Is The Mars Rover Cam Life-Blind?, page 1
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Topic started on 10-2-2004 @ 07:50 PM by ArchAngel


Here you can see the response of the cam.




Here you can see the respose of chlorophyll.

What do you think?


reply posted on 10-2-2004 @ 09:39 PM by BarryKearns
Looks to me like you're simply mis-reading the graphs. There are several appropriate filters that can capture both high-response and high-absorption regions from chlorophyll A and B.

Chlorophyll A has a high absorption in the 390-430 nm range, looks like. Filters R1 and L7 are perfect for seeing that darkness. It also has another sharp peak at around 670 nm. Lo and behold, filter L3 is dead-centered on that range.

Chlorophyll B is strong in the 420-480 range... filters R1, L7 and L6 provide solid coverage there. The secondary signal is at 610-630... filter L4 isn't a great match, but the edge of it might see the 610 nm signal (or more accurately, the lack thereof).

Of course, to understand what you'd really see, though, keep in mind that these are the ABSORPTION characteristics of chlorophyll.

The reason chlorophyll makes plants seem primarily green is because it DOESN'T absorb green... it instead absorbs a lot of human-visible blue and red... so a light source with all three frequency ranges (like sunlight, which is black-body radiation) bouncing off of a plant leads to a chunk of the human-visible red and blue being absorbed, and the green reflected.

Hence, plants look green to us.

OK then, if we are looking for plants on Mars, which filters will they show bright in?

Why, the green filter, of course!

Filter L5 at 530 nm sits smack-dab in the middle of the human-visible light frequencies that are reflected (not absorbed) by chlorophyll A and B. So green plants would show as bright in L5, and dark in R1, L7, L6, L3 and very slightly darker in L4.

A typical Earth green plant shot with a simple mix of L4-L5-L6 would look primarily green, with a stronger than typical red signal. Any doubts about whether cholorphyll was present could be verified by closely examining the relative darkness of the signal in L7, L6, and L3, with a very strong signal from L5 (All of the R2-R8 filters would probably show bright as well)

For a near-perfect mix for detecting the presence of chlorophyll, use an RGB mix of L3-L5-L6... and it should give a wall-to-wall undeniably green signal.

I doubt you could ask for much better narrow-bandpass filter coverage.

I don't know what might have led you to any other conclusion...

Except perhaps ignorance that response (i.e. transmittance) is the opposite of absorption?

If so, I'm glad that I'm able to deny the ignorance.

The Pancam is quite a fantastic tool... I'd go so far as to call it something of an engineering masterpiece. It's all the more pity that we seem to have a set of Keystone Kops running the darned thing and mangling the results along the way.


[Edited on 2-10-2004 by BarryKearns]


reply posted on 11-2-2004 @ 08:16 AM by BarryKearns
Originally posted by ArchAngel
BarryKearns:

I believe you are mistaken.


You can believe what you like... but I'd be interested to find out which aspect of my explanation you believe is a mistake.

You do understand that chlorophyll is the component that makes plants green, right?

And from your own chart, you posted, the peaks on the absorbance chart show that they are strongest in frequencies that are identified as red and blue, and very low at green frequencies... right?

From those two pieces of info, you should be able to determine why chlorophyll looks green to humans... and why it should reflect light which would give a very weak signal in L3 and L6, but very strong in L5.

Belief has little to do with it... it's a matter of understanding the dynamics of reflectance and absorption of light frequencies.

Science is not about belief. It's about following the data and making logical conclusions that are consistent with that data.

Your conclusion is utterly contradictory to the data you've presented. That tells me you (most likely) don't understand what the data means.

I'm sorry if you find that bothersome, but that's just the way it is. If you'd like to learn more about the frequencies present in sunlight, I'd recommend Googling on "black body radiation", and then finding some good reference materials on absorption, transmittance, and frequency response in digital images.

To see what the REFLECTANCE of chlorophyll looks like (and that's what the filtered images would show as bright... the reflectance, not the absorption), please see Figure 2A on page 5 of
this paper.

Ignorance is not a vice... but seeking to eliminate it from ourselves when we find it is (IMO) a definite virtue.
Avail yourself of the opportunity to learn.


[Edited on 2-11-2004 by BarryKearns]
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