Tool Name	Valley and Ridge Detection (Top Hat Approach)
Tool ID	24
Library ID	ta_morphometry
Version	1.0
Author(s)	O.Conrad (c) 2013

Description

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 extracting 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.

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
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