Use the Target Signature Selection panel to define the targets to search within the hyperspectral image. Target signatures can be derived from spectral libraries and/or image-derived regions of interest (ROIs).

See the following sections:

Selecting Targets from Spectral Libraries

  1. Select the Spectral Library tab. The Library Signatures list is blank unless other spectral libraries from previous tasks have already been loaded into THOR.
  2. To load a spectral library, click the Select Library drop-down button and select one of the following options:
    • Select MRSL Library: Select a Metadata Rich Spectral Library (MRSL) file (.msl). The MRSL format is specific to THOR and accommodates variable-range and variable-resolution spectra with metadata for each signature.
    • Select SLI Library: Select any spectral library file.
  3. The drop-down list may also show all libraries that are included in the speclib directory in the ENVI installation path. You can copy your own libraries to this directory so they are included in this list by default.

    Select a spectral library file, and click Open. The Library Signatures list in the Target Signature Selection panel shows the spectral libraries you selected.

  4. Double-click a spectral library name (in the Library Signatures list) to display its spectrum in a plot window. You can also right-click on one or more signatures and select Plot selected signatures to plot their spectra. If a signature contains metadata (only available in MRSL libraries), you can right-click on the signature and select Display metadata. (Or, click Show Info and select Plot spectrum or Display metadata.)

Query Library

  1. If you load an MRSL library file that contains metadata, use the Query Library section of the Target Signature Selection panel to narrow down the list of signatures that meet your query criteria.
  2. Signatures are typically categorized by Group, Class, and Sub-Class; and each has a Country of Origin. Select the desired metadata values from the lists, and click Run Query. Signatures that contain metadata matching the query will appear in the Library Signatures list. You can also search for keywords using the Keyword Search field. THOR will search every metadata field for the word or phrase you enter. THOR must find all of the query fields within a signature's metadata for it to appear in the Library Signatures list.

  3. To designate signatures as targets to search for in the hyperspectral image, select the desired signatures and click the arrow button to move them to the Target Signatures list. To remove an item from the Target Signatures list, select the signature name and click Remove Signatures. Or, right-click the signature(s) and select Remove selected target or Remove all targets.
  4. If your target signatures have different wavelength units, THOR will convert them to the same units as the input image before performing spectral matching later in the workflow.

Selecting Targets from Image-Derived ROIs

  1. Select the Image tab. The input image or atmospherically corrected image is loaded into a display group, and the ROI Tool appears. The Available ROIs list in the Target Signature Selection panel and the list of ROIs in the ROI Tool are synchronized so that when one list changes, the other updates too.
  2. Use the ROI Tool to define ROIs for each desired target, and draw the ROIs. Name the ROIs so that you will recognize them later in the workflow. As you create ROIs, they will appear in the Available ROIs list in the Target Signature Selection panel.
  3. Click Plot Signature(s) to plot the mean signatures for the selected ROIs. Click ROI Options to create new ROIs, delete ROIs, or save the ROIs to a file. You can also perform these functions through the ROI Tool. If you accidentally close the image or the ROI Tool, click Reload Image and ROIs.
  4. To designate ROIs as targets, select the desired ROIs in the Available ROIs list, then click the arrow button to move them to the Target ROIs list. You can remove ROIs from the Target ROIs list by clicking Remove ROIs or by right-clicking the desired ROIs and selecting the appropriate option. This will remove them from the Target ROIs list, but it will not delete them.
  5. The following figure shows an example of selecting target signatures from image-derived ROIs. ROIs in the ROI Tool appear in the Available ROIs list and may be designated as Target ROIs.

Confirming Your Selections

When you click Next, THOR will display the selected target signatures (from spectral libraries and ROIs) and will prompt you to confirm before proceeding.