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55-405: The topography of Switzerland is such that certain areas and even radar shadows do not allow surveillance by permanently installed radars placed on mountains. In 1985, five mobile radar systems were purchased for 254 million Swiss francs in order to address this problem. Switzerland procured the mobile radars to improve the nation's aerial warfare capability. However, the system's viability in

110-428: A DSM may be useful for landscape modeling , city modeling and visualization applications, a DTM is often required for flood or drainage modeling, land-use studies , geological applications, and other applications, and in planetary science . There is no universal usage of the terms digital elevation model (DEM), digital terrain model (DTM) and digital surface model (DSM) in scientific literature. In most cases

165-400: A Digital Land Surface Model in the form of a TIN . The DLSM can then be used to visualize terrain, drape remote sensing images, quantify ecological properties of a surface or extract land surface objects. The contour data or any other sampled elevation datasets are not a DLSM. A DLSM implies that elevation is available continuously at each location in the study area, i.e. that the map represents

220-492: A complete surface. Digital Land Surface Models should not be confused with Digital Surface Models, which can be surfaces of the canopy, buildings and similar objects. For example, in the case of surface models produces using the lidar technology, one can have several surfaces – starting from the top of the canopy to the actual solid earth. The difference between the two surface models can then be used to derive volumetric measures (height of trees etc.). Topographic survey information

275-539: A digital elevation map tens of kilometers on a side with a resolution of around ten meters. Other kinds of stereoscopic pairs can be employed using the digital image correlation method, where two optical images are acquired with different angles taken from the same pass of an airplane or an Earth Observation Satellite (such as the HRS instrument of SPOT5 or the VNIR band of ASTER ). The SPOT 1 satellite (1986) provided

330-470: A distance. As an active protection measure against electronic countermeasures the frequency can be changed to pulse . The heart of the TAFLIR system is the rotating antenna mounted on a truck. Containers hold further components such as radar electronics, terminal operation and cooling equipment. The modular TAFLIR system allows vehicles can be exchanged and the TAFLIR may relocate within hours. Radar data of

385-472: A matrix of numbers, but the data from a DEM is often rendered in visual form to make it understandable to humans. This visualization may be in the form of a contoured topographic map , or could use shading and false color assignment (or "pseudo-color") to render elevations as colors (for example, using green for the lowest elevations, shading to red, with white for the highest elevation.). Visualizations are sometimes also done as oblique views, reconstructing

440-734: A military operation was a controversial matter that was brought to attention and addressed in the initial attack waves of the Iraq War . TAFLIR is a version of the AN/TPS-70 radar produced by Westinghouse (now Northrop Grumman ), modified for Swiss requirements. It replaced the Target Allocation Radar TPS-1E . These AN/MPQ-64 radars are a variant of the Northrop Grumman AN/TPS-75 and can be deployed in areas of difficult terrain to improve

495-527: A number of ways, but they frequently use remote sensing rather than direct survey data. Older methods of generating DEMs often involve interpolating digital contour maps that may have been produced by direct survey of the land surface. This method is still used in mountain areas, where interferometry is not always satisfactory. Note that contour line data or any other sampled elevation datasets (by GPS or ground survey) are not DEMs, but may be considered digital terrain models. A DEM implies that elevation

550-405: A part of geovisualization , whether maps or GIS systems. False-color and non-visible spectra imaging can also help determine the lie of the land by delineating vegetation and other land-use information more clearly. Images can be in visible colours and in other spectrum. Photogrammetry is a measurement technique for which the co-ordinates of the points in 3D of an object are determined by

605-583: A place or places, what is now largely called ' local history '. In Britain and in Europe in general, the word topography is still sometimes used in its original sense. Detailed military surveys in Britain (beginning in the late eighteenth century) were called Ordnance Surveys , and this term was used into the 20th century as generic for topographic surveys and maps. The earliest scientific surveys in France were

