IR & Water: a robust debate continues...

["Editor - P.O.V. Image Service" <editor@xxxxxxxxxxxxxxx>]

Rolland Elliot wrote:

> A few more points to clarify........
>
> Kieth wrote: "I will assume over 20 scientific studies, done over nearly 70
> years by
> varying scientists,  showing optical absorptive qualities of water
> throughout the spectrum will satisfy you... Look at the data and weep
> (those near IR-absorptive tears)..."
>

>
> You are absolutely right Kieth! I'll just have to burn my "American Infrared
> Survey Book"
> because it has an IR picture of a lady getting out of a lake and the shallow
> shoreline water looks transparent.

As it should... I never said water was transparent to IR... or to Near IR... If
you go back over the posts, you were the one who said that there was NO absorption
-- even when told that your camcorder simply could not measure the difference...

> According to you, it should be black or
> at least very dark.

Never meant to imply that, and do not believe I di...  The darkness will depend,
in part, upon scattering by suspended particulate matter.

But, assume for now, that it is pure water... If you care to check the data
between 600 and 900 nm wavelengths you will see for yourself that water is between
1/2 and 1 full order of magnitude more absorptive than it is for the visible
wavelengths below it..

Start with the Hale and Querry results on the page I referenced earlier - The
Optical Qualities of Water Compendium.  I'll even give you a direct URL to the
data:

http://omlc.ogi.edu/spectra/water/data/hale73.dat

Check out the other studies listed that show absorption in the Near IR and IR
wavelengths.. They give the same results...

BTW: I chose 600-900 nm because it approximates the predominant imaging Red-Near
IR recording range for HIE...  The data for that is at:

http://webs.kodak.com/global/en/professional/support/techPubs/f13/f13.shtml

You can even see the actual spectral sensitivity curve for HIE/HSI at:

http://webs.kodak.com/global/en/professional/support/techPubs/f13/f002_0333ac.gif


That is assuming you can comprehend and internalize the data.  Something I am
beginning to doubt, given your almost complete reliance solely on direct empirical
evidence or books of photographic imagery...

> I'll also have to burn my book " Photography by
> Infrared, It's principles and applications" because it blatantly states
> that:
>
> " When infrared film is exposed through a red filter, the sensitization in
> the red and near infrared makes the film useful for penetrating water to an
> appreciable degree."  It also has a graph on page 168 that shows a greater
> than 90% transmission of IR light below 900nm (which is similar to what
> Kodak HIE film can record) through 1 cm of water.

OK time for the math kiddies...

YAY!!!

Guess what?  If water attenuates Near IR by 10% each centimeter, how many
centimeters of water does the light need to pass through until 50% of the near IR
is attenuated..?

<Final Jeopardy Music Playing>


Approximately 6.2 cm, according to YOUR book..

Last time I checked, that means at about 15.75 inches, 50% of the available IR
light will be absorbed...

Thanks for the data..

So, if the water is totally pure, you will have a 50% attenuation of Near IR  by
the water at 15 3/4 inches... Real world water is unlikely to be of the pure
de-ionized variety... Therefore, the attenuation will be increased...


> I'll also dig through all
> my old negatives and pictures and purge any of them that show water that
> looks even slightly transparent.
>

Never said that... The data show that for very shallow pool, etc, the water will
appear transparent...

OH, yeah,, BTW... At 22 cm, or approximately 4 feet  7 7/8 inches, according again
to YOUR data, 90% of the available NEAR IR will have been attenuated or absorbed
completely...  I bet you don't find that problem when looking with your eyes into
a 5 foot deep swimming pool...



>
> >From now on all my IR water shots will be dark and black! Who am I to stand
> in the way of your precious data tables? All sarcasm aside, what does the
> unit of 1/cm for absorption mean on that web site?
>

No-one said all water would be dark and black..  Simply that it water absorbs
NEAR-IR and IR more readily than it does the visible spectrum!

>  A thin 87 IR gel is transparent to near IR
> light but a five foot thickness of the same material would not be

Dunno about that, would need to know hoe absorptive it is of Near IR...

Hell, it could be clearer than water of the same thickness to Near IR..


> I guess it's just your point
> of view. I've been talking mainly about small amounts of water, while you've
> been talking about large ones.  The thicker the water the more IR it
> absorbs. Therefore small amounts of water absorb relatively small amounts of
> IR while larger amounts of water absorb rather large amounts of IR.
>

Depends how small, 10% at 2.54 inches is a good amount...

