Appendix 2. ArcGIS® systematic instructions: how to generate an arc-chord ratio (ACR) rugosity raster from an elevation raster

Note: Step numbers correspond to workflow illustrated in Fig. 1.

1)Download the DEM (Digital Elevation Model) Surface Tools (version 2.1) extension for ArcGIS® <

2)Open ArcGIS®ArcMap™ (instructions written for version 10.2).

3)Activate the necessary extensions. To do this navigate to: Customize/Extensions. Check the boxes beside 3D Analyst and Spatial Analyst.

4)Import the elevation (or bathymetric) raster using Add data.

5)To start the analysis and derive contoured arearaster, navigate to: DEM Surface Tools/Surface area and ratio.

6)In the “Surface Area Analysis Parameters” dialog box, check and insert the references for the following parameters:

  1. Select Elevation Raster: insert the name of the elevation raster.
  2. Check the box beside Calculate Surface Area Raster. Below, name and specify the location to store the surface area raster.
  3. Leave the other parameters blank or at the default settings.
  4. Click Okay. The new contoured arearaster will appear in the Table of Contents.

7)To derive a slope raster, navigate to: ArcToolbox/3D Analyst Tools/Raster Surface/Slope

8)In the “Slope” dialog box, insert the references for the following parameters:

  1. Input Raster: insert the name of the elevation raster.
  2. Output Raster: name and specify the location to store the resulting slope raster.
  3. Leave the other parameters blank or at the default settings.
  1. Click Okay. The new slope raster will appear in the Table of Contents.

9)To derive a planar area raster, navigate to: ArcToolbox/Spatial Analyst Tools/Map Algebra/Raster Calculator.

10)In the “Raster Calculator” dialog box, write the equation and insert the references into the space provided:

  1. Note: the input values for trigonometric functions are interpreted to be radians. To use degrees as inputs, convert to radians by multiplying the input values by pi/180 or approximately 0.01745.
  2. The raster cell area is required for this calculation (in square meters; information available in metadata).
  3. Use the following adapted cosine law equation to solve for theplanarareaof each cell:

planararea =

The text should be entered in the space provided as:

[insert cell area]/(Cos("[insert slope raster file name]" * 0.01745))

or for example: 25/(Cos("slope_raster" * 0.01745))

  1. Click Okay. The new planararearaster will appear in the Table of Contents.

11)To generate the arc-chord ratio (ACR) rugosity raster, navigate to the Raster Calculator again (see step 9).

12)In the “Raster Calculator” dialog box, write the rugosity equation and insert your references into the space provided:

  1. Use the rugosityequation to solve for the ACR rugosity value of each cell (Equation 1 in paper):

rugosity

The text should be entered in the space provided as:

" [insert contoured area raster] "/" [insertplanar area raster] "

  1. Click Okay. The new ACR rugosity raster will appear in the Table of Contents.

13)To view the ACR rugosity rastercheck the box beside the file name in the Table of Contents. The raster imagine will appear in the Data View window.

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