UAV-Derived Data Application for Environmental Monitoring of the Coastal Area of Lake Sevan, Armenia with a Changing Water Level

Abstract

The paper presents the range and applications of thematic tasks for ultra-high spatial resolution data from small unmanned aerial vehicles (UAVs) in the integral system of environmental multi-platform and multi-scaled monitoring of Lake Sevan, which is one of the greatest freshwater lakes in Eurasia. From the 1930s, it had been subjected to human-driven changing of the water level with associated and currently exacerbated environmental issues. We elaborated the specific techniques of optical and thermal surveys for the different coastal sites and phenomena in study. UAV-derived optical imagery and thermal stream were processed by a Structure-from-Motion algorithm to create digital surface models (DSMs) and ortho-imagery for several key sites. UAV imagery were used as additional sources of detailed spatial data under large-scale mapping of current land-use and point sources of water pollution in the coastal zone, and a main data source on environmental violations, especially sewage discharge or illegal landfills. The revealed present-day coastal types were mapped at a large scale, and the net changes of shoreline position and rates of shore erosion were calculated on multi-temporal UAV data using modified Hausdorff’s distance. Based on highly-detailed DSMs, we revealed the areas and objects at risk of flooding under the projected water level rise to 1903.5 m along the west coasts of Minor Sevan being the most popular recreational area. We indicated that the structural and environmental state of marsh coasts and coastal wetlands as potential sources of lake eutrophication and associated algal blooms could be more efficiently studied under thermal UAV surveys than optical ones. We proposed to consider UAV surveys as a necessary intermediary between ground data and satellite imagery with different spatial resolutions for the complex environmental monitoring of the coastal area and water body of Lake Sevan as a whole.

A Review of Unoccupied Aerial Vehicle Use in Wetland Applications: Emerging Opportunities in Approach, Technology, and Data

“…Wetland monitoring at the whole-site and regional scale often aims to make diagnostic assessments of ecological status and health and, ideally, to detect early warning signals of degradation, decline, or disturbance that may lead to irreversible long-term disruptions such as losses of water quality, critical habitat, or similar issues [34,47,138,144]. Emerging applications of UAVs are extremely promising for informing cost-effective yet spatially comprehensive indicators of wetland health at the landscape scale and support long-term monitoring needs.…”

“…Emerging applications of UAVs are extremely promising for informing cost-effective yet spatially comprehensive indicators of wetland health at the landscape scale and support long-term monitoring needs. Our pool of studies in this category included seven mapping, three modeling, three change analysis, and one novel method application that either targeted a particular aspect of wetland ecological health such as water quality (e.g., [105]) and vegetation indicators (e.g., [42,108,111]) or assessed the overall ecological status using different indicators (e.g., [7,34]). These studies employed RGB, Multispectral, Hyperspectral, and SAR sensors, as well as combinations of RGB and Multispectral and RGB and Thermal sensors (Figure 3).…”

“…These studies employed RGB, Multispectral, Hyperspectral, and SAR sensors, as well as combinations of RGB and Multispectral and RGB and Thermal sensors (Figure 3). Multi-sensor combinations especially benefit holistic assessments targeting multiple health indicators by helping to strategically optimize surveying workload between less demanding and easily replicable tasks (such as visual recognition from passive RGB imagery) and more intensive data processing endeavors (such as LiDAR-derived modeling of geomorphology and vegetation structure) [7,34,35].…”

“…A common, notable characteristic among these studies was the focus on disturbance and stress factors leaving a sizable fingerprint on wetland ecosystems that can be detected with the help of UAVs more comprehensively and cost-effectively than with field surveys [34,111]. Certain assessments are almost uniquely made possible by the customizable aspects of UAV surveying, such as monitoring wetland body volumes and water budgets based on the 3D information enabled by image overlap [107].…”

“…UAVs are uniquely positioned to cost-effectively overcome these challenges at local observation scales via spatially comprehensive coverage, customizable flight schedules, and diverse sensor instruments for specific applications [18,[30][31][32][33]. The high spatial resolution of UAV-derived imagery makes them an especially valuable surrogate for field assessments by enabling visual recognition of landscape elements and evaluation of multiple indicators of wetland habitat and ecological status (e.g., [7,[34][35][36]). At the same time, some essential aspects of UAV workflows pertaining to in situ infrastructure-e.g., positioning of launching and landing sites, installation of georeferencing markers, among others-may be challenged by wetland landscape properties and accessibility similarly to ground surveys.…”