Jump to content
PDS Geosciences Node Community

Ray Arvidson

Members
  • Content Count

    19
  • Joined

  • Last visited

2 Followers

About Ray Arvidson

  • Rank
    Member

Recent Profile Visitors

The recent visitors block is disabled and is not being shown to other users.

  1. 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
  2. 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
  3. 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
  4. 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
  5. 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
  6. 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
  7. 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
  8. 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
  9. 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
  10. 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
  11. 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
  12. 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
  13. 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
  14. 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
  15. 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
×
×
  • Create New...