Advanced Spaceborne Thermal Emission and Reflection Radiometer

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is a Japanese sensor which is one of five remote sensory devices on board the Terra satellite launched into Earth orbit by NASA in 1999. The instrument has been collecting data since February 2000.

Rub' al Khali (Arabian Empty Quarter) sand dunes imaged by Terra (EOS AM-1)
ASTER image of Rub' al Khali (Arabia's Empty Quarter)

ASTER provides high-resolution images of the planet Earth in 14 different bands of the electromagnetic spectrum, ranging from visible to thermal infrared light. The resolution of images ranges between 15 and 90 meters. ASTER data are used to create detailed maps of surface temperature of land, emissivity, reflectance, and elevation.

In April 2008, the SWIR detectors of ASTER began malfunctioning and were publicly declared non-operational by NASA in January 2009. All SWIR data collected after 1 April 2008 has been marked as unusable.[1]

The ASTER Global Digital Elevation Model (GDEM) is available at no charge to users worldwide via electronic download.[2]

As of 2 April 2016, the entire catalogue of ASTER image data became publicly available online at no cost.[3] It can be downloaded with a free registered account from either NASA's Earth Data Search delivery system[4] or from the USGS Earth Explorer delivery system.[5]

Etna TAS2002209
ASTER image draped over terrain model of Mount Etna


2010 Eruption at Mount Merapi, Indonesia (ASTER)
ASTER false-colour satellite image of 2010 eruption of Mount Merapi, showing evidence of a large pyroclastic flow along the Gendol River south of Mount Merapi
Band Label Wavelength
Nadir or
B1 VNIR_Band1 0.520 - 0.60 15 Nadir Visible green/yellow
B2 VNIR_Band2 0.630 - 0.690 15 Nadir Visible red
B3N VNIR_Band3N 0.760–0.860 15 Nadir Near infrared
B3B VNIR_Band3B 0.760–0.860 15 Backward
B4 SWIR_Band4 1.600–1.700 30 Nadir Short-wave infrared
B5 SWIR_Band5 2.145–2.185 30 Nadir
B6 SWIR_Band6 2.185–2.225 30 Nadir
B7 SWIR_Band7 2.235–2.285 30 Nadir
B8 SWIR_Band8 2.295–2.365 30 Nadir
B9 SWIR_Band9 2.360–2.430 30 Nadir
B10 TIR_Band10 8.125–8.475 90 Nadir Long-wave infrared
or thermal IR
B11 TIR_Band11 8.475–8.825 90 Nadir
B12 TIR_Band12 8.925–9.275 90 Nadir
B13 TIR_Band13 10.250–10.950 90 Nadir
B14 TIR_Band14 10.950–11.650 90 Nadir


ASTER Global Digital Elevation Model

Comparison SRTM3 vs ASTER
SRTM3 vs. ASTER comparison (Île d'Yeu), inaccuracies and errors of the latter are indicated by arrows

Version 1

On 29 June 2009, the Global Digital Elevation Model (GDEM) was released to the public.[7][8] A joint operation between NASA and Japan's Ministry of Economy, Trade and Industry (METI), the Global Digital Elevation Model is the most complete mapping of the earth ever made, covering 99% of its surface.[9][10] The previous most comprehensive map, NASA's Shuttle Radar Topography Mission, covered approximately 80% of the Earth's surface,[11] with a global resolution of 90 meters,[12] and a resolution of 30 meters over the USA. The GDEM covers the planet from 83 degrees North to 83 degrees South (surpassing SRTM's coverage of 56 °S to 60 °N), becoming the first earth mapping system that provides comprehensive coverage of the polar regions.[11] It was created by compiling 1.3 million VNIR images taken by ASTER using single-pass[13] stereoscopic correlation techniques,[7] with terrain elevation measurements taken globally at 30-meter (98 ft) intervals.[9]

Despite the high nominal resolution, however, some reviewers have commented that the true resolution is considerably lower, and not as good as that of SRTM data, and serious artifacts are present.[14][15]

Some of these limitations have been confirmed by METI and NASA, who point out that the current version of the GDEM product is "research grade".[16]

Penang island.stl
STL 3D model of Penang Island terrain based on ASTER Global DEM data

Version 2

During October 2011, version 2 of Global Digital Elevation Model was publicly released.[17] This is considered an improvement upon version 1. These improvements include increased horizontal and vertical accuracy,[18] better horizontal resolution, reduced presence of artifacts, and more realistic values over water bodies.[2] However, one reviewer still regards the Aster version 2 dataset, although showing 'a considerable improvement in the effective level of detail', to still be regarded as 'experimental or research grade' due to presence of artefacts.[19] A 2014 study[18] showed that over rugged mountainous terrain the ASTER version 2 data set can be a more accurate representation of the ground than the SRTM elevation model.

