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:
- From the Toolbox, select Spectral > Vegetation > Forest Health Vegetation Analysis. The Forest Health Classification dialog appears.
- Select an input raster, perform optional spatial and spectral subsetting and/or masking, then click OK.
- Select a broadband or narrowband Greenness Index from the drop-down list.
Tip: Best results are achieved by using Narrowband Greenness vegetation indices because these are more sensitive to the condition of forest canopies. Broadband Greenness vegetation indices tend to be inaccurate for dense forest conditions because forests have an abundance of green vegetation that can overwhelm and saturate the calculation.
- 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.
- Select a vegetation index from the Leaf Pigment Index drop-down list.
- Select a vegetation index from the Canopy Water or Light Use Efficiency Index drop-down list.
- Enter a filename and location for the Output Raster.
- Enable the Preview check box to see a preview of the settings before you click OK to process the data. The preview is calculated only on the area in the view and uses the resolution level at which you are viewing the image. See Preview for details on the results. To preview a different area in your image, pan and zoom to the area of interest and re-enable the Preview option.
- Enable the Display result check box to display the output image in the Image window when processing is complete.
To run the process in the background, click the down arrow and select Run Task in the Background. If an ENVI Server has been set up on the network, the Run Task on remote ENVI Server name is also available. The ENVI Server Job Console will show the progress of the job and will provide a link to display the result when processing is complete. See ENVI Servers for more information.
- Click OK.
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.
Spectral Indices, Vegetation Indices, Vegetation Analysis Tools, Agricultural Stress Tool, Fire Fuel Tool, Vegetation and Its Reflectance Properties