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Fig. 2. Colour photographs (without polarizers) of the mirror image of the clear
sky reflected from the grey water-dummy (glass pane underlaid by matt light
grey cloth), patterns of the degree (d) and angle (
; measured
from the local mirror meridian) of linear polarization of reflected skylight,
and the area detected polarotactically as water versus the solar
elevation (
s) and time (local solar time = UTC + 2 h). The
polarization patterns are measured by 180° field-of-view imaging
polarimetry in the blue part of the spectrum. Chequered areas show those
regions that are inappropriate for comparative analyses due to unwanted
overexposure, shadows and mirror images of the polarimeter, its holder and
remote cord. In column 4, regions are shaded by black where
d>dtr=5% and 85°
95°. An
imaginary polarotactic water insect is assumed to consider a surface as water
if these two conditions are satisfied for the partially linearly polarized
reflected light. In column 4, the regions where these criteria are not
satisfied remain blank. The positions of the mirror image of the sun are shown
by dots, and the Brewster angle (56° from the nadir for glass with an
index of refraction of 1.5) is represented by an inner circle within the
circular patterns. Because of disturbance by early morning dewfall,
reflection-polarization patterns at low solar elevations are presented here
only for the sunset and dusk period.
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