ALBERT

Description: Study presented in this paper is focused on comparison and statistical assessment of differences between the selected Level 2 products of the satellite mission Gravity Recovery and Climate Experiment (GRACE). Global monthly gravity field models in terms of spherical harmonic coefficients produced by three institutes of GRACE Science Data System are compared with the partially independent MASCON global gravity field model. Detailed comparison and statistical analysis of differences is performed in 5 selected river basins: Amazon, Congo, Danube, Yenisei and Lena. For each spherical harmonic solution, 8 different filtrations available at International Center for Global Gravity Field Models (ICGEM) are tested over the time span from April 2002 to July 2016. Fischer test at two significance levels 10% and 5% has been performed in order to qualify the statistical significance between the particular solutions.

Description: BeiDou Navigation Satellite System (BDS) is composed of satellites in geostationary Earth orbit (GEO), medium Earth orbit (MEO) and inclined geosynchronous orbit (IGSO). However, the orbit determination of geostationary Earth orbits and of geosynchronous orbits (GSO) with small inclination angle and small eccentricity is a challenging task that is addressed in this paper using Extended Kalman Filter (EKF). The satellite positions were predicted in Earth-centred inertial (ECI) reference frame when propagated through Keplerian model and perturbation force model for different values of right ascension of ascending node (RAAN). Root mean square (RMS) errors of 9.61 cm, 6.73 cm and 11.46 cm were observed in ECI X, Y and Z satellite position coordinates of GSO respectively, whereas, the RMS errors for GEO satellite were 8.89 cm, 7.92 cm, and 0.93 cm respectively in ECI X, Y and Z coordinates; for perturbation force model with maximum value of RAAN when compared with dynamic orbit determination model. Kolmogorov-Smirnov test for EKF reported a p-value 〉 0.05, indicating a good fit of perturbation force model for orbit propagation. Orbit determination using EKF with perturbation force model were compared with that using EKF with Kepler's model. Wilcoxon Rank Sum test was used to compare the residuals from EKF algorithm through Kepler's model and perturbation force model. EKF with Perturbation force model showed improvement in predicting the satellite positions as compared to Kepler's model. EKF with Perturbation force model was further applied to International GNSS Service (IGS) station data and kilometre level accuracy was achieved. RMS errors of 0.75 km, 2.53 km and 1.91 km were observed in ECI X, Y and Z satellite position coordinates of GSO, respectively, whereas, the RMS errors for GEO satellite were 3.89 km, 4.20 km and 6.66 km respectively in ECI X, Y and Z coordinates for perturbation force model.

Description: Santorini is located in the central part of the Hellenic Volcanic Arc (South Aegean Sea) and is well known for the Late-Bronze-Age “Minoan” eruption that may have been responsible for the decline of the great Minoan civilization on the island of Crete. To use gravity to probe the internal structure of the volcano and to determine whether there are temporal variations in gravity due to near surface changes, we construct two gravity maps. Dionysos Satellite Observatory (DSO) of the National Technical University of Athens (NTUA) carried out terrestrial gravity measurements in December 2012 and in September 2014 at selected locations on Thera, Nea Kameni, Palea Kameni, Therasia, Aspronisi and Christiana islands. Absolute gravity values were calculated using raw gravity data at every station for all datasets. The results were compared with gravity measurements performed in July 1976 by DSO/NTUA and absolute gravity values derived from the Hellenic Military Geographical Service (HMGS) and other sources. Marine gravity data that were collected during the PROTEUS project in November and December 2015 fill between the land gravity datasets. An appropriate Digital Elevation Model (DEM) with topographic and bathymetric data was also produced. Finally, based on the two combined datasets (one for 2012–2014 and one for the 1970s), Free air and complete Bouguer gravity anomaly maps were produced following the appropriate data corrections and reductions. The pattern of complete Bouguer gravity anomaly maps was consistent with seismological results within the caldera. Finally from the comparison of the measurements made at the same place, we found that, within the caldera, the inner process of the volcano is ongoing both before, and after, the unrest period of 2011–2012.

Description: Interpretation and inversion of microgravity anomalies belong to important tasks of near-surface geophysics, mostly in cavities detection in engineering, environmental and archaeological applications. One of the mostly used concepts of inversion in applied gravimetry is based on the approximation of the model space by means of 2D or 3D elementary sources with the aim to estimate their densities by means of the solution of a corresponding linear equation system. There were published several approaches trying to obtain correct and realistic results, which describe real parameters of the sources. In the proposed contribution we analyse the properties of two additional functionals, which describe additional properties of the searched solution – namely so-called L2-smoothing and minimum support focusing stabilizers. For the inversion itself, we have used the regularized conjugate gradient method. We have studied properties of these two stabilizers in the case of one synthetic model and one real-world dataset (microgravity data from St. Nicholas church in Trnava). Results have shown that proposed algorithm with the minimum support stabilizer can generate satisfactory model results, from which we can describe real geometry, dimensions and physical properties of interpreted cavities.

