Vegetation Analysis Workflow

Use the Vegetation Analysis Workflow to create spatial maps of the following:

See the following for help on a particular step of the workflow:

Workflow Tips

This workflow is not “modal,” meaning it will not block you from using other ENVI tools or working with additional data. This is useful in that the workflow will not prevent you from doing multiple things at a time. However, be aware that if you close all of your files in the middle of the workflow process, you might not be able to continue the workflow and will need to start over.

Navigating Workflow Steps

The number of steps provided in the workflow will depend on the input image data. For example, not all images will contain the data needed for every step; therefore, some steps will be skipped automatically.

Some steps can be optional; in those cases, the Perform this step radio button is selected by default. To skip that step and go to the next step in the workflow, select the Skip this step radio button, then click Next.

The timeline at the bottom of the workflow will display the order of steps available for the workflow and your data, and the title of your current location in the workflow will flash. The title is also an active link that you can click, to jump backward or forward to a desired step in the workflow.

Preview/Display Result

Some workflow steps provide options to preview the settings and/or to display the processed result.

Open Workflow in Modeler

On the last step of the workflow, the Open Workflow in Modeler link will take your full workflow - the exact data, choices, and parameter values that you selected - and create a Model that can be manipulated in the ENVI Modeler. For example, you could create a Model to perform batch processing with multiple similar input datasets.

Select Data

  1. From the Toolbox, select Workflows > Vegetation Analysis Workflow. The Select Data panel appears.
  2. Select an input file and perform optional spatial and spectral subsetting and/or masking, then click OK.
  3. Click Next.

Mask

The Index for Mask from Spectral Index panel appears.

  1. Select the vegetation index to apply from the Index drop-down list.

  2. Click Next.

Threshold

The Threshold panel appears with a suggested threshold value applied to the image. The value shows the data range of the vegetation analysis calculation result.

  1. To change the threshold value, drag the bar, or type the desired value in the text box. Regions in the image that are black will be masked as areas of no interest.
  2. Click Next.

Classify

The Vegetation Analysis Product panel appears. The parameters that are shown in the panel will depend on the classification method you select.

  1. Select one of the following from the Method drop-down list:

    • Vegetation Delineation: (default) Identifies the presence of vegetation and visualizes its level of vigor.
    • Agricultural Stress Classification: Creates a spatial map showing the distribution of crop stress.
    • Fire Fuel Classification: Creates a spatial map showing the distribution of fire fuels and burn hazards for a region.
    • Forest Health Classification: Creates a spatial map showing the overall health and vigor of a forested region.

  2. You can change the Index to apply use by selecting a different one from the drop-down list.

  3. Set the parameters for the method you choose, as described in the next sections.

  4. Click Next.

Agricultural Stress Classification

When doing Agricultural Stress Classification, it is best to create a mask when you select the input data, 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.

The following settings are available when you select the Agricultural Stress Classification method:

  1. Select a broadband or narrowband Greenness Index from the drop-down list.
  2. 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.
  3. Select a vegetation index from the Canopy Water or Nitrogen Index drop-down list.
  4. Select a vegetation index from the Light Use Efficiency or Leaf Pigment Index drop-down list.

Fire Fuel Classification

The following settings are available when you select the Fire Fuel Classification method:

If fire fuels are located beneath a closed canopy, they may not be detected by Fire Fuel Classification. The higher greenness values caused by canopy closure automatically reduce the fire risk calculation. Additionally, dry or senescent vegetation indices are only sensitive to the top layer of the vegetation, causing the dry vegetation beneath it to be obscured by the upper layer of green vegetation. As such, dry materials under a closed canopy may not be properly detected.

  1. Select a broadband or narrowband Greenness Index from the drop-down list.
  2. Enter a Minimum Valid Greenness Value to use in the fire fuel 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.
  3. Select a vegetation index from the Canopy Water drop-down list.
  4. Select a vegetation index from the Dry or Senescent Carbon Index drop-down list.

Forest Health Classification

The following settings are available when you select the Forest Health Classification method:

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.

  1. 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.

  2. 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.
  3. Select a vegetation index from the Leaf Pigment Index drop-down list.
  4. Select a vegetation index from the Canopy Water or Light Use Efficiency Index drop-down list.

Vegetation Delineation Classification

The following settings are available when you select the Vegetation Delineation method:

  1. The default settings for Class Colors are [[160,82,45],[255,255,0],[0,238,0],[0,139,0]], one RGB color for each of the Class Names specified. Use the and buttons to add or remove class color definitions.
  2. The default settings for Class Ranges are [[-1,0.25],[0.25,0.5],[0.5,0.7],[0.7,1]], one for each of the Class Names specified. The numbers displayed for each range indicate the bottom NDVI threshold. For example, the default for the "No Veg" Class Range are pixels with an NDVI value falling between -1 and 0.25. The default NDVI ranges are general rules of thumb that apply in many, but not all cases. The Normalized Difference Vegetation Index (NDVI) generates an image that ranges from -1.0 to 1.0. Pixels with no vegetation tend towards -1.0, while pixels with vigorous vegetation tend towards 1.0. You can edit the values as desired directly in the field.

  3. The default Class Names are as follows. You can edit the names as desired directly in the field:

    • No Veg

    • Sparse Veg

    • Moderate Veg

    • Dense Veg

Export

The Export Final Result panel displays.

  1. Enter a filename and location for the Output Raster.
  2. Click Finish.

See Also

Vegetation Indices Background