Juraj Papčo

The calculation of building corrections in microgravity surveys using close range photogrammetry

Use of the microgravity technique for cavity detection in the exploration of historical buildings requires careful data acquisition and modern processing procedures. We have developed a new method for the calculation of building effects, where geodetic measurements and special photogrammetric software are used. In our new approach, a three-dimensional polyhedral model of an historical building is created from images using Eos System’s PhotoModeler Scanner software. A comparison of equations for the calculation of the gravitational effect of polyhedral bodies is presented on a simple test model. The methodology of microgravity data processing is demonstrated on a small Slovak church, where two crypts were successfully detected using microgravity and GPR techniques in summer 2009. We have shown that close range photogrammetry methods offer a possibility to improve the microgravity data processing procedure.

Role of Near Topography and Building Effects in Vertical Gravity Gradients Approximation

Importance of precise vertical gradient of gravity (VGG) determination by means of relative gravity measurements is mainly connected with absolute gravity measurements and setting of global and local gravity reference networks. The gravitational effect of the topography and near building structures and their contribution on the vertical gradient of gravity (VGG) was studied. A strong impact of near topography on the VGG values was found in the case of the mountainous areas - deviations up to 88 percent of normal value were obtained by means of relative gravity measurements. Near building structures gravitational effect was estimated by means of simple polyhedrons - very specific nonlinear behaviour of VGG is demonstrated on two model examples. Synthetic tests for the estimation of determined VGG precision are also presented. The error of polynomial estimation of the VGG can be several times higher than the error within measured gravity. For a set of 29 real measurement points a relatively good coincidence between the measured and calculated VGG values was achieved. Application of predicted values of the VGG instead of the normal ones in cases of unknown actual values can lead to a quality improvement of gravimetric reference networks, as well as prospecting VGG measurements.

Case history: integrated geophysical survey at Katarínka Monastery (Slovakia)

Katarinka (St. Catherine) is the ruin of an abandoned Franciscan monastery from the early 17th century located in the western Small Carpathians in Slovakia. Historical sources and paintings suggest that, beside the remains of the monastery that are still visible, a circle of eight chapels, a pilgrim’s hospice, a cemetery, and garden terraces originally surrounded the main building of the monastery. From 2009 to 2012, geophysical campaigns were performed to find evidences and positions of remains of these buildings of the monastery campus. An initial magnetic overview survey revealed multiple local accumulations of disordered dipole anomalies. Since these accumulations did not allow a structural interpretation, ground penetrating radar measurements were conducted. The ground penetrating radar results clearly showed wall structures beneath almost all magnetic anomaly accumulations. In between the remains of the monastery main building, ground penetrating radar and electrical resistivity tomography were performed at different areas that were difficult to access because of a strong cover of vegetation and steep topography.

The role of near topography and building effects in vertical gravity gradients approximation

The gravitational effect of the topography and near-building structures and their contribution on the vertical gradient of gravity (VGG) was studied. The strong impact of near topography on the VGG values was found in the case of the mountainous areas – deviations of up to 88% of normal value were obtained by means of relative gravity measurements in selected parts of Slovakia. Newly developed software and a high-quality detailed digital terrain model of Slovakia was used for the evaluation of the topographical effect. The gravitational effect of near-building structures was estimated by means of simple 3D bodies approximation, i.e., rectangular or polygonal prisms. A very specific non-linear behaviour of VGG is demonstrated on model examples. A relatively good agreement between the measured and calculated (predicted) VGG values was achieved for a set of selected 32 real measurement points. The application of estimated (predicted) values of the VGG instead of the normal ones can lead to a quality improvement of global and local gravimetric reference networks, as well as prospecting VGG measurements.

The estimation of errors in calculated terrain corrections in the Tatra Mountains

The estimation of errors in calculated terrain corrections in the Tatra Mountains In general, calculation of terrain corrections can be a substantial source of errors in evaluating Bouguer anomalies, especially in rugged mountainous areas like the Tatra Mountains where we also get the largest values of the terrain corrections as such. It is then natural that analysis of their calculations in this area can shed light on the magnitude of correction-related errors within the whole Slovak territory. In the framework of our analysis we have estimated the effect of different computing approaches as well as the influence of accuracy of the inputs, i.e. the heights and positions of the measuring points, together with the used digital terrain models. For the sake of testing the computer programs which are currently in use, we have also substituted the real terrain by synthetic topography. We found that among the concerned constituents the most important factor is the used digital terrain model and its accuracy. The possible model-caused errors can exceed 10 mGal in the Tatra Mountains (for the density of 2.67 g.cm-3).

