High-Precise Gravity Observations at Archaeological Sites: How We Can Improve the Interpretation Effectiveness and Reliability (original) (raw)
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Proceedings of SAGEEP, USA, 2009
Gravity survey is comparatively rarely applied for searching for hidden ancient targets. It is caused mainly by the small geometric size of the desired archaeological objects and various noises complicating the observed helpful signal. At the same time, developing a modern generation of field gravimetric equipment allows the register microGal (10^{-8}m/s^2) anomalies that offer a new challenge in this direction. Correspondingly, the accuracy of gravity variometers (gradientometers) is also sharply increased. Archaeological targets in Israel have been classified by their density/geometrical characteristics in several groups. It is supposed to apply in archaeological microgravity original methods for terrain relief computing developed earlier to examine ore deposits under mountainous conditions. 3-D modeling and advanced analysis of gravity anomalies have been applied to estimate the desirable gravity anomalies intensity and projected gravimetric grid. The second and third derivatives of gravity potential have been computed to estimate the resolution of derivative graphs from different models. It is underlined that the physical measurement of vertical gravity derivatives in archaeological studies is important and cannot be replaced by any transformation methods. The performed computations indicate that at least microgravity investigations might be successfully applied in 20-25% of archaeological sites in Israel.
International Journal of Geophysics, 2011
Microgravity investigations are widely applied at present for solving various environmental and geological problems. Unfortunately, microgravity survey is comparatively rarely used for searching for hidden ancient targets. It is caused mainly by small geometric size of the desired archaeological objects and various types of noise complicating the observed useful signal. At the same time, development of modern generation of field gravimetric equipment allows to register promptly and digitally microGal (10 −8 m/s 2) anomalies that offer a new challenge in this direction. An advanced methodology of gravity anomalies analysis and modern 3D modeling, intended for ancient targets delineation, is briefly presented. It is supposed to apply in archaeological microgravity the developed original methods for the surrounding terrain relief computing. Calculating second and third derivatives of gravity potential are useful for revealing some closed peculiarities of the different Physical-Archaeological Models (PAMs). It is underlined that physical measurement of vertical gravity derivatives in archaeological studying has a significant importance and cannot be replaced by any transformation methods. Archaeological targets in Israel have been ranged by their density/geometrical characteristics in several groups. The performed model computations indicate that microgravity investigations might be successfully applied at least in 20-25% of archaeological sites in Israel.
Identification of Buried Archeological Objects with Radial Derivatives of Micro Gravity Data
Indonesian Physical Review, 2019
The development of recent gravimetric technology allows us to measure gravity anomalies with accuracy of micro Gal. Micro gravity is able to detect very small gravity anomalies such as anomaly due to buried archeological objects below the earth surface. Radial Derivatives of gravity data is used to sharpen anomaly due to lateral changes of density contrast. Horizontal derivatives carried out by previous researchers have some weaknesses, i.e. the loss of derivative values in certain directions and inconsistence values at the source boundary of the same anomaly edge. To solve the horizontal derivative problem, a radial derivative is made. Radial derivative is derivative of gravity anomaly over horizontal distance in the radial direction from a certain point which is considered as the center of anomaly. There are two kind of radial derivative i.e. First Radial Derivative (FRD) and Second Radial Derivative (SRD). Blade Pattern is another way to enrich the ability of SRD to detect bounda...
