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Using polarization to estimate surface normals at air–water interfaces for correction of refraction in seafloor imaging

Year: 2024
Type: article
Abstract: The retrieval of sea surface normal vectors using shape-from-polarization is investigated for the purpose of correcting for refraction at the water–air interface when imaging from above the water. In shallow clear water and overcast conditions, spectral longpass filtering (using a hard-coated 850 nm cut-on wavelength filter) is demonstrated to 1) avoid artifacts from the ground in the measured polarization state, and 2) reduce polarization from water-leaving radiance sufficiently to derive shape information exclusively from the polarization produced by specular reflection. The dependence of the method on meteorological conditions is studied. Measurements are performed with a commercial polarization filter array (PFA) camera. Due to the decreasing PFA efficiency towards the near-infrared, rigorous characterization and calibration measurements were performed and recommendations (e.g., on the f-number) elaborated. Overcoming the paraxial approximation, normal vectors are then retrieved with systematic errors of 0.1 ∘ (image center) to 0.5 ∘ −0.8 ∘ (edges/corners) for a flat water surface. An image of the sea floor corrected for surface refraction shows maximum displacements of 10–20 pixels only (corresponding to 0.25 ∘ ) with respect to a validation image without water.
DOI: 10.1364/ao.544305
Language: English
Open Access status: hybrid
OpenAlex ID: W4404672215
FWCI: 0.314
Cites: 40
Cited by: 3
Related to: 10