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

Abstract

Small unmanned aircraft systems (sUASs) are fostering novel approaches to marine mammal research, including baleen whale photogrammetry, by providing new observational perspectives. We collected vertical images of 89 gray and 6 blue whales using low cost sUASs to examine the accuracy of image based morphometry. Moreover, measurements from 192 images of a 1 m calibration object were used to examine four different scaling correction models. Results indicate that a linear mixed model including an error term for flight and date contained 0.17 m less error and 0.25 m less bias than no correction. We used the propagation uncertainty law to examine error contributions from scaling and image measurement (digitization) to determine that digitization accounted for 97% of total variance. Additionally, we present a new whale body size metric termed Body Area Index (BAI). BAI is scale invariant and is independent of body length (R2 = 0.11), enabling comparisons of body size within and among populations, and over time. With this study we present a three program analysis suite that measures baleen whales and compensates for lens distortion and corrects scaling error to produce 11 morphometric attributes from sUAS imagery. The program is freely available and is expected to improve processing efficiency and analytical continuity.

New views of humpback whale flow dynamics and oral morphology during prey engulfment

“…These new technologies are rapidly changing the study of wildlife (Bevan et al 2016, Rümmler et al 2016, Schofield et al 2017, Sykora-Bodie et al 2017, Rees et al 2018, Rieucau et al 2018, Weimerskirch et al 2018, Verfuss et al 2019, especially in marine settings where observation had been mostly limited to vessel-based or airborne observers. Because new camera systems allow more rapid (near instantaneous) changes in orientation than most boats and manned aircraft can achieve, animals can be followed and stable vantage points maintained or switched very quickly (Hodgson et al 2013(Hodgson et al , 2017Goebel et al 2015;Koski et al 2015;Durban et al 2016;Fiori et al 2017;Johnston et al 2017;Krause et al 2017;Torres 2017;Burnett et al 2018;Torres et al 2018). Not only have these video recording systems become less expensive and more readily available (Goldbogen and Meir 2014, Nowacek et al 2016, Dawson et al 2017, they are also less noisy and less dangerous to operate (Christiansen et al 2016b), so that they pose fewer risks to animals and likely cause fewer changes in wild animals' natural behavior (Ditmer et al, 2015, Dominguez-Sanchez et al 2018.…”

AragoJ: A free, open‐source software to aid single camera photogrammetry studies

“…Yet, and paradoxically, software specifically designed to aid in obtaining simple planimetric measurements in 2D CRP are scarce and often tailored to specific problems, narrowing their applicability (e.g. Burnett et al, ; Hsiang et al, ). Instead, 2D CRP studies often make use of image editing software to obtain measurements from digital photographic reproductions (e.g.…”

MorphoMetriX: a photogrammetric measurement GUI for morphometric analysis of megafauna

“…MorphoMetriX was inspired by the image processing program ImageJ (Schneider, Rasband, & Eliceiri, 2012) and other UAS photogrammetry tools written in R (Christiansen, Dujon, Sprogis, Arnould, & Bejder, 2016) and MATLAB (Burnett et al, 2018;Dawson, 2017) that were developed specifically for measuring body condition of cetaceans. While ImageJ is an open source software with a powerful zoom function and the freedom and flexibility to measure any object of interest in an image, it lacks the ability to automatically section animals proportionally for perpendicular width measurements (i.e., body width measurements at 10% intervals along the total length of an animal), a key method used for comparative studies of body condition in cetaceans (Christiansen et al, 2016;Christiansen et al, 2018;Dawson, 2017;Miller et al, 2012).…”

“…Several software systems, written in MATLAB and R, have been developed to extract photogrammetric measures from aerial images of megavertebrates. However, some of these tools have slow workflows, are designed with only particular aircraft/sensor combinations and/or specific measurements in mind e.g., (Burnett et al, 2018;Dawson, 2017), have limited image zoom capabilities e.g., (Burnett et al, 2018;Christiansen et al, 2016;Dawson, 2017), and in some cases are not open source, requiring purchased or institutional licensing e.g., (Burnett et al, 2018;Dawson, 2017). These existing tools written in R and MATLAB are relatively feature-rich, allowing the measurement of proportional body widths based on total length, as well as a set of additional pre-fixed morphometric measurement options, such as 'width of eyes', 'rostrum to blowhole', and 'fluke width'.…”