SCI/TECH: What Color Is Mars, Really?

There are 5 image filters on the Martian rovers that cover about half the visible light spectrum. You get better results if you assign an RGB value to each of these filters and combine the 5 images, rather than picking one to be completely R, one G, and one B.

I converted most of the Rover images with 5 color bands on this site, with pretty good results. At least I think they're pretty good. I need to go to Mars with my digital camera and find out.

xpda.com...

Bob Webster

Beautiful job!
Thanks for putting this together so nicely.
I recommend others definitely take a look at
this work.
Here is one that I like, it reminded me of an
Oyster

cool pics. also happened to notice something that kinda looks like a log in one of them. its in the middle on the right hand side cant miss it if u look:

xpda.com...

I read that mars is supposed to be a salmon colored desert with blue sky. I don't get it,if the sun hits a planet, wouldn't the atmosphere be blue like earth? Mars isn't *THAT* far away.

Well since this is the right thread here it is.

xfacts.com...

And this one is from the enterprise mission ( i forget where).

img496.imageshack.us...

The reason for wanting to change the colour is imo to make colonization seem expensive and thus easy to move off the table while Nasa goes on with it's primary military orientated mission.

Stellar



[edit on 15-1-2006 by StellarX]

[edit on 15-1-2006 by StellarX]

Originally posted by malakiem
I read that mars is supposed to be a salmon colored desert with blue sky. I don't get it,if the sun hits a planet, wouldn't the atmosphere be blue like earth? Mars isn't *THAT* far away.

Nope, not necessarily. The blue color comes from a process called Rayleigh scattering. This is the scattering of photons at molecules, ie particles that are smaller than the wavelength of the incoming light. Short wave light is scattered a lot more than long wavelength light. In numbers, the effect grows with 1/(wavelength to the power of four), in short (1/lambda^4). This means that "red light" is passing the atmosphere less disturbed than "blue light". If the sun's high above the horizon then blue light is scattered from all directions into the observer's eyes.
But the very same effect is responsible for the reddish sky at sunset or sunrise on earth. If the sun's near the horizon the light rays travel a much longer distance through the atmosphere and all the blue light is scattered away from the observer, only the long wavelength (red) light arrives at the observer's viewpoint.

In the full range of visible light (approx. 360 to 830 nm) the ratio of scattering strength is 1/(360^4) / (1/830^4) = 28.26
This means that the shortest visible wavelength is scattered 28 times stronger than the longest visible wavelength.

If you take the more commonly used range of 380 to 780 nm the ratio still is 17.75.

There are several factors that influence the appearance of the atmosphere of Mars. The atmosphere of Mars is a few orders of magnitude thinner and there's a lot of dust in the atmosphere. The amount of dust varies very much, depending on the weather conditions/storm activities.
Color appearance of light scattering at bigger particles (bigger than the wavelength of light) is described by the effect of Mie scattering.
On earth Mie scattering makes the sky look white/bleached near the sun and at the horizon. The color of the sky also changes considerably near big cities because of the vast amount of dust particles from industry and car exhaust. That#s why the sky can look brownish above big cities.
If you look closely you can see that on color measurment photographs taken by the MERs the sky can look slightly bluish around the sun.

Another factor changes the atmospherical appearance very much. If you're inside the atmosphere you're subject to a lot of stray light, indirect lighting which is visible only in certain directions (especially in the direction you're are standing: downwards, or better: away from the sun). Looking down to the planet from space the visual effect of this stray light is very different, as a lot of this light isn't scattered back to you but first towards the ground and then back to you. The way of the light through the atmosphere is longer (depending on the shallowness of the viewing angle) than viewing from inside the atmosphere.
On earth even the thickness of the ozone layer influences the color appearance of the atmosphere.

[edit on 17-1-2009 by ColorScientist]

[edit on 17-1-2009 by ColorScientist]

Originally posted by edibobb
There are 5 image filters on the Martian rovers that cover about half the visible light spectrum. You get better results if you assign an RGB value to each of these filters and combine the 5 images, rather than picking one to be completely R, one G, and one B.

I converted most of the Rover images with 5 color bands on this site, with pretty good results. At least I think they're pretty good. I need to go to Mars with my digital camera and find out.

xpda.com...

Bob Webster

You get the most precise color estimates if you take all visible light filters from the left camera (the geology filters) L2 to L7.
If you want good color fidelity then you take the data from those six filters. The spectral properties of those filters are known but there's one major problem. The bandwidths of the filters are small, so there are "holes" in the recorded spectrum. But it's not a hopeless task to reconstruct the spectrum from this sparse data set. Because natural spectra, be it from light sources like the sun or from natural materials, are mostly smooth you can interpolate the original spectra from the few data points you have. This is done by bicubic spline interpolation. The spectral data of the sun (the light source) are known from direct measurements. The Spectrum of the sunlight is also measured by the rovers, which makes it possible to draw conclusions on the amount of dust and ice particles in the atmosphere, which filter the sunlight.

Now you can directly operate with spectral data, which is the most reliable way to calculate the resulting colors. The reliability is smaller if smaller filter sets are used.

The next step is to use a sophisticated color appearance operator on the calculated image colors. The operator used in the case of the Pancam photos is known as CIECAM02 [CIE=Commision international d'Eclairage aka International Color Comittee, CAM=Color Appearance Model, 02=year of publication].
This operator takes several effects into account that influence the appearance of colors in an image. For example the image viewing conditions (dark, dim or bright), the luminance of the original scene, the apparent change of color brightness with stronger saturation (Hunt effect), white point adaptation to the new viewing conditions (monitor whitepoint) and a lot more things that take place in the human visual system.

Using only three spectral channels and allocating these to the three color primaries of the sRGB color space that's commonly used in monitors is only an approximation that's more or less deemed to fail. That doesn't mean that the resulting pictures have to be vwery far from the real appearance. It's just an easier and faster way to get results that are still satisfying.

All this is explained in detail in the documents written by Jim Bell and several other places, especially the Pancam web page of Cornell University.

hi i need to find out characterisics of mars for a science project.

reply to post by SkepticOverlord

... they were sloppy in not creating a "mask" ...

Or was there some other 'motivation?' - as some of the 'lunar landing hoax' advocates suggest that the 'real reason' so many 'strange artifacts' are apparent in the lunar landing images is that 'whistleblowers' intended these 'clues' would tip-off an alert outsider to the fact that there was 'something rotten in Denmark' ...

Just a thought.

This link:

areo.info...

Has mars rover images since the beginning (where possible) with corrected color. At least that is, according to them.

Found it in the links section on vorchester.com...

Originally posted by StellarX
Well since this is the right thread here it is.

xfacts.com...

And this one is from the enterprise mission ( i forget where).

img496.imageshack.us...

The reason for wanting to change the colour is imo to make colonization seem expensive and thus easy to move off the table while Nasa goes on with it's primary military orientated mission.

Stellar

Don't forget that the color you define as "true" (yellow cables) is partly the result of artificial lighting (fluorescent lamps), that has a strong yellowish tint depending on the white point you use for taking the photo. Secondly, the atmospheric and dust scattering and indirect lighting change the illumination towards a brownish/orange color. And last but not least a lot of dust settles on the surfaces after a certain time. This can easily be observed as here and then Martian storms blow the surfaces free again.



[edit on 15-1-2006 by StellarX]

[edit on 15-1-2006 by StellarX]