Browsing by Subject "UAV"
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(2023)The island of Suur-Pellinki is located near the town of Porvoo in the southern Finland. The bedrock in the area consists of different rock types such as plutonic rocks and rock types that are rare in the southern Finland, for example agglomerate and different kinds of metavolcanites. The bedrock has undergone several tectonic events, of which Svecofennian orogenesis (1.9-1.8 Ga) has been the most notable. The orogenesis caused compression, extension and shearing of the bedrock, and signs of these stresses can be seen as fractures, folds, foliations and faults. The development of unmanned aerial vehicles, such as drones, has been significant in recent years. Thus, usage of them has increased in different fields of science, of which geosciences are not an exception as drones are used in data collecting. In this study, a drone was used to study outcrops of Suur-Pellinki. Four outcrops were photographed by a drone, and photographs were used to build three-dimensional models. The models were built in Pix4D and Metashape software using Structure-from-Motion photogrammetry. In addition, the models were exported to GeoVis3D software, in which orientation of fractures was studied. The aim was to study the bedrock with traditional fieldwork methods and technology that has not been used in the area. It was studied if three dimensional modelling can provide any significant additional benefits over traditional fieldwork methods. Moreover, the aim was to find ways to operate a drone efficiently and build three-dimensional models straightforwardly. The bedrock was found to be undergone extensional and differently oriented compressional events during the orogeny, and the maximum principal stress (σ1) orientations had been firstly NW-SE and later NE-SW. These stress orientations formed the main structures of the bedrock such as fractures, folds, and foliation, which is prevalent in metavolcanites of the area. In addition, some strike-slip faults were seen in the area, which have not been studied significantly in the previous studies. The three-dimensional models turned out to be useful in order to study the bedrock. Critically, building of the models was not fast and straightforward. The final resolution of the models is under three centimetres, which let to study even the smallest structures of the bedrock.
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(2020)The condition of Tahmelanlähde spring in city of Tampere has been under discussion for over two decades. Between 1906–1966, the spring was being used for municipal water supply and the water quality was good. The quality of discharging groundwater has since heavily deteriorated, bearing now high concentrations of iron, manganese, nitrogen, phosphorus and very low oxygen. The cause of this deterioration has remained unclear. The aims of this study were to increase the hydrogeological knowledge of Tahmela-Pispala area in order to get a better understanding of the regional groundwater flow patterns and sources of the groundwater discharging at the artesian spring area, to assess the cause for the spring deterioration and to give suggestions to a possible rehabilitation plan. Tahmelanlähde spring is located on a clay or silt soil under artesian circumstances, down the southern slope of Pispalanharju interlobate esker formation. The esker forms a longitudinal neck between Lake Näsijärvi and Lake Pyhäjärvi, rising up to 160 meters above sea level. The water level of Lake Näsijärvi is approx. 95 m a.s.l. and the water level of Lake Pyhäjärvi approx. 77 m a.s.l. Considering the distance of only a few hundred meters between these two lakes, the difference of 18 meters in the lake water levels is quite unusual in Finland’s geological context, especially because the lakes are separated by a major esker formation. For the assessment of the hydrogeological features in the study area we had two field campaigns including ground penetrating radar (GPR) survey, thermal infrared survey using unmanned aerial vehicle (UAV-TIR), measuring of water tables as well as water sampling from springs, surface water bodies, groundwater observation wells and groundwater discharging into the Lake Pyhäjärvi. 23 water samples were analyzed for main ion composition, stable isotopic (δ18O / δD) composition, pH, EC and trace elements such as iron and manganese. 14 samples were additionally analyzed for CODMn, N, P, O and microbial indicators. Some previous studies have suggested infiltration of Lake Näsijärvi water into the esker. Our results reveal that most of the groundwater in the Pispalanharju area contain a variable amount of surface water component. The samples east from the spring present good-quality groundwater and show nonexistent surface water impact. This and the complex sedimentology revealed by the GPR survey indicate that the regional groundwater flow patterns are not simple and there are at least two water components with different origins discharging at Tahmelanlähde spring. The results imply that the primary cause for the spring deterioration could be a major shift in the groundwater – surface water interaction in the northern esker area, probably driven by urbanization and the heavy construction during the last few decades. The study was a collaboration between the City of Tampere, Pirkanmaa Center for Economic Development, Transport and Environment (ELY Center) and University of Helsinki, Department of Geosciences and Geography.
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