Inexpensive Aerial Photogrammetry for Studies of Whales and Large Marine Animals

We describe a simple system enabling accurate measurement of swimming marine mammals and other large vertebrates from low-altitude single-frame photogrammetry via inexpensive modifications to a “prosumer” unmanned aerial vehicle (UAV) equipped with gimballed micro4/3 camera and 25 mm lens. Image sca...

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Bibliographic Details
Published in:Frontiers in Marine Science 2017-11, Vol.4
Main Authors: Dawson, Stephen M., Bowman, M. Hamish, Leunissen, Eva, Sirguey, Pascal
Format: Article
Language:English
Subjects:
Accuracy
aerial
Aircraft
Altitude
Aquatic mammals
Bridges
Calibration
Digital cameras
Image processing
Lasers
LIDAR
Logging
Marine mammals
Marine organisms
Measurement
Photogrammetry
Software
Swimming
Terrestrial environments
UAV
Unmanned aerial vehicles
Vehicles
whale
Whales
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Description
Summary:We describe a simple system enabling accurate measurement of swimming marine mammals and other large vertebrates from low-altitude single-frame photogrammetry via inexpensive modifications to a “prosumer” unmanned aerial vehicle (UAV) equipped with gimballed micro4/3 camera and 25 mm lens. Image scale is established via an independently powered LIDAR/GPS data-logging system recording altitude and GPS location at 1 Hz. Photogrammetric calibration of the camera and lens allowed distortion parameters to be rigorously accounted for during image analysis, via a custom-programmed Graphical User Interface running in MATLAB. The datalogger, camera calibration methods and measurement software are adaptable to a wide range of UAV platforms. Mean LIDAR accuracy, measured from 10 bridges 9-39 m above water, was 99.9%. We conducted 136 flights in New Zealand’s subantarctic Auckland Islands to measure southern right whales. Mean lengths of 10 individual whales, each photographed between 7 to 15 times, had CVs (SD/mean) ranging from 0.5-1.8 % (mean = 1.2 %). Repeated measurements of a floating reference target showed a mean error of c.1 %. Our system is relatively inexpensive, easily put together, produces accurate, repeatable measurements from single vertical images, and hence is applicable to a wide range of ecological questions in marine and terrestrial habitats.
ISSN:2296-7745
2296-7745
DOI:10.3389/fmars.2017.00366