engleski

Application of geodetic techniques in geological studies of the Plitvice Lakes National Park

Plitvice Lakes, a unique hydrocarstic phenomenon situated in the External Dinaridic region, is the oldest and largest national park in Croatia. Understanding the evolution and formation of the lakes through the Quaternary and the fragile natural balance that sustains them inevitably requires consideration of their inherited geological framework that underlies the lakes. In 2017, a three-year project funded by the Plitvice Lakes National Park was initiated in order to improve existing knowledge on the tectonostratigraphic evolution, paleogeography and Quaternary evolution of the Plitvice lakes area through the application of carbonate sedimentology, micropaleontology, structural geology and state-of-the-art geodetic techniques. UAS photogrammetry and interferometric multibeam sonar system are used to build models of individual geological outcrops and bathymetric maps of lakes (Fig. 1) with a high level of resolution and spatial accuracy. These first time applied geodetic techniques and tools in the Plitvice Lakes National Park offer exceptional visualization opportunities for Park visitors to comprehend the geological framework of the lake system and its evolution through the Quaternary. Moreover, applied geodetic techniques provide an essential analytical dataset for understanding and improving existing geological models that may help in the protection of this fragile hydrocarstic system exposed to enormous anthropogenic pressure. Beside excellent educational and science popularization tool, recorded digital outcrop and bathymetry map of the lakes are effective methods of documenting and surveying important geological locations potentially endangered by human activity. In this study three Triassic and Cretaceous carbonate outcrops, together with Lakes Kozjak and Prošćansko bathymetry were digitally captured within the Plitvice Lakes National Park using UAS photogrammetry and multibeam sonar, respectively. The outcrops were recorded using a custom made unmanned multi-rotor system and Sony Alpha 7R digital camera with 36.3- megapixel full-frame sensor and Sony FE 35mm Carl Zeiss lens. High precision positioning of camera shots was achieved using multi-frequency Septentrio AsteRx-m GNSS receiver. Over 1000 oblique photographs were used together with positioning data to construct 3D scenes (Fig. 1) employing Structure from Motion algorithms. Hydrographic surveying of Lakes Kozjak and Prošćansko bottom surface was performed using Bathyswath-2-UW interferometric multibeam echosounder (PUJOL et al., 2012), whereas positioning and orientation was achieved using SBG-Systems Ekinox-A motion reference units (MRU) that gives attitude information for roll, pitch and heave parameters. Precise position and heading information was obtained using Hemisphere Vector VS330 dual antenna with Eclipse GNSS technology. The results are detailed high-resolution 2D and 3D outcrop and lake-bottom models (Fig. 1) with centimeter level accuracy in the form of colored-code point clouds or mesh surfaces. Besides effective visualization, constructed outcrop and lake-bottom models can be analyzed structurally, stratigraphically and hydrographically (e.g. PRINGLE et al., 2010). This may imply interpretation and modeling of specific lithostratigraphic facies and discontinuities, as well as accurate measurement of identified structural features, i.e., bedding, fault and fracture plane systems. The digital models are particularly useful for spatial reconstruction of dislocated features, i.e., strata beds, fault planes, tectonostratigraphic facies that are in most cases visible only on individual parts of large segmented outcrops. Modeled surfaces and facies can be further used for volume calculations and 3D modeling. Bathymetry data can also be used for temporal monitoring of lakes bottom changes.

NP Plitvice Lakes, UAV photogrammetry, inteferometric multibeam sonar system, 3D geological modelling, hydrographic surveying

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