SMALL UNMANNED AERIAL SYSTEM (SUAS) BASED ANALYSIS OF EMERGENT VEGETATION & WATER INUNDATION EXTENT AT OLD WOMAN CREEK

Wetlands function as a nutrient sink, natural filter for agricultural runoff, and as a productive habitat for a multitude of plant and animal species. In recent years, wetlands have been restored or created to improve water quality. Quantifying water volume moving through a wetland area is important to understanding wetland function. In the past, satellites and aerial platforms have been used to map changes in wetlands by various methods. Although satellite revisit times are predictable, cloud cover is not and can often render a scene useless. Satellite spatial resolution is too low to use in smaller wetland areas without pairing larger pixels with subpixel data from other sources. Aerial imagery improves these shortfalls but is expensive and not accessible to many wetland managers. Small unmanned aerial systems (sUAS) add an inexpensive, repeatable, and high-resolution solution to the tools used to map wetlands.

Old Woman Creek (OWC) National Estuarine Research Reserve is a barrier-protected freshwater estuarine system on Lake Erie in north-central Ohio. OWC is a dynamic system where the barrier beach breaches either seasonally or from large precipitation storm events. Scenes at OWC were observed via a sUAS equipped with a multispectral 3-band 12 MegaPixel camera attached to a commercial drone. The camera takes images at 550, 660 and 850 nanometers at a 5 cm pixel resolution from 120-meter altitude. These bands allow for normalized difference vegetation index (NDVI) and normalized difference water index (NDWI) values to be calculated. The scenes were calibrated to bottom-of-atmosphere values using calibration targets of known reflectance and ASD spectrometer measurements. Elevation values were calibrated to National Geodetic Survey benchmarks.

Water storage is calculated using bathymetric data and water-land boundaries acquired from NDWI values. Measurements of wetland water storage over time are useful in calculating nutrient load changes, water retention, and making observations about wetland habitat stability. Spatial resolution from the sUAS provides a 200-fold increase and resolves features lost to pixel mixing in satellite remote sensing. Results show a significant improvement in spatial and temporal resolution from satellite derived data which is comparable in quality to aerial remote sensing.