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Ray Arvidson

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  1. Hi Ralph: The min and max stretch values for parameter maps are scene dependent. Just make sure that you do not set the minimum to less than zero because then the negative values would correspond to bumps and not absorption dips. I typically set values for min and max based on comparing the stretched parameter maps to what can be seen in the false color CRISM images and whatever CTX and HiRISE data one can find. Mapping contiguous pixels in the parameter maps that overlay areas that look like geomorphic or geologic units gives me some certainty that I am mapping some mineral parameter that makes sense. Random detections across the scene just mean that you are mapping noise. Remember for your crater you should be looking for rim and crater ejecta deposits that are windows beneath the regolith, sand, and dust covers. Small areas but pixels should map close to one another. Ray Arvidson
  2. Hi Ralph: I hope our Zoom session and discussion of how to process and interpret CRISM data was useful. Unfortunately, I forgot to check the button saying record this session. Anyway, if you have any other questions let me know by email or via the Forum. Best of luck with your master's degree research. Remember to think about where in the crater you might expect some underlying bedrock to be exposed. Ray
  3. HI: Talor: I am a CRISM Science Team Member and also the manager our our PDS Geosciences Node. I will look later today at your note and respond. In the meantime I would highly recommend starting to use the ENVI 5.5.3 interface and not the Classic mode. Many more functions and CAT7.4 works well with it. Ray Arvidson
  4. Hi Ralph: Looks like you got pretty far along. Are you using CAT7.4 installed on ENVI 5.5.3? Also, typically, S data for CRISM do not contain as much mineral information as L data. I would use CAT 7.4 and the atmospheric correction in CAT to remove L data gas bands, then generate 2014 IR parameter maps and examine those for the presence of minerals like olivine, pyroxene, sulfates, and clays. Let me know if you downloaded and installed CAT7.4 from our web site. Ray
  5. Hi Ralph: I would be glad to help you through CRISM processing, both as a CRISM Team Member and PDS Geosciences Node Manager. First what version of ENVI/IDL are you using? I suggest not using Classic but rather the new 5 series interface. I use version 5.5.3. Once we are set with ENVI then I can tutor you through the steps using a Zoom session, which I will record so you can play it back as needed. Waiting to hear from you. Ray Arvidson
  6. You need to find an area in the corrected spectral data cube that looks spectrally neutral and divide your spectrum of interest by the spectrum that looks spectrally neutral. No DDR involved. Ray
  7. Hi There: I am the manager of the PDS Geosciences Node and also a CRISM Science Team Member. The I/F data you are using come from the spectral radiance for each band and pixel location divided by the solar spectral irradiance divided by pi. The is a ratio of spectral radiances and the pi converts solar spectral irradiance to spectral radiance. The solar value used is specific for the heliocentric distance when the scene was acquired, i.e., Mars distance relative to he sun. Your I/F spectra, put through the volcano scan correction using CAT, look good. Here is what you are missing. The next step typically is to then divide the volcano scan corrected I/F spectra by a spectrum from the same corrected data for an area that looks like it is spectrally neutral. This removes any instrument artifacts and tends to de-emphasize the ubiquitous basaltic sands and regolith and thus emphasizes what might be unique in terms of mineral signatures for the area of interest. It kind is like in the lab when you use reflectance spectrometers you ratio your data relative to some standard surface. Remember there are no pure outcrops of given minerals on Mars, rather wind mixes things a lot. I hope this note helps. Please ask more questions if needed. Ray Arvidson
  8. Rachel: I am a CRISM Team Member and we have processed MSP data. The destriping is really for full resolution data, not so much for multispectral data. One of my graduate students, Thomas Condus, has been processing a lot of CRISM multispectral data. He can provide details as to how he has processed the data. His email is tcondus@wustl.edu. I will mention to him that you might be contacting him via email to ask for advice. It is currently about 7:30 AM CST and he typically comes in around 9 AM. He has helped several other students move through the sometimes complicated processing procedures and avoiding pitfalls in CRISM processing. Ray Arvidson
  9. Wladimir: I suggest you use ENVI 5.5.2 interface and upgrade to CAT 7.4. You can use the flatten function in CAT to suppress column dependent striping. And with ENVI 5.5.2 it is easy to co-register CRISM images with CTX or HiRISE images. Let me know if you have these versions of ENVI and CAT. The CAT 7.4 is available from our PDS web site. https://pds-geosciences.wustl.edu/missions/mro/crism.htm Ray Arvidson PDS Geosciences Node Manager CRISM Team Member
  10. Hi There: I am going to try and talk you though use of our PDS Geosciences Node Orbital Data Explorer to get to Lunar Reconnaissance Orbiter DIVINER thermal data and maps that you can make for particular times and locations for brightness temperature of portions of the Moon of interest to you. First go to our PDS Geosciences Node site: pds-geosciences.wustl.edu Then go to Orbital Data Explorers, one of the choices on the upper left. Next select Lunar Orbital Data Explorer. Then select under additional tools Diviner RDR Query. This will take you to a template to fill out that will search the DIVINER data for brightness temperatures for your time and location (e.g., UTC or local solar time, latitude range, longitude range) and ask you which channels to show. I selected channel 6 to show radiance for this band range. Try small boxes like maybe a 1/2 degree across to avoid long search times. Now hit the query button to tell you how many observations are within your search area. Then go to Request Results and include tabular data and a Grayscale (local range). Next generate the products and when finished you will have a tiff image of brightness temperatures in Kelvins and a large spread sheet with the values used to make the image. If this is all you need, fine. Need more and let me know so I can provide more help. Remember these are brightness temperatures and one needs emissivity to get the actual kinetic termperatures. But you should be pretty close. Ray Arvidson PDS Geosciences Node Manager
  11. Hi there: Would you please let me know which MTRDR scene you have been examining and I will take a look at the data and spectral plots and then answer your questions. Ray Arvidson PDS Geosciences Node Manager and CRISM Science Team Member
  12. Jue Wang and I have downloaded the LOLA and M3 data. We used ENVI 5.4 interface (not Classic) to map project the M3 data and then coregistered the mapped data to the LOLA map. Jue will be sending our instructions for you to do this, along with posting on our FTP site the final products. Ray Arvidson
  13. Please give me the M3 product ID that you would like to coregister to the LOLA data quoted above. That way I can try it myself with ENVI before I reply to you with instructions. Ray Arvidson PDS Geosciences Node Manager
  14. Yes, I tend to use continuum removed spectra rather than ratioed spectra because the former does not introduce any biases introduced by ratioing to non-gray spectra. You might first subset your data to the wavelength interval containing the candidate absorptions and shoulders in order to highlight just the absorption features of interest. Ray Arvidson
  15. M3 operates in different spatial modes depending on the orbit. Would you please supply the actual M3 data set ID that produced different spatial pixels for different wavelengths? That way we can replicated the issue using ENVI's map projection code. Ray Arvidson PDS Geoscience Node Manager
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