Description: 3D post-stack time migrated seismic data and a suite of composite well log data from six wells drilled within the “AFUN” field Niger delta were used to effect a detailed interpretation of the field. This was with a view to delineating architectural elements that control reservoir quality of a deepwater turbidite reservoir. The data analyses were done using the Petrel software. LAS file of logs were imported into the Petrel software as well as SEG.Y. seismic data. Fault interpretation and horizon mapping were based on the well-seismic tie from the generated seismogram. Time and depth structure maps were created. Thirty faults which include growth faults, reverse faults, collapsed crest structure and as well as faults that are synthetic and antithetic to the growth faults were mapped. The growth faults are believed to act as pathways for the updip movement of hydrocarbon from the Akata Formation to Agbada Formation. The structural interpretation showed that the area has been subjected to compressional deformation which resulted in reverse faulting system in toe thrust zone influenced by shale diapirs. The maps revealed contour closures that belong to an anticlinal structure which is forming traps in the reservoirs. The structures are faulted North-South trending rollover anticlines. It has also been shown that the distribution and type of architectural elements i.e. fractures within the fan system have major impact upon the reservoir distribution, continuity and connectivity of sand/shale bodies. The study concluded that structural style and facies architecture are the two fundamental elements that defined the reservoir heterogeneity of the “AFUN” Field.

Description: A quasi 3D electrical resistivity (ERT) survey was undertaken at a UNESCO World Heritage site, Saqqara, Giza, Egypt, during a joint archaeological-geophysical mission from Cairo University. The main objective is to detect the locations of the subsurface archaeological tombs/or crypts and to allocate any possible archaeological bodies/features buried underneath the study area. In this survey, SYSCAL Pro system with 24 electrodes and a multi-core cable is used for automatic data acquisition of profiling data. The dipole–dipole array was used to enhance resolution, 14 resistivity lines are conducted during this Survey. The processed data were analysed in order to produce resistivity tomography (ERT) for qualitative and quantitative interpretations. Inversion of the ERT data identified variation of resistivity values and the expected locations of the underground galleries and highlight the presence of regular shape structures probably due to features of archaeological interest. Excavations made accordingly in the study area led to an interesting discovery of a tomb of the Great Army General, Iwrhya. The tomb is approximately 2000 years old as it covers the reigns of both Kings Seth I and Ramesses II. Using the 3D resistivity tomography with such a multi-electrode technique proved its efficiency and applicability for non-invasive archaeo-geophysical prospecting.

Description: 2D integrated modelling approach was applied to determine the lithospheric structure along transect HT-1 located in the Carpathian-Pannonian Basin–European platform region. Our approach combines simultaneous interpretation of surface heat flow, topography, gravity and geoid data. All available geophysical and geological data were used to create an initial model that has been afterwards modified by trial and error method until reasonable fit was obtained between input data and model predictions. The main focus of our study was the position and shape of the lithosphere-asthenosphere boundary (LAB). In the Pannonian Basin the modelled LAB is at depths of about 80–90 km and rapidly dips towards the Western Carpathians where its depth reaches values 145 to 150 km. Beneath the European platform the LAB depth is about 135–140 km. We can observe a slight lithospheric root under the Western Carpathians. This lithospheric thickening is interpreted as a small remnant of a subducted slab. This result is in a good agreement with the previous lithospheric models in the Carpathian-Pannonian Basin.

Description: The National Network of Seismic Stations of Slovakia (NNSS) consists of eight short period and five broadband permanent seismic stations and a data centre located at the Earth Science Institute of the Slovak Academy of Sciences (ESI SAS). The NNSS recorded and detected 11,487 seismic events from all epicentral distances in 2019. Totally 91 earthquakes originated in the territory of Slovakia in 2019. This paper provides basic information on the configuration of the NNSS, routine data processing, seismic activity on the territory of Slovakia in 2019 as well as macroseismic observations collected in 2019.

Description: The gravitational effects caused by normal and reverse faults are very close to each other, both in amplitude and in the shape. We demonstrate the usage of the first curvature as a tool for the setting the slope orientation without the additional geological information. The curvature is calculated not only for the measured data, but for their upward continuation, too. This step helps to lower instability of the curvature computation and is important in the interpretation of the resultant curvature as well. We applied this method on the synthetic test and on the real regional gravimetric data as well. The results show the method could be useful step before the density modelling process and generally during qualitative interpretation in applied gravimetry.

Description: A detailed knowledge of the thickness of crust and upper mantle structure is important for understanding a plate tectonics and geodynamics in the region. We use body wave for detecting details of the subsurface structure. The information in this research is collected from a seismic linear profile that extends across the Sanandaj-Sirjan metamorphic zone in seismic states of Central Iran and Zagros. We compute P receiver functions to investigate crustal and upper mantle discontinuities. We use teleseismic events (mb ≥ 5.5, 30° 〈 Δ 〈 95°) registered between 1996 and 2018 and recorded at 10 short-period stations with 3 components and 17 broadband stations with high signal to noise ratio. The observed depth of Moho in the study area is approximately 50 km and rises to 70 km at the end of the seismic linear profile beneath Sanandaj-Sirjan zone. In Central Iran, depths discontinuities in the transition zone are shown by the reference model of deviation, which can be attributed to the convergence of Arabian plate with the Central Iran plateau. Also, the study area was identified as geothermal susceptibility by SUNA and this observation was confirmed.