Tool Valley and Ridge Detection (Top Hat Approach)

The tool allows one to calculate fuzzy valley and ridge class memberships from a DEM using the Top Hat approach. The mathematical morphology functions "Opening" and "Closing" form the basis of "The Top Hat Transform" function. The function extracts peaks and valleys with a size condition corresponding to the size of the considered structuring element.
Peaks are extracted by the "White Top Hat" (WTH) function:

WTH = DEM - Opening >= t

Valleys are extracted by the "Black Top Hat" (BTH) function:

BTH = Closing - DEM >= t

The threshold value "t" works as an additional cut-off to extract only the highest peaks and deepest valleys. This means that the functions permit to extract peaks and valleys based on width and height criterions. For details see the referenced paper.
The tool is based on the AML script 'tophat' by Jochen Schmidt, Landcare Research.

References

Rodriguez, F., Maire, É., Courjault-Radé, P., Darrozes, J. (2002): The Black Top Hat function applied to a DEM: A tool to estimate recent incision in a mountainous watershed (Estibère Watershed, Central Pyrenees). Geophysical Research Letters, 29(6): 9-1 - 9-4. doi:10.1029/2001GL014412.

Author: O.Conrad (c) 2013
Menu: Terrain Analysis|Terrain Classification

Parameters

	Name	Type	Identifier	Description	Constraints
Input	Elevation	grid, input	`DEM`	-	-
Output	Valley Depth (*)	grid, output, optional	`VALLEY`	-	-
	Hill Height (*)	grid, output, optional	`HILL`	-	-
	Valley Index	grid, output	`VALLEY_IDX`	-	-
	Hill Index	grid, output	`HILL_IDX`	-	-
	Hillslope Index (*)	grid, output, optional	`SLOPE_IDX`	-	-
Options	Grid System	grid system	`PARAMETERS_GRID_SYSTEM`	-	-
	Valley Radius	floating point number	`RADIUS_VALLEY`	The radius used to fill valleys [map units].	Minimum: 0.000000 Default: 1000.000000
	Hill Radius	floating point number	`RADIUS_HILL`	The radius used to cut hills [map units]	Minimum: 0.000000 Default: 1000.000000
	Elevation Threshold	floating point number	`THRESHOLD`	The elevation threshold used to identify hills/valleys [map units].	Minimum: 0.000000 Default: 100.000000
	Slope Index	choice	`METHOD`	Choose the method to calculate the slope index.	Available Choices: [0] default [1] alternative Default: 0
(*) optional

Command-line

Usage: saga_cmd ta_morphometry 24 [-DEM <str>] [-VALLEY <str>] [-HILL <str>] [-VALLEY_IDX <str>] [-HILL_IDX <str>] [-SLOPE_IDX <str>] [-RADIUS_VALLEY <double>] [-RADIUS_HILL <double>] [-THRESHOLD <double>] [-METHOD <str>]
  -DEM:<str>             	Elevation
	grid, input
  -VALLEY:<str>          	Valley Depth
	grid, output, optional
  -HILL:<str>            	Hill Height
	grid, output, optional
  -VALLEY_IDX:<str>      	Valley Index
	grid, output
  -HILL_IDX:<str>        	Hill Index
	grid, output
  -SLOPE_IDX:<str>       	Hillslope Index
	grid, output, optional
  -RADIUS_VALLEY:<double>	Valley Radius
	floating point number
	Minimum: 0.000000
	Default: 1000.000000
  -RADIUS_HILL:<double>  	Hill Radius
	floating point number
	Minimum: 0.000000
	Default: 1000.000000
  -THRESHOLD:<double>    	Elevation Threshold
	floating point number
	Minimum: 0.000000
	Default: 100.000000
  -METHOD:<str>          	Slope Index
	choice
	Available Choices:
	[0] default
	[1] alternative
	Default: 0