# Three-Dimensional Reconstruction and Scour Volume Detection of Offshore Wind Turbine Foundations Based on Side-Scan Sonar

## TL;DR

This paper introduces a method using sonar imagery to accurately detect and measure scour around offshore wind turbine foundations in 3D.

## Contribution

A novel 3D reconstruction and volume detection method for scour pits using optimized Shape-from-Shading and a weight-corrected AlphaShape algorithm.

## Key findings

- The method achieved 97.495% average volume measurement accuracy in simulated scenarios.
- Field tests confirmed the method's effectiveness in real-world offshore environments.
- Curvature and normal vector filtering improved point cloud data quality for accurate scour pit extraction.

## Abstract

To enable timely, effective, and high-accuracy detection of scour around offshore wind turbine pile foundations, this study proposes a three-dimensional reconstruction and scour volume detection method based on side-scan sonar imagery. First, the sonar images of pile foundations are preprocessed through grayscale conversion, binarization, and region expansion and merging to obtain an effective grayscale representation of scour pits. An optimized Shape-from-Shading (SFS) method is then applied to reconstruct the three-dimensional geometry from the effective grayscale map, generating point cloud data of the scour pits. Subsequently, the point cloud data are filtered using curvature and normal vector constraints, followed by depth-based z-axis descent detection, clustering, and morphological restoration to extract individual scour pit point clouds. Finally, a weight-corrected AlphaShape algorithm is employed to accurately calculate the volume of each scour pit. Numerical experiments involving five simulated scour scenarios across three types demonstrate that the proposed method achieves accurate identification and extraction of scour pit point clouds, with an average volume measurement accuracy of 97.495% compared with theoretical values. Field measurements in real-world environments further validate the effectiveness of the proposed method for practical scour volume detection around offshore wind turbine foundations.