1. From the Toolbox, select Spectral > Spectral Unmixing > Spectral Hourglass Wizard. The ENVI Spectral Hourglass Wizard displays the Introduction panel.
  2. Typically, data that have been converted to reflectance via atmospheric correction are used as input, particularly if library spectra or other external spectra are used as endmembers in the mapping process. You must assign wavelength values in the ENVI header of the input file. If you are not using any external spectra in the processing, then you can use radiance or even uncalibrated data as input. However, unless you use reflectance data, you cannot use the Spectral Analyst (later in the Wizard) to identify the image-derived endmembers by reference to a spectral library.

  3. Click Next. The Select Input/Output Files panel appears.
  4. Click Select Input File, choose a file, and perform optional spatial and spectral subsetting, and/or masking.
  5. As a guideline to help with spectral subsetting, vegetation analysis and iron-oxide mineral mapping typically use wavelength ranges in the visible near-infrared (VNIR) and shortwave infrared (SWIR) regions from 0.4 to 1.3 μm, while the 2.0 to 2.5 μm range is used to map most other geologic materials.

    A mask may help you to exclude selected pixels such as image borders, bad pixels, or specific materials such as water or clouds.

    Be careful with your choices of spatial and spectral subsets; avoid unnecessary complications, data volumes, and scene complexity.

  6. Click OK.
  7. In the Select Input/Output Files panel, the Output Root Name defaults to the root name of the selected input file. For example, if the input file is boulder.img, then the output file for each process is boulder appended with a function-dependent suffix (for example, boulder.mnf). Click Select Output Root Name and enter or choose a different root name if desired.
  8. Click Next. The Forward MNF Transform panel appears.