>
> "Just because absorption is not easily measurable with
> small volumes of water, that does not mean it is not a fact!"
>
> Everthing absorbs light to some extent (unless you are using a vacuum), so I
> guess you're right on a theoretical level, but what is to be learned on a
> practical level from this info?
>

That pools of pure water will be darker in Near Ir than in Visible light...

And that you can expect the water to seem to get darker more quickly as depth
increases when observed in the Near IR, than it would when observed in the visible
spectrum...

Besides, this whole argument has provided some very useful data I never had the
time or reason to search out.. Information that helps me put a rough mental guide
into my head of how deep a pool I need before it becomes significantly darker in
Near IR..  I would think that useful

>
> "Or, wow, how cool it would be to have a cheetah the size of an elephant.."
>
> You're right again! That would be really cool!

Except that when one scales a cheetah up to that size it's legs cannot support
it's own weight...



>
> I wrote:
> >>you're .....talking about theoretical IR photographic situations, that
> >>you've never had
> >any hands on experience with.
> Kieth's response: "I make my living taking photos...INCLUDING INFRA-RED
> IMAGES."
>
> Good for you! Wouldn't it be great if more of us could do this?

It would be, but I'm hungry enough as it is... If you were all working as
full-timers I would probably die of starvation...

> Let's see
> some of those Underwater IR pictures you claim to have experience with.

Didn't say that... Said, that I have significant experience with IR and water...
Not IR and UNDERWATER photography...

>
> Afterall I've shared specific book and picture references for my agruments,
> I even did a couple of quick tests with an IR camcorder, the least you could
> do is share.
>

Fair enough, my only scanner at home is my Polaroid SS4000, so I can't scan any
prints...  That knocks out the image I mentioned before with the woman's
reflection in the water... I will though pull out some IR images taken surfside in
Hawaii and of Cook Inlet in Alaska..  The water appear appreciably darker than a
purely visible spectrum photo would have it..  I'll set up a page on my website
and put them up...  I would get more for you, but I blew out my knee while setting
up a remote cam at a Temple University hoops game some weeks back... Traveling to
the office is out of question for now..

In the interim, there are some neat High-Contrast HIE shots on my website in the
Fine-Art section. Although I don't have any imagery of water up there, you might
find the imagery of the Actress Christina Ricci (as Little Red Riding Hood)
interesting... The URL for my site is in the signature of this correspondence...

> No, need to do that I already have one. It's on page 168 of above referenced
> book. But you might want to get one for yourself. Better yet, come over to
> my office and I'll take an IR picture of you crying I'm sure the tears will
> show up to be quite transparent in the final picture.

Of course they will!

Would be wild if we could make them black though, the apparent viscosity of water
but black.. Would look way cool!

> It may be seen from
> the chart that in a thickness of 1cm, water is transparent to light of
> wavelengths in the visible spectral region (400-760nm); from 700 to 900nm it
> is about 90% transparent; it is only partly transparent in the longer near
> IR region; it is opaque to radiations longer in wavelength than 1400nm  in
> the infrared.
>

And refer to the math above...

>
> Mine's for 1 cm thick water, if you have one for 1 or 2 meters of water they
> would be neat to compare.

The math creates one..

> One thing you could do is get rid of that legal
> mumbo jumbo disclaimer for me;  I find them particularly annoying.

As do I, but with the state of the law in the US and the fact that these
statements go out from my business account, no can do...

I think we should finally have reached a point that we both can agree upon..

90% Transparency for 1 cm = 10% attenuation per cm...

Ipso facto..

PHEW!

Keith


--
{       The views expressed in the preceding are those of the        }
{       author, alone, and  are neither the responsibility of,        }
{          nor, should they be understood to represent the            }
{            official viewpoint of  P.O.V. Image Service.             }
                 (Persistence of Vision Image Service)
                  "Your link to outstanding imagery."
                      http://www.p-o-v-image.com/


*
****
*******
******************************************************
*  To remove yourself from this list, send:          *
*         UNSUBSCRIBE INFRARED                       *
*       to                                           *
*         MAJORDOMO@xxxxx                            *
*----------------------------------------------------*
*   For the IR-FAQ, IR-Gallery and heaps of links:   *
*  http://www.a1.nl/phomepag/markerink/mainpage.htm  *
******************************************************