Page 18 - Studia Universitatis Hereditati, vol 13(2) (2025)

Osor lies at the northern most part of a tively quickly using a dense point cloud. Af-
karstified and tectonic depression (Lošinj Chan- ter the points are classified, products, primari-
nel), with a sediment infill > 200 m above a Cre- ly digital terrain models, can be derived. These
taceous basement (Brunović et al. 2024) (fig. show the terrain, and all traces of human activ-
3). The modern-day bathymetry of the Lošinj ity preserved in relief. In the last decade, ALS
Channel indicated the existence of several dis- has greatly improved large-scale archaeological
tinct areas within the basin. The shallow north- research in the Mediterranean (e.g. Vinci et al.
ernmost part of the channel extends from the 2024). Of special interest is also the use of green
shoreline to a depth of ~40 m with a slope of < laser scanners with small footprints for airborne
11° that separates this area from the central part laser bathymetry (ALB). They have the capabil-
of the Lošinj Channel with a maximum wa- ity to penetrate clear water and consequently
ter depth of 74 m. The lateral decrease in depth measure the underwater topography in high de-
18 along the basin margins occurs relatively abrupt- tail resulting in DSMs/DTMs with 0.5 m raster
ly (Brunović et al. 2024). Marine flooding of the width combining the topography of underwater,
Lošinj Channel occurred during the Holocene, terrestrial surfaces as well as the intertidal zone
studia universitatis hereditati, letnik 13 (2025), številka 2 / volume 13 (2025), number 2
with data from the channel indicating relative (Doneus et al. 2015; Doneus et al. 2013).
tectonic stability or weak subsidence during this ALB data acquisition was conducted on
period (Brunović et al. 2020; 2024). 29th of March 2012 between 10:54 and 11:33 lo-
Prevalent strata on the islands Lošinj and cal time at low tide and at calm wind and wa-
Cres are carbonate deposits of Cretaceous age ter conditions. A RIEGL VQ-820-G was operat-
(Korbar et al. 2001; Korbar and Husinec 2003, ed at an effective measurement rate of 200 kHz
Fuček et al. 2014). The wider area is characterised and a 60° scan angle. The flying height of 450
by 18 lithostratigraphical units of various geolog- m resulted in footprints of 0.45 m diameter on
ical age (Cretaceous, Palaeogene, Quaternary). the water surface. The flying strips had an over-
Several reverse faults were recognized on geolog- lap of 70%. Processing was done using the soft-
ical maps of islands Lošinj and Cres (Mamužić ware RiPROCESS, OPALS (Mandlburger et al.
1968; Magaš 1968, Fuček et al. 2014). Osor and 2009), and SCOP++ (Pfeifer et al. 2001) includ-
its wider surroundings are located within two ing strip adjustment to remove systematic errors
lithostratigraphic units, which are composed of between overlapping strips and robust interpola-
alternations of dolomites and shallow marine tion with an eccentric and asymmetrical weight
limestones assigned to the Upper Albian-Lower function to identify off-surface points (for a de-
Cenomanian boundary (Sis unit) and Cenoma- tailed description of the process, see Doneus et
nian pelagic limestones (Belej unit) (Fuček et al. al. 2020). The average final ground point den-
2014). Town of Osor was built on the karstified sity is not uniform because it varies depending
limestones of the Belej lithostraigraphic unit on the number of overlapping strips in an area,
(Fuček et al. 2014). the density of vegetation, steepness of terrain or
the presence of deeper water, which does not re-
Methodology turn echoes. Typical values are between 3 (dense
Surveys maquis vegetation) and 20 points per square me-
ter. The remaining point cloud was interpolat-
Airborne Laser Survey (ALS/ALB) ed to a digital feature model (DFM – Pingel et
Airborne laser scanning (ALS, based on LiDAR al. 2015) with a raster width of 0.5 m using lin-
technology) is an active remote sensing meth- ear prediction (equivalent to ordinary Kriging,
od in which the Earth’s surface is measured di- see Doneus et al. 2020) and imported into a GIS
rectly from the air using infrared or green laser environment for further visualisation. The pen-
pulses. It allows large areas to be mapped rela- etration depth, which depends on the type of la-