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660-720: A product of national lidar dataset programs. Free DEMs are also available for Mars : the MEGDR, or Mission Experiment Gridded Data Record, from the Mars Global Surveyor 's Mars Orbiter Laser Altimeter (MOLA) instrument; and NASA's Mars Digital Terrain Model (DTM). OpenTopography is a web based community resource for access to high-resolution, Earth science-oriented, topography data (lidar and DEM data), and processing tools running on commodity and high performance compute system along with educational resources. OpenTopography

715-405: A synthetic visual image of the terrain as it would appear looking down at an angle. In these oblique visualizations, elevations are sometimes scaled using " vertical exaggeration " in order to make subtle elevation differences more noticeable. Some scientists, however, object to vertical exaggeration as misleading the viewer about the true landscape. Mappers may prepare digital elevation models in

770-598: A valuable set of information for large-scale analysis. The original American topographic surveys (or the British "Ordnance" surveys) involved not only recording of relief, but identification of landmark features and vegetative land cover. Remote sensing is a general term for geodata collection at a distance from the subject area. Besides their role in photogrammetry, aerial and satellite imagery can be used to identify and delineate terrain features and more general land-cover features. Certainly they have become more and more

825-570: A vector-based triangular irregular network (TIN). The TIN DEM dataset is also referred to as a primary (measured) DEM, whereas the Raster DEM is referred to as a secondary (computed) DEM. The DEM could be acquired through techniques such as photogrammetry , lidar , IfSAR or InSAR , land surveying , etc. (Li et al. 2005). DEMs are commonly built using data collected using remote sensing techniques, but they may also be built from land surveying. The digital elevation model itself consists of

880-472: Is superficial human anatomy . In mathematics the concept of topography is used to indicate the patterns or general organization of features on a map or as a term referring to the pattern in which variables (or their values) are distributed in a space. Topographers are experts in topography. They study and describe the surface features of a place or region. Digital Elevation Model A digital elevation model ( DEM ) or digital surface model ( DSM )

935-495: Is a 3D computer graphics representation of elevation data to represent terrain or overlaying objects, commonly of a planet , moon , or asteroid . A "global DEM" refers to a discrete global grid . DEMs are used often in geographic information systems (GIS), and are the most common basis for digitally produced relief maps . A digital terrain model ( DTM ) represents specifically the ground surface while DEM and DSM may represent tree top canopy or building roofs. While

990-453: Is available continuously at each location in the study area. One powerful technique for generating digital elevation models is interferometric synthetic aperture radar where two passes of a radar satellite (such as RADARSAT-1 or TerraSAR-X or Cosmo SkyMed ), or a single pass if the satellite is equipped with two antennas (like the SRTM instrumentation), collect sufficient data to generate

1045-621: Is between 50 and 500 meters. In gravimetry e.g., the primary grid may be 50 m, but is switched to 100 or 500 meters in distances of about 5 or 10 kilometers. Since 2002, the HRS instrument on SPOT 5 has acquired over 100 million square kilometers of stereo pairs used to produce a DTED2 format DEM (with a 30-meter posting) DEM format DTED2 over 50 million km . The radar satellite RADARSAT-2 has been used by MacDonald, Dettwiler and Associates Ltd. to provide DEMs for commercial and military customers. In 2014, acquisitions from radar satellites TerraSAR-X and TanDEM-X will be available in

1100-499: Is combined, a truly global relief model is obtained. The SRTM30Plus dataset (used in NASA World Wind ) attempts to combine GTOPO30, SRTM and bathymetric data to produce a truly global elevation model. The Earth2014 global topography and relief model provides layered topography grids at 1 arc-minute resolution. Other than SRTM30plus, Earth2014 provides information on ice-sheet heights and bedrock (that is, topography below

1155-460: Is concerned with underlying structures and processes to the surface, rather than with identifiable surface features. The digital elevation model (DEM) is a raster -based digital dataset of the topography ( hypsometry and/or bathymetry ) of all or part of the Earth (or a telluric planet ). The pixels of the dataset are each assigned an elevation value, and a header portion of the dataset defines

