Droning On

Unmanned Aerial Vehicles (UAVs), or drones, are remotely or autonomously piloted aircraft. Whilst UAVs have recently been most associated with military applications, their use in the field of atmospheric science and environmental monitoring is rapidly growing, from the monitoring of carbon dioxide (Watai et al., 2006) and ozone (Illingworth et al., 2013) concentrations, to studying emissions at active volcano sites (Diaz et al., 2010).

Ground-based monitoring sites such as the Automatic Urban and Rural Network (AURN) in the UK, operated by the Department for Environment, Food and Rural Affairs (Defra), can provide measurements of surface level pollution concentrations. However, such fixed measurements are limited in their spatial coverage, as shown in Figure 1. Measurements from AURN are often used as validation datasets for regional air quality models such as the Met Office Air Quality Unified Model. Clearly, the inability of such sites to inform on a highly resolute scale can lead to a poor interpretation (and validation) of local environments.

Figure 1: Locations of AURN sites in the UK plotted on Google Earth. Pollution levels correspond to measurements taken on Friday 7th July 2013; data courtesy of Defra (http://uk-air.defra.gov.uk/).
Figure 1: Locations of AURN sites in the UK plotted on Google Earth. Pollution levels correspond to measurements taken on Friday 7th July 2013; data courtesy of Defra (http://uk-air.defra.gov.uk/).

An alternative to ground-based measurements is to use aircraft. However, such flight campaigns are not only expensive, but still also lack the required spatial resolution for many applications. Take  Manchester city centre as an example: this area has a diameter of approximately 2 km, while the UK’s atmospheric research aircraft is able to travel at ~ 100 ms–1. This means that a typical 1 Hz instrument (i.e. one that is able to take one measurement per second) would only be able to make approximately twenty measurements during an overpass of the city. Large research aircraft are also restricted by the Civil Aviation Authority (CAA), which often means they are unable to fly around urban centres or within the lower boundary layer.

UAVs offer an ideal alternative at such scales, bridging the gap between ground-based and traditional airborne methods, with the potential to deliver detailed, high-resolution and precise measurements at the local scale.

Low Altitude, Short Endurance (LASE) UAVs are relatively simple to operate, with simple ground-control stations and control mechanisms, requiring only a small crew. Their small size means that they can be hand-launched (i.e. thrown) from a variety of terrains, and in the UK, UAVs with an operating mass of 7 kg or less are exempt from the majority of the regulations that are normally applicable to large and manned aircraft.

Figure 2: An RQ-4 Global Hawk flying in 2007 (Photo credit: Wikipedia).
Figure 2: An RQ-4 Global Hawk flying in 2007 (Photo credit: Wikipedia).

High Altitude, Long Endurance (HALE) UAVs can be larger than many general-aviation manned aircraft and may fly at altitudes of up to 20 km or more on missions that can extend for thousands of km. The NASA Global Hawk, a well-known example of a HALE UAV (shown in Figure 2), has a wingspan of almost 40 m, and a length of approximately 15 m.  The Global Hawk has been involved in a number of scientific campaigns since 2008 and has an operating altitude of 19,800 m and a flight endurance of over 30 hours, with a payload of ~750 kg.

Whilst UAVs undoubtedly get a bad rep because of their recent and well-documented use in military manoeuvres, with the continued miniaturization of highly accurate and precise sensors, the potential effectiveness of UAVs to make low-cost measurements, especially in remote, hazardous and politically unstable regions, continues to be the subject of much scientific and technological interest. And with Amazon recently getting in on the act, with Amazon Prime Air, their drone delivery service, it looks as though UAVs are here to stay.

Post by: Sam Illingworth

References:

DIAZ, J. A., PIERI, D., ARKIN, C. R., GORE, E., GRIFFIN, T. P., FLADELAND, M., BLAND, G., SOTO, C., MADRIGAL, Y. & CASTILLO, D. 2010. Utilization of in situ airborne MS-based instrumentation for the study of gaseous emissions at active volcanoes. International Journal of Mass Spectrometry, 295, 105–112.

ILLINGWORTH, S. M., ALLEN, G., PERCIVAL, C. J., HOLLINGSWORTH, P., GALLAGHER, M. W., RICKETTS, H., HAYES, H., LADOSZ, P., CRAWLEY, D. & ROBERTS, G. 2013. Measurement of boundary layer ozone concentrations on-board a skywalker unmanned aerial vehicle. Atmospheric Science Letters, 15, 252–258.

WATAI, T., MACHIDA, T., ISHIZAKI, N. & INOUE, G. 2006. A lightweight observation system for atmospheric carbon dioxide concentration using a small unmanned aerial vehicle. Journal of Atmospheric and Oceanic Technology, 23, 700–710.

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