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Ausiàs R

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Posts posted by Ausiàs R

  1. Hi Ray,

    First of all I want to thank for your reply, it is really apreciated.

    You said that:

    On 3/3/2020 at 4:37 PM, Ray Arvidson said:

    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.

    I understand that the area that looks like it and is spectrally neutral means an area that exhibes a constant reflectivity or transmissivity over the electromagnetic spectrum. But, where can I find this kind of surface/area?

    Is the data that I need on the ddr files of the image? I saw that there are 14 bands on the ddr images. On this document (pages 76-77) it is explained what those bands represents. I'm not pretty sure which band I shoud use, or if any.

    Once again, thanks for your answer,


  2. Good afternoon.

    I'm an undergraduate student of geomatics and remote sensing, and I was trying to use the CRISM images to classify minerals and chemical compounds on the surface of Mars.

    I collected some information about all the products to use, also I followed the workflow proposed here and I installed CAT on ENVI. I was trying to use a an image of the Jezero Crater data product: frt00005c5e_07_if166j_mtr3, which is projected, atmosferically and geometrically corrected. The data is on I/F which as is explained here, on the FAQs means:

    Q: What does I/F stand for?

    A: CRISM is a reflectance spectrometer, and I/F is how reflectance is represented algebraically: I is the energy (actually radiance) observed by the CRISM instrument, and F is the energy (actually solar irradiance) incident at the top of the Martian atmosphere. I/F is a ratio of energies (radiance/irradiance), with some additional scaling so the ratio is unitless.

    Acording to my knowledge radiance/irradiance=reflectance (unitless), maybe I'm wrong.

    The case is that I tried to classify the minerals on the image of the Jezero Crater using this library from Viviano et al using the "CRISM RATIOED I/F CORRECTED" spectra but I get wrong or absurd results.

    I noticed that the spectra of my images is clearly different from the spectra that I find on the Viviano library ratioed i/f. My Spectra always follow this pattern, and never reaches a reflectance of 0.5.



    Nevertheless on the Viviano library I found spectra like this one of epidote:



    Why the spectra of my image is so different? Is my data really on reflectance? How can I get real reflectances?



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