Canopy Cover

Summary

Canopy cover is the percentage of vertical projection of forest canopy to forest land area (Jennings et al., 1999). It is an important parameter in forest management, and it is also an essential factor for estimating forest volume.

Canopy Cover

Principle

LiDAR360 adopts two different algorithms for calculating canopy cover for point cloud with and without return number information respectively. If the point cloud has return number information, it will be first divided into different grids according to a user-defined xsize and ysize. In each pixel, canopy cover can be calculated as the ratio of LiDAR first vegetation returns (higher than the user-defined threshold) to the total number of LiDAR first returns.

where CC is canopy cover, nvegfirst is the number of vegetation first returns, and nfirst is the number of all first returns.

If point cloud does not have return number information, it will also be first divided into different grids according to a user-defined xsize and ysize. In each pixel, canopy cover can be calculated as the ratio of LiDAR vegetation returns to the total number of LiDAR returns. Similar to the calculation of gap fraction, any points higher than 2m will be treated as vegetation points in the calculation.

where CC is canopy cover, nveg is the number of vegetation return, and ntotal is the total number of returns.

According to (Ma et al., 2017), the canopy cover generated from these two methods have no significant difference. The resultant product is a raster file in TIFF format, the value ranges from 0 (no canopy cover/completely open) to 1 (completely covered by canopy).

Usage

To generate Canopy Cover, navigate to ALS Forest > Forest Metrics > Canopy Cover.

Canopy Cover

Settings

  • Input Data: Ensure that each input point cloud data is Normalize by DEM or Normalize by Ground Points. The input file can be a single file or multiple data files. Point cloud data should be opened in LiDAR360 before being processed.
  • XSize (meter)(default value is "15"): The length of a grid size should be greater than an individual tree crown width. For most forest types, the grid size should be greater than 15 meters.
  • YSize (meter)(default value is "15"): The width of a grid size should be greater than an individual tree crown width. For most forest types, the grid size should be greater than 15 meters.
  • HeightBreak (meter)(default value is "2"): Usually, it is desirable to ignore points below a particular elevation to avoid influence low vegetations (e.g., grass and shrub). The "HeightBreak" parameter can be set in many ALS forestry tools, allowing users to ignore points below a specified height (a value of 2 m is commonly used).
  • Output Path: Path of the output file. A corresponding raster file (*.tif format) will be generated for each input point cloud data.
  • DefaultValue: Restore the default parameters.

Note: Only when the point cloud data is loaded in the software can you use the Canopy Cover function; otherwise, the message "There is no point cloud data meeting the conditions of calculation!" will pop up. If the maximum Z value of the point cloud is greater than 200 m or the maximum Z minus the minimum Z is greater than 200 m, the data is not considered to have been normalized, and the prompt information shown in the figure below will pop up. Click “YES” to keep using this type of data in the operation; otherwise, click "NO" and reselect the input data file.

Canopy Cover
    @inproceedings{
        author={Jennings S B, Brown N D and Sheil D},
        title={Assessing forest canopies and understorey illumination: canopy closure, canopy cover and other measures},
        booktitle={Forestry,72(1): 59-73},
        year={1999}
    }
    @inproceedings{
        author={Ma Q, Su Y J and Guo Q H},
        title={Comparison of Canopy Cover Estimations From Airborne LiDAR, Aerial Imagery, and Satellite Imagery.},
        booktitle={IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing,10(9): 4225-4236},
        year={2017}
    }

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