Collect airborne canopy spectra
In July 2017, we obtained multispectral images covering a total of four sites each of c. 500 m length. Sites were overflown by an UAS (Tarot, T560 Sport) flying a raster scan pattern at c. 90–120 m above ground level (i.e. 5–7 cm/pixel ground resolution or c. 5–6 cm² pixel treetop resolution). Flights occurred in late-morning conditions during fully sunlight or fully cloudy conditions (i.e. minimizing shadows from partly cloudy skies). Due to weather and permitting issues, flights were only carried out at the Burke or Jolanta-4 sites, nor at the very eastern edge of the Jolanta-3 site. Data were collected using a multispectral camera (Micasense, RedEdge) on gimbal mount. The camera obtained co-registered coverage of five spectral bands: blue (475 ± 20 nm), green (560 ± 20 nm), red (668 ± 21 nm), red edge (717 ± 10 nm) and near-infrared (840 ± 40 nm). Immediately prior to data collection, a calibration image was obtained of a ground-based grey reference panel (Micasense, Calibrated Reflectance Panel). UAS flight plans were implemented using Universal Ground Control Software (SPH Engineering), which automatically accounts for approximate elevation gradients within the flight area by maintaining the elevation above ground level via an integrated pressure sensor on the flight controller (Pixhawk). The flight missions specified 70%–80% front and side image overlap. Simultaneous to imaging, incident radiation was collected using a downwelling sensor at 1 s intervals. The multispectral images were stitched using Pix4D Mapper software. Pixel values were then converted to reflectance values based on calibration against the downwelling radiation and grey reference data.
Quantities: 4 sites, c. 500 m length each, 90-120 m flight altitude, 5-7 cm/pixel resolution, 5 spectral bands, 70-80% image overlap, 1 s intervals for radiation sensorDuration: July 2017, late-morning flightsConditions: Fully sunlight or fully cloudy conditions to minimize shadows
Equipment: Tarot T560 Sport UAS, Micasense RedEdge multispectral camera, gimbal mount, Micasense Calibrated Reflectance Panel, Universal Ground Control Software, Pixhawk flight controller, downwelling radiation sensor, Pix4D Mapper software