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1210-428: Is essential for the planning and construction of any major civil engineering , public works , or reclamation projects. There are a variety of approaches to studying topography. Which method(s) to use depends on the scale and size of the area under study, its accessibility, and the quality of existing surveys. Surveying helps determine accurately the terrestrial or three-dimensional space position of points and

1265-506: Is free to download non-commercially and through the developer's website at a cost commercially. An alternative free global DEM is called GTOPO30 (30 arcsecond resolution , c. 1  km along the equator) is available, but its quality is variable and in some areas it is very poor. A much higher quality DEM from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument of

1320-438: Is historically based upon the notes of surveyors. They may derive naming and cultural information from other local sources (for example, boundary delineation may be derived from local cadastral mapping). While of historical interest, these field notes inherently include errors and contradictions that later stages in map production resolve. As with field notes, remote sensing data (aerial and satellite photography, for example),

1375-547: Is often considered to include the graphic representation of the landform on a map by a variety of cartographic relief depiction techniques, including contour lines , hypsometric tints , and relief shading . The term topography originated in ancient Greece and continued in ancient Rome , as the detailed description of a place. The word comes from the Greek τόπος ( topos , "place") and -γραφία ( -graphia , "writing"). In classical literature this refers to writing about

1430-588: Is raw and uninterpreted. It may contain holes (due to cloud cover for example) or inconsistencies (due to the timing of specific image captures). Most modern topographic mapping includes a large component of remotely sensed data in its compilation process. In its contemporary definition, topographic mapping shows relief. In the United States, USGS topographic maps show relief using contour lines . The USGS calls maps based on topographic surveys, but without contours, "planimetric maps." These maps show not only

1485-436: Is required to operate a TAFLIR system. All the mobile companies belong to Air Force Radar Battalion 2. The Austrian Tiefflieger Acquisition Radar (TER) is a comparable system. TAFLIR deployment locations are at Dübendorf and Payerne. In times of crisis or war they can be redeployed elsewhere. Topography Topography is the study of the forms and features of land surfaces . The topography of an area may refer to

1540-449: Is the morphology presented (relative accuracy). Quality assessment of DEM can be performed by comparison of DEMs from different sources. Several factors play an important role for quality of DEM-derived products: Common uses of DEMs include: Released at the beginning of 2022, FABDEM offers a bare earth simulation of the Earth's surface at 30 arc-second resolution. Adapted from GLO-30, the data removes all forests and buildings. The data

1595-422: Is to something else). Topography has been applied to different science fields. In neuroscience , the neuroimaging discipline uses techniques such as EEG topography for brain mapping . In ophthalmology , corneal topography is used as a technique for mapping the surface curvature of the cornea . In tissue engineering , atomic force microscopy is used to map nanotopography . In human anatomy , topography

1650-634: The Cassini maps after the family who produced them over four generations. The term "topographic surveys" appears to be American in origin. The earliest detailed surveys in the United States were made by the "Topographical Bureau of the Army", formed during the War of 1812 , which became the Corps of Topographical Engineers in 1838. After the work of national mapping was assumed by the U.S. Geological Survey in 1878,

1705-695: The Mars Orbiter Laser Altimeter (MOLA) mapping of Mars, the Lunar Orbital Laser Altimeter (LOLA) and Lunar Altimeter (LALT) mapping of the Moon, and the Mercury Laser Altimeter (MLA) mapping of Mercury. In planetary mapping, each planetary body has a unique reference surface. The quality of a DEM is a measure of how accurate elevation is at each pixel (absolute accuracy) and how accurately

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1760-497: The Recognized Air Picture . Peacetime TAFLIR deployment locations are at Dübendorf and Payerne. In times of crisis or war they can be deployed anywhere. They employ a phased array antenna , which reduces the appearance of side lobes by more than 50%, thus reducing vulnerability to anti-radar missiles and a secondary radar . The radar uses a phase-encoded pulse compression to improve accuracy and resolution at

