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.
You can also write a script to do agricultural stress analysis using the AgriculturalStressClassification task.
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 vegetation index 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:
- From the Toolbox, select Spectral > Vegetation > Agricultural Stress Vegetation Analysis. The Agricultural Stress 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.
- 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.
- Select a vegetation index from the Canopy Water or Nitrogen Index drop-down list.
- Select a vegetation index from the Light Use Efficiency or Leaf Pigment 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 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.
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