Photogrammetry of killer whales using a small hexacopter launched at sea

Abstract

Conventional aircraft have been used for photogrammetry studies of free-ranging whales, but are often not practical in remote regions or not affordable. Here we report on the use of a small, unmanned hexacopter (APH-22; Aerial Imaging Solutions) as an alternative method for collecting photographs to measure killer whales (Orcinus orca) at sea. We deployed and retrieved the hexacopter by hand during 60 flights (average duration 13.2 min, max 15.7 min) from the upper deck of an 8.2 m boat, utilizing the aircraft's vertical takeoff and landing (VTOL) capability. The hexacopter was quiet and stable in flight, and therefore could be flown at relatively low altitudes without disturbing whales. The payload was a Micro Four-Thirds system camera that was used to obtain 18920 still images from an altitude of 35–40 m above the whales. Tests indicated a ground-resolved distance of <1.4 cm across the full extent of a flat and undistorted field of view, and an onboard pressure altimeter enabled measurements in pixels to be scaled to true size with an average accuracy of 5 cm. As a result, the images were sharp enough to differentiate individual whales using natural markings (77 whales in total) and preliminary estimates resolved differences in whale lengths ranging from 2.6 to 5.8 m. This first application at sea demonstrated the APH-22 hexacopter to be a safe and cost-effective platform for collecting photogrammetry images to fill key scientific data gaps about whales, and we anticipate this utility will extend to studies of other wildlife species.

Inexpensive Aerial Photogrammetry for Studies of Whales and Large Marine Animals

“…The APH-22 flew well and collected data for 2 days, but crashed into the water when the velcro strap holding its battery in place failed. This incident was in contrast to the usual reliability of this aircraft (e.g., Durban et al, 2015). One of the Splashdrones flew briefly, and crashed into the water.…”

“…We also took along an APH-22 hexacopter equipped with an Olympus E-PM2 and 25 mm f1.8 lens (Durban et al, 2015) and two Swellpro Splashdrones equipped with Canon D30 waterproof point-and-shoot cameras programmed to take images every 2 s (Christiansen et al, 2016). The APH-22 flew well and collected data for 2 days, but crashed into the water when the velcro strap holding its battery in place failed.…”

“…The first uses data logged from a high-precision air pressure sensor (e.g., Durban et al, 2015). Provided there are no substantial atmospheric changes during the flight, such data can accurately record altitude.…”

An Economical Custom-Built Drone for Assessing Whale Health

“…UAVs also provide an alternative, safer, quieter and often cost-effective option for monitoring fauna and flora, from individuals and populations to entire ecosystems, and in so doing are replacing expensive manned systems such as helicopters and fixed-wing aircraft Christie et al, 2016). UAV applications in wildlife research now encompass almost all environments, from arid deserts, through rainforests, oceans to polar regions (Linchant et al, 2013(Linchant et al, , 2015Durban et al, 2015;Goebel et al, 2015;Duffy et al, 2017).…”

“…In the marine environment, UAVs are revolutionizing the way marine species can be studied due to their small size, apparent minimal disturbance of wildlife and improved safety for both operators and animals (Nowacek et al, 2016;Fiori et al, 2017). UAVs have been utilized for a wide variety of applications including aerial surveys, monitoring, habitat use, abundance estimates, photogrammetry and biological sampling e.g., whale "blow" (Hogg et al, 2009;Acevedo-Whitehouse et al, 2010;Hodgson et al, 2013;Durban et al, 2015;Pomeroy et al, 2016;Schofield et al, 2017).…”