Charlie Flats Spectra

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PostPosted: February 29, 2004 8:25 PM 

The chart on the right shows examples of spectra, or light wave patterns, extracted from the region of the Meridiani Planum rock outcrop dubbed “Charlie Flats,” a rich science target for the Mars Exploration Rover Opportunity. The spectra were extracted from the similarly colored regions in the image on the left, taken by the rover’s panoramic camera. The green circle identifies a bright, dust-like soil deposit. The red circle identifies a dark soil region. The yellow identifies a small, angular rock chip with a strong near-infrared band. The pink identifies a sphere-shaped pebble with a different strong near-infrared band. The cyan circle shows a dark, grayish pebble.

Image credit: NASA/JPL/Cornell


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PostPosted: March 1, 2004 7:35 PM 

Does anyone know how to interpret the spectra data? The pink, yellow, and red lines seem to indicate different reflectance levels at each wavelength but have similar wavelength curves. Does this mean each color is nearly the same mineral and only more or less shiney? Rolling Eyes

How about a reading on the base strata peeking out at the top right?


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PostPosted: March 1, 2004 8:32 PM 

I'll take a stab. Let's look at one line, the cyan one, reprsenting the data from some part or all of the cyan circle.

The line is made up. It's not really there, but just educated guesses as to what is between 11 firm data points. Those data points reflect (heh) measurements taken from 11 photos of the area taken with 11 different filters in front of the cameras -- i.e. measurements of brightness of the area when viewed through filters that allows different very narrow ranges of light frequencies through. See [link] for a nice chart of the filters.

The vertical bars probably represent the range of brightnesses measured when examing the individual pixels within the area of interest. The squares upon the bars represents some kind of average brightness for all the pixels examined.

So what does it tell you? It tells you how the cyan area reflects light of 11 different narrow ranges of light frequency. That tells me almost nothing -- because I don't have tables of how certain materials reflect light. But, to someone who does, it tells what possible material or materials behave similarly to the one or ones in the area of interest. Possibly it leads to exactly an indentity of the mineral in question. More likely, it eliminates a lot of possible materials and leaves one with a relatively small number of materials to consider.

That cyan line genrally says the cyan object is very gray. It is a fairly flat line, and therefore is reflecting almost equally all the different frequencies. It's not predominantly red, green, blue, or even various infra-red and ultra-violet colors.

The different curves vary enough to show that the different areas are made of different materials. Which ones, I know not.

Base strata? Yeah they could do that. They might have. They just presented a few areas here, as an example of what can be done. Every picture tells a thousand stories. That's a lot of data. Amateurs armed with the known reflectance of materials could probably parse apart brightness levels of objects in raw images, or much better the uncompressed high resolution images that NASA lets trickle out, if they wanted. I personally have no desire.

Marvin Lipford

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PostPosted: March 1, 2004 9:03 PM 

What I noticed immediately was no spectra on any of the clean "blueberries"! The orange spectra seems to be the top of a dusty, partially burried berry.

If you're wondering why 11 data points and not, say 16, it is because the 16 filters are split between the left pancam (L) and the right pancam (R). The L1 filter is clear ( no filter), L8 is a neutral density solar filter, and L1 and L2 are almost identical: 753nm and 754nm.

The really annoying thing about the pancam spectra is you have to do a complete scene reconstruction to tie the left and right spectra together!

This design seems to me was meant to obfuscate the data.

And of course you really, really need the original images to tie 2D points to 3D points!


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