Satoshi Ishiguro

A Photogrammetric Correction Procedure for Light Refraction Effects at a Two-Medium Boundary

We report on a correction procedure for light refraction effects at a two-medium boundary, based on the stereo view of underwater objects, to estimate underwater topography using photogrammetry. Because theoretically, no solution exists for photogrammetrically observed positions when the incident angles of light rays from an underwater object of interest to two cameras are different; approximation in solving the positions is needed. We show the feasibility of the approximation theoretically by examining the horizontal differences between the observed and true positions when objects are in line along an airplane track or when the incident angles are identical. We applied the procedure to bathymetric mapping of Shiraho Reef, southwest Japan, using a stereo-pair of aerial photographs. Comparison of the corrected depths with measured depths at 658 points showed a mean error and standard deviation of 20.06 m and 0.36 m, respectively, for measured depth range of 23.4 m to 20.2 m.