos T. Christou, GEOID and Its GEOPHYSICAL INTERPRETATIONS, 2020
Even with the 30′ × 30′ and 1° × 1° estimates, there are still large areas of the land world for which gravity anomaly information based on terrestrial measurements is not available. The problem of estimating the anomalies for these unsurveyed areas is a continuing one in geodesy. A recent procedure suggested by Pavlis and Rapp20 incorporates knowledge of the topographic elevation and ice thickness, with ani sostatic geophysical model to define a gravitational potential from which gravity anomalies can be computed using Equation 11. However, it is recognized that such a representation will have poor long wavelength information since such information does not arise in the crust but in the deeper interior of the Earth. Consequently, the applications of the topography implied anomalies have been carried out by replacing the lower degree (2–9 or 2–36) with a satellite implied potential coefficient model. With this procedure, it is possible to have some estimate of the anomalies in unsurveyed areas although it is recognized that such estimates will not be as accurate as those based on actual measurements.
Petroleum Geophysical Survey
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
A gravity anomaly is a variation in gravity. Gravity variations occur due to different locations of measurements or one object influencing another. Variation in gravity is also expressed as ‘change in acceleration due to gravity’. Gravity and acceleration due to gravity can be expressed by single word ‘g’.
A two million-year history of rifting and caldera volcanism imprinted in new gravity anomaly compilation of the Taupō Volcanic Zone, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2021
Vaughan Stagpoole, Craig Miller, Fabio Caratori Tontini, Thomas Brakenrig, Nick Macdonald
The largest contribution to errors in the gravity anomaly data are from incorrectly recorded locations and inaccurate estimates of observation height. Historically (prior to c. 2000), the locations of gravity observations were read off maps in the field, which resulted in location errors of typically 20–250 m, depending on the scale of the map. Mis-located gravity observation sites will have erroneous terrain corrections recalculated for this study using digital terrain models, particularly for near terrain zones in steep and hilly country. Data acquired before c. 2000 often used barometric levelling for obtaining the observation height. Barometric levelling typically has an accuracy of ±5 m or more (Reilly and Woodward 1971). Most surveys since 2005 use precise GPS or LIDAR data to record the height of the gravity observation with a typical accuracy of c. 0.1 m. The pre-2000 data have an estimated average error of 2 mGal. Data acquired since about 2005 that are located with high precision GPS have an estimated average error of 0.8 mGal, reflecting the more accurately determined elevation and location for gravity observations sites.
Improving the Arctic Gravity Project grid and making a gravity anomaly map for the State of Alaska
Published in GFF, 2019
Bernard Coakley, Jeffery Johnson, James Beale, Rose Ganley, Monica Youngman
Properly collected and reduced (e.g. Long & Kaufman 2013; Dehlinger 1978), gravity anomaly data track mass beneath the earth’s surface, providing a means to study geologic structures at depth. Any proposed structure defines a distribution of mass. Calculating what the gravity anomalies would be if this structure were correct and comparing it to the observed gravity data test the hypothetical structure. Refinement of the proposed structure to improve the fit of the calculated anomaly to the observed anomaly makes it possible to, through successive adjustments, find a structure that best reproduces the observed anomalies.