Dry-Lab Benchmarking Of A Structure From Motion Workflow Designed To Monitor Marine Benthos In Three Dimensions

Structure from motion (SfM) has emerged as a popular method for characterising marine benthos (seabed organisms), particularly in clear, tropical waters. However, there are many environmentally sensitive benthic organisms inhabiting temperate waters, including the reef-forming glass sponges of the northeast Pacific Ocean. Broader questions are raised, not just about whether SfM is a capable spatial data acquisition and ecological characterisation method in temperate waters; but whether a systematic assessment of capture methods in dry and wet laboratory conditions reveals critical relationships between SfM parameters, data products and their implications for underwater surveys. This paper, the first of two empirical assessments, reports on a series of dry-lab tests quantifying the impact that lighting, camera type, camera settings and capture strategy have on data accuracy. These tests provide a crucial accuracy baseline for subsequent wet-lab and field-based surveys, revealing that photographs captured from a controlled and stable platform produce superior data products. While the measurable differences were small, they may be critical for accurate change detection in temperate environments.