Use the Agricultural Stress Tool to create a spatial map showing the distribution of crop stress. This tool is intended specifically for use on agricultural land to support precision agriculture analysis. The conditions that cause agricultural stress are the same as those that cause forest stress; however, agricultural stress analysis concentrates more on growth efficiency. Dry or dying crops do not efficiently use nitrogen and light, indicating agricultural stress, whereas a crop showing healthy, productive vegetation indicates low stress. The Agricultural Stress Tool uses the following VI categories:

When using the Agricultural Stress Tool, it is best to create a mask to separate crop varieties, and process each crop type individually. Because different crop types have different phenological cycles, canopy closure characteristics, and vegetative properties, the signals within and between crop types may be confused. If masking the different crop types is not feasible, carefully analyze the results. Compare only the results from one crop type to other results from the same crop type. Results from different crop types are not comparable.

To calculate agricultural stress:

  1. From the Toolbox, select Spectral > Vegetation > Agricultural Stress 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 Agricultural Stress Tool may further refine the results.
  4. Apply optional masking to the data by clicking Select Mask Band and selecting the desired mask image.
  5. Click OK. The Agricultural Stress 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 index from the Greenness Index drop-down list.
  7. Enter a Minimum valid greenness value to use in the agricultural stress 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 Canopy Water or Nitrogen Index drop-down list.
  9. Select a VI from the Light Use Efficiency or Leaf Pigment 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 Agricultural Stress Tool divides the input scene into nine classes, from lowest stress to highest stress. Following is the classification map for the Agricultural Stress 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. The classes cannot be compared 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 with a classification color of orange in another.

Related Topics

Spectral Indices, Vegetation Indices, Vegetation Analysis Tools, Fire Fuel Tool, Forest Health Tool, Vegetation and Its Reflectance Properties, EO-1 Hyperion Vegetation Indices Tutorial