Preprints
https://doi.org/10.5194/amt-2021-275
https://doi.org/10.5194/amt-2021-275

  08 Oct 2021

08 Oct 2021

Review status: this preprint is currently under review for the journal AMT.

Simulation and Field Campaign Evaluation of an Optical Particle Counter on a Fixed-Wing UAV

Joseph Girdwood1, Warren Stanley1, Chris Stopford1, and David Brus2 Joseph Girdwood et al.
  • 1Centre for Atmospheric and Climate Physics, School of Physics, Astronomy and Mathematics, University of Hertfordshire, Hatfield, Hertfordshire, AL10 9AB
  • 2Atmospheric Composition Research, Finnish Meteorological Institute, PO Box 503, FI-00101, Helsinki, Finland

Abstract. Unmanned aerial vehicles (UAVs) have great potential to be utilised as an airborne platform for measurement of atmospheric particulates and droplets. In particular, the spatio-temporal resolution of UAV measurements could be of use for the characterisation of aerosol, cloud, and radiation (ACR) interactions, which contribute to the largest uncertainty in the radiative forcing of climate change throughout the industrial era (Zelinka et al., 2014). Due to the infancy of the technique however, UAV-instrument combinations must be extensively validated to ensure the data is of high accuracy and reliability. This paper presents an evaluation of a particular UAV-instrument combination: the FMI-Talon fixed-wing UAV and the UCASS open-path optical particle counter. The performance of the UCASS was previously evaluated on a multi-rotor airframe by Girdwood et al. (2020). However, fixed-wing measurements present certain advantages—namely endurance, platform stability, and maximum altitude. Airflow simulations were utilised to define limiting parameters on UAV sampling—that is, an angle of attack limit of 10° and a minimum airspeed of 20 ms−1—which were then applied retroactively to field campaign data as rejection criteria. The field campaign involved an inter-comparison with reference instrumentation mounted on a research station, which the UAV flew past through stratus cloud. The effective diameter measured by the UAV largely agreed within 2 μm. The droplet number concentration agreed within 15 % on all but 5 profiles. It was concluded that UCASS would benefit from a mechanical redesign to avoid calibration drifts, and UAV attitude variations during measurement should be kept to a minimum.

Joseph Girdwood et al.

Status: open (until 12 Nov 2021)

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Joseph Girdwood et al.

Joseph Girdwood et al.

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Short summary
UAVs have great potential to be used for airborne measurements of cloud and aerosol properties, which are of particular importance due to the largely uncharacterised nature of such phenomena. However since UAVs are a new tool in atmospheric physics expensive platform validation and characterisation of UAV-instrument combinations needs to be performed. This paper presents an evaluation of a fixed-wing UAV in combination with an instrument which measures cloud droplet diameter.