Basics of Digital Elevation Models

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Digital Elevation Model (DEM) is the name given to certain type of digital terrain model (DTM) that provides a representation of an area's surface, topographical features. Specifically, it refers to one that provides continuous elevation data at different portions of the mapped region. Contour line maps and topographical maps are considered DTMs but not DEMs, as they do not provide continuous elevation data.

Remote sensing techniques such as airplane or satellite radar mapping are the most common methods of creating digital elevation models. However, the traditional, direct land survey method is sometimes employed as well. Today, DEMs are being used in a wide variety of emerging technological fields that involve location based tasks and services.

Methods of creating DEMs

The most powerful remote sensing technique for producing digital elevation models is called interferometric synthetic aperture radar. This technique relies on radar images taken by orbiting satellites that can map an area of up to 10 kilometers per side with a resolution of no less than 10-meters. Such a DEM can be achieved with only two passes.

Another technique for producing digital elevation data is called digital image correlation, and it involves combining two optical images taken from an airplane or an earth observation satellite over the course of a single pass.

The first usable set of elevation data was captured by the earth observation satellite SPOT 1 in 1986 using the digital image correlation method. SPOT 1's data covered a huge portion of the earth's continental land surface.

Lastly, though not as common as other methods, there's the traditional method of direct land survey, the data from which is used in the creation of digital elevation models as it pertains to certain mountainous terrains that are difficult to map using the more sophisticated remote sensing techniques.

Uses

Digital elevation models today are being used in flight simulators, GPS devices, wireless location based services, intelligent transportation systems, precision farming and the development of vehicles that use smart-car technology to anticipate the conditions of the road ahead, known as advanced driver assistance systems. This last field is one of the most dynamic areas in which DEMs are being implemented.