Microgravity for detecting cavities in an archaeological site in Sardinia (Italy)
Near Surface Geophysics, 2015
We present a microgravity study over an archaeological site in Sardinia (Italy) subject to local subsidence, which could be correlated with subterranean cavities. Taking into account the local geological conditions and other factors such as topography, the high urbanization of the area, and financial factors, the micro-gravity method was used to determine the presence of voids and whether these voids are correlated with the local subsidence. A complete Bouguer anomaly map was produced with topography corrections with a density of 1.80 g/cm 3. The density used for the corrections was determined in the laboratory on samples of the geological formations from the same area. The gravity anomaly has been further corrected for the effect of massive structures such as walls and isolated blocks. After removing a third-order polynomial regional trend, the residual anomaly shows small but well-identified anomalies of circular shapes with amplitudes between 15 μGal and 40 μGal. The anomalies are spatially well correlated with the local subsidence, and a map of the vertical gradient of the residual field shows peaks located exactly over the small anomalies previously cited. Using two-dimensional qualitative and quantitative modelling, it is possible to assume that the voids are the cause of the anomalies and therefore could be also the cause of the local subsidence. of the subsurface of the area to identify the possible causes or origin of this subsidence and further, if necessary, to take appropriate steps to stabilize the area. Generally speaking, cavities may be natural, such as solution cavities in limestone, dolomite, and evaporites, or man-madelike tunnels, crypts, or mines (Butler 1984). In the area of investigation, subsidence affected the most superficial lithological unit made up of heterogeneous deposits of anthropogenic origin. In the subsident site, the substrate of the aforementioned unit is represented by a formation made up of sandstones more or less cemented and well compacted, alternating with less coherent sandy facies and the place of an aquifer. It should also be noted that empty or partially filled subsurface cavities are present in the archaeological site as shown by a few standard penetration tests (SPTs) not far from the investigated sector carried out before the subsident event. Therefore, the aim of the microgravity survey was to detect potential subsurface cavities or other anomalous conditions that could produce instability in the investigated area. The choice of the micro-gravimetric method was made considering first that the area was highly urbanized and therefore producing electric and electromagnetic noises that disturb the
Gravity Surveying in Early Geophysics. II. From Mountains to Salt Domes
Earth Sciences History, 2007
Progress in measurement of the force of gravity and its contribution to the understanding of geology, and to exploration for oil and mineral deposits, from the eighteenth to the early twentieth century is reviewed. Initially, work focused on determination of the mean density of the Earth. Pendulum observations during the trigonometric survey of India (1805-43) revealed a low-density zone beneath the Himalayas and led to development of the Pratt and Airy compensation models in 1855, followed by Dutton's concept of isostatic compensation in 1889. Use of the Eötvös torsion balance (1889) to map the gravity field over an oil-bearing structure in 1915-16 heralded economic applications. By the 1920s, it was being widely used to search for oil-bearing salt domes, coal and mineral deposits. With the introduction of the gravity meter in the 1930s, the torsion balance fell into disuse and the modern era of gravity surveying and prospecting began. With the development of progressively more sensitive instruments, the gravity meter has retained its place, becoming an essential companion to 3-D seismic surveys and, with new instrumentation, gradiometry has seen a revival as an extremely powerful exploration tool.
Gravity Gradiometry – Today and Tomorrow
11th SAGA Biennial Technical Meeting and Exhibition, 2009
Gravity gradiometry is coming of age as a standard exploration process. The acceptance and scope of airborne surveys is on the rise, with success stories published and documented. A renewed interest in marine surveys for hydrocarbons is also occurring. New sensor and system developments are nearing a point where they may be ready for field tests and commercial deployment. It is accurate to say that the state of gravity gradiometry is healthy in today's commercial marketplace. As good as this is, there remain a number of challenges and opportunities for full utilization of gravity gradiometry as a tool for the explorationist. A number of questions and concerns need to be addressed ranging from sensor performance to operational efficiency to data handling to educating users. While these challenges might seem daunting, the future looks bright for gradiometry as innovation and acceptance continue to grow. In fact, the time seems right to ask some thought-provoking "What if" questions: Is the era of gradiometry just beginning to dawn? How will the future unfold for this capability? What is the optimal exploration system? What if multiple gravity components could be measured at the same time (i.e. scalar gravity, 2 nd order tensors, and 3 rd order tensors)? Are the physical limits of measurement already being met? What if data were available without limits throughout the world?