Post on 22-Feb-2016
description
Digital Elevation Model &
Terrain Analysis
Terrain Analysis
• Terrain - an integral part of – determining the natural availability and location of
surface water, soil moisture and drainage– determining transportation networks– site suitability for a variety of applications (cost
and methods of house and road construction)
• Elevation and slope:– flood zones and watershed boundaries delineation – hydrologic networks
Terrain Analysis
• Slope• Aspect• Catchment/watershed area• Viewshed• Flow path and direction
Slope and Aspect
• Slope– change is elevation (a rise) with a change in
horizontal position (a run)– Slope is often reported in degrees (0° is flat, 90° is
vertical)
Slope (continued)
Slope direction at a point in the landscape is measured in the steepest direction of the elevation change
Slope (continued)
• slope direction often does not point parallel to raster rows and columns
• which cells to use?
• How to obtain the values for rise/run?
• there are different methods• Examples:
– Four nearest cells– 3rd Order Finite Difference
Fig: Direction of steepest slope
Slope (continued)
• Elevation expressed as Z• Calculated with a symmetrical
moving window (3x3, 5x5, other odd numbered windows)
• Slope at each center cell is calculated from:
Where:• s = slope• Z = elevation• x, y coordinate ases• dz/dx = rise (change
in z) over run in x-direction
• dz/dx = rise (change in z) over run in y-direction
Slope (continued)
• Many different formulas proposed for calculating dz/dx and dz/dy
• Most simplest – based on cells adjacent to the center cell
• Four nearest = uses 4 nearest cells
Aspect• Azimuth angle, measured
clockwise in degrees from north (0 – 360 degrees)
• Aspect at a point is the steepest downhill direction
• Flat areas have no aspect (no downhill direction)
• Used to define:– water flow direction– Amount of sunlight at a location– Portion of landscape visible from
viewing point
Aspect calculation
• .
Profile curvature and plan curvature
• Derived form DEM• Helpful in measuring and predicting– Soil water content– Overland flow– Rainfall-runoff response in small catchment– Distribution of vegetation
• Profile curvature– Index of surface shape in the steepest downhill
direction• Pane curvature– Profile shape in the direction of the contour – at
right angle to the steepest direction
Hydrologic Functions
• Watershed– An area that contributes flow to a point on the
landscape– Water falling anywhere in the upstream area of a
watershed will pass through that point• Drainage network– A set of cells through which surface water flows– Based on the flow direction surface
Drainage network and watersheds
Watershed delineation
• Condition DEM• Fill DEM• Flow Direction• Flow Accumulation• Stream Definition• Outlet Identification• Watershed Delineation
Flow direction
Hydrologic Functions
Viewshed• Is the collection of areas
visible from a specific point– Non flat areas block the
view– Elevation will hide points if
the elevations are higher than the line of sight between viewing point and target point
Shaded relief surfaces
• Depicts brightness of terrain reflections given a terrain surface and sun location