Toward Improving Wind Speed Estimates from an Ascending Rotary-Wing UAS

The CopterSonde is a rotary wing Unmanned Aerial System (rwUAS) developed by the Center for Autonomous Sensing and Sampling (CASS) at the University of Oklahoma specifically for thermodynamic and kinematic profiling of the atmospheric boundary layer. Through careful consideration of sensor placement and design, as well as including adaptive sampling features in the autopilot, the CopterSonde has been shown to be capable of making accurate thermodynamic measurements in a wide range of conditions (Barbieri et. al, 2019; Bell et. al, 2019). However, there are still improvements that can be made to the wind estimation algorithm.

Wind speed estimation using the CopterSonde is achieved using a kinematic technique that relates the environmental wind speed to the tilt angle of the aircraft as it attempts to maintain a constant latitude and longitude. In the past, to determine this relationship, the CopterSonde hovered next to the Washington Oklahoma Mesonet site’s 10 m anemometer. The 1 minute average environmental wind speed was compared to the 1 minute average tilt of the craft and a relationship was determined. However, when the CopterSonde performs a vertical profile by ascending at a constant rate, the dynamics of the thrust vector are modified from when the aircraft is at a stationary hover. The tilt angle of the aircraft is overall decreased to compensate for larger vertical thrust, which is likely the reason that the CopterSonde has tended to underestimate wind speeds in the past.

This study sets out to determine how to better determine the relationship between an ascending rwUAS tilt angle and the environmental wind speed. Using a combination of UAS and Doppler wind lidar data from multiple field campaigns, as well as simple simulations, multiple methods are analyzed to determine the optimal wind speed estimator for an ascending craft. Results from this study will be provided and discussed, along with recommendations on how to improve the accuracy of wind estimates collected using rwUAS.