## 1 Introduction  
Overview of Current Thematic Applications of Unmanned Aerial Vehicles (UAV) Surveys in Coastal Environments  
The last decade has seen rapidly increasing interest in a large range of thematic applications for ultra-high spatial resolution data derived from small, low-cost, unmanned aerial vehicles (UAVs) as an essential component for remote sensing monitoring in coastal environments [1; 2; 3]. UAV-based remote sensing is also considered a rather simple and easily replicable tool for environmental coastal monitoring even for non-experts in specific surveying technologies and processing of derived data [4]. The clear advantages of this approach are cost-effectiveness and flexibility. Provision of data with very high spatial (sub-centimeters) and temporal (on demand and simultaneously with field measurements) resolutions allows reliable identification of specific objects and processes in highly dynamic conditions and areas at risk of human or natural-induced degradation [1; 5; 6]. Currently, operational and prospective thematic applications of UAV-derived data in environmental remote sensing monitoring and management of coastal marine, lacustrine, and riverine areas with high anthropogenic impacts are very diverse. Among them there are such issues as: (a) short-term and long-term dynamics of shorelines [7; 8; 9; 10], (b) reconstruction of submerged topography in shallow waters [11], (c) high-resolution surveys of coastal morphology and hazardous processes [12; 13; 14], (d) delimitation and large-scale mapping of nearshore aquatic and intertidal ecosystems [15; 16; 17; 18], estuarine habitats [19], and coastal wetlands [20; 21]. Within the sphere of coastal management, one very novel and specific application of UAVs is the monitoring of littering, resulting from recreational activities, as well as of nearshore marine and lacustrine waters and adjacent coasts with high and diverse anthropogenic impacts [22; 23; 24].  
Since many marine coastal waters and inland freshwaters worldwide are now exposed to severe water quality issues connected with persistent outbreaks of harmful algal blooms (HABs) due to anthropogenic eutrophication [25], UAV-based monitoring of HABs and sources of water pollution is now considered a very promising and powerful tool [2; 26; 27]. UAV-derived water quality data with high spatial resolution are the most appropriate for smaller lakes, reservoirs, irrigation ponds, and riverine and coastal waters, which often have high anthropogenic loads but are not properly recognizable at the spatial resolutions of existing satellite sensors [5]. The significance of UAV-based monitoring of water quality and distribution of algal blooms as a part of an \"early warning\" remote sensing system is clearly demonstrated in References [6; 27].  
As a whole, UAV surveys can now be considered a necessary intermediary between in situ measurements and satellite remote sensing for integral multi-temporal and multi-scale environmental monitoring of coastal areas [27]. Consequently, the elaboration and realization of an appropriate protocol on the collection, and processing of UAV data, by taking into consideration both the possibilities and limitation of surveys in defined areas, are rather urgent study tasks [28; 29].