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NAME

r.valley.bottom - Calculation of Multi-resolution Valley Bottom Flatness (MrVBF) index

KEYWORDS

raster, terrain

SYNOPSIS

r.valley.bottom
r.valley.bottom --help
r.valley.bottom [-s] elevation=name mrvbf=name [mrrtf=name] [t_slope=string] [t_pctl_v=string] [t_pctl_r=string] [t_vf=string] [t_rf=string] [p_slope=string] [p_pctl=string] [min_cells=string] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

-s
Use square moving window instead of circular moving window
--overwrite
Allow output files to overwrite existing files
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog

Parameters:

elevation=name [required]
Name of elevation raster map
mrvbf=name [required]
Name of output MRVBF raster map
mrrtf=name
Name of output MRRTF raster map
t_slope=string
Initial Threshold for Slope
Default: 16
t_pctl_v=string
Threshold (t) for transformation of Elevation Percentile (Lowness)
Default: 0.4
t_pctl_r=string
Threshold (t) for transformation of Elevation Percentile (Upness)
Default: 0.3
t_vf=string
Threshold (t) for transformation of Valley Bottom Flatness
Default: 0.3
t_rf=string
Threshold (t) for transformation of Ridge Top Flatness
Default: 0.35
p_slope=string
Shape Parameter (p) for Slope
Default: 4
p_pctl=string
Shape Parameter (p) for Elevation Percentile
Default: 3
min_cells=string
Minimum number of cells in generalized DEM
Default: 1

Table of contents

DESCRIPTION

r.valley.bottom calculates the Multi-resolution Valley Bottom Flatness (MRVBF) index (Gallant and Dowling, 2003). The MRVBF index assesses the flatness and lowness of terrain over multiple scales and DEM resolutions in order to identify valley bottoms, which represent areas that are flat across multiple scales, and remain low relative to the surrounding relief at coarser scales. The algorithm uses a sigmoid/logistic transform to rescale terrain slope angles and elevation percentile into a 0 to 1 range, and then combines these results across multiple levels of DEM smoothing and coarser grid resolutions. Although the resulting index represents a continuous value, values < 0.5 do not generally represent valley bottoms, values from 0.5 to 1.5 represent the steepest resolvable valley bottoms, and flatter/larger valley bottoms are represented by values > 1.5.

NOTES

The user must specify the input elevation raster map as a required input. The output is given by the mrvbf argument. Optionally, the complementary Multiresolution Index of Ridge Top Flatness can be calculated by specifying the mrrtf argument. In addition, there are several parameters than can be used to change the behaviour of the argument, although note that in this case the results and their interpretation will differ from what was envisaged in the original paper. However, in practice, this is often required especially for high-resolution DEMs. The arguments are:

The calculation of elevation percentile by default is performed using a circular window. With the -s flag a square moving window is used in calculations.

In practice, the user does not usually need to alter the threshold-related parameters other than t_slope. However, changing the shape parameters can be useful for to emphasize more local vs. more regional variations in relief. The degree of generalization can also be adjusted by the min_cells argument. The default value of 1 is equivalent to generalizing the input elevation raster to 100 percent of its original cell size. To reduce processing time, or focus the results on more local-relief, try increasing the number of min_cells.

EXAMPLE

Here we are going to use the GRASS GIS sample North Carolina data set as a basis to calculate the MRVBF index.

  # align region to DEM
  g.region -a raster=el_D782_6m
  
  # run r.valley.bottom
  r.valley.bottom elevation=el_D782_6m mrvbf=mrvbf_el_D782_6m t_slope=40 p_slope=3 p_pctl=2
  
  # set colors
  r.colors map=mrvbf_el_D782_6m color=bcyr -n
  
  # display over a shaded relief map
  r.relief input=el_D782_6m output=hs_D782_6m altitude=45 azimuth=315 zscale=4 scale=1
  r.shade shade=hs_D782_6m color=mrvbf_el_D782_6m output=mrvbf_shade
  d.rast map=mrvbf_shade
 
Multiresolution Index of Valley Bottom Flatness

SEE ALSO

r.mapcalc, r.slope.aspect

REFERENCES

J.C. Gallant & T.I. Dowling 2003. A multiresolution index of valley bottom flatness for mapping depositional areas. Water Resources Research, Vol. 39, No. 12, 1347. doi:10.1029/2002WR001426

AUTHOR

Helmut Kudrnovsky & Steven Pawley

Last changed: $Date: 2018-05-08 15:38:21 +0200 (Tue, 08 May 2018) $

SOURCE CODE

Available at: r.valley.bottom source code (history)


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