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Material Identification

Material Identification

Use the Material Identification tool to attempt to identify unknown spectral signatures by comparing them to spectral libraries. Follow these steps to continue:

  1. Choose one of the following options to run Material Identification:
    • Click Identify Material in the Review Detections panel.
    • Select THOR > THOR Material Identification from the Toolbox.
  2. The Material Identification panel appears.

    By default, the Material Identification tool will compare an unknown signature to every signature within THOR's embedded spectral libraries, located in the speclib directory of ENVI’s installation path. You can also add your own libraries (either MRSL or SLI) to this directory to make them available for immediate use. To add your own libraries to this list, click Add Library and select an MRSL or SLI spectral library file.

  3. Select one or more spectral libraries (under Select Libraries to Search) from which you want to search for an unknown signature.
  4. To designate an unknown signature for identification, click Select New Signature. A Material Identification dialog appears, with a list of all signatures currently open in plot windows.
  5. Select a signature name, then click OK. The Material Identification tool will then attempt to automatically determine the proper scale factor needed to scale the unknown signature into the same scale as the reflectance libraries. It will use the Spectral Angle Mapper (SAM) algorithm to compare the unknown signature to every signature in the designated spectral libraries.
  6. You can adjust the scale factor by entering a new value in the Input signature scale field and pressing the Enter key. The matching results are displayed in the bottom portion of the Material Identification panel, sorted with the best matches on top (smaller spectral angles are better matches). The results are colored to provide a quick visual glance of the good and bad matches.

    The plot area displays the unknown signature in red, the currently selected library signature in the results table in green, and the band importance in blue. The band importance signifies how important each spectral band is relative to the others for differentiating the unknown and library signatures. The larger the band importance, the more effect that band has on enlarging the spectral angle between the unknown and library signature. You can turn off the band importance by unchecking the Plot band importance option.

  7. Click Export to ENVI Plot to export the plots to a standard ENVI plot window.
  8. At times, you may want the Material Identification tool to ignore certain noisy or otherwise bad bands when comparing signatures. To designate which bands should be ignored, select the Edit bad bands option. The plot area will be shaded green for "good" bands and red for "bad" (ignored) bands. Click the red Bad Bands button, then click and drag in the plot area to designate those bands as "bad." Click the green Good Bands button, then click and drag in the plot area to designate those bands as "good."
  9. After specifying bad bands, uncheck the Edit bad Bands option to compare signatures using the new set of good bands. Bad bands are blanked out in the plot area.
  10. The following example plots show an original band selection (left), new bad band selection (middle), and final results with the bad bands blanked out (right).

    The following figure shows an example of updated results for the same signature after specifying bad bands.

  11. To view metadata for the selected signature in the results table, click View Metadata. The Spectrum Metadata dialog appears:
  12. You can export the results table to an ASCII text file by clicking Export Table.

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