3d Modelling in Temperate Waters: Building Rigs and Data Science to Support Glass Sponge Monitoring Efforts in Coastal British Columbia

Abstract

Abstract. Structure-from-motion (SfM) has emerged as a popular method of characterizing marine benthos in tropical marine environments and could be of tremendous value to glass sponge monitoring and management efforts in the Northeast Pacific Ocean. However, temperate marine environments present a unique set of challenges to SfM workflows, and the combined impact that cold, dark, and turbid waters have on the veracity of SfM derived data must be critically evaluated in order for SfM to become a meaningful tool for ongoing glass sponge research. This paper discusses the design, development, testing, and deployment of an innovative underwater SfM workflow for generating high-resolution 3D models in temperate marine environments. This multi-phase research project (dry-lab, wet-lab, and field), while possibly seen as unconventional, was designed to innovate in two ways. First to build an operational data capture platform to support low-cost SfM-based seafloor surveys. And second, to enable systematic isolation and evaluation of SfM data capture parameters and their implications for representational veracity and data quality. This paper reports the challenges and outcomes from a series of field surveys conducted in Howe Sound, BC, one of which serves as the first of two data sets in a temporal analysis of 3D morphometric change. This research demonstrates that accurate, high-resolution morphometric characterization, of all benthic species and habitats, is dependent on a range of equipment, procedural, and environmental variables. It is also intended to share our applied problem-solving path to successful 3D capture, backed up by robust data science.

Evaluating the 3D Integrity of Underwater Structure from Motion Workflows

“…As dive time, and thus data collection, is constrained by depth, identifying the quantity and configuration of photographs required to maximise SfM performance was critical. While underwater SfM workflows have proven to be a relatively low-cost, simple, and informative method of documenting the 3D structure of benthic organisms in tropical regions, this wet-lab study, as well as prior dry-lab research (Lochhead and Hedley, 2021), were necessary steps preceding subsequent field surveys (Lochhead and Hedley, 2020).…”

“…Therefore, it was found to be prudent that a clear set of data quality benchmarks is established before collecting field-based data: assessing the performance of HEXYZ-1 in a marine setting, quantifying the performance of the SfM workflow in cold, dark temperate waters, and identifying the relationship between the number of photograph, camera formation and 3D model accuracy. These distinct wet-lab tests provided an essential basis to inform field-based surveys (Lochhead and Hedley, 2020) and enabling informed decisions regarding the balance between data requirements, data quality and survey efficiency. This study confirmed that HEXYZ-1 is well equipped to provide camera stability and world-stabilised artificial light in a temperate marine environment.…”

“…This paper provides contextual benchmarks to support the applied fieldwork of others, as well as our own. The next phase of this research employed these benchmarks to inform the field-based activities deploying HEXYZ-1 in the north-east Pacific Ocean (Lochhead and Hedley 2020). Future research efforts will look to capture sets of photographs, collected approximately six months apart, to quantify temporal changes in glass sponge morphology.…”

“…The analysis of the impact that different quantities and configurations of photographs have on model accuracy was designed to identify ways to reduce data collection time in accordance with restricted SCUBA dive times at depths up to 30 m. Extracted 4K video frames were excluded from the analysis, despite the fact that video capture is significantly quicker than photography, as extracted video frames from the camera (3840 × 2160 pixels) do not provide the recommended highest resolution (Agisoft 2018) output of the digital camera (6000 × 4000 pixels), and prior SfM research reports lower resolution 3D models (Hollick et al., 2013; Bennecke et al., 2016) and less accurate 3D measurements (Lochhead and Hedley, 2021) from lower resolution images. Nevertheless, extracted video frames may have provided a useful comparator for this study, as field‐based data collection did necessitate the use of 4K video (Lochhead and Hedley, 2020).…”

“…There were three main objectives for this research: (1) to assess the performance of a custom‐made SfM data‐capture platform (named HEXYZ‐1) in a controlled underwater environment; (2) to compare the results of wet‐lab SfM surveys against their dryland equivalents and use manual measurements to quantify the performance of the underwater SfM workflow; and (3) to determine the optimal number and configuration of photographs so as to maximise model accuracy while accounting for the temporal constraints (approximately 20 min per dive) imposed by subsequent field‐based data collection at depths of 20–25 m. The wet‐lab research discussed here was an essential step in this research programme because it was informed by the initial dry‐lab system and SfM workflow performance tests (Lochhead and Hedley, 2021) and informed subsequent field‐based surveys of glass sponge morphology (Lochhead and Hedley, 2020). This approach not only delivers an operable field survey architecture but also establishes the data science and data quality benchmarks necessary to understand SfM performance in temperate marine environments.…”