Ocean Waves Under Polarizar

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microb
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Joined: Wed Mar 27, 2019 6:39 am

Ocean Waves Under Polarizar

#1 Post by microb » Mon Apr 05, 2021 4:17 am

I never saw this before, but with polarizing sunglasses horizontal, looking down at the waves at 45 degrees and sun maybe also at 45 (but maybe that info is unrelated), the specular highlights were intensely blue. Off angle the effect disappeared. No polarizer, the highlights were just bright white.

I tried to capture it here, but it's not as intensely blue in the image. My question is what am I looking at? Was effect always there and I never noticed it?
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PeteM
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Joined: Tue Dec 06, 2016 6:22 am
Location: N. California

Re: Ocean Waves Under Polarizar

#2 Post by PeteM » Mon Apr 05, 2021 6:22 am

Here's one guesstimate, based on too-long-ago memories of physics class. Start with "why is the sky blue" (the full spectrum of sunlight has the shorter blue wavelengths scattered more widely in our atmosphere). So indirect skylight looks blue. The scattering process also polarizes much of this blue sky source. So we've got this big blueish polarized light source called the sky above our heads, out on the horizon. It is the "fill light" added to direct sunlight.

A camera polarizer makes blue skies appear an even darker blue.

My guess, perhaps wrong, is that waves/froth scatter light further (much as does an overcast sky) - but the polarizer is still somewhat effective at rejecting any light not proceeding from the big blue sky? Could also be the angles work out so that the light you saw coming through the waves to your camera was mostly indirect skylight rather than direct sunlight?

PeteM
Posts: 2982
Joined: Tue Dec 06, 2016 6:22 am
Location: N. California

Re: Ocean Waves Under Polarizar

#3 Post by PeteM » Mon Apr 05, 2021 6:46 am

Maybe another way to look at it - when we view something like a reflective silicon wafer with polarized light in an epi microscope - the light source is polarized (just like skylight is a polarized light source). Rotate the analyzer just right and the reflected light shows up as blue (or some other color depending upon analyzer orientation and the surface characteristics in the wafer case).

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