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Ray Arvidson

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Ray Arvidson last won the day on August 4 2018

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  1. Ray Arvidson

    CRISM DATA PROCESSING: CRISM Ratioed I/F Corrected Spectra

    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
  2. Ray Arvidson

    Assigning Map Information to PDS Images in ENVI

    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
  3. Ray Arvidson

    CRISM TRR3 Map projection Algorithm

    Greetings: I am the Director of the PDS Geosciences Node and also a CRISM Team Member. I believe that the top image you show is one called sensor space, i.e., how the instrument acquires data row after row. The bottom one is map projected. The DDR file has planes that include the latitude and longitude in sensor space, corresponding to the pixel locations of the actual data. Are you trying to project the data to map form? If so would you be trying to do this in Matlab? ENVI can be used with the CRISM Analysis Tool (CAT) to do this for you. But if you need to use Matlab let me know in more detail what you are trying to do and we can help you get there. Ray Arvidson
  4. Ray Arvidson

    CRISM DATA PROCESSING: CRISM Ratioed I/F Corrected Spectra

    Oh and to remove artifacts in the spectra many scientists ratio the data to a "bland" spectrum from the same column in the data. You just need to make sure that the spectrum you ratio to does not have spectral features that would make some artifacts in the ratioed data. I personally do not do the ratios for this very reason. Ray Arvidson
  5. Ray Arvidson

    CRISM DATA PROCESSING: CRISM Ratioed I/F Corrected Spectra

    Hi There. You are doing the processing correctly. The reason that the map projected plot looks different relative to the before projected plot is that the map projected plot has its scale enlarged. It does look like these plots have been made using Classic ENVI and CAT rather than the ENVI5.3 interface and CAT. I so I recommend you switch to the ENVI5.3 interface, much more powerful than the Classic interface. Ray Arvidson CRISM Science Team Member and PDS Geosciences Node Manager
  6. Ray Arvidson

    CRISM Analysis in CAT 7.3.1

    Hi Emran: I am a CRISM Science Team Member and PDS Geosciences Node Manager. . With regard to processing CRISM data there is no need to convert from radiance to I/F files for the TRDRs because there are already I/F file versions of the TRDRs that have been cleaned up for noise. Use those I/F files. These have values of radiance detected by CRISM divided by the solar radiance at the heliocentric distance for the time of the observation. CAT at this time only has a volcano scan atmospheric correction. It is under ATP correction. I usually check photometric correction on and the program divides by the cosine of the incidence angle, this makes it a Lambert albedo. The display error message sometimes appears in ENVI classic and 5.4. Feng can talk you through it. Let me now what you are trying to get from the CRISM data and I can help walk you through what I would do to try and get there. Pretty complicated data sets and it is easy to get lost in them and become a bit frustrated. I look forward to hearing from you. Ray Arvidson
  7. Ray Arvidson

    Overlay M3 and RELAB spectra

    Attached are some slides showing how I used ENVI to ingest M3 lunar data and lab data, resample the lab data to the M3 wavelengths, and overplot the two data sets. Ray Arvidson PDS Geosciences Node Manager spectral_resampling.pdf
  8. Ray Arvidson

    Overlay M3 and RELAB spectra

    Here to help. I am not sure why you have a screen shot of a vertical profile, which suggests to me you opened the spectral library as an image. To examine the spectral library data you need to open the file as a spectral library, not as an image. Did you open it as a spectral library, and could you display spectra? If you did this and can display spectra, resampled to M3 bandpasses, you should be able to overlay spectra from an M3 cube pixel with the lab spectra. Let me know what you did and I can help more if the instructions above are not enough. Worst case is for me to try what you wanted to do with the exact data sets you used. Ray Arvidson
  9. Ray Arvidson

    Overlay M3 and RELAB spectra

    Greetings: You can use both the new ENVI5 series interfaces or the Classic ENVI interface to a resample spectral data set to a new set of center wavelengths and, optionally, band passes. You will find the spectral resampling procedure under the toolbox on the right hand side of the ENVI5 series interface, and under the spectral heading on the pull down Classic menu. Next select an input data file (it needs to have wavelengths in the header record) that you designate as the new wavelengths for the spectrally resampled data. The dialog box then asks you for the output file that will be resampled. If there are band passes (like Gaussians) in the input data file header these will also be used in resampling the output data set. I just tried it with an OMEGA L data set as the input and one of the ENVI JHU spectral libraries as an example and it worked. It resampled the JHU data to the OMEGA wavelengths and made a new JHU spectral library. Also works with spectral cubes as input and output data sets, etc. Let me know if you still have some problems and we can talk on the phone. Ray Arvidson PDS Geosciences Ndoe Manager. 11/6/17