Gravimetric Model of Quasigeoid in the Area of Slovakia

The gravimetric model of quasigeoid in the area of Slovakia was determined by using the revised and homogenised gravity mapping data in the scale of 1:25 000 from the area of Slovakia, and by using the mean Bouguer gravity anomalies with the resolution of 5´x7.5´ in the area 44°<φ<56° and 12°<λ<30° from abroad and by the digital terrain model DMR-2/ERTS89 with the resolution 3“ in the ellipsoidal latitude and 5“ in the ellipsoidal longitude from the area of Slovakia and the digital terrain model GTOPO30 with the resolution of 30“ in the ellipsoidal latitude and 30“ in the ellipsoidal longitude from abroad. The global part of the height anomaly was determined from the global geopotential model EGM96. The residual part of the height anomaly was determined by the Stokes integral formula. For the solution of the Stokes integra,l the Fast Fourier Transformation method in the spherical approximation was used. The gravimetric quasigeoid was tested by the GPS/levelling method using 46 points distributed on the area of Slovakia. The systematic trend of differences between height anomalies was rejected by the surface polynomial of second degree with 6 coefficients. The standard deviation after removing a systematic trend was 0.017

In Search of Hidden Chambers at Newgrange Passage Tomb

Kevin Barton, Roman Pašteka, Palo Zahorec, Juraj Papčo and Conor Brady describe the first use of microgravity on a passage tomb in Irelan

Identifikácia a mapovanie potenciálne ilegálnych aktivít v krajine aplikáciou metód diaľkového prieskumu Zeme

Prezentované výsledky boli dosiahnuté riešením projektu „Detekcia diverzity krajiny Slovenska a jej zmien na báze údajov diaľkového prieskumu v kontexte Zelenej dohody EÚ“ podporeného grantom VEGA 2/0043/23

Interpretation of spatiotemporal gravity changes accompanying the earthquake of 21 August 2017 on Ischia (Italy)

We analyse spatiotemporal gravity changes observed on the Ischia island (Italy) accompanying the destructive earthquake of 21 August 2017. The 29 May 2016 to 22 September 2017 time-lapse gravity changes observed at 18 benchmarks of the Ischia gravimetric network are first corrected for the gravitational effect of the surface deformation using the deformation-induced topographic effect (DITE) correction. The co-seismic DITE is computed by Newtonian volumetric integration using the Toposk software, a high-resolution LiDAR DEM and the co-seismic vertical displacement field derived from Sentinel-1 InSAR data. We compare numerically the DITE field with its commonly used Bouguer approximation over the island of Ischia with the outcome that the Bouguer approximation of DITE is adequate and accurate in this case. The residual gravity changes are then computed at gravity benchmarks by correcting the observed gravity changes for the planar Bouguer effect of the elevation changes at benchmarks over the same period. The residual gravity changes are then inverted using an inversion approach based on model exploration and growing source bodies, making use of the Growth-dg inversion tool. The found inversion model, given as subsurface time-lapse density changes, is then interpreted as mainly due to a co-seismic or post-seismic disturbance of the hydrothermal system of the island. Pros and weak points of such interpretation are discussed

Corrigendum: Interpretation of spatiotemporal gravity changes accompanying the earthquake of 21 August 2017 on Ischia (Italy)

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Multi-sensor and multi-temporal approach in monitoring of deformation zone with permanent monitoring solution and management of environmental changes: A case study of Solotvyno salt mine, Ukraine

Salt deposits were a rich source of mineral resources in the past, and some are still mined today. However, salt mines, especially abandoned ones, pose a threat to populated areas, infrastructure and the natural environment. Solotvyno (Ukraine) is one of the most significantly affected areas, with a deformation zone where significant year-on-year subsidences occur. Mining activities have caused a disturbance of the balance in the mountain massif, and as a consequence, the mountains are being reshaped, and the land cover is deformed. Deformation zone of the historical salt mine Solotvyno (Ukraine), Tyachiv district of Zakarpattia region is situated on the right bank of the Tisza river in the border area with Romania in Central Europe. This paper deals with the multi-sensor monitoring of the active deformation zone over the Solotvyno salt mine using satellite radar data (Sentinel-1), optical satellite imagery (Pleiades, SPOT) and in-situ UAV photogrammetry. Since the area represents a significant geohazard from a hydrogeological (Tisza River) and civil security standpoints (infrastructure of the inhabited regions), the design of a high-precision monitoring system to monitor and evaluate current environmental changes is proposed. Multi-temporal InSAR analysis exposed steeper subsidence tendencies of &gt;−2 cm in the central part of the monitored area. Optical satellite and UAV images confirmed the increase in water surface in sinkhole areas up to 28,500 m2 and proved the emergence of new sinkholes in the central part of the Solotvyno mine. The aim of this study is to describe the post-collapse deformation processes by Pleiades and SPOT multi-spectral sensors and Sentinel-1 satellite SAR sensors since the 2010 collapse in order to describe the trends of deformation due to undermining and propose a high-precision permanent monitoring system based on satellite radar interferometry (InSAR)