See also


  1. ^
  2. ^ a b "METI and NASA Release Version 2 ASTER Global DEM". U.S. Geological Survey / NASA LP DAAC. Retrieved 21 December 2013.
  3. ^
  4. ^
  5. ^
  6. ^
  7. ^ a b "ASTER Global Digital Elevation Map". NASA. 29 June 2009. Archived from the original on 3 July 2009. Retrieved 2009-06-30.
  8. ^ "ASTER Imagery". NASA. 29 June 2009. Retrieved 2009-06-30.
  9. ^ a b "Most complete earth map published". BBC News. 30 June 2009. Retrieved 2009-07-01.
  10. ^ "Nasa satellite map reveals 99% of Earth's land surface for first time". Daily Mail. 1 July 2009. Retrieved 2009-07-01.
  11. ^ a b "NASA, Japan publish detailed map of Earth". 30 June 2009. Archived from the original on 4 July 2009. Retrieved 1 July 2009.
  12. ^ "What is ASTER?". Archived from the original on 27 April 2009. Retrieved 1 July 2009.
  13. ^ Nikolakopoulos, K. G.; Kamaratakis, E. K; Chrysoulakis, N. (10 November 2006). "SRTM vs ASTER elevation products. Comparison for two regions in Crete, Greece" (PDF). International Journal of Remote Sensing. 27 (21): 4819–4838. Bibcode:2006IJRS...27.4819N. doi:10.1080/01431160600835853. ISSN 0143-1161. Archived from the original (PDF) on 21 July 2011. Retrieved 1 July 2009.
  14. ^ "Virtual Earth Products Reviews". Archived from the original on 31 May 2009. Retrieved 2009-07-01.
  15. ^ Hirt, C.; Filmer, M.S.; Featherstone, W.E. (2010). "Comparison and validation of recent freely-available ASTER-GDEM ver1, SRTM ver4.1 and GEODATA DEM-9S ver3 digital elevation models over Australia". Australian Journal of Earth Sciences. 57 (3): 337–347. Bibcode:2010AuJES..57..337H. doi:10.1080/08120091003677553. Retrieved 5 May 2012.
  16. ^ "METI and NASA Release ASTER Global DEM". Archived from the original on 29 May 2009. Retrieved 2009-07-01.
  17. ^ "Release of ASTER GDEM Version 2". Archived from the original on 29 May 2009.
  18. ^ a b Rexer, M.; Hirt, C. (2014). "Comparison of free high-resolution digital elevation data sets (ASTER GDEM2, SRTM v2.1/v4.1) and validation against accurate heights from the Australian National Gravity Database" (PDF). Australian Journal of Earth Sciences. 61 (2): 213. Bibcode:2014AuJES..61..213R. doi:10.1080/08120099.2014.884983. Archived from the original (PDF) on 7 June 2016. Retrieved 24 April 2014.
  19. ^ de Ferranti, Jonathan. "ASTER Digital Elevation Data". Viewfinder Panoramas, UK. Retrieved 21 December 2013.

External links

2006 Southern Leyte mudslide

On February 17, 2006, a massive rock slide-debris avalanche occurred in the Philippine province of Southern Leyte, causing widespread damage and loss of life. The deadly landslide (or debris flow) followed a 10-day period of heavy rain and a minor earthquake (magnitude 2.6 on the Richter scale). The official death toll was 1,126.

Diavik Diamond Mine

The Diavik Diamond Mine is a diamond mine in the North Slave Region of the Northwest Territories, Canada, about 300 kilometres (190 mi) northeast of Yellowknife.

Digital elevation model

A digital elevation model (DEM) is a 3D CG representation of a terrain's surface – commonly of a planet (e.g. Earth), moon, or asteroid – created from a terrain's elevation data. A "global DEM" refers to a Discrete Global Grid.


GTOPO30 is a digital elevation model for the world, developed by United States Geological Survey (USGS). It has a 30-arc second resolution (approximately 1 km), and is split into 33 tiles stored in the USGS DEM file format.

Index of physics articles (A)

The index of physics articles is split into multiple pages due to its size.

