INTEGRATING UNMANNED AERIAL SYSTEM (UAS) BASED SPECTROMETER MEASUREMENTS WITH AIRBORNE AND SATELLITE DATA FOR MEASURING WATER QUALITY

Water quality issues impact recreational and resource use of waterways in the rivers, lakes, reservoirs, and other smaller inland water bodies. Recent advancements in small unmanned aerial systems (sUAS) coupled with decreases in sensor and logging equipment sizes mean that sUAS offer increased flexibility to enhance results from satellite and airborne systems and complement their measurements in this environment. Lake Erie, like many other inland lakes and reservoirs, is used as the principal water for several major metropolitan areas. In the summer of 2014, approximately 300,000 residents of the Toledo area had their water placed under a use advisory due to elevated toxin levels from a harmful algae bloom. Combined measurements from UAS to Satellite provide a robust combination for mapping the spatial extent and intensity of harmful algae blooms from small reservoir to large lake scale.

During the summers of 2017 and 2018, we deployed Ocean Optics STS hyperspectral Vis-NIR Spectrometers on a low-cost sUAS quadcopter configuration. This system is boat launchable and capable of making measurements over an approximately 1 square mile area, below the cloud deck in the nearshore and open lake environment. Flights of this systems were conducted over Lake Erie and the Maumee River during algae bloom conditions. Hyperspectral measurements were made by the airborne NASA GRC Hysperspectral imager (HSI2, HSI3), and multispectral images were obtained from the temporally closest available MODIS and Sentinel-2 satellite acquisitions. At surface ASD Fieldspec measured spectra were made contemporaneously with the sUAS flights. We utilized the UAV based spectrometer measurements, together with a fixed on-land blacktop target to conduct vicarious calibration of the airborne and satellite data.

We constructed transect maps of reflectance spectra and the derived Cyanobacteria Index (CI) product from the UAS flights, which show the fine scale spatial variability in algae abundance in open water. These were spatially aggregated to the airborne and satellite imager scales. UAS based measurements provided high quality high spatial resolution data for river and nearshore locations, without complications of mixed water-shoreline pixels.