What is Digital Elevation Model (DEM)?

  1. Digital elevation model gives digital representation of a topographic surface.
  1. A digital elevation model is a raster grid of bare-earth referenced to a vertical datum.  At the point when you sift through non-ground focuses, for example, extensions and streets, you get a smooth advanced height model. The fabricated (electrical cables, structures and towers) and regular (trees and different sorts of vegetation) are excluded from a DEM.
  1. DEM’s are used to determine terrain attributes and answer questions as elevation at any point, slope and aspect with respect to given area
  1. DEM only represents height information without any further definition about the surface  and used as a common term for DSM’s and DTM’s, only representing height information without any further definition about the surface

It is obvious that DEM is a great tool which simplifies if any circumstances such as (heavy rainfall, soil erosion etc ) has any direct or indirect relationship, with terrain slope and elevation. Using DEM we can better visualize and model what is going on, on the ground and evolve sciences like geomorphology, gravimetry, geodesy etc. with new discoveries.

Types of DEM: 

A DEM can be represented as a raster data-set (a grid of squares, when representing elevation) or as a vector-based Triangular Irregular Network (TIN).

 The TIN DEM data-set is called as a primary (measured) DEM, and the Raster DEM is referred to as a secondary (computed) DEM.

Free Available Open Data Sets (Please click on the links to know in detail)

  1. SRTM ( Shuttle Radar Topographic Mission):   
    Python Library For Elevation API
  3. JAXA’s Global ALOS
  4. Open DEM
  5. LiDAR Datasets High Resolution (Unfortunately, No Open data for India)

LiDAR and DEM:

 Light Detection and Ranging (LiDAR)  This article suggests how lidar operates. The Pulses are sent from a laser onboard an aircraft and the scattered pulses are recorded. 

Lidar  also enables DEM generation of a large area within a short period of time with minimum human dependence and as the technology is growing faster, the means of creating DEM’s are also changing. The disadvantage of procuring high resolution LiDAR data is the expenses involved are high.

                                                                                                                                                 source: Wikipedia


Few Definitions That We Need To Know:

  • Slope:

    Slope is the steepness or the degree of incline of a surface.

    The maximum rate of change of elevation between that location and its surroundings is called Slope.

         Slope can be expressed either in degrees or as a percentage.


  • Aspect:
     Aspect is the orientation of slope, it is  measured clockwise in manner. The degrees from 0 to 360, where 0 is facing North, 90 is facing east, 180 is facing south, and 270 is facing west.


                                                                                                                                                                          Source: http://www.geography.hunter.cuny.edu/

  • Hillshade:

    To visualize terrain as shaded relief,it is  illuminated with a hypothetical light source. This illumination value for each cell of a raster is determined by its orientation to the light source, which is based on slope and aspect. The overall process is known as Hillshade.




Applications  of DEM:

  1.  Drainage basin network development and delineation. 
  2.  Hydrological run-off modeling for flood analysis. 
  3.  Geo-morphological simulation and classification.  
  4. Geological mapping.  
  5. Generation of slope and aspect maps. 
  6. Dispersion models for Wind flow and pollution.
  7. Volumetric calculations in construction sites, dams and reservoirs. 

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