To navigate by individual letter use the table of contents below.

List of GIS data sources

This is a list of GIS data sources (including some geoportals) that provide information sets that can be used in geographic information systems (GIS) and spatial databases for purposes of geospatial analysis and cartographic mapping. This list categorizes the sources of interest.

Multispectral pattern recognition

Multispectral remote sensing is the collection and analysis of reflected, emitted, or back-scattered energy from an object or an area of interest in multiple bands of regions of the electromagnetic spectrum (Jensen, 2005). Subcategories of multispectral remote sensing include hyperspectral, in which hundreds of bands are collected and analyzed, and ultraspectral remote sensing where many hundreds of bands are used (Logicon, 1997). The main purpose of multispectral imaging is the potential to classify the image using multispectral classification. This is a much faster method of image analysis than is possible by human interpretation.

The Iterative Self-Organizing Data Analysis Technique (ISODATA) algorithm used for Multispectral pattern recognition was developed by Geoffrey H. Ball and David J. Hall, working in the Stanford Research Institute in Menlo Park, CA. They published their findings in a technical report entitled: ISODATA, a novel method of data analysis and pattern classification (Stanford Research Institute, 1965). ISODATA is defined in the abstract as: 'a novel method of data analysis and pattern classification, is described in verbal and pictorial terms, in terms of a two-dimensional example, and by giving the mathematical calculations that the method uses. The technique clusters many-variable data around points in the data's original high- dimensional space and by doing so provides a useful description of the data.' (1965, pp v.)ISODATA was developed to facilitate the modelling and tracking of weather patterns.

NASA WorldWind

WorldWind is an open-source (released under the NOSA license) virtual globe. It was first developed by NASA in 2003 for use on personal computers and then further developed in concert with the open source community since 2004. As of 2017, a web based version of WorldWind is available online. An Android version is also available.The original version relied on .NET Framework, which ran only on Microsoft Windows. The more recent Java version, WorldWind Java, is cross platform, a software development kit (SDK) aimed at developers and, unlike the old .NET version, not a standalone virtual globe application in the style of Google Earth. The SDK includes a suite of basic demos, available at The WorldWind Java version was awarded NASA Software of the Year in November 2009. The program overlays NASA and USGS satellite imagery, aerial photography, topographic maps, Keyhole Markup Language (KML) and Collada files.

Remote sensing (geology)

Remote sensing in geology is remote sensing used in the geological sciences as a data acquisition method complementary to field observation, because it allows mapping of geological characteristics of regions without physical contact with the areas being explored. About one-fourth of the Earth’s total surface area is exposed land where information is ready to be extracted from detailed earth observation via remote sensing. Remote sensing is conducted via detection of electromagnetic radiation by sensors. The radiation can be naturally sourced (passive remote sensing), or produced by machines (active remote sensing) and reflected off of the Earth surface. The electromagnetic radiation acts as an information carrier for two main variables. First, the intensities of reflectance at different wavelengths are detected, and plotted on a spectral reflectance curve. This spectral fingerprint is governed by the physio-chemical properties of the surface of the target object and therefore helps mineral identification and hence geological mapping, for example by hyperspectral imaging. Second, the two-way travel time of radiation from and back to the sensor can calculate the distance in active remote sensing systems, for example, Interferometric synthetic-aperture radar. This helps geomorphological studies of ground motion, and thus can illuminate deformations associated with landslides, earthquakes, etc.Remote sensing data can help studies involving geological mapping, geological hazards and economic geology (i.e., exploration for minerals, petroleum, etc.). These geological studies commonly employ a multitude of tools classified according to short to long wavelengths of the electromagnetic radiation which various instruments are sensitive to. Shorter wavelengths are generally useful for site characterization up to mineralogical scale, while longer wavelengths reveal larger scale surface information, e.g. regional thermal anomalies, surface roughness, etc. Such techniques are particularly beneficial for exploration of inaccessible areas, and planets other than Earth. Remote sensing of proxies for geology, such as soils and vegetation that preferentially grows above different types of rocks, can also help infer the underlying geological patterns. Remote sensing data is often visualized using Geographical Information System (GIS) tools. Such tools permit a range of quantitative analyses, such as using different wavelengths of collected data sets in various Red-Green-Blue configurations to produce false color imagery to reveal key features. Thus, image processing is an important step to decipher parameters from the collected image and to extract information.

