shooting images of and through water

[Adam Griffith]

Beverly Pearce recently asked me a great question recently:

Are there any polarizers or anything that will help show river features through the water?  I assume infrared wouldn't really help with something like this, as the temperature of the riverbed is probably the same as the river itself.

Anyone have any thoughts?

Thanks,

Adam

[Alex Mandel]

Yes, polarizers are one tool for this, however the optimum angle is
something like 35 degrees not the normal 90 you get from most air
photos. Temperature is much further into the infrared than you think,
NIR or near infrared is what comes after Red and can be shot with
modified normal cameras. I haven't experimented much with NIR and water
but the biggest issue is actually distortion.

For an explanation
http://www.seafriends.org.nz/phgraph/water.htm

Exposure would likely be tricky too, but on rivers with a polarizer you
can probably get some good shots from straight above at certain times of
day.

Enjoy,
Alex

[Ned Horning]

Hi Adam,

Polarizers will help but near-infrared won't. Water absorbs in the
near-IR wavelength which is why near-IR is so good at helping detect
water/land interfaces. UV on the other hand penetrates water better than
the visible wavelengths. There is a good bit of information about doing
UV conversions on the web. Sometimes just using a filter that cuts out
most (some short wavelength blue is probably ok) of the visible light is
all that's needed. I'm having a camera modified in a couple week
specifically to test water penetration qualities and will report on how
well it works in the research notes.

Ned

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[Stewart Long]

I like these tips. If you can also avoid flying around solar noon +- 1.5hrs it will help reduce glare, in addition to polarization that has been mentioned.

On Tue, Jun 26, 2012 at 10:16 AM, Ned Horning <ne...@lightlink.com> wrote:

Hi Adam,

Polarizers will help but near-infrared won't. Water absorbs in the near-IR wavelength which is why near-IR is so good at helping detect water/land interfaces. UV on the other hand penetrates water better than the visible wavelengths. There is a good bit of information about doing UV conversions on the web. Sometimes just using a filter that cuts out most (some short wavelength blue is probably ok) of the visible light is all that's needed.  I'm having a camera modified in a couple week specifically to test water penetration qualities and will report on how well it works in the research notes.

Ned

On 06/25/2012 11:41 PM, Adam Griffith wrote:

Beverly Pearce recently asked me a great question recently:

Are there any polarizers or anything that will help show river features through the water?  I assume infrared wouldn't really help with something like this, as the temperature of the riverbed is probably the same as the river itself.

Anyone have any thoughts?

Thanks,

Adam

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[Michele Tobias]

I guess there might be two issues to solve with this question: 1. How do
you avoid glare off of the water surface, and 2. How do you reduce the
distortion of the water.

For the glare, picking a time of day with a lower sun angle will
probably help so the light doesn't bounce off the water surface and
directly into the camera lens. An example of this working is in my
research note about photographing tidepools:
http://publiclaboratory.org/notes/micheletobias/11-26-2011/intertidal-zone-leo-carrillo-state-park-ca
You can't even see that there's water but about half of the area in the
image was submerged. That was all luck though. I can't claim that it
was planned.

I'm not sure there is much you can do about the distortion from the
water. I imagine it's not constant throughout the river because it
probably depends on water depth and the movement of the water (like
ripples).

best,
Michele

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--
Michele Tobias

PhD Candidate
Geography Graduate Group
University of California, Davis

mmto...@ucdavis.edu
http://ggg.ucdavis.edu/student/michele-m-tobias
http://ucdavis.academia.edu/MicheleTobias

"The purpose of R-sig-ecology is two fold.
First, we want to provide a discussion forum for those analyzing ecological and environmental data with R.
Second, we want to encourage R users of all ability and experience to participate so that we may grow the
community of ecologists and environmental scientists that use R." https://stat.ethz.ch/mailman/listinfo/r-sig-ecology

[Jeffrey Warren]

For UV photography, the ~$200 Canon SD4000 IS is great; it has a rear-illuminated CMOS sensor very sensitive to UV light. I just got some new Hoya 340 UV filters and will try calibrating them with the PLOTS spectrometer so we know exactly what their range is. 

The only problem is that the Hoya filters are quite small and just barely cover the front of the lens; they're also too thick to put inside the camera.

http://publiclaboratory.org/notes/warren/4-28-2011/cheap-uv-photos-using-uv-pass-filter-cmos-camera

http://publiclaboratory.org/notes/warren/5-3-2011/hoya-uv-filter-profiles

Jeff

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Michele Tobias

PhD Candidate
Geography Graduate Group
University of California, Davis

mmto...@ucdavis.edu
http://ggg.ucdavis.edu/student/michele-m-tobias
http://ucdavis.academia.edu/MicheleTobias

"The purpose of R-sig-ecology is two fold.
First, we want to provide a discussion forum for those analyzing ecological and environmental data with R.
Second, we want to encourage R users of all ability and experience to participate so that we may grow the
community of ecologists and environmental scientists that use R." https://stat.ethz.ch/mailman/listinfo/r-sig-ecology

[Liz Barry]

Hey folks on this thread, 

We're thinking about giving these solutions a try on some Bronx River Oyster mapping with a community coalition here in NYC (more soon). 

We will definitely fly when sun is at low angle -- we've determined a 7:30AM lunar low tide in about a week and a half when the reefs should be well-exposed.

@Jeff have you had any luck with the Hoya filters?

@Ned @ Alex have you ever flown with polarizers? Is there a link to a product you recommend?

Thanks!

Liz

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@lizbarry

[Jeffrey Warren]

UV photo: http://www.flickr.com/photos/jeffreywarren/7705651824/in/photostream

But sadly I forgot to try taking a calibrated photo through a spectrometer before hot gluing on the filter. I'd love to use the spectrometer to empirically test the filter + camera combo. But in theory its a 340 nanometer filter.

[Liz Barry]

@jeff have you ever flown this camera+UVfilter over water?

[Jeffrey Warren]

No but I could take it out to the charles river. That's opaque even to visible light though :-)

How deep is the place you're going to be mapping and how deep do you wanna see?

[Stewart Long]

Suggest collaborating with Pioneer Valley Open Science's Aerial Shark Alert Program

https://github.com/Pioneer-Valley-Open-Science/pioneer-valley-open-science.github.com/wiki/Aerial-Shark-Alert-Platform-%28ASAP%29

--

Stewart