Category:CliffMetrics

CliffMetrics

CliffMetrics is an advanced software tool crafted to precisely determine the positions of cliff tops and toes along highly irregular coastlines using nothing but a Digital Elevation Model (DEM). Its innovative functionality includes an automated coastline delineation feature, which can be fine-tuned with various smoothing options to generate a streamlined coastline points layer. This layer serves as the foundation for customizable transects of variable lengths, while leveraging coastline orientation to accurately portray the coastline's normal direction. For users seeking to constrain specific locations, the tool seamlessly integrates input coastline points layers. In CliffMetrics, the concepts of cliff top and toe are rigorously defined in purely geometric terms, denoting a sharp transition in elevation along the coastaline. This definition is established through an initial detrended elevation process, followed by the specification of an input threshold, as illustrated in Fig. 1. In addition, the tool operates under the assumption that the cliff represents the predominant feature along the elevation transect. At present, CliffMetrics can be used within a GIS environment (via SAGA GIS software) or programmatically via the Linux version.

Fig. 1. CliffMetrics extracts the profile elevations and detects the locations at the cliff top and toe (left) from Detrended elevation (right)

Getting Started

SAGA WINDOWS INTEGRATION

CliffMetrics has been seamlessly integrated into the System for Automated Geoscientific Analyses (SAGA), a robust and open-source Geographic Information System (GIS) software. As of August 2019, it became an official component of the SAGA Repository, featuring firstly in version v7.3.0. CliffMetrics can be accessed in two ways:

• in Geoprocessing menu, go to “Terrain Analysis” >> “Coastal Morphology” >> “CliffMetrics”,
• in the Tools pane as it is shown in Fig. 2, “Tools”>> “Terrain Analysis” >> “CliffMetrics”.

Fig.2. Integration of CliffMetrics into SAGA software

INPUTS

The SAGA-CliffMetrics-input window is divided into the “Data Objects” and the “Options” inputs sections. Data-Objects-values are indicated by the symbol “>>” before the name and by <not set> or <create> in value box. Fig. 3 shows the default Options-values, and all inputs are explained below.

Fig. 3. The CliffMetrics input data window

The “Data Objects” section is composed by the “Elevation” (bellow “Grids”>> “Grids System”) in “Grid System” subsection and the “User Defined Coastline Points” in “Shapes” subsection. Optional parameters need to be defined in “Options” section. In more detail: - Grid System:

• Elevation: Define the Grid System used in SAGA, and it is the primary elevation source. All types of DEM files supported in SAGA can be used. IMPORTANT! For the automatic coastline delineation option (no User Defined Coastline Points as input), the user-defined DEM must NOT have non-data values around the edges. CliffMetrics starts searching for the coastline by traversing the edges of the DEM.

- Shapes:

• User Defined coastline points: This layer sets the starting points of transect positions on the coastline if you include it. All vector file types supported in SAGA can be used. CliffMetrics only read the coordinates of the point and the ordinal (sequential order of saving to the file). Ordinals identify the Start (n=1) and End (n=last) points of User Defined Coastline Points, so the points must have been stored along the coastline. If the starting point is outside of the DEM domain, the first user-defined shoreline point within the DEM boundaries is automatically selected as the starting point. The User Defined Coastline Points are used as an initial reference to find the centre of the raster DEM cell closest to them. This centre will be the starting point for the transects. In addition, it is necessary to define three aspects in advance:

1. Sea handiness: This parameter establishes which DEM side of the coastline is the sea if a person is imagined walking from the starting point to the end of the user defined coastline, see Fig.4.
2. Start edge coastline: Defines which DEM edge (North, East, South, West) the user defined coastline starts at, see Fig. 4.
3. End edge coastline: This parameter identifies which DEM edge (North, East, South, West) the user defined coastline ends at, see Fig. 4.

- Options:

• Still Water Level: the user-defined vertical elevation for the automatically delineated coastline. Default is 1 m above the datum used for the DEM. This will likely be different for your DEM.
• Coastline Smoothing Algorithm: Smoothing algorithm to apply. There are three options: “None”, “running mean” or “Savitsky-Golay”, see Fig. 4. The default is “running mean” (https://en.wikipedia.org/wiki/Moving_average).
• Coastline Smoothing Window Size: The number of selected points to smooth the coastline. Smoothing the coastline produces normals that are more parallel to each other, see Fig. 4. The default value is “30” points.