Unmanned Aerial Survey of Elephants (2013)

Vermeulen C, Lejeune P, Lisein J, Sawadogo P, Bouche´ P (2013) Unmanned Aerial Survey of Elephants. PLoS ONE 8(2): e54700. doi:10.1371/ journal.pone.0054700

Introduction

The rise of drones in the scientific community raises a question for their possible use in future wildlife surveys.  A study conducted by Vermulean et. al. (2013)  in the Nazinga Game Ranch, located in southern Burkina Faso along the international border with Ghana, aimed to define the methodology to survey elephants with UAS and determine the parameters, as well as the animals’ reaction to the passage of the UAS.

Traditional methods for wildlife surveys in rural and remote locations include the classic foot and aerial surveys that implement the use of manned light aircraft. In large remote landscapes such aerial surveys can prove to be a logistical nightmare due to the lack of appropriate aircraft, adequate fuel supplies and the expense associated with hiring and operating a light aircraft operation. Due to these complexities the time between surveys can often reach up to a decades apart and sometimes a quarter of a century – during that time many species could have disappeared.

Materials and Methods

The Gatewing x 100 (wingspan: 100 cm , weight: 2kg, cruise speed: 80km/h, flight height: 100 m – 750 m, maximum flight duration: 40 minutes) was chosen for this experiment based on its silent electrical propulsion.

The UAS was catapulted with an elastic launcher system, flight was fully automatic up to the landing and complete stop. Features onboard the Gatewing x100 included an automatic return to home feature after 15 minutes without contact with the Ground Control System (GCS). The user could also call back the UAS or interrupt the flight at any time and an onboard VHF radio tracker with a range of 180km could be employed during recovery of a crashed UAS. With six 12V Nimh batteries a total of 6 flights per day were possible at 40 minute flight durations with an average 1.5 to 2 hours charging time for each battery.

Overall the X100 proved its reliability in field conditions (Vermeulen, C., 2013).  The flight plan of the X100 was not affected by the wind or by the heat (up to 43C in the shade). The UAS was operated at any time of the day even during the hottest hours. The risk of overheating is low due to batteries that can withstand heat while charging.

The imaging system mounted on the UAS was a Ricoh GR3 still camera (10 megapixels, 28mm). Shutter speed (from 1/1600 to 1/2000) and camera sensor sensitivity ISO (from 100 to 400) were selected according to luminosity.  During a 40 minute flight a total of 700 images were generated (over 17.5 images per minute).The spatial resolution of the images obtained varied from 3 cm at a height of 100 m to 20 cm at a height of 600 m.

 

Animal Reaction to the Passage of the UAS

Two tests of animal reaction to the passage of the UAS were implemented. For each test, the UAS passed 10 times in the morning above the Akwazena pond at a height of 100 m along parallel lines 25 m apart from each other. A ground observer located close to the pond recorded all the animals seen as well as their reactions as the UAS passed.

 

Animal Visibility

A block of 1km2 was covered by 10 to 12 parallel lines flown at a height of 100 m and strip-transect 10 km long, with a ground swatch of 120 m. Elephants were detected visually by displaying images on a laptop screen.

 

Animal Count

Ten straight lines of 10 km were flown along the 4 transects used to carry out the annual foot count in NGR between the 11th and 17th of February 2012 at a height of 100 m. A total of of 2732 images were recorded by the research group during these fligths.

elephants

Results

Animal Reaction to the Passage of the UAS

No flight or warning behaviour was recorded for any of the species recorded. A total of 3 mammal species were present along or in the pond during the 2 tests.

 

Animal Visibility

The first significant result of this study regarded animal visibility. The 5 flights demonstrated that the elephant is easily visible at an altitude of 100 m. For example, a group of 13 individuals bathing and 1 on the bank of the water body were photographed simultaneously from the ground and from the UAS at an altitude of 100 m. Each individual was clearly identifiable on the aerial image. Elephants remained discernible up to an altitude of 300 m in its natural habitat, however, the Buffon kob was difficult to observe on the images and the baboon could not be formally detected.

The analysis of images captured at 100 m (where elephants were easily discernible) enabled the research team to conclude that the observation and thus the count of elephants in the Sudano-Sahelian savannah ecosystem was possible on such images.

 

Animal Count

The succession of images acquired along the flight lines recreated classic strip-transect aerial count conditions. Image count was carried out at a mean rate of 27.81 images per minute. Finally, cross-checked counts revealed that 34 elephants were present inside the sampling strips. Independant counts showed that, on average, 14.7% elephant were missed.

 

Discussion

The research team noted that the absence of animal reaction as the UAS passed was remarkable and indicated an absence of animal disturbance. One observation from the study indicated that the absence of reaction could appear as a potential drawback in the future because animals are more easily visible when they are moving than when they are standing. The use of video cameras would provide the ability to record animal movements and improve their detectability.

Adult elephants’ visibility is excellent at a height of 100 m and possibly 300 m. At a height of 100 m, the width of the sample strip is 120 m according to the camera used. These images can even be used to determine the age of the elephants by measuring back lengths, considering the pixel size (from 3 to 10 cm).

The results show that an aerial sampling count is possible with a small UAS and that experienced observers are required to analyze the images. Missing a group has important consequences on the final estimate especially when elephants are few in number.
The use of UAS such as the x100 opens interesting possibilities for counting elephants and large mammals. The technology is sufficient to count African elephants in savannahs: flight implementation is easier (very short airfield), safer (due to no operators on board) and the UAS is reliable in very rough conditions.

2016-11-03T09:02:38+00:00