Boundary Layer Profiling Using Rotary-Wing Unmanned Aircraft Systems: Filling the Atmospheric Data Gap
The planetary boundary layer (PBL) is comprised of energy exchanges with the Earth’s surface, and as such plays a large factor in the evolution of weather condi- tions. However, traditional methods of observing the atmosphere, such as radioson- des and surface weather stations, drastically underrepresent processes occurring in the PBL. More recently, surface-based remote sensing capabilities have advanced, but these instruments are often expensive and difficult to implement across large scales operationally.
Using small unmanned aircraft systems (sUAS) to make atmospheric ob- servations is rapidly being realized as a means to collect previously unobtainable observations in the lowest part of Earth’s atmosphere. However, in order for these systems to provide meaningful kinematic and thermodynamic data, it is impera- tive to establish an understanding of the strengths and limitations of the sensors and retrieval algorithms implemented, as well as how they perform under vari- ous configurations and flight conditions. This initial objective is comprised of two experimental stages, the first of which is calibration of thermodynamic sensors against reference measurements from the Oklahoma Mesonet in order to under- stand response characteristics in quasi-ideal environments. Furthermore, efforts have been made to estimate horizontal wind fields using Euler angles derived from the rotary-wing’s autopilot. The second stage is validation of these sensor perfor- mances once mounted onto a rotary-wing sUAS by comparing measurements with instrumented towers, radiosondes, and other sUAS. It appears that these mea- surements are robust provided that instrument packages are properly mounted in locations that provide adequate air flow and proper solar shielding.
The CopterSonde, a rotary-wing UAS designed and built by the Center for Autonomous Sensing and Sampling (CASS) at the University of Oklahoma (OU), was optimized for thermodynamic and kinematic measurements in the PBL. Its utility has been proven across many applications, including measurements of heat fluxes during diurnal PBL transitions. The Environmental Profiling and Initiation of Convection (EPIC) was a field campaign in the spring of 2017 that demon- strated the utility of UASs to provide forecasters with quasi-real time profiles of pre-convective environments. The Collaboration Leading Operational UAS Devel- opment for Meteorology and Atmospheric Physics (CLOUD-MAP) project, sup- ported by the National Science Foundation (NSF), is a significant financial invest- ment awarded to push the limits of UAS capabilities in the context of atmospheric sciences through a multi-disciplinary, multi-university collaboration. The results presented herein represent foundational efforts towards tapping into the service- ability of rotary-wing sUAS for atmospheric sciences, and an outlook for future applications is discussed.