Notes

6/30/2015

SAGA has a lot of useful tools for classifying topographic positions, e.g. TWI, TPI, Relative slope positions.

SAGA GIS > Terrain Analysis > Compound Analysis > Basic Terrain Analysis

Creates multiple outputs from different Morphometry packages (example tutorial pdf) including:

Analytic Hillshading
Slope
Aspect
Cross-sectional curvature
Profile Curvature
Convergence Index
Closed Depressions
Catchment Area
Topographic Wetness Index
LS-Factor
Channel Network Base Level
Channel Network Distance
Valley Depth
Relative Slope Position

SAGA GIS > Terrain Analysis > Morphometry> Relative Heights and Slope Positions

Reference paper: Dietrich and Böhner (2008) - "Cold Air Production and Flow in a Low Mountain Range Landscape in Hessia (Germany)."

The Relative Heights and Slope Position module creates multiple outputs that can be used in relation to the 3-zone model (Brooks et al. in review).

Slope Height (m) - height above channel
Valley Depth (m) - height below ridgeline
Normalized Height (unitless) - normalized height of local environment
Standardized Height (m) - standardized height of local environment
Mid-Slope Position (unitless) - middle slope position.

SAGA GIS > Terrain Analysis > Morphometry > TPI Based Landform Classification

6/19/2015

Note from Peter Troch - look up Sally Thompson's research.

SAGA workflow

Load GeoTiff layers into SAGA 2.1.4

In Tools, selected the Morphometry > Slope, Aspect, Curvature'

Selected the Grid System and Elevation

Created all of the possible output options:

Slope
Aspect
General Curvature
Profile curvature
Plan Curvature
Tangential Curvature
Longitudinal Curvature
Cross-Sectional Curvature
Minimal Curvature
Maximal Curvature
Total Curvature
Flow Line curvature

The Options were set to:

Method: 9 parameter 2nd order polynomial (Zevenbergen & Thorne 1987)
Slope Units: Radians
Aspect Units: Radians

In tools selected the Hydrology > Catchment Area (Recursive)

In tools selected the Hydrology > Topographic Wetness Index (TWI)

6/5/2015

In exploring the question about ground water subsidy and its affect on overall tree biomass (estimated from height and canopy diameter) I generated topographic curvatures at multiple length scales (e.g. 1m, 3m, 5m, 10m, 15m, 30m).

It can be readily observed local profile curvature exhibits concave and convex shapes that appear as terracing above and below clusters of trees, which are in general aligned perpendicular to the hill slope.

Curvatures are one of three values:

Convex > 0

Concave < 0

Flat = 0

The root swell around trees growing on steep slopes results in a positive feedback where water is slowed across a concave slope on the uphill side, resulting in deposition and greater wetness. This may also have an affect on the snow on south facing aspects, as is also observable in the Valles Caldera data.

Curvature calculations are typically conducted upon a 3x3 moving window at varying length scales.

Plan curvature is defined as curvature in a horizontal plane.

Profile curvature is the curvature of the surface in the direction of the steepest slope (with respect to the vertical plane of a flow line).

General curvature (also called total curvature) is the curvature of the surface itself (not the curvature of a line formed by the intersection of the surface with a plane). General curvature = plan curvature + profile curvature

Preliminary Results