Observing Atmospheric Parameters Using Quadcopters

The recent reduced cost and technological advances in Unmanned Aerial Vehicles (UAVs) has brought about a large increase in applications for atmospheric observations. Compact, lightweight atmospheric sensors have been developed for UAVs. Many questions remain regarding this new technology including 1) optimal sensor placement on the UAV; 2) sensor data validation; 3) development of sensors to measure wind speed and direction from vertical take-off and landing aircraft; and 4) usefulness of UAV data in predicting convective initiation. These 4 questions will be addressed in this presentation.

One year of data collected using two 3DRobotics Inc. Iris+ quadcopters equipped with InterMet Inc. iMET XQ sensors and pitot sensors to measure temperature, relative humidity, pressure, wind speed, and wind direction will be presented. The quadcopters were flown next to a South Alabama Mesonet weather station tower to validate quadcopter data against tower observations at 2 m and 10 m elevations. Additionally, the quads were flown in vertical profiles up to 120 m elevation in various locations in Mobile County in southwest Alabama during the convective season. During all flights, 5 or more iMET sensor were mounted in different locations on the UAVs to determine optimal sensor placement. Factors like the effects of propellor downwash and exposure to sunlight on temperature and relative humidity measurements will be investigated.

Four pitot probes are used to measure wind speed in four directions. The goal is to use all 4 sensor measurements to determine magnitude and wind speed. However, many challenges stand in the way of determining wind speed from such a device. First, any lateral change in velocity or angular velocity in the quadcopter creates biased data from an increase in inflow on the pitot probe when the quadcopter translates or rotates. Furthermore, sensor placement of the pitot probe is difficult given the large amount of propellor downwash created by all four rotors. Multiple designs have been considered including placing the pitot probes above the rotors rather than in the same plane. Finally, vibration noise from the quadcopter creates a significant amount of signal noise. The amount of noise is enough to warrant the need for low pass filters and vibration dampeners such as rubber mounts or foam pads on sensors.