Martian sky is BLUE, tell NASA!

[silylene old]

Scattering increases as a function of alpha^2, where alpha is the molecular polarizability. Polarizability is the ease at which a molecule's (or atom's) electron density can be distorted. O2 has a greater polarizability than N2, hence it is a more effective Rayleigh scatterer. CO2 has a London dispersivity parameter (i.e. ability to polarize) about 1.5x that of N2. So my guess is that CO2 would be an effective Raleigh scatterer. But I couldn't find any reference to this. <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[extrasense]

Jon,<br /><br />the scatering considerations are so far inconclusive, and can not be used to impeach the facts that I have started with.<br /><br />As Earth sky can be red or yellow or white at some contitions, Mars sky can be blue or yellow or red or white at some conditions. <br /><br />This is what we eventually are going to find out.<br /><br />e <img src="/images/icons/smile.gif" /> s<br />

 

[nacnud]

So its not always blue then?<br />

 

[extrasense]

Sure it is not, the pictures for decades have shown different tints of the Martian sky. But nitwits can not have that, they want to be the high priests of Universe...<br /><br /><img src="/images/icons/smile.gif" /> <img src="/images/icons/smile.gif" /> <img src="/images/icons/smile.gif" /> <img src="/images/icons/smile.gif" /> <img src="/images/icons/smile.gif" /><br />es<br />

 

[nacnud]

So it can be dust coloured?

 

[extrasense]

Those who come up with calibrations, have no idea what they are talking about. I take raw data every time in stead of their convoluted crap.<br /><br />When the data show that the sky is cyan, it is cyan - no matter how many idiots have written paper saying it is red.<br />When the data show that the sky is brown, it is brown.<br /><br />This is all that there is to it.<br /><br />The dust probably plays a big role in forming the color, but nobody knows what that role actually is. The theories on that account not worth the paper they are written on.<br /><br />e <img src="/images/icons/smile.gif" /> s<br />

 

[yevaud]

<img src="/images/icons/rolleyes.gif" /><br /><br />As opposed to *your* "crap..." <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[telfrow]

<font color="yellow">nitwits... <br />idiots...</font><br /><br />And who would those people be, ES? Take it out of the thread title and you work it back in anyway. <img src="/images/icons/mad.gif" /><br /> <div class="Discussion_UserSignature"> <strong><font color="#3366ff">Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild.</font> - <font color="#3366ff"><em>Tennyson</em></font></strong> </div>

 

[yevaud]

you, Sir, are not a person...you are a Pathology. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[telfrow]

<font color="yellow">You, Sir, are not a person...you are a Pathology.</font><br /><br /><img src="/images/icons/wink.gif" /> <br /> <div class="Discussion_UserSignature"> <strong><font color="#3366ff">Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild.</font> - <font color="#3366ff"><em>Tennyson</em></font></strong> </div>

 

[lowendfreq]

Hey guys,<br />Extrasense, with regards to the raw data, would you care to eleborate or even show me/us how you come to that conclusion?<br />Just out of curiosities sake, wouldn't you think the boys and girls who get paid to sort through all that info would leave an opening for Joe Citizen to get a hold of raw data that shows that they have presented 'convoluted crap' to the masses? hmmmmmmmmm.

 

[JonClarke]

Well, certainly I hope that people will see the Martian sky in person, the varying intensities of ochre, the dark zenith, the blue sunsets and sunrises, the white clouds and hazes, the blue-white solar halo. No doubt they will be entranced by these naunces, much as we are by earthy skies.<br /><br />Until then we have to make do with lander images. They have shown us all of these phenomena already.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

ES "Those who come up with calibrations, have no idea what they are talking about. I take raw data every time in stead of their convoluted crap."<br /><br />Then engage the data.<br /><br />EX "When the data show that the sky is cyan, it is cyan - no matter how many idiots have written paper saying it is red. When the data show that the sky is brown, it is brown."<br /><br />The data from Viking 1, Viking 2, Pathfinder, Spirit, Opportunity all show that the sky is ochre. You want spectral curves? I can give you spectral curves - and the spectral peak is not cyan. You want data on the amount of dust in the atmosphere? I have given that - and it is enough to cause strong and heavy scattering - and slight scattered by dust isn't cyan. This is the data, and you are one one who does not engage it. Come up with a data that shows the Martian sky is cyan (and no tweaked images does not count) and I will consider it.<br /><br />ES "The dust probably plays a big role in forming the color, but nobody knows what that role actually is. The theories on that account not worth the paper they are written on."<br /><br />I am glad you recognise the importance of dust. However the physics of scattering by gas and aerosols is very well understood. Its amount has been measured at five sites on the ground on Mars over periods ranging from months to years. The HRSC on Mars Rxpress also maps atmospheric optical, these have been cross calibrated by simultaneous observations with the Mars Rovers. We we know a lot about Martian atmsopheric dust and its role.<br /><br />It is very easy for you to write stuff like "crap" and "not worth the paper they are written on". However unless you present contrary data and superior analysis your opinion is worth even less.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[extrasense]

OK, <br />these discussions made me think about the color prpcessing chain. Here is my opinion, for what it is worth.<br /><br />Consider, that here are three MER filters, L4, L5, L6 that are pretty good approximation of Red, Green, Blue.<br /><br />1. The picture is taken with each of them, and it produces, on the CCD, values, roughly proportional to the number of photons of the particular color.<br />2. The number is transmitted, and used to make a raw image.<br />3. The values of L4, L5,L6 are concatenated into pixel value.<br />4. This value is send to the color monitor; <b>up till now, the color information is precisely as it was on Mars.</b><br /><br />5. The pixel is displayed on the monitor, and the actual image depends on the monitor settings.<br />This might introduce color modifications, but all the information is still there, and under normal monitor setting the colors are still keeping their identity red, green,blue<br />6. The eye gets three subcolor signals to the brain, still with correct identity<br />7. The brain does its magic, and recognizes the presented color<br /><br />The same sequence happens for the calibration target and for the sky.<br /><br />What we observe, at least in some cases:<br />1. The brain correctly recognizes the calibration colors<br />2. The brain recognizes sky color as white, tinted with cyan.<br /><br />I submit to you, that anyone who suggests that he can <b>improve</b> on this process, so that results of sky color recognition would be different, is a charlatane.<br /><br />e <img src="/images/icons/wink.gif" /> s<br />

