Research ArticleOCEANOGRAPHY

Bioinspired polarization vision enables underwater geolocalization

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Science Advances  04 Apr 2018:
Vol. 4, no. 4, eaao6841
DOI: 10.1126/sciadv.aao6841
  • Fig. 1 Schematic of in-water polarization patterns.

    (A) The cylinder shows the polarization states that the detector observes, in false color. (B) Polarization states predicted by the single-scattering model, in false color (see key at right), for Sun elevations of 10°, 45°, and 80° above the horizon. For clarity, lines oriented at the polarization angles are overlaid on the graphs. Neutral points in the polarization occur where the polarization state of the scattering event cancels that of the refraction.

  • Fig. 2 Example measurements and residuals.

    (A) Polarization angle measurements from four experiments at varying Sun elevations. Measurements are indicated by dots; model predictions, by solid lines; the heading to the Sun, by the vertical dotted lines. (B) Differences between each measurement and the single-scattering model prediction, indicated by color. The smoothly varying nature of the residuals indicates additional dependencies between the underwater polarization angle and the Sun’s position that the single-scattering model does not capture.

  • Fig. 3 Maps of position estimates.

    (A) World map of all position estimates. The blue pluses show the locations of the measurement sites, the red exes and dotted contour lines show the centroid and distribution of position estimates using just the single-scattering model for inference, and the green diamond and contours show the centroid and distribution of position estimates using the kNN method. The contours are at 1, 2, and 3 SDs from the centroid. Too few data were collected in Finland to estimate the SD contours. (B and C) Maps of position estimates from data taken at the Lizard Island Research Station when the Sun was at least 40° above the horizon, using only the single-scattering model (B) or the kNN method (C). The blue pluses show the location of the collection site, black dots are individual position estimates, and the red exes show the mean position estimate. The concentric curves are at 1, 2, and 3 SDs from the mean.

  • Fig. 4 Example sensitivity data.

    (A) Intensity image taken during a sensitivity experiment performed during the morning. The camera is set vertically, with a disc to block the Sun. The colored circles around the periphery show the regions over which the polarization angles are measured. Regions with partial polarization less than 5% were rejected. (B) Polarization angles measured during the sensitivity experiment; colors correspond to the regions shown in (A). The polarization angles vary almost linearly at the time of day the data were recorded. The vertical dotted line shows how long it takes the angles to change with 99% confidence.

  • Fig. 5 Model schematics.

    (A) Single-scattering model geometry. (B) Refraction-event geometry. (C) Scattering-event geometry.

Supplementary Materials

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. RMS error statistics.
    • fig. S2. Sensitivity data recorded under windy conditions.
    • fig. S3. Camera hardware in use.
    • Legend for movie S1

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mp4 format). Data collection with bioinspired polarization imaging sensor.

    Files in this Data Supplement:

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