Stereo Measurement of Objects in Liquid and Estimation of Refractive Index of Liquid by Using Images of Water Surface

In this paper, we propose a new stereo measurement method of objects in liquid whose refractive index is unknown. In recent years, demands for underwater tasks, such as digging of ocean bottom resources, exploration of aquatic environments, rescues, and salvages, have increased. Therefore, underwater robots or underwater sensing systems that work instead of human become important, and technologies for observing underwater situations correctly and robustly from cameras of these systems are needed (Yuh, 2001). However, it is very difficult to observe underwater environments with cameras (Hulburt, 1945; Stewart, 1991; Caimi, 1996), because of the following three big problems. 1. View-disturbing noise (Fig. 1(a)) 2. Light attenuation effect (Fig. 1(b)) 3. Light refraction effect (Fig. 1(c)) The first problem is about suspended matters, such as bubble noises, small fishes, small creatures, and so on. They may disturb camera's field of view (Fig. 1(a)).