AN UNMANNED AERIAL VEHICLE (UAV) BASED SPECTROMETER FOR OBSERVING WATER QUALITY

We integrated and deployed a waterproof UAV based hyperspectral spectrometer for measuring radiance and reflectance over approximately 1 km long transects from 10-50m above the lake surface. Measurements were made from the UAV via land and boat deployments in the Western Lake Erie Basin (WLEB). These measurements are used to assess water quality, specifically algae and sediment concentrations, in lakes and reservoirs of varying sizes.

Lake Erie, like many other inland lakes and reservoirs, is used as the principal water for several major metropolitan areas. In the summer of 2015, 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. This system provides a method of assessing the spatial extent and intensity of harmful algae blooms across lake transects to complement existing satellite and airborne methods.

The UAV spectrometer hardware was installed in an aquacopter bullfrog frame along with a pixhawk flight controller for GPS controlled flight routes. The spectrometer system included an Ocean Optics STS-VIS miniaturized spectrometer controlled by a Raspberry Pi micro-computer for measuring upwelling radiance, and an STS-VIS system fitted with RCR receptor made simultaneous continual base station downwelling irradiance measurements. The system was deployed in flights of 10-50m altitude over the Western Lake Erie Basin (WLEB). Results compared favorably with those acquired at lake using an ASD Field spec 3 Pro, and measurements acquired from an aircraft based hyperspectral imager (NASA GRC HSI 3). Algae concentrations were derived using the Wynne et al cyanobacterial index (CI) and a hyperspectrally adjusted CI. Results showed high correlation of spectrometer derived concentrations and algae abundance based on field based sampling.