EO-1 Hyperion Vegetation Indices Tutorial

Use the Forest Health Tool to create a spatial map showing the overall health and vigor of a forested region. Forest health mapping is useful for detecting pest and blight conditions in a forest, and it is useful in assessing areas of timber harvest. A forest exhibiting low stress conditions is usually made up of healthy vegetation, whereas a forest under high stress conditions shows signs of dry or dying plant material, very dense or sparse canopy, and inefficient light use. The Forest Health Tool uses the following VI categories:

To calculate forest health:

  1. From the Toolbox, select Spectral > Vegetation > Forest Health Vegetation Analysis. The Vegetation Products Calculation Input File dialog appears.
  2. Select the input file. The file may be a VI output file you created previously using the Vegetation Index Calculator or Spectral Index tool. Or you can select a hyperspectral data file that has been radiometrically calibrated and corrected for atmospheric effects.
  3. Select a spatial subset by clicking Spatial Subset. Using spatial subsetting with the Forest Health Tool may further refine the results.
  4. Apply an optional mask to the data by clicking Select Mask Band and selecting the desired mask image.
  5. Click OK. The Forest Health 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.

  6. Select a broadband or narrowband greenness VI from the Greenness Index drop-down list.

    Tip: Best results are achieved by using Narrowband Greenness VIs because these are more sensitive to the condition of forest canopies. Broadband Greenness VIs tend to be inaccurate for dense forest conditions because forests have an abundance of green vegetation that can overwhelm and saturate the calculation.

  7. Enter a Minimum valid greenness value to use in the forest health calculation. Any values in the image less than the value you specify are masked out in the classification result. This setting, along with a proper mask selection, is useful for areas that contain different terrain types. The default value is 0.
  8. Select a VI from the Leaf Pigment Index drop-down list.
  9. Select a VI from the Canopy Water or Light Use Efficiency Index drop-down list.
  10. Output the result to File or Memory.
  11. Click OK. ENVI adds the resulting output to the Layer Manager.

The Forest Health Tool divides the input scene into nine classes, from weakest, or least healthy forest, to healthiest forest. The following is the classification map for the Forest Health Tool output:

The classifications are relative to the particular input scene only and cannot be generalized to other areas or other scenes. Field examination is essential to link the classes provided by the tool with the real-world conditions they represent. You cannot compare classes between scenes, as the vegetative variability between scenes could be significant, and the actual classification values may not match. For example, a classification color of green in one scene could represent the same field conditions as a classification color of orange in another.

Related Topics

Spectral Indices, Vegetation Indices, Vegetation Analysis Tools, Agricultural Stress Tool, Fire Fuel Tool, Vegetation and Its Reflectance Properties