On the Trajectory Dependence of Atmospheric Boundary Layer Turbulence Sensing using Small Unmanned Vehicles

Abstract

Atmospheric turbulence, especially in the near-surface boundary layer is known to be under-sampled due to the need to capture a wide separation in length and time-scales and limitation in the number of sensors. Over the past decade, the use if Unmanned Aircraft Systems (UAS) technology is approaching ubiquitous proportions for a wide variety of applications, especially with the recent FAA relaxation of flying restrictions. From a geophysical sciences perspective, such technology would allow for sensing of large-scale atmospheric flows, particularly, atmospheric boundary layer (ABL) turbulence, air quality monitoring in urban settings where multitude of small, minimally-invasive and mobile sensors can drastically alter our ability to study such complex phenomena. Currently available observational data of atmospheric boundary layer physics is so sparse and infrequent which significantly limits analysis. With the quantity and resolution of the data that can be measured using a swarm of UAS, three-dimensional reconstruction and deduction of coherent structures in ABL turbulence may be feasible. However, key challenges remain in the form of identifying optimal trajectories to fly the UAS to obtain the relevant quantifications of the turbulence, interpretation of the sensor data from mobile sensors and understanding how representative are the sparse measurements of the overall turbulent boundary layer. This leads to many fundamentally interesting questions that are itemized here: (a) How does UAS trajectory influence sensing and measurements of turbulence? (b) How does ABL turbulence impact UAS trajectory? (c) How to design optimal sensing strategy for canonical turbulence? The key to answering these questions requires the study and understanding of the coupled system of sUAS flight dynamics, controller and ABL turbulence. It is also worth mentioning that some of the above are relevant issues only for small UAS such as quadcopters whose trajectory can be modulated to ABL gusts as against medium-scale fixed wing UAS. In this paper, we leverage a unique sUAS-in-ABL simulation infrastructure that couples high fidelity Large-eddy Simulation (LES) of the ABL with 6-DOF model for the