Camera Calibration for Underwater 3D Reconstruction Based on Ray Tracing Using Snell’s Law

TLDR

Accurately estimating underwater 3D positions is crucial for marine research, but refraction invalidates the single‑viewpoint assumption. The study compares three underwater 3D reconstruction methods: in‑air calibration, underwater calibration, and ray tracing with Snell’s law. The authors evaluate each method by applying the respective calibration procedures and measuring the resulting 3D position accuracy. In‑air calibration was the least accurate, while underwater calibration and ray‑tracing produced comparable precision, with ray‑tracing offering greater flexibility by decoupling intrinsic and extrinsic parameters.

Abstract

Accurately estimating the 3D position of underwater objects is of great interest when doing research on marine animals. An inherent problem of 3D reconstruction of underwater positions is the presence of refraction which invalidates the assumption of a single viewpoint. Three ways of performing 3D reconstruction on underwater objects are compared in this work: an approach relying solely on in-air camera calibration, an approach with the camera calibration performed under water and an approach based on ray tracing with Snell's law. As expected, the in-air camera calibration showed to be the most inaccurate as it does not take refraction into account. The precision of the estimated 3D positions based on the underwater camera calibration and the ray tracing based approach were, on the other hand, almost identical. However, the ray tracing based approach is found to be advantageous as it is far more flexible in terms of the calibration procedure due to the decoupling of the intrinsic and extrinsic camera parameters.