Investigation and mapping of the temporary dynamics of the highest Lithuanian outcrop using ground-based measurements and UAV imagery

Abstract

The main goal of the study is to evaluate changes that have occurred in the Pūčkoriai outcrop surface over the 2014–2019 period and to compare the accuracy of ground-based measurements with that of UAV aerial image models. Ground-based measurements were performed applying the original methodology, which involves comparison of the first one and subsequent beam direction. For surface change surveys, we used repeated terrestrial geodetic measurements and UAV imagery. Ground-based measurements were performed using a Trimble M3 Total Station (with RTK); aerial images were captured using UAV INSPIRE1 with a ZENMUSE X3 camera. Pix4D photogrammetric software was used to create a DEM. The comparison of repeated terrestrial measurements and UAV aerial imagery revealed that the average change in the outcrop surface altitude over the period 2014–2019 amounted to 8.3 cm, with a maximum of 24.23 cm and a minimum of 0.33 cm. Contactless remote sensing allows obtaining data without affecting or altering the surface of the exposed deposits. The difference between terrestrial geodetic measurements and the UAV-based DEM did not exceed the following values: ΔX and ΔY ≤ 68 mm; ΔZ ≤ 21 mm. Previous research has shown that the use of UAV aerial photography images for assessing changes in outcrops consisting of loose sediment layers yields sufficiently accurate results. The present study focuses on the determination of quantitative indicators of seasonal changes in the outcrop surface. Quantitative surface changes of the outcrop were mapped based on dynamic signs, surface comparison and a formal choropleth map (10 × 10 m); dynamic zones of the outcrop were distinguished based on the results obtained employing these methods. The data obtained can be extrapolated to other Lithuanian river outcrops, which are characterized by a variety of sediments.