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Narrow band at 1.2 micron in CRISM dataset


Deepali
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Hello,

I am a PhD scholar exploring water associated morphology and mineralogy of the Martian surface. While analysing CRISM dataset for secondary minerals in my study area, I have observed a narrow band near 1.2 micron. This feature was observed in at least 3 datasets. 

I carried out literature survey for clarification regarding this feature. Some studies have attributed this an artifact while others propose it to be a result of (i) fe substitution in plagioclase feldspar (ii) fe-rich/coarse grained olivine (iii) weathering of impact glasses etc. (based on band centre and depth).

Can anyone give pointers regarding its classification. 

Thank you.

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These are spike artifacts in the data. Sometimes the instrument individual detectors are ill behaved and this is an example. Sometimes it is associated with going over sharp albedo boundaries where a detector has memories of what it was just sampling. There are no minerals that I know of that have such narrow single detector absorptions. Please ignore these spikes.

Ray

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Dear Ray,

The absorption at 1.2 are curved and do not appear as spikes. I apologise if I am wrong in assuming so, I am new to this field.

The second picture represents putative carbonate signatures. I studied that hydrous carbonates also have absorption bands at this wavelength.

You obviously know better than me but I am not sure therefore I want to confirm.

Thank you.

Deepali

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Dear Ray, 

I studied the 8778 spectra (Attachment 2) again and the locations from which both these spectra were recorded did not have any sharp boundaries. I also noted (please see 1.2-1.3 micron range) that despite being taken from different locations both the 8778 spectra have absorption at 1.2 micron. The feature has shoulders at 1.18 and 1.27 micron it appears as a curve rather than a spike.

In fact this is true for all spectra in fig. 2 although I didn't reexamine all of them. I'll do that again and probably look at radiance data.

Various explanations for decrease in band depth are also available through experimental studies. Therefore, I am in doubt that if artifacts display curved absorptions?

I'll be grateful if you could give your insight in this. 

Thank you. 

Deepali

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Dear Ray,

Please find the plot showing spectra in which I observed features around 1.2 micron. The wavelength region in question has been highlighted with a yellow box. The CRISM IDs are mentioned next to their respective spectrum. Full IDs were shared in one of the previous comments.

Thank you.

Deepali

Picture1_043831.jpg

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OK, now I see what you mean. These 1.2 micrometer features could be real absorptions. Smectite clays present such an absorption. Look at the ENVI spectral library that is part of CAT. Given that my job is to help you get to the spectra and interpret without interpreting artifacts, I will leave it to you to do the assignments.

Ray

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