COMMERCIALLY AVAILABLE UNOCCUPIED AERIAL SYSTEMS FOR MONITORING HARMFUL ALGAL BLOOMS: A COMPARATIVE STUDY

Reliable remote sensing platforms and methods for monitoring phytoplankton are needed for mitigating the detrimental impacts of cyanobacterial harmful algal blooms (CyanoHABs) on small inland waterbodies. Commercial unoccupied aerial systems (UAS) present an affordable high-resolution solution for rapid assessment of cyanobacterial abundance in small (<30 m) aquatic systems by recording the reflectance of photosynthetic pigments found in all phytoplankton (i.e., chlorophyll-a) and those unique to cyanobacteria (i.e., phycocyanin). This study evaluates the performance of four sensors, including visible light spectra (RGB) sensors on the Phantom 4 and Phantom 4 Professional platforms, the MAPIR Survey3W modified multispectral (near-infrared, green, blue) sensor, and the Parrott Sequoia multispectral (green, red, near-infrared, red-edge) sensor for estimating cyanobacterial abundance. Each sensor’s performance was determined by comparing 26 vegetation indices to chlorophyll-a and phycocyanin measurements of 54 ponds that varied in productivity. Vegetation indices that included the red and near-infrared wavelengths generated from Parrot Sequoia aerial images provided the best chlorophyll-a (i.e., NDVI, r² = 0.78, p-value <0.0001) and phycocyanin (i.e., EVI2, r² = 0.57, p-value <0.0001) estimates. The RGB sensors were moderately effective for estimating chlorophyll-a, whereas the MAPIR Survey3W generated poor estimates of both pigments due to differences in recorded wavelengths.