1815-620: The Terra satellite is also freely available for 99% of the globe, and represents elevation at 30 meter resolution. A similarly high resolution was previously only available for the United States territory under the Shuttle Radar Topography Mission (SRTM) data, while most of the rest of the planet was only covered in a 3 arc-second resolution (around 90 meters along the equator). SRTM does not cover

1870-432: The Terra satellite using double-pass stereo pairs. The HRS instrument on SPOT 5 has acquired over 100 million square kilometers of stereo pairs. A tool of increasing value in planetary science has been use of orbital altimetry used to make digital elevation map of planets. A primary tool for this is laser altimetry but radar altimetry is also used. Planetary digital elevation maps made using laser altimetry include

1925-492: The USGS topographic maps record not just elevation contours, but also roads, populated places, structures, land boundaries, and so on. Topography in a narrow sense involves the recording of relief or terrain , the three-dimensional quality of the surface, and the identification of specific landforms ; this is also known as geomorphometry . In modern usage, this involves generation of elevation data in digital form ( DEM ). It

1980-677: The TAFLIR are fed directly to the FLORAKO system. In times of peace, the system is stationed near military airfields to improve the Recognized Air Picture. Any systems not in use are stored in particular electromagnetic pulse -protected caverns . The TAFLIR system can operate in any location accessible by truck and can be deployed within a few hours. TAFLIR is deployed to support security during annual World Economic Forum meetings in Davos , Switzerland. A mobile radar LW company

2035-669: The area of coverage, the units each pixel covers, and the units of elevation (and the zero-point). DEMs may be derived from existing paper maps and survey data, or they may be generated from new satellite or other remotely sensed radar or sonar data. A geographic information system (GIS) can recognize and analyze the spatial relationships that exist within digitally stored spatial data. These topological relationships allow complex spatial modelling and analysis to be performed. Topological relationships between geometric entities traditionally include adjacency (what adjoins what), containment (what encloses what), and proximity (how close something

2090-455: The basis for much derived topographic work. Digital Elevation Models, for example, have often been created not from new remote sensing data but from existing paper topographic maps. Many government and private publishers use the artwork (especially the contour lines) from existing topographic map sheets as the basis for their own specialized or updated topographic maps. Topographic mapping should not be confused with geologic mapping . The latter

2145-454: The contours, but also any significant streams or other bodies of water, forest cover , built-up areas or individual buildings (depending on scale), and other features and points of interest. While not officially "topographic" maps, the national surveys of other nations share many of the same features, and so they are often called "topographic maps." Existing topographic survey maps, because of their comprehensive and encyclopedic coverage, form

2200-515: The direct survey still provides the basic control points and framework for all topographic work, whether manual or GIS -based. In areas where there has been an extensive direct survey and mapping program (most of Europe and the Continental U.S., for example), the compiled data forms the basis of basic digital elevation datasets such as USGS DEM data. This data must often be "cleaned" to eliminate discrepancies between surveys, but it still forms

2255-476: The distances and angles between them using leveling instruments such as theodolites , dumpy levels and clinometers . GPS and other global navigation satellite systems (GNSS) are also used. Work on one of the first topographic maps was begun in France by Giovanni Domenico Cassini , the great Italian astronomer. Even though remote sensing has greatly sped up the process of gathering information, and has allowed greater accuracy control over long distances,

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2310-680: The first usable elevation data for a sizeable portion of the planet's landmass, using two-pass stereoscopic correlation. Later, further data were provided by the European Remote-Sensing Satellite (ERS, 1991) using the same method, the Shuttle Radar Topography Mission (SRTM, 2000) using single-pass SAR and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER, 2000) instrumentation on

2365-430: The form of a uniform global coverage with a resolution of 12 meters. ALOS provides since 2016 a global 1-arc second DSM free of charge, and a commercial 5 meter DSM/DTM. Many national mapping agencies produce their own DEMs, often of a higher resolution and quality, but frequently these have to be purchased, and the cost is usually prohibitive to all except public authorities and large corporations. DEMs are often

