Drones provide added dimension to monitoring experimental burns


Scion and the University of Canterbury’s UAV teams were on hand to help during the Rural Fire Research team’s recent gorse burn experiments at Rakaia Gorge in March.

There were up to five craft in the air at once monitoring different aspects of the burns. The spread and temperatures of each fire were tracked using infrared and regular RGB video cameras mounted on a UAV flying above each burn at altitudes up to ~1000 feet (300 m). This footage (see examples below) provides exciting new insights into the convective fire spread theory being tested in these experiments.

The regular visual video (see below) shows streams of smoke separated by clear air that support the theory of inflows of air into the flame front from behind. Areas of updraft, and especially downdrafts and outbursts of flame, can also be seen across the flame front in the infra-red video (also see below). This further supports the theory that the movement hot and cool parcels of air (convection) creates the peaks and troughs observed in the flame front. The figure below is an hypothesised schematic of the physics dominating forward spread of the fire front.

Covective theory graphic (ex Finney et al-PNAS)_LI                                                 [Source, Finney et al. 2015, PNAS 112(32)]

The detailed spatial information on fire behaviour obtained from the aerial videos supplement the data collected from sensors on the ground. These ground sensors include thermocouple arrays, radiant heat flux and pressure sensors purpose-designed for the experiments by the US Forest Service team from the Missoula Fire Lab. Infra-red imagery from UAVs at lower altitudes above and oblique to the flame front is also being used by the University of Canterbury team to track the movement of the hot air parcels ahead of the fire front. UAVs also monitored wind speeds above the burns and within the smoke column, to support observations made by the San Jose State University’s ground-based scanning lidar and to provide information on winds high above the fire.

Drones were also used prior to the burns to fly the site with high definition cameras and lidar to provide high resolution maps and three-dimensional models of the site. This information was used for planning the operations, including siting equipment and producing site maps for firefighters. Drone-mounted aerial lidar is also being investigated for use in capturing fuel properties such as fuel particle sizes and arrangement, as well as estimating fuel loadings.

The new information provided by the UAV observations adds an exciting new dimension to the data collected during the burn experiments, and they will be used again during the next phase of the research with wilding pine crown fires.

Short snippets from Rakaia gorse burn visual (left) and infra-red (right) video. Both are from a UAV centred above the burn plot with the camera looking straight down.
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