Scientists from the US National Oceanic and Atmospheric Administration (NOAA) Southwest Fisheries Science Center have validated an efficient method of inspecting leopard seals (Hydrurga leptonyx) with a c-drone in Antarctica after several years of tests, according to a peer-reviewed paper in the scientific journal PLOS. These animals prey upon penguins and fur seals, which in turn feed on krill, an important commercial harvest, so monitoring the seals provides indicators of the health of Antarctic fisheries.
After catching and measuring 15 leopard seals – a species which can grow to 4m (12 ft) length and weigh over 450kg (1000 lb) – the researchers returned and photographed the seals from a c-drone. Length measurements were within 2% of the manual measurements, and weight within about 4%, meaning the c-drone monitoring is precise enough to replace manual measurement. However, there was a spectacular gain in time and resources – with the c-drone, a crew of two performed the same measurements per seal in twenty minutes versus a manual crew of five in four hours.
The c-drone, a MikroKopter-based APH-22 hexacopter fitted with large differently colored foam landing skids to orient the pilot and equipped with an Olympus EP-1 camera and a 45mm lens, was provided by Aerial Imaging Solutions of Old Lyme, CT after a field selection process for suitability in the harsh Antarctic environment. Wind was of particular concern and trials showed the c-drone could operate in winds up to 10m/s (23mph, 20 knots) when topped with a dome. Live video was transmitted to the visual-line-of-sight (VLOS) base station and the still images were processed with an algorithm published by the Antarctic team.
The scientists tested the c-drone’s noise level at different altitudes in California. Later, in the field, the seals were observed to ignore the c-drone when it hovered above an altitude of 75ft (43m). Douglas J. Krause, an author of the study, said: “We can get measurements that are just as good, or better, without ever bothering the animals. Catching a single seal can take hours, but the drone can photograph every seal on a beach in a few minutes.”