2420-615: The ice) over Antarctica and Greenland. Another global model is Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010) with 7.5 arc second resolution. It is based on SRTM data and combines other data outside SRTM coverage. A novel global DEM of postings lower than 12 m and a height accuracy of less than 2 m is expected from the TanDEM-X satellite mission which started in July 2010. The most common grid (raster) spacing

2475-404: The land forms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary science and is concerned with local detail in general, including not only relief , but also natural , artificial, and cultural features such as roads, land boundaries, and buildings. In the United States, topography often means specifically relief , even though

2530-439: The measurements made in two photographic images (or more) taken starting from different positions, usually from different passes of an aerial photography flight. In this technique, the common points are identified on each image . A line of sight (or ray ) can be built from the camera location to the point on the object. It is the intersection of its rays ( triangulation ) which determines the relative three-dimensional position of

2585-480: The most applications in environmental sciences , land surface is represented and modelled using gridded models. In civil engineering and entertainment businesses, the most representations of land surface employ some variant of TIN models. In geostatistics , land surface is commonly modelled as a combination of the two signals – the smooth (spatially correlated) and the rough (noise) signal. In practice, surveyors first sample heights in an area, then use these to produce

2640-525: The point. Known control points can be used to give these relative positions absolute values. More sophisticated algorithms can exploit other information on the scene known a priori (for example, symmetries in certain cases allowing the rebuilding of three-dimensional co-ordinates starting from one only position of the camera). Satellite RADAR mapping is one of the major techniques of generating Digital Elevation Models (see below). Similar techniques are applied in bathymetric surveys using sonar to determine

2695-458: The polar regions and has mountain and desert no data (void) areas. SRTM data, being derived from radar, represents the elevation of the first-reflected surface—quite often tree tops. So, the data are not necessarily representative of the ground surface, but the top of whatever is first encountered by the radar. Submarine elevation (known as bathymetry ) data is generated using ship-mounted depth soundings . When land topography and bathymetry

2750-475: The position of any feature or more generally any point in terms of both a horizontal coordinate system such as latitude, longitude, and altitude . Identifying (naming) features, and recognizing typical landform patterns are also part of the field. A topographic study may be made for a variety of reasons: military planning and geological exploration have been primary motivators to start survey programs, but detailed information about terrain and surface features

2805-439: The term digital surface model represents the earth's surface and includes all objects on it. In contrast to a DSM, the digital terrain model (DTM) represents the bare ground surface without any objects like plants and buildings (see the figure on the right). DEM is often used as a generic term for DSMs and DTMs, only representing height information without any further definition about the surface. Other definitions equalise

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2860-399: The term topographical remained as a general term for detailed surveys and mapping programs, and has been adopted by most other nations as standard. In the 20th century, the term topography started to be used to describe surface description in other fields where mapping in a broader sense is used, particularly in medical fields such as neurology . An objective of topography is to determine

2915-634: The terms DEM and DTM, equalise the terms DEM and DSM, define the DEM as a subset of the DTM, which also represents other morphological elements, or define a DEM as a rectangular grid and a DTM as a three-dimensional model ( TIN ). Most of the data providers ( USGS , ERSDAC , CGIAR , Spot Image ) use the term DEM as a generic term for DSMs and DTMs. Some datasets such as SRTM or the ASTER GDEM are originally DSMs, although in forested areas, SRTM reaches into

2970-417: The terrain of the ocean floor. In recent years, LIDAR ( LI ght D etection A nd R anging), a remote sensing technique that uses a laser instead of radio waves, has increasingly been employed for complex mapping needs such as charting canopies and monitoring glaciers. Terrain is commonly modelled either using vector ( triangulated irregular network or TIN) or gridded ( raster image ) mathematical models. In

3025-432: The tree canopy giving readings somewhere between a DSM and a DTM). DTMs are created from high resolution DSM datasets using complex algorithms to filter out buildings and other objects, a process known as "bare-earth extraction". In the following, the term DEM is used as a generic term for DSMs and DTMs. A DEM can be represented as a raster (a grid of squares, also known as a heightmap when representing elevation) or as

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