Deepali Posted September 29, 2021 Share Posted September 29, 2021 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. Link to comment Share on other sites More sharing options...
Ray Arvidson Posted September 30, 2021 Share Posted September 30, 2021 Please attach a spectrum that shows this feature. I strongly suspect that it is an instrument artifact. Include the scene ID from which the spectrum was retrieved. Ray Arvidson PDS Geosciences Node Manager CRISM Science Team Member Link to comment Share on other sites More sharing options...
Deepali Posted September 30, 2021 Author Share Posted September 30, 2021 Thanks Ray. Here are two images of the spectra in which I observed the feature. The image IDs are FRT00008778, FRT0002BAD2, FRS0003C0E8, FRT00007A2D. Deepali Link to comment Share on other sites More sharing options...
Ray Arvidson Posted October 1, 2021 Share Posted October 1, 2021 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 Link to comment Share on other sites More sharing options...
Deepali Posted October 1, 2021 Author Share Posted October 1, 2021 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 Link to comment Share on other sites More sharing options...
Deepali Posted October 2, 2021 Author Share Posted October 2, 2021 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 Link to comment Share on other sites More sharing options...
Ray Arvidson Posted October 4, 2021 Share Posted October 4, 2021 You lost me. Please resend the plots with the features labeled at 1.2 micrometers that you think might be due to mineralogy. Ray Link to comment Share on other sites More sharing options...
Deepali Posted October 4, 2021 Author Share Posted October 4, 2021 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 Link to comment Share on other sites More sharing options...
Ray Arvidson Posted October 5, 2021 Share Posted October 5, 2021 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 Link to comment Share on other sites More sharing options...
Deepali Posted October 5, 2021 Author Share Posted October 5, 2021 Thanks Ray. I only had doubts of them being artifact and not real absorptions. I'll find out explanation for them like you suggested. Deepali Link to comment Share on other sites More sharing options...
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