1.1. Overview of Current Thematic Applications of Unmanned Aerial Vehicles (UAV) Surveys in Coastal Environments
1.2. Study Objectives Associated with Environmental Issues of Lake Sevan when Changing Its Water Level
2. Materials and Methods
2.1. Study Site
2.2. Mapping of Land Use and Present-Day Shoreline on a Basis of Satellite and UAV Imagery
2.3. UAV-Based Optical Survey for Detection of Coastal Processes and Phenomena
2.4. Thermal Survey of the Coastal Zone
2.5. Determining Rates of Shore Erosion and Shoreline Location Modeling
3.1. Point and Non-Point Sources of Anthropogenic Impacts on Coastal Lands and Waters
3.2. Coastal Types and Processes
3.3. Monitoring of Marsh Shores and Coastal Wetlands
4.1. UAV Surveys as a Part of Multi-Platform Environmental Monitoring of the Lake Sevan Coastal Zone
- Illegal land development;
- Discharge of untreated sewage water;
- Environmentally unsound behavior of local people and tourists.
4.2. Applications of UAV-Derived Highly Detailed Optical and Thermal Data for Monitoring Coastal Processes
- Research in the habitat structure and the state of vegetation cover. UAV survey data can identify the types of vegetation communities not only through their species composition but also through indirect indicators in the form of specific plants, which indicate the degree of water abundance in those cases when it is impossible to interpret ground features beneath thick vegetation cover. UAV-based optical survey data allow reliable interpretation of vegetation species’ composition and habitat types, while thermal surveys additionally enable identifying the areas of different water abundance and determining species structure, spatial patterns, and the ecological status of forest plantations, shrubland, and grassland from their thermal images.
- The monitoring of processes related to decay of macrobiota. The processes of biota decomposition at flooded coastal sites lead to heat emissions and irreversible chemical reactions. These exothermic reactions in coastal waters can contribute to eutrophication and, combined with high aerial temperatures especially during the spring–summer period, can also exacerbate algal blooms in surface waters. Locations of vegetation decay were identified from UAV-derived thermal surveys (Figure 11). Some uncertainties remain, however, regarding the interpretation of nadir thermal images as well as living and decaying vegetation on hillocks within marshes. Oblique aerial thermal and optical survey seems to be the only means of resolving this problem.
- Monitoring of the hydrothermal regime. Research into hydrothermal regimes and representation of processes related to mixing of lagoon, marsh, or river waters with the lake waters are important constituents of water quality monitoring. UAV-based thermal images identified the main mixing areas of waters flowing out of marsh swamps and lagoons (Figure 11). In the coastal zone of the Norashen Peninsula, which is an extremely dynamic area among all key study sites, the thermal survey results helped to elucidate the complex structural dynamic system of nearshore waters, semi-closed and closed lagoons, foreshores, and marsh swamps of different types (reed and cattail species). Such a landscape is unique for Lake Sevan shores. The temperature gradient at different habitats on the Norashen peninsula manifested not only in UAV-based thermal surveys but also tested by hydrobiological studies that revealed a distinct spatial pattern of local communities of zoobenthos .
4.3. Prospective Applications of UAV Surveys in the System of Environmental Coastal Monitoring
- Detection of small domestic wastes and plastics. To resolve this task, UAV-derived data obtained at very low survey altitudes (100 m and less) should be used as the recognition of such features is possible only with imagery of sub-decimeter spatial resolution. The surveys identified construction waste in coastal zones as well as clusters of abandoned fishing nets in waters. These nets are traces of illegal, uncontrolled fishing and often become places of active organic decay of macro-biota (including both fish and bird fauna caught in them).
- Monitoring of camping sites or temporary stay by tourists as sources of coastal littering. Tourist activities along the southern and eastern coasts of Lake Sevan have generated spontaneous and uncontrolled miniature landfills that are not included in waste disposal systems of settlements and static tourist accommodation sites.
- Detection of points of illegal sewage discharge into the lake. Some recreational housing in the coastal zone comprises temporary structures lacking adequate sewage treatment system, often with all waste waters discharged by the pipeline directly into the lake.
Conflicts of Interest
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|Flight Altitude, m||Thematic|
|Overlap of Acquired Imagery, %||Mean Spatial Resolution of Orthomosaics, cm||Mean DEM’s and DSM’s Spatial Resolution, cm||Mean Point Density in Dense Point Clouds, Points Per sq. Meters|
|100 RGB||detection of shoreline positions, |
monitoring of pollution and littering.
|200 RGB||monitoring of coastal waters’ pollution, constructing DSM, modeling of shoreline position||80||6.4||12.8||63/137|
|400||RGB||land use mapping, constructing DSM.||90||12.7||25.4||11/29|
|Thermal||detection of the shoreline positions and wetlands structure, identification of water mixing, decay of submerged vegetation||80||47.3||94.6||6/13|
|Coastal Types by Genesis and Dominating Processes||Length of the Total Coastline, %|
|developed under wave effect||accumulative coasts||38.6|
|coasts with active shore erosion and accumulation||17.8|
|developed under the effect of biogenous factors||marsh coasts||10.1|
|developed under the effect of permanent stream accumulation||fluvial coasts||5.4|
|Thematic Task||Spatial Scope |
|Monitoring land use structure and changes||Drainage basin|
|Annually||Multi-spectral multi-seasonal satellite data (Landsat 8 OLI, Sentinel-2 MSI)|
|Annually||Annual mosaics of highly detailed satellite imagery|
|Monitoring pollution point-sources in the coastal zone and their state||Coastal zone|
(1–3 m, first cm)
|Annually and on request||Annual mosaics of highly detailed satellite imagery and on-demand UAV-derived imagery|
|Monitoring spontaneous littering||Coastal zone outside of developed recreation facilities|
(better than 0.1 m)
|Weekly and on request||Optical surveys from UAV|
|Monitoring of shore erosion||Infrastructure and communication facilities in the coastal zone and adjacent areas|
(better than 0.1 m)
|Daily and on request||Optical surveys from UAVs|
|Monitoring the submerged and flooded shores||Waterlogged or submerged coastal habitats|
(better than 0.1 m)
|Weekly and on request||Optical surveys from UAV|
|Water body of Lake Sevan, |
|Daily||Multi-spectral, low-resolution satellite data (Sentinel 3 OLCI, Terra/Aqua MODIS)|
|Monitoring water quality and environmental state of water bodies||Water body of Lake Sevan, |
|Once per 3–7 days||Multi-spectral, multi-seasonal satellite data of medium resolution (Landsat 8 OLI, Sentinel-2 MSI)|
|Recreationally developed areas in coastal zone and adjacent waters, nearshore waters around river mouths|
|Daily||Multi-spectral data from PlanetScope microsatellite constellation|
|Recreationally developed areas in coastal zone and adjacent waters, nearshore waters around river mouths, coastal wetlands|
(better than 0.1 m)
|In cases of early warning and prompt response up to several times per day, |
|UAV-derived data in the visible, infrared, and thermal bands|
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