Small UAS for Atmospheric Surface Layer Measurements

While most of the previous research on the marine atmospheric surface layers has focused on surface flux parameterization, the mean vertical profiles of wind, temperature, and humidity near the sea surface have not been thoroughly characterized, although they are generally considered to follow the same flux-profile relationship as those in the surface layers over land. This raised a general concern of the applicability of the currently used surface layer models in applications where characterizing the surface layer profiles becomes crucial. One such application is to predict the surface layer temperature and humidity gradients in order to characterize the atmospheric refractive properties that affect the propagation of radar and communication signals in the evaporation duct occurring at the air-sea interface. The lack of in situ measurements in the lowest 10-30 meters of the atmosphere with sufficient vertical resolution and statistical representation thus becomes a serious predicament in developing new and improved surface layer model (or evaporation ducting models). Accurate characterization of the near surface vertical variations of wind, temperature, and humidity requires measurements to be made in undisturbed air away from the ship and other large platforms. Small Unmanned Aircraft System (SUAS) deployable from ships have great potential, and in particular, very low-cost SUAS that exploit the open-source hobby-market products, where the cost of losing the asset for the sake of the data is an acceptable proposition.

We intend to explore the use of small fixed wing UAVs for the aforementioned research topic by developing an expendable system that can be fielded from land or ship. The objective is to design a low cost asset that is simple to assemble and deploy. The design will rely heavily on COTS products, open-source components and rapid prototyping techniques such as 3D printing and desk-top CNC machining. The airframes selection process will take into account the weight and volume of the sensor components, clean access to the air for sensing, and a size and wing-loading that is able to support the desired speed range and endurance. The entire package must be able to survive an at-sea landing in mild seas for recovery and possible reuse.

There are many options for instrumenting the small UAS, constrained by available payload size, weight, and power consumption (SWaP). Various existing sensor packages such as radiosondes and wind finding techniques will be explored including utilizing the UAV's navigation system and additional sensors. These various options and their potential use on the UAS will be discussed.