 

[petepan]

Extrasense, i may be a bit out of my depth here so bear with me.<br /><br /><font color="yellow"> 5. The pixel is displayed on the monitor, and the actual image depends on the monitor settings. <br />This might introduce color modifications, but all the information is still there, and under normal monitor setting the colors are still keeping their identity red, green,blue </font><br /><br />This may be an area of confusion. The 'true' colour values as you state can be different from monitor to monitor, but I think it can be represented via L*A*B readings? With the appropriate software you can then set the LAB data as the target and then colour match it.<br /><br />I noticed Jon mentioned spectral curves earlier, so i am assuming that LAB data can be gathered also.<br /><br />So to see the 'true' colour, how many monitors are actually callibrated to represent 'true' colour?<br />

 

[thechemist]

<font color="yellow">4. This value is send to the color monitor; up till now, the color information is precisely as it was on Mars.</font><br /><br />No, you got it wrong here. The three RGB filter greyscales have to be corrected for different exposure times, and illumination conditions. The RAW data you use are not corrected for these. Hence the color changes from Sol to Sol.<br /><br />Can you see colors even in a dark room ?<br /><br />Don't make me look for the links, they have been posted here repeatedly. <div class="Discussion_UserSignature"> <em>I feel better than James Brown.</em> </div>

 

[extrasense]

--- The three RGB filter greyscales have to be corrected for different exposure times, and illumination conditions ---<br /><br />Not much correction there, since the 3 images are taken in about the same time under the same conditions. But I welcome this step, if applicable.<br /><br />As to the intensity, yes, to recognize color you want to normalize its intensity, since the eye/brain have limited ability of that.<br /><br />ES<br />

 

[extrasense]

---- The 'true' colour values as you state can be different from monitor to monitor ---<br /><br />Normally they are not different much, so that brain can make up for that, if having known colors in the picture.<br /><br />Here is an experiment that is crying to be done:<br /><br />All anyone needs, is a digital color camera, 3 filters for Red, Green and Blue, and color painted "calibration target"<br /><br />You take 4 pictures of the sky, 4 pictures of calibration target/one without filter/<br /><br />Then you publish 6 color images, 3 for the sky and 3 for the target:<br />1. Without "correction" <br />2. With "correction"<br />3. Direct color picture<br /><br />So, we will see if the "correction" helps or harms, or does nothing to the representation of sky color.<br /><br />ES<br />

 

[thechemist]

<font color="yellow">Not much correction there, since the 3 images are taken in about the same time under the same conditions.</font><br /><br />No, the exposure times really make a BIG difference.<br /><br />Read this please : http://www.highmars.org/niac/education/mer/mer00e.html<br /><br />I mean, really read it, not just look at the images. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <em>I feel better than James Brown.</em> </div>

 

[petepan]

<font color="yellow"> Normally they are not different much, so that brain can make up for that, if having known colors in the picture </font><br /><br />No, i don't think it quite works that way. Yes i can agree that say, we see a picture with green grass, <br />you say green , <br />i say green, <br />but what green is it?<br /><br />spectral curves and/or LAB readings give the 'true' answer.<br /><br />Just because we both see green, but with different monitors, we could be worlds apart.

 

[extrasense]

Chemist,<br /><br />what they do, if am correct, is to imitate the different exposure time by changing intensity of filtered images, to make it the same on R,G,B., claiming that it is the result of what is happening when MER is taking a picture<br /><br />Do you have access to those exposure times? Or you are supposed to guess them by the intensity of calibration target?<br /><br />Anyway, it is a sick way of doing business, for the visual specter.<br /><br />ES<br />

 

[thechemist]

extrasense,<br /><br />what they do is leave the shutter open until all three rgb images have about the same intensity. Which is exactly what is done on Mars by the rovers.<br /><br />Visit this wonderful site by slinted for details of the procedure and reference work.<br /><br />http://www.lyle.org/~markoff/methods.html<br /> <div class="Discussion_UserSignature"> <em>I feel better than James Brown.</em> </div>

 

[extrasense]

Chemist,<br /><br />thanks for the great reference.<br />So, I have used the radiometrically corrected images,<br />and the sky still comes up blue.<br /><br />What do you suggest is next step?<br /><br />ES<br />

 

[voyagerwsh]

I do not intend to jump into this prolonged debate thread, just post what other science institute studies the true color of martian sky, for reference purpose. <br /><br />"...Further careful analysis of Viking Lander data revealed a Martian sky which is generally "butterscotch" (yellow/brownish) in color, except for the pink/red of sunset and sunrise. This was confirmed by Mars Pathfinder." <br /><br />"If the Martian atmosphere were to be completely cleansed of dust, the daytime sky would appear blue, just as our own sky, because of Rayleigh scattering by the molecules (primarily carbon dioxide molecules) which make up the atmosphere..."--<br /><br />http://calspace.ucsd.edu/marsnow/library/science/climate_history/sky_color1.html <br /><br />

 

[extrasense]

So, tell us why radiometrically corrected MER pictures of the Martian sky are blue?<br /><br />ES