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Vegetation Index Calculator

Vegetation Index Calculator

Use the Vegetation Index Calculator to compute vegetation indices (VIs) that are applicable to your imagery. When you select an input file, ENVI determines which VIs it can calculate from the input dataset and you choose the specific VIs for ENVI to calculate.

Also refer to the Spectral Indices tool, which provides the same vegetation indices plus many more.

ENVI provides VIs you can use to detect the presence and relative abundance of various vegetation properties. All, some, or none of the VIs may be available for a given file. Each VI depends upon sensor response in two or more spectral bands, which are combined to create a single index value that corresponds to the density, intensity, or volume of a biophysical parameter significant to vegetation.

Applying VIs to vegetative materials to analyze their conditions does not produce absolute results. The results derived from the VIs are relative when determining where distribution or stress is, providing a theoretical level ranging from a low to high value.

Shadowed or highly shaded areas in an input file may not have enough light to cause the vegetation signal to register for the VIs. Atmospheric correction does not improve the quality of these areas. Under these conditions, the VIs may provide inaccurate representations of the vegetation conditions.

To generate ecosystem-specific classifications from your data, see Vegetation Analysis Tools.

To calculate VIs:

  1. From the Toolbox, select Spectral > Vegetation > Vegetation Index Calculator. The Vegetation Indices Input File dialog appears.
  2. Select an input file and perform optional spatial and spectral subsetting, and/or masking, then click OK.
  3. Click OK. The Vegetation Indices Parameters dialog appears.

    If the ENVI header for the input file contains a bad bands list, the bad bands are excluded from the VI calculation.

  4. Select one or more VIs to calculate for the input file from the Select Vegetation Indices list. This list shows the VIs that ENVI verified as applicable to the input file. All applicable VIs are selected by default. You must select at least one VI to continue. The number of selected VIs appears in the Number of items selected field.
  5. Use the Biophysical Cross Checking toggle button to specify whether or not to perform biophysical cross-checking for this calculation. Biophysical cross-checking compares VIs to validate their results. If conflicting values exist between VIs (for example, a greenness index shows insufficient vegetation to support the water content measurement from a canopy water index), those data values are ignored. When biophysical cross-checking is turned off, masking is not applied, and ENVI stores all output data in the result. The default value is On.

    Note: Do not set Biophysical Cross Checking to On if you plan to use the VI calculations in the vegetation analysis tools.

  6. Select output to File or Memory.
  7. Click OK. ENVI adds the resulting output, a band for each calculated VI, to the Layer Manager. From the Available Bands List, you can open each VI for analysis.

Related Topics

Spectral Indices, Vegetation Indices, Vegetation Analysis Tools, Vegetation and Its Reflectance Properties

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