What is a digital elevation model?
Digital elevation models, or DEMs, are digital representations of a geographic region's topographical (or surface terrain) features. They are also referred to sometimes as "digital terrain models" or DTMs. However, unlike DTMs, DEMs offer continuous elevation data on an area of land. DTMs like contour line maps and topographical maps are not considered, for this reason, DEMs.
Most digital elevation models are constructed using remotes sensing techniques and tools, like satellite radar and airplane imaging. However, in some cases data procured via the traditional method of direct land surveying is also implemented into the creation of DEMs. Some of the most common uses of DEMs are in what is known as digital information systems (DIS). These are systems used by governments and large industries to assess and analyze the conditions of a given region. However DEMs and DIS is more and more being used in the field of mobile consumer electronics that implement location bases services and technology.
Methods of creating DEMs
The most sophisticated and powerful tool for coming up with digital elevation models is called interferometric synthetic aperture radar. It works by using radar images taken from orbiting satellites to create maps of areas of 10 kilometers per side. Two passes are all that is required to produce one such map, which usually has a resolution of 10 meters.
Digital image correlation is another, albeit older and less powerful, method of producing digital elevation models. This method combines two optical images taken from an airplane or earth observation satellite during a single pass. These two images, taken from different angles, create a more complete data set for a particular geographical area. The first usable set of elevation data was produced using this method. The satellite used was SPOT 1, back in 1986.
Lastly, there's the direct land survey. This method has been used for over a hundred years and data gathered with this method is still used in digital elevation models today, especially for mountainous regions which are difficult to map accurate using remote sensing techniques.
Current Uses
Digital elevation maps are being used today in a variety of fields. Among these are GPS services and other consumer location based services, flight simulators, land assessment, precision farming, intelligent transportation systems and advanced driver assistance systems.
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