3D Wind Vector Measurements using a 5-hole Probe with Remotely Piloted Aircraft

The importance of 3D winds (in particular updraft) in atmospheric science has motivated the adaptation of airborne wind instruments developed for manned aircraft, to the small size of Remotely Piloted Aircraft Systems (RPAS). Simultaneously, enhancements in RPAS technology have increased their contribution to many fields. In atmospheric research, lightweight RPAS (< 2.5 kg) are now able to accurately measure 3D wind vectors, even in a cloud, which provides new observing tools for understanding aerosol-cloud interactions. The European project BACCHUS (Impact of Biogenic versus Anthropogenic Emissions on Clouds and Climate: towards a Holistic Understanding) focuses on these specific interactions. Vertical wind velocity at cloud base is a key parameter for aerosol-cloud interactions. To measure the three components of wind, one RPAS is equipped with a 5-hole probe and an Inertial Measurement Unit (IMU), synchronized on an acquisition system. The 5-hole probe is calibrated and validated on a multi-axis platform in a wind tunnel, each probe and its associated pressure sensors have specific calibration coefficients. Once mounted on a RPAS, 3D winds and turbulent kinetic energy (TKE) derived from the 5-hole probe are validated with a sonic anemometer on a meteorological mast. During the BACCHUS field campaign at Mace Head (Ireland), a fleet of RPAS has been utilized to profile the atmosphere and complement ground-based and satellite observations. To study aerosol-cloud interactions, the RPAS with the 5-hole probe flew at level legs near cloud base to measure vertical wind speeds. The vertical velocity measurements from RPAS are validated with vertical velocities derived from the Mace Head Doppler cloud radar, and the results illustrate the relationships between the distributions of vertical velocity and the different cloud fields.