Earth's land surface can be classified into highlands, midlands and lowlands depending upon their height or elevation, compared to the sea level. The altitude determination of the land surface is a strenuous task as it requires generation of large number of land images and scaling. Precise measurement is almost impossible while measuring the land altitudes because of the land deformations. To ensure approximate height and depth of land surfaces, several methods are being employed. These measurements are then used to create Digital elevation Model, which is a source for detailed topographical studies.

Digital Elevation Model is the representation of earth's topography using digital methods. Digital elevation model is also called as digital terrain model (DTM). DEMs or DTMs can be represented as original maps, square grids or irregular network of triangles.  They are mainly created through land surveying methods and remote sensing methods. DEMs are used in geographic information systems, especially for creating digital relief maps.

DEMs are mainly produced using remote sensing technologies. There are several other ways to produce DEMs. The DEMs or DTMs requires precision and high quality. Therefore, most precise techniques are necessary for creating DEMs. Some of the recent techniques employed for creating the DEMs are

• Real Time Kinematic GPS
• LiDAR
• Stereo Photogrammetry
• Topographic Maps
• Doppler Radar
• Theodolite Or Total Station

Real Time Kinematics GPS

Real Time Kinematics GPS is a satellite signal system used in land surveying. It gives accurate measurements of the distant objects, thereby enabling quick determination of geographical dimensions. This method is helpful in generating accurate DEMs and it is largely used for geographical studies and its variations.

LiDAR

LIDAR (Light Detection And Ranging) is a technology that uses the scattering property of light to measure the altitudes and distances of the objects. In other words, it is an optical remote sensing technology. It is similar to the radar technology and helps to generate precise DEMs or DTMs.

Stereo Photogrammetry

Stereo Photogrammetry employs photographic techniques to create DEMs. A three dimensional image of the plane or land area is created using images taken from different angles. The images are stitched using photogrammetric techniques. This helps to produce high quality DEMs.

Topographic Maps

Topographic maps are informative maps with contour lines and other specific colour markings indicating topographic features. There are different types of topographic maps that record different types of information. While creating DEMs several topographic maps are compared to ensure precise representation of topography.

Doppler Radar

Doppler Radar uses sound waves to determine the height, depth and distance of land area. The amount of sound wave pulses reflecting from the searched land area provides accurate measurements of terrains, which helps to make precise DEMs.

Theodolite or Total Station

Theodolite is an instrument used in triangulation networks. It measures horizontal and vertical angles to determine the elevation or the heights of the ground, the output of which is used for DEM or DTM generation.