Some Remarks on the Early History of the Bouguer Anomaly

When discussing the various aspects of the Bouguer anomaly calculation in the past we came across numerous discrepancies in its definition expressed either in textbooks (sometimes even including modern texts) or in not less than 10 important articles and discussions which have been published within the last 25 years. Therefore we continued in investigating in more detail to determine how and when some of the key notions involved, as well as the used terminology, came into existence. For instance, one can find that the term “Bouguer reduction” is most likely accreditable to Helmert. This term was used in the context of the then popular geodetic concept of reducing gravity from the Earth surface to the sea level, although Bouguer himself had never reduced gravity values or pendulum lengths in such a manner. Another well-known procedure, namely the “free-air reduction” which was sometimes called “Faye reduction,” had in fact very little to do with Faye himself, as can be deduced from Faye’s original memoirs. However, we confirm that the foundations of the so-called “Bouguer anomaly” and the procedures applied to the measured gravity which are required by the gravity method of applied geophysics can be well tracked back to originate from the famous book of Pierre Bouguer published in 1749. Among others we call attention especially to one specific historical artefact, namely the misunderstanding associated with the gravity data reductions to the sea level in applied geophysics which, although geophysically unacceptable, has withstood the ravages of time and can be found in the literature even in the 21th century, as we illustrate in this contribution.

Chapter 7 – National Gravimetric Database of the Slovak Republic

Compilation of the Slovak gravimetric database with the actual amount of about 320,000 observation points is presented. Gravity data were collected during more than 50 years, which yields a very heterogeneous dataset, with large variations in the station coverage and processing methods. The regional gravimetric database (more than 212,000 points) was resumed in 2001. The compilation discussed herein (with more than 107,000 detailed gravity measurements) was made during 2011–14. Quality-control process and complete recalculation of the Bouguer anomalies is presented. Primary focus of this project was on a proper recalculation of the terrain corrections. New detected linear features in the Bouguer anomaly map were verified by the field measurements. A new software solution for reconstruction of the gravity acceleration values from the Bouguer anomaly map was developed for geodetic applications.

Comparison of Different Approaches to Gravity Determination and Their Utilization for Calculation of Geopotential Numbers in the Slovak National Levelling Network

Vertical reference system in the Slovak Republic is realized by the first and second order of the National levelling network with the normal heights according to Molodenski. The reference heights are still calculated by the traditional method using the components of gravity correction. Nowadays we are preparing a new realization of the height system which will be based on geopotential numbers. But there is a problem with the absence of the measured gravity values. Only at approximately 8% of levelling points we have the measured values of gravity. Therefore, we are trying to find the most reliable method for estimation of the gravity values and use them subsequently for determination of the geopotential numbers. The aim of this study is to analyze the different ways to the gravity determination and their application for calculation of the geopotential numbers on the points of the National levelling network. The first method is based on the reconstruction of the gravity on levelling points from the interpolated values of the complete Bouguer anomaly using the proprietary software. The second method is based on the modern global geopotential models improved by the residual terrain model approach. Calculated gravity was compared with directly measured gravity. The set of the points contained all geodetic control points within Slovakia where the gravity has been measured. Then, the calculated value of gravity was used to determine the geopotential numbers and normal heights according to Molodenski in the first order levelling lines of the National levelling network which connect the reference points determined within EVRF2007 adjustment for area of Slovakia.

Integration of Heterogeneous Data in the Support of the Forest Protection: Structural Concept

The basic precondition for effective management and protection of a forest is a concept built on modern methods of collection, processing, analysis and publication of spatial data about forest coverage, as well as its health status. This paper provides a structural concept for integration of heterogeneous data in the support of the forest protection with implementation of the latest methods of remote sensing data collection. The main principles of the structural concept of Forest protection management system (FPMS) result from the assessment of the current and new available data sources (represented by the Diagram of data sources), data analysis and development of innovative mathematical techniques of image processing (represented by the Diagram of methods and tools). Mind maps of the proposed diagrams were created in the free mind mapping application FreeMind. The structural concept is represented by an analytical model of the co-operation of data sources, tools and applications. The dynamic structure was proposed using Unified Modelling Language (UML). The Diagram of the use cases is represented by a Use Case Diagram in UML. The Diagram of the processes, which describes the main processes realized within forest protection management, is represented by an Activity Diagram in UML. The UML diagrams were created in open-source software StarUML. The resulted structural concept of FPMS is the basis of a predictive model improvement and a web application development for the forest protection from the bark beetle.

High resolution Slovak Bouguer gravity anomaly map and its enhanced derivative transformations: new possibilities for interpretation of anomalous gravity fields

Abstract The paper deals with the revision and enrichment of the present gravimetric database of the Slovak Republic. The output of this process is a new version of the complete Bouguer anomaly (CBA) field on our territory. Thanks to the taking into account of more accurate terrain corrections, this field has significantly higher quality and higher resolution capabilities. The excellent features of this map will allow us to re-evaluate and improve the qualitative interpretation of the gravity field when researching the structural and tectonic geology of the Western Carpathian lithosphere. In the contribution we also analyse the field of the new CBA based on the properties of various transformed fields – in particular the horizontal gradient, which by its local maximums defines important density boundaries in the lateral direction. All original and new transformed maps make a significant contribution to improving the geological interpretation of the CBA field. Except for the horizontal gradient field, we are also interested in a new special transformation of TDXAS, which excellently separates various detected anomalies of gravity field and improves their lateral delimitation.