Cover of Bare Ground

Method 1: Unsupervised Classification

Workflow Reference: Everitt, J. H., C. Yang, R. S. Fletcher, and D. L. Drawe. 2006. Evaluation of High-Resolution Satellite Imagery for Assessing Rangeland Resources in South Texas. Rangeland Ecology and Management 59:30-37

Study Area: Welder Wildlife Refuge, southern Texas

Ecological Site:

Imagery Used: Quickbird 2.8 meter resolution; green, red, and nir bands

Step 1

Field reflectance measurements using a spectrometer were taken on 6 vegetation types and a bare ground type at green, red and nir wavelengths

Step 2

The imagery was acquired and radiometrically corrected from digital numbers to reflectance values. Imagery was also georeferenced.

Step 3

Unsupervised Classification using the ISODATA method was used to create distinct land cover classes, including bare ground, in 4 test sites. Identifying the classes was aided by the field spectral measurements taken.

Step 4

To assess the accuracy of the imagery, 100 ground truth points were assigned in a stratified random pattern and visited.

Step 5 (not in the reference)

To obtain bare ground cover proportion, divide the number of bare ground pixels by the number of total pixels in your area of interest. This method works best if the imagery you are using has high spatial resolution and the area of interest in fairly small. Larger pixel sizes increase the chance they will contain more than one cover type, thus reducing accuracy.

Soil Adjusted Total Vegetation Index (SATVI)

Workflow Reference: Marsett, R.C., Qi, J., Heilman, P., Biedenbender, S.H., Watson, M.C., Amer, S., Weltz, M., Goodrich, D., Marsett, R. 2006. Remote sensing for grassland management in the arid southwest. Rangeland Ecology and Management 59:530-540.

Study Area: Grassland sites in Arizona, New Mexico, and Chihuahua Mexico

Ecological Site:

Imagery Used: Landsat TM 30 meter resolution

Step 1

Imagery was acquired and converted to reflectance values

Step 2

The SATVI was used to differentiate vegetation (green or senesced) from bare ground.

Step 3

Using the SATVI image, the estimated vegetation canopy cover percentage in each pixel can be calculated using the Total Vegetation Fractional Cover (TVFC).

Step 4 (Not in the Reference)

If you subtract the canopy cover percentage, as calculated in Step 3, from 100, you are left with total non-vegetation cover. Depending on the site, non-vegetation cover could be interpreted to be bare ground.

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