Quad-tree Based Finite Volume Method for Diffusion Equations with Application to SAR Imaged Filtering

summary:In this paper we present a method to remove the noise by applying the Perona Malik algorithm working on an irregular computational grid. This grid is obtained with a quad-tree technique and is adapted to the image intensities—pixels with similar intensities can form large elements. We apply this algorithm to remove the speckle noise present in SAR images, i.e., images obtained by radars with a synthetic aperture enabling to increase their resolution in an electronic way. The presence of the speckle in an image degrades the quality of the image and makes interpretation of features more difficult. Our purpose is to remove this noise to such a degree that the edge detection or landscape elements detection can be performed with relatively simple tools. The progress of smoothing leads to grids with significantly less number of elements than the original number of pixels. The results are compared with measurements performed on an inspected area of interest. At the end we show the possibility to modify the scheme to the adaptive mean curvature flow filter which can be used to smooth the boundaries

Searching for hidden chambers at Newgrange Passage Tomb; some results with an evaluation of the multi-method geophysical techniques used.

Newgrange Passage Tomb is 76m in diameter and 12m high. A single 19m inner passage leads to a chamber some 6m in diameter and height. The possibility of further chambers existing has been the subject of interest since the partial excavation completed in 1975. Multiple passageways and chambers exist at nearby tombs at Knowth and Dowth - could there be hidden chambers at Newgrange that could be detected using geophysical methods? We present the results from a multi-method geophysical survey. The principal method used was microgravity which has found hidden cavities in the Great Pyramid at Giza in Egypt. The method has also been used to detect the presence of medieval crypts but there has been little research in the use of microgravity in the detection of chambers in mounds due to their generally small dimensions. The situation in mounds at Brú na Bóinne is different. The major chambers have quite large dimensions, thus enhancing the detection capability of microgravity. A computer simulation to predict the gravity anomaly over the Newgrange chamber was carried out. This showed that the calculated effect on gravity of the chamber volume together with its depth within the mound would produce a measurable negative gravity anomaly. The key objective of the survey was to investigate the potential of the microgravity method in the initial detection of the known chamber and subsequently in searching for possible hidden chambers. The processing and interpretation of the microgravity survey was informed by ground penetrating radar, electrical resistivity tomography, multi-frequency electromagnetic and earth resistance results. Initial gravity measurements were made over and in the vicinity of the known chamber. The position of each measurement point was precisely determined using a combination of differential GPS and laser tachymetry methods. Strong winds at the time of survey required windshields to be used to protect the instruments from gusts and each measurement was verified by repeat readings. The average error from repeated and independently controlled measurement points was +/-15 microGals. This is relatively high but acceptable in the case of this survey. Data were processed to remove the effects of elevation, tidal variation, topography, latitude, and instrument drift. Topography corrections were made using LiDAR data. The output was a gravity anomaly map draped on a 3-D model made from the LiDAR data which presents the properties and geometry of sub-surface inhomogeneities. The map shows a well developed negative anomaly over the centre of the chamber. The size of the anomaly at its centre is several times larger than the precision of the instrument and also the average error of the instruments. Further gravity measurements were made on the mound and in the chamber in order to seek further anomalies and refine the gravity model of the known chamber. The results confirm the measured gravity anomaly is significantly larger than the computed anomaly based on laser tachymetry measurements of the spaceform of the chamber. This leads us to believe there is an unknown feature or structure of low density associated with the known chamber

Surface strain rate colour map of the Tatra Mountains region (Slovakia) based on GNSS data

The surface deformation of the Tatra Mountains region in Western Carpathians can nowadays be studied directly thanks to precise geodetic measurements using the GNSS. The strain or stress tensor field is, however, a rather complex “data structure” difficult to present legibly and with sufficient resolution in the form of a classical map. A novel and promising approach to the solution of this problem is coding the three principal strain or stress values into the three colour channels (red, green, blue) of an RGB colour. In our previous study, the colour depended on the stress tensor shape descriptors. In the current study, the adapted colouring scheme uses a subset of shape descriptors common to stress and strain, which differ only in the scaling factor. In this manner, we generate the colour map of the surface strain rate field, where the colour of each grid point carries the information about the shape of the strain rate tensor at that point. The resulting strain rate colour map can be displayed simultaneously with the map of the faults or elevations and be easily checked for the data or interpolation method errors and incompatibility with the geophysical and geological expectations

A detailed quasigeoid model of the Hong Kong territories computed by applying a finite-element method of solving the oblique derivative boundary-value problem

New gravity and precise levelling measurements have been performed throughout the Hong Kong territories to modernize a vertical geodetic datum that is currently realized by heights of levelling benchmarks defined in the Hong Kong Principal Datum (HKPD). Modernization of the HKPD involved delivering various products, including new detailed geoid and quasigeoid models and newly determined orthometric and normal heights of levelling benchmarks. In this study, we present the result of gravimetric quasigeoid modelling. The method used to compute a detailed gravimetric quasigeoid model is based on the finite-element method to solve the geodetic boundary-value problem with oblique derivative boundary conditions considered directly at computational nodes on the discretized Earth’s topography. The result of a gravimetric quasigeoid modelling shows a good agreement with a geometric quasigeoid model at the Global Navigation Satellite System (GNSS)-levelling benchmarks. The standard deviation of differences between the gravimetric and geometric quasigeoid heights of ±3.3 cm is compatible with the expected accuracy of gravity, levelling, and GNSS measurements