Reason for infrared boundary values?

Why is the boundary between the “near infrared” range and the “intermediate infrared” range defined as 1500nm (wavelength) and the boundary between the “intermediate infrared” range and the “far infrared" range defined as 20000nm (wavelength) ?
-what I mean is are these values just totally arbitrary values that someone just haphazardly and mindlessly conjured up in his head or is there some either practical or theoretical or scientific significance to these approximate boundary values and, if so, what is it? -just always wondered.
Does anyone here know?

Originally posted by Andrew Hamilton
Why is the boundary between the “near infrared” range and the “intermediate infrared” range defined as 1500nm (wavelength) and the boundary between the “intermediate infrared” range and the “far infrared" range defined as 20000nm (wavelength) ?
-what I mean is are these values just totally arbitrary values that someone just haphazardly and mindless ...[text shortened]... oximate boundary values and, if so, what is it? -just always wondered.
Does anyone here know?

Originally posted by PBE6
All sorts of practical reasons, apparently:

http://en.wikipedia.org/wiki/Infrared#Different_regions_in_the_infrared

I am trying to understand the exact mathematical meaning of the term “Absorption coefficients” for water at the graph at the bottom of:

http://www.lsbu.ac.uk/water/vibrat.html

-but just can’t quite understand what it says.
I want to understand it in terms of what proportion of the radiation is absorbed per, say, one cm distance of liquid water the radiation travels through.
For example, according to the graph, the “Absorption coefficients” for 2000nm wavelength of infrared is “100 per cm”; so if a beam of infrared all of 2000nm wavelength is shone through one cm distance of liquid water, what percentage of that beam's energy would be absorbed by that water?

Originally posted by Andrew Hamilton
I am trying to understand the exact mathematical meaning of the term “Absorption coefficients” for water at the graph at the bottom of:

http://www.lsbu.ac.uk/water/vibrat.html

-but just can’t quite understand what it says.
I want to understand it in terms of what proportion of the radiation is absorbed per, say, one cm distance of liquid water ...[text shortened]... istance of liquid water, what percentage of that beam's energy would be absorbed by that water?

Originally posted by PBE6
See footnote "d":

http://www.lsbu.ac.uk/water/vibrat.html#d

Originally posted by Andrew Hamilton
I am trying to understand the exact mathematical meaning of the term “Absorption coefficients” for water at the graph at the bottom of:

http://www.lsbu.ac.uk/water/vibrat.html

-but just can’t quite understand what it says.
I want to understand it in terms of what proportion of the radiation is absorbed per, say, one cm distance of liquid water ...[text shortened]... istance of liquid water, what percentage of that beam's energy would be absorbed by that water?

Originally posted by KazetNagorra
It means the fraction of transmitted light is exp(-100).

Originally posted by Andrew Hamilton
Oh, I see now! Thanks for that 🙂

So, for example, if we want to know how much light of 2000nm wavelength is absorbed if it passes through, say, 0.01 of a cm ( =0.1mm ) of liquid water, then, according to the graph, the ‘absorption coefficient’ is 100 for that wavelength so the proportion that gets through that 1/100th of a cm is:

e^( -100 * 0 ...[text shortened]... e rest being absorbed -and also scattered? -or is it only absorption we are talking about here?)

Originally posted by KazetNagorra
I haven't really read the article so I can't tell how they defined it. I guess it's only absorption, though there will be scattering as well.