An analysis of wind retrieval algorithms for small unmanned aerial systems

There is increasing interest in the use of Unmanned Aerial Systems (UASs) as tools for monitoring and researching the lower atmosphere due to their relatively low cost and their ability to collect sample with high spatial and temporal resolution. Along with the potential for an increasing use of small UASs for atmospheric observations comes the need for accurate instrumentation and measurement methods suitable for these platforms. Furthermore, the instrumentation must be small and lightweight by necessity. Recently, the Atmospheric Radar Research Center (ARRC) at the University of Oklahoma (OU) has been developing a small UAS, the SMARTSonde (Small Multi-function Autonomous Research and Teaching Sonde), for planetary boundary layer research. It is capable of measuring thermodynamic parameters such as pressure, temperature, and relative humidity, amounts of trace gases such as ozone, and provide estimates of the three-dimensional wind field.

In this presentation we discuss the challenges of obtaining three-dimensional wind measurements in an inertial reference frame using data from a limited set of sensors placed aboard a non-inertial sampling platform (the UAS). These wind estimates are based on inputs from a GPS unit on the plane and when available data from a wing-mounted pitot tube. We consider two different sampling strategies. One relies on observations being made while the plane flies in a circular or near-circular pattern. The other simply requires that the plane experience a change in attitude during course of the measurement sequence and utilizes the direction cosine matrix. Wind estimates obtained using both strategies will be presented. Additionally the impact of having pitot tube data to supplement the GPS information will be considered. Comparisons will be made of these wind retrieval methods against rawinsonde observations in order to determine the accuracy of the various methods.