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Digital elevation model SRTM

Digital elevation model SRTM

This digital image shows the relief of two islands of the Kuril ridge - 3-3-3325. Onecotan 3-3-3184. and Makanrushi , - separated by Evreinov Strait . The image is oriented so that the observer is looking in the north-west direction. In the foreground is the island of Onekotan with calderas 3-3-3184. two volcanoes. The larger volcano in the southern part of the island is Krenitsyna volcano . Its southern caldera is Tao Rusyr filled with water, forming lake Ring from which a new volcanic cone rises. The wall of the caldera of the Krenitsyn volcano is called the Ring Range. In the north of the island is the volcano Nemo 3-3-3184. . Its caldera is only partially filled with water, so near the volcanic cone Lake Black formed. The wall of the caldera of the volcano Nemo also has its own name - the Soviet ridge.

To create this image, we used a fragment of the digital elevation model SRTM and the program QGIS . Using this program, a three-dimensional surface with superimposed shadows was generated from SRTM, which was colorized by elevation values. The acronym SRTM stands for Shuttle Radar Topographic Mission - radar topographic mission shuttle . This is a mission STS-99 performed in February 2000 by the space shuttle 3-3-3353. "Endeavor" . This orbital flight became the 14th for Endeavor and the 97th for the entire 3-3-3355 program. Space Shuttle 3-3-3184. . For 11 days, from February 11 to February 222000 Endeavor performed a radar survey, having made 176 turns around the Earth.

Radar imaging is not the only way to create digital elevation models (DEM, see also 3-3-3359. Digital map 3-3-3184.). Digital elevation models can be made based on ground data. geodetic survey or using interpolation contour lines and elevations digitized by existing topographic maps. DTMs also do photogrammetric in a manner based on stereo pair images (paired images of the same territory, taken from different angles) obtained from satellites or during 3–3–369. aerial photography . In addition, there is air technology laser scanning , allowing to determine the height of the surface.

Digital elevation model SRTM

A shot of Onekotan from the International Space Station. Photo from the site flickr.com

The main advantage of radar imagery is its independence from the time of day and weather conditions. With its help, you can get an image of the earth's surface, even with continuous cloudiness. And if you conduct a radar survey from space, then you can get very quickly, in a matter of days, global coverage data. But to measure surface heights, just a radar image is not enough. For this, a special shooting technology is used - the radar 3-3-399. interferometry 3-3-3184. . Its essence lies in the fact that shooting is carried out immediately by two antennas located at a distance from each other. It turns out immediately two images. Based on the differences between these images, the surface height is calculated. Moreover, if there are any towering objects above the surface (for example, a forest or buildings), then their height will be determined, and not the height of the surface below them. Therefore, the SRTM is called a digital elevation model with a certain degree of conventionality. The expression “digital surface model” would be more accurate, but it is used much less frequently. This applies to any DEMs that are created on the basis of remote images of the Earth (see 3-3-3011. Remote sensing of the Earth 3-3-3184.), Both radar and stereo pairs of optical images. To create a DEM containing only surface heights, you need to use ground surveying. And for airborne laser scanning data, there are methods that allow you to separate measurements taken from the surface of the earth and from superficial objects.

On the space shuttle Endeavor, the technology of radar interferometry was implemented as follows. One antenna was located inside the Endeavor - in its cargo compartment. And the second was located outside - at the end of a sliding metal trusses . This farm had 87 sections and a length of 6095 m. For 2000 it was a record. Such a long rigid construction had never been launched into space.

Digital elevation model SRTM

Illustration showing Endeavor in orbit at an altitude of about 233 km above the Earth. The Earth's surface was scanned by an antenna in the cargo compartment of the shuttle and an antenna at the end of a metal truss at a distance of about 61 m from the shuttle. Image from commons.wikimedia.org

The Endeavor survey covered the entire terrestrial land, except for the polar and circumpolar regions located north of 60 ° north latitude and south of 56 ° south latitude (such coverage was predetermined by the shape of the Endeavor’s orbit). 12 terabytes of data were captured, which is approximately equal to the volume of Libraries of Congress 3-3-3184. USA. After ground processing, a DEM was obtained with a pixel size of 1 arc second longitude (approximately 30 m). Subsequently, these initial SRTM data were modified several times. Trimming along the coastline of the continents, leveling of the surface of water bodies of the land, correction of the found errors of heights was carried out. The current version of SRTM is the fourth in a row.

In the main image, strictly speaking, it is not the SRTM data itself that is shown, but the derivative product made on their basis - a perspective image of a three-dimensional surface, painted according to the height values. This is a bitmap whose pixels contain the value absolute height (DEM). Such a raster is called a digital elevation model. In Russian, the DEM abbreviation is accepted for it, and in English - DEM (3-3-3139. Digital elevation model 3-3-3184.).

Digital elevation model SRTM

SRTM source data view with height scale. The data source is the site earthexplorer.usgs.gov

Various DEMs are mainly used in 3-3-3161. geomorphology , geology, geoinformatics . In addition, they are used in environmental studies, where the topography is considered as an important environmental factor. DTMs are also used in spatial planning and civil engineering surveys. DTMs allow not only to visualize a relief in the form of three-dimensional surfaces (as in the main image) or in a flat two-dimensional form (as on topographic maps) - with the help of DTMs, various are calculated. morphometric elevation parameters, such as slope surface, exposure 3-3-3184. and curvature of the slopes. Based on the DEM, visibility zones are constructed (territories that are visible from the selected observation point, taking into account the relief), the volume of embankments and 3–3–3171 are calculated. notches 3-3-3184. , the paths of water runoff over the surface are determined and catchment areas stand out.

To date, the SRTM model is one of the most popular DTMs. This is due not only to its extensive territorial coverage, but also to accessibility for a wide range of users. SRTM data is distributed free of charge. Everyone can download them on the Internet, for example on the website earthexplorer.usgs.gov which belongs to US Geological Survey 3-3-3184. (USGS). For the convenience of downloading, SRTM is not laid out there entirely, but cut into rectangular fragments the size of one degree of latitude by one degree of longitude.

Image created using the site. earthexplorer.usgs.gov and programs. QGIS .

Pavel Ukrainian

22 май 2020 /
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