Abstract
Abstract. Small unmanned aircraft (SUA) have the potential to be used as platforms for the measurement of atmospheric particulates. The use of an SUA platform for these measurements provides benefits such as high manoeuvrability, reusability, and low cost when compared with traditional techniques. However, the complex aerodynamics of an SUA – particularly for multi-rotor airframes – pose difficulties for accurate and representative sampling of particulates. The use of a miniaturised, lightweight optical particle instrument also presents reliability problems since most optical components in a lightweight system (for example laser diodes, plastic optics, and photodiodes) are less stable than their larger, heavier, and more expensive equivalents (temperature-regulated lasers, glass optics, and photomultiplier tubes). The work presented here relies on computational fluid dynamics with Lagrangian particle tracking (CFD–LPT) simulations to influence the design of a bespoke meteorological sampling system: the UH-AeroSAM. This consists of a custom-built airframe, designed to reduce sampling artefacts due to the propellers, and a purpose-built open-path optical particle counter (OPC) – the Ruggedised Cloud and Aerosol Sounding System (RCASS). OPC size distribution measurements from the UH-AeroSAM are compared with the cloud, aerosol, and precipitation spectrometer (CAPS) for measurements of stratus clouds during the Pallas Cloud Experiment (PaCE) in 2019. Good agreement is demonstrated between the two instruments. The integrated dN∕dlog (Dp) is shown to have a coefficient of determination of 0.8 and a regression slope of 0.9 when plotted 1:1.
Highlights
Aerosols and their interactions with clouds and radiation have been consistently highlighted by the Intergovernmental Panel on Climate Change (IPCC) as the largest uncertainty in predicting climate change today (IPCC, 2013)
While there exists a limited number of aerosol and droplet measurements on Small unmanned aircraft (SUA), previous SUA studies have attempted to measure the physical properties of atmospheric particles and droplets
In order to evaluate the quality of the data collected by the UH-AeroSAM, a practical test was devised involving the comparison of SUA data with a calibrated in situ cloud probe
Summary
Aerosols and their interactions with clouds and radiation have been consistently highlighted by the Intergovernmental Panel on Climate Change (IPCC) as the largest uncertainty in predicting climate change today (IPCC, 2013). Rotary-wing platforms (e.g. multi-rotors) on the other hand have been used much less extensively in atmospheric physics, likely due to problems with the validation of measurements – because of stronger aerodynamic distortions – and limitations to their endurance If these issues can be overcome, multi-rotor platforms present many advantages over fixed-wing-based platforms since they can fly directly upwards for a vertical profile; they integrate very well with autopilot systems, allowing precise flights with minimal human interference; they require less pilot experience to operate effectively; and measurements can be repeated in the same location, providing superior spatio-temporal sampling abilities. This is especially true when sampling atmospheric aerosol and droplets using a multi-rotor SUA due to artefacts resulting from the aerodynamic disturbances created by the propellers Quantifying this distortion and its effect on particles can be difficult due to the complexity of flow measurements (especially when considering turbulence). The field validation took place during the Pallas Cloud Experiment (PaCE; campaign year 2019) – a biennial experiment at the Pallas atmosphere–ecosystem supersite (Lohila et al, 2015) with the aim of characterising sub-Arctic clouds and validating instruments
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