Chlorophyll Fluorometer for Intelligent Water Sampling by a Small Uncrewed Aircraft System (sUAS)

We describe a waterproof, lightweight (1.3 kg), low-power (similar to 1.1 W average power) fluorometer operating on 5 V direct current deployed on a small uncrewed aircraft system (sUAS) to measure chlorophyll and used for triggering environmental water sampling by the sUAS. The fluorometer uses a 450 nm laser modulated at 10 Hz for excitation and a standard photodiode and transimpedance amplifier for the detection of fluorescence. Additional detectors are available for measuring laser intensity and light scattering. Control of the fluorometer and communication between the fluorometer and the Raspberry Pi 4B computer controlling the sampler were provided by an Arduino microcontroller using the robot operating system (ROS). Calibrations were based on standards of dissolved chlorophyll extracted from Chlorella powder (a widely available dietary supplement). The detection limit for chlorophyll from these calibrations was found to be 0.2 mu g per liter of water for a single 0.1 s differential measurement. The detection limit decreases with the square root of the integration time as expected. Detection limits increase by a factor of two to three when mounted in the sUAS due to electrical noise; sUAS acoustic noise and vibration do not appear to contribute significantly.

Automated summary

We introduce a waterproof, lightweight, low-power fluorometer that operates on a small unmanned aircraft system (sUAS) to measure chlorophyll and trigger water sampling. The fluorometer utilizes a 450 nm laser for excitation and a standard photodiode for fluorescence detection. Control and communication are achieved through an Arduino microcontroller and the robot operating system (ROS). Calibrations based on dissolved chlorophyll standards yield a detection limit of 0.2 μg per liter for a single 0.1 s measurement, decreasing with integration time. Mounting the fluorometer on the sUAS increases detection limits due to electrical noise.