Inexpensive Aerial Photogrammetry for Studies of Whales and Large Marine Animals

Abstract

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 (GUI) 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 and 15 times, had CVs (SD/mean) ranging from 0.5 to 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.

Estimating morphometric attributes of baleen whales with photogrammetry from small UASs: A case study with blue and gray whales

“…In terms of ranging accuracy, the DJI Phantom sUAS barometric altimeter is less precise than the LIDAR employed by Dawson et al . (), yet the mean coefficients of variation for the WL of gray whales and blue whales were 2.24% and 3.64%, respectively. These are in the range of those reported by both Durban et al .…”

“…() and Dawson et al . (). In terms of ranging accuracy, the DJI Phantom sUAS barometric altimeter is less precise than the LIDAR employed by Dawson et al .…”

“…In terms of ranging accuracy, the DJI Phantom sUAS barometric altimeter is less precise than the LIDAR employed by Dawson et al . (). In terms of ranging accuracy, the DJI Phantom sUAS barometric altimeter is less precise than the LIDAR employed by Dawson et al .…”

“…(), and Dawson et al . (), the DJI Phantom series employed in this study are much smaller and cheaper aircraft. The smaller size of the DJI Phantom is inherently more compatible with space constraints associated with small vessel operations, and the low‐cost makes the financial risk of a total loss more palatable to researchers with limited budgets.…”

“…Another leap in the evolution the sUAS whale photogrammetry field was presented by Dawson et al . () who used a DJI Inspire Pro sUAS to conduct photogrammetric surveys of southern right whales ( Eubalaena australis ) with the added innovation of a lightweight precision LIDAR instrument to estimate altitude. The improved precision and accuracy of altitude measurements resulted in whale length estimates having 0.5%–1.8% coefficient of variation.…”