Vegetation Suppression

Use Vegetation Suppression to remove the vegetation spectral signature from multispectral and hyperspectral imagery, using information from red and near-infrared bands. This method helps you better interpret geologic and urban features and works best with open-canopy vegetation in medium spatial resolution (30 m) imagery.

You can also write a script to perform vegetation suppression using the VegetationSuppression task.

The algorithm models the amount of vegetation per pixel using a vegetation transform. The model calculates the relationship of each input band with vegetation, then it decorrelates the vegetative component of the total signal on a pixel-by-pixel basis for each band. You can use the results of vegetation suppression for qualitative analysis, but not for subsequent spectral analysis.

Vegetation suppression is most commonly used in lithologic mapping and linear feature enhancement in areas with open canopies. For closed canopies in moderate-resolution data, vegetation suppression is primarily used for linear feature enhancement.

Reference: Crippen, R. E., and R. G. Blom. 2001. Unveiling the lithology of vegetated terrains in remotely sensed imagery. Photogrammetric Engineering & Remote Sensing, Vol. 67, No. 8, pp. 935-943.

1. From the Toolbox, select Spectral > Vegetation > Vegetation Suppression. The Vegetation Suppression dialog appears.
2. Select a multispectral Input Raster, and perform optional spatial or spectral subsetting. For spectral subsetting, you must select two or more bands.
• If the associated header contains wavelength information, ENVI automatically determines the proper red and infrared bands to use for vegetation suppression. ENVI uses the band closest to 0.66 μm as the red band, and it uses the band closest to 0.83 μm as the near-infrared band.
• If the image file has wavelength information but does not have a near-infrared or red band, or if it has only one band, ENVI issues an error message and ends vegetation suppression.
3. Optional: Specify the band number to use for the Red Band when the image does not contain wavelength information.
4. Optional: Specify the band number to use for the Near Infrared Band when the image does not contain wavelength information.
5. In the Output Raster field, select an output location and filename for the vegetation suppression raster.
6. 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.
7. Enable the Display result check box to display the output in the view when processing is complete. Otherwise, if the check box is disabled, the result can be loaded from the Data Manager.

8. To reuse these task settings in future ENVI sessions, save them to a file. Click the down arrow and select Save Parameter Values, then specify the location and filename to save to. Note that some parameter types, such as rasters, vectors, and ROIs, will not be saved with the file. To apply the saved task settings, click the down arrow and select Restore Parameter Values, then select the file where you previously stored your settings.

9. 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.

10. Click OK.