## 1 Introduction and Background  
Coastal zones represent oscillating, highly dynamic environments between the water surface and a certain land surface [1]. Today, coastal zones are economic and population hotspots, highly endangered by various anthropogenic pressures (e.g., excessive urbanization and construction, agricultural exploitation, pollution) [2, 3] and natural or climate change-related processes (e.g., sea-level rise, storm surges, coastal erosion, tsunamis, salinization) [4, 5, 6, 7]. Anthropogenic pressures are caused by the nearly 2.4 billion people (40% of the total world's population) living within the 100 km from the coastline [8]. In this manuscript, the precise demarcation line between land and water is defined as a _ coastline_. Sometimes, the term _shoreline_ is also used, although there are minor differences between [9, 10, 11, 12]. In simple terms, the coastline is the boundary of the continent/island, while the shoreline is the boundary of the land [13]. The _ coastline_ term was used following these two reasons (1) this manuscript studies the Iz-Rava island group and (2) the term \" coastline\" is used within a large number of papers about automatic extraction of that demarcation line, published in the last couple of years [14; 15; 16; 17]. The instantaneous coastline can be most easily defined as the physical interface of land and water (LWI) [18] at one instant in time [10] which are very hard to extract due to constant water level changes [19]. An alternative definition of coastline can be a _particular elevation contour of the land (or water) surface_[20]. Coastline changes are regarded as one of the most dynamic processes (a time-dependent phenomenon) in coastal zones [21; 22] and critical information in the _Coastal Geographic Information System_ (CGIS) [19]. The combination of these factors made a study of changing coastlines _more than a topic of scientific curiosity_[23]. Therefore, they are considered _as one of the most important linear dynamic features on the Earth's surface_[12]. Coastline mapping is crucial for detection and monitoring of various coastal spatiotemporal changes [24; 25; 26], the study of specific coast-related processes and pressures such as coastal erosion [27; 28], urbanization [29; 30], management and protection of endangered coastal areas [31; 32; 33], maritime affairs and safe navigation, sustainable coastal development and planning, and monitoring and protection of endangered coastal ecosystems [34; 35; 36; 15]. Therefore, accurate coastline mapping is crucial not only from a scientific perspective but for its importance for society, as it can provide valuable information that can be essential in mitigating the above-mentioned problems and pressures [37; 38]. However, accurate coastline mapping is not a simple task, especially over large, intended, and remote areas [39]. The complexity of coastline mapping can be best expressed by the \"coastline paradox\" (Figure 1), which means that coastline length depends on the research scale and accuracy of the used measurement method [40; 41]. Less detailed research scale and less accurate measurement methods result in generalized coastline depiction, where the actual length of the coastline is reduced. At the same time, more detailed and accurate methods result in a more accurate representation of the actual coastline. Many different methods for coastline extraction have been developed [19; 24; 42]. However, the accuracy and quality of coastline depictions were often inadequate due to the modest mapping capabilities, which were limited by earlier field data collection methods [24]. These traditional coastline mapping methods required labor-intensive and extensive mapping processes, which often resulted in generalized and inaccurate coastline representations [43]. With the emergence of different remote sensing techniques and very high resolution (VHR), satellite imagery new automatic and semi-automatic coastline extraction methods have been developed [14; 15; 22; 44; 45; 46].