An RGB‐D framework for capturing soft‐sediment microtopography

Abstract

Capturing sediment topography is one component in understanding how large animals in soft sediment ecosystems affect ecosystem processing. Traditional approaches for sampling soft‐sediment systems are too invasive and destructive for the fragile sediment structures. In contrast, non‐invasive approaches, such as LIDAR and monocular structure‐from‐motion (SfM) systems, can be expensive and cumbersome for data processing. We developed a low cost and practical framework for measuring morphological characteristics of soft sediment topography at the millimetre scale. Using an RGB‐D (red, green, blue and depth) device and a semi‐opaque container, the sediment surface can be imaged rapidly while operating in outdoor environments. The RGB‐D device imaged 0.3 m2 intertidal sediment surfaces, creating depth imagery over seven sites and 82 surfaces. First, using simulated surface data, we formulated and tested four variations of a geometrical detrending model to extract and measure the undulating surface microtopography. We then computed nine morphological characteristics, including arithmetic mean roughness, mean sediment peaks and rugosity, for the detrending models. We then used the two best performing models, linear and quadratic detrending models, to compare extracted morphological characteristics from the field data. We found a strong correlation between the models for extracted surface measures and similar extracted sediment trends. The results showed that RGB‐D real‐time imaging is a promising rapid scanning tool for collecting field data in intertidal regions and can be expanded to other fragile sediment surfaces outside the marine environment. The low costs and real‐time feedback makes it an attractive data collection tool for environments where data collection is challenging.

Towards time and cost‐efficient habitat assessment: Challenges and opportunities for benthic ecology and management

“…Recent advancements in these fields of computer science, in concert with the improvement of camera technologies, have allowed the quantification of seafloor structures from high‐resolution photogrammetry. To date, this has had three different ecological applications in soft sediments: firstly, mapping patch structure features such as seagrass beds or shellfish reefs (Nahirnick et al, 2019; Ridge et al, 2020); secondly, identifying and counting individual animal signatures of the sediment surface (Azhar et al, 2020; Schenone et al, 2022); and thirdly, supporting the statistical characterization of sediment microtopographic features (Azhar et al, 2022) (Figure 3). In the third case, the offset between sequences of two‐dimensional images extrapolated from underwater videos and images collected by scuba divers, remotely operated vehicles and towed underwater cameras can be used to develop three‐dimensional structural models (Storlazzi et al, 2016).…”

“…photogrammetry. To date, this has had three different ecological applications in soft sediments: firstly, mapping patch structure features such as seagrass beds or shellfish reefs(Nahirnick et al, 2019;Ridge et al, 2020); secondly, identifying and counting individual animal signatures of the sediment surface(Azhar et al, 2020;; and thirdly, supporting the statistical characterization of sediment microtopographic features(Azhar et al, 2022) (Figure3). In the third case, the offset between…”