Abstract
Abstract. Integrating sensors with a rotary-wing unmanned aircraft system (rwUAS) can introduce several sources of biases and uncertainties if not properly accounted for. To maximize the potential for rwUAS to provide reliable observations, it is imperative to have an understanding of their strengths and limitations under varying environmental conditions. This study focuses on the quality of measurements relative to sensor locations on board rwUAS. Typically, thermistors require aspiration and proper siting free of heat sources to make representative measurements of the atmosphere. In an effort to characterize ideal locations for sensor placement, a series of experiments were conducted in the homogeneous environment of an indoor chamber with a pedestal-mounted rwUAS. A suite of thermistors along with a wind probe were mounted inside of a solar shield, which was affixed to a linear actuator arm. The actuator arm was configured such that the sensors within the solar shield would travel underneath the platform into and out of the propeller wash. The actuator arm was displaced horizontally underneath the platform while the motors were throttled to 50 %, yielding a time series of temperature and wind speed that could be compared to temperatures being collected in the ambient environment. Results indicate that temperatures may be biased in the order of 0.5–1.0 ∘C and vary appreciably without aspiration, sensors placed close to the tips of the rotors may experience biases due to frictional and compressional heating as a result of turbulent fluctuations, and sensors in proximity to motors may experience biases approaching 1 ∘C. From these trials, it has been determined that sensor placement underneath a propeller on an rwUAS a distance of one quarter the length of the propeller from the tip is most likely to be minimally impacted from influences of turbulence and motor, compressional, and frictional heating while still maintaining adequate airflow. When opting to use rotor wash as a means for sensor aspiration, the user must be cognizant of these potential sources of platform-induced heating when determining sensor location.
Highlights
The planetary boundary layer (PBL) is the lowest layer of the troposphere, which exchanges energy with the Earth’s surface on timescales of less than 1 h (Stull, 1988), and acquiring atmospheric measurements in this region has proven to be challenging (National Research Council, 2009; Hardesty and Hoff, 2012)
We focus on the effects of sensor placement on temperature observations
To account for the longer response function of the Campbell Scientific model 109 thermistors (CS 109) probes and to make more appropriate comparisons, a moving 10 s average of the International Met Systems (iMet) temperature data was calculated before each analysis point (Fig. 5)
Summary
The planetary boundary layer (PBL) is the lowest layer of the troposphere, which exchanges energy with the Earth’s surface on timescales of less than 1 h (Stull, 1988), and acquiring atmospheric measurements in this region has proven to be challenging (National Research Council, 2009; Hardesty and Hoff, 2012). PBL flows are highly complex and nonlinear in space and time, even with several layers of assumptions applied in theory. As such, it has always been a challenge for atmospheric scientists to collect representative measurements of the environment, even with continual advances in technology. Being limited in vertical extent, the convective boundary layer often ex-
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