UAV Cloud Particle Sensor

The need for cloud and aerosol measurements is increasing, and new tools are being developed to address the lack of precise cloud particle data. These measurements have typically been carried out using specialized manned aircraft, limiting the measurement opportunities to organizations with larger resources. Unmanned Aerial Vehicles (UAVs) can serve as a flexible platform for various measurement tasks across a broad user group. In this study, we present the first prototype of a lightweight UAV-mounted cloud particle measurement system. The system is described, and results from the initial test flights are presented. Computational fluid dynamics (CFD) simulations were employed to evaluate the effects of the UAV and the sensor on droplet trajectories. The measurement system is based on lensless digital holographic imaging, which allowed us to construct a compact and lightweight imaging system with a large sampling volume. The combination of a large sampling volume and the UAV's relatively low airspeed enabled the acquisition of spatially precise cloud particle data. The holographic imaging system comprises a 660 nm wavelength laser diode and a 12-megapixel camera. Cloud particles in the size range from 5 µm to 1 mm are measured using this sensor. During the 30-minute test flight, the frame rate of the hologram recording was found to be on average 10.0 fps, with a standard deviation of 0.3 fps, resulting in an average sampling rate of 20 cm³/s. Overall, the test flight yielded 3.7 million measured cloud particles between altitudes of 500 m and 1200 m above sea level