Ultra-wide-field displacement measurement using the sampling moiré method with a fisheye lens

Abstract Digital image-based full-field displacement measurement is a critical technique for assessing the structural health of infrastructure like bridges, dams, tunnels, and railroads, including hard-to-access areas such as power plants. Traditional camera lenses are limited in capturing wide areas, so we explored using fisheye lenses to overcome this constraint. Fisheye lenses offer a wide field of view at short distances, making them advantageous for internal structure inspections and minimizing environmental interference. However, these lenses typically suffer from significant lens aberrations, which can complicate optical displacement measurements. This study proposes an innovative solution using the sampling moiré method, which uniquely can automatically cancel lens aberration effects by determining phase differences in moiré fringes before and after deformation. This approach enables accurate, wide-field displacement measurement, even with the optical distortions inherent in fisheye lenses.