GRASS GIS manual: r.divergence

NAME

r.divergence - Computes divergence of a vector field defined by magnitude and direction

KEYWORDS

SYNOPSIS

r.divergence

r.divergence --help

r.divergence magnitude=name direction=name output=name [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

--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:

magnitude=name [required]: Name of input raster map representing magnitude
direction=name [required]: Name of input raster map representing direction; Direction is in degrees ccw from the east
output=name [required]: Name of output divergence raster

DESCRIPTION
EXAMPLES
SEE ALSO
AUTHOR

DESCRIPTION

Module r.divergence computes the divergence of a vector field given by magnitude and direction raster maps. Direction is in degrees counterclockwise from the east and can be computed using r.slope.aspect. This module can be used for estimating erosion and deposition rates for a steady state overland flow using USPED (Unit Stream Power based Erosion Deposition) model. Net erosion/deposition is estimated as a change in sediment flow rate expressed by a divergence in sediment flow.

EXAMPLES

In North Carolina sample dataset, we compute net erosion/deposition.

g.region raster=elev_lid792_1m -p
r.slope.aspect elevation=elev_lid792_1m slope=slope aspect=aspect
r.flow elevation=elev_lid792_1m flowaccumulation=flowacc

# exponents m=1.3 and n=1.2
# multiply flowaccumulation by cell area/resolution to get contributing area per unit width
r.mapcalc "sflowtopo = pow(flowacc * 1.,1.3) * pow(sin(slope),1.2)"

# Compute sediment flow by combining the rainfall, soil and land cover factors
# with the topographic sediment transport factor.
# We use a constant value of 270. for rainfall intensity factor.
r.mapcalc "sedflow = 270. * soils_Kfactor * cfactorbare_1m * sflowtopo"
r.divergence magnitude=sedflow direction=aspect output=erosion_deposition

# set suitable color table
r.colors map=erosion_deposition rules=- << EOF
0% 100 0 100   #dark magenta
-100 magenta
-10 red
-1 orange
-0.1 yellow
0 200 255 200     #light green
0.1 cyan
1 aqua
10 blue
100 0 0 100       #dark blue
100% black
EOF

AUTHOR

Anna Petrasova, NCSU OSGeoREL
Helena Mitasova, NCSU OSGeoREL

Last changed: $Date: 2015-04-06 15:29:05 +0200 (Mon, 06 Apr 2015) $

SOURCE CODE

Available at: r.divergence source code (history)