Ring ditch

In archaeology, a ring ditch is a trench of circular or penannular plan, cut into bedrock. They are usually identified through aerial photography either as soil marks or cropmarks. When excavated, ring ditches are usually found to be the ploughed‐out remains of a round barrow where the barrow mound has completely disappeared, leaving only the infilled former quarry ditch. Both Neolithic and Bronze Age ring ditches have been discovered.

The term is most often used as a generic description in cases where there is no clear evidence for the function of the site: for instance where it has been ploughed flat and is known only as a cropmark or a geophysical anomaly. The two most frequent monument types represented by ring ditches are roundhouses (where the 'ditch' is actually a foundation slot or eaves drip gully) and round barrows. The term is not normally used for larger features than these. Larger features would instead be described as 'circular enclosures'.

Also related to ring ditches, is the causewayed ring ditch, which is a roughly circular ditch with a central area and multiple causeways which cross it. The causewayed ring ditch is a subcategory of the ring ditch.

Satellite imagery

Satellite imagery (also Earth observation imagery or spaceborne photography) are images of Earth or other planets collected by imaging satellites operated by governments and businesses around the world. Satellite imaging companies sell images by licensing them to governments and businesses such as Apple Maps and Google Maps.

Shuttle Radar Topography Mission

The Shuttle Radar Topography Mission (SRTM) is an international research effort that obtained digital elevation models on a near-global scale from 56°S to 60°N, to generate the most complete high-resolution digital topographic database of Earth prior to the release of the ASTER GDEM in 2009. SRTM consisted of a specially modified radar system that flew on board the Space Shuttle Endeavour during the 11-day STS-99 mission in February 2000, based on the older Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar (SIR-C/X-SAR), previously used on the Shuttle in 1994. To acquire topographic data, the SRTM payload was outfitted with two radar antennas. One antenna was located in the Shuttle's payload bay, the other – a critical change from the SIR-C/X-SAR, allowing single-pass interferometry – on the end of a 60-meter (200-foot) mast that extended from the payload bay once the Shuttle was in space. The technique employed is known as interferometric synthetic aperture radar. Intermap Technologies was the prime contractor for processing the interferometric synthetic aperture radar data.

The elevation models are arranged into tiles, each covering one degree of latitude and one degree of longitude, named according to their south western corners. For example, "n45e006" stretches from 45°N 6°E to 46°N 7°E and "s45w006" from 45°S 6°W to 44°S 5°W. The resolution of the raw data is one arcsecond (30 m along the equator) and coverage includes Africa, Europe, North America, South America, Asia, and Australia. A derived one arcsecond dataset with trees and other non-terrain features removed covering Australia was made available in November 2011; the raw data are restricted for government use. For the rest of the world, only three arcsecond (90 m along the equator) data are available. Each one arcsecond tile has 3,601 rows, each consisting of 3,601 16 bit bigendian cells. The dimensions of the three arcsecond tiles are 1201 x 1201. The original SRTM elevations were calculated relative to the WGS84 ellipsoid and then the EGM96 geoid separation values were added to convert to heights relative to the geoid for all the released products.The elevation models derived from the SRTM data are used in geographic information systems. They can be downloaded freely over the Internet, and their file format (.hgt) is widely supported.

The Shuttle Radar Topography Mission is an international project spearheaded by the U.S. National Geospatial-Intelligence Agency (NGA) and the U.S. National Aeronautics and Space Administration (NASA). NASA transferred the SRTM payload to the Smithsonian National Air and Space Museum in 2003; the canister, mast, and antenna are now on display at the Steven F. Udvar-Hazy Center in Chantilly, Virginia.

Terra (satellite)

Terra (EOS AM-1) is a multi-national NASA scientific research satellite in a Sun-synchronous orbit around the Earth. It is the flagship of the Earth Observing System (EOS). The name "Terra" comes from the Latin word for Earth. A naming contest was held by NASA among U.S. high school students. The winning essay was submitted by Sasha Jones of Brentwood, Missouri. The identifier "AM-1" refers to its orbit, passing over the equator in the morning.

Thermal Emission Imaging System

The Thermal Emission Imaging System (THEMIS) is a camera on board the 2001 Mars Odyssey orbiter. It images Mars in the visible and infrared parts of the electromagnetic spectrum in order to determine the thermal properties of the surface and to refine the distribution of minerals on the surface of Mars as determined by the Thermal Emission Spectrometer (TES). Additionally, it helps scientists to understand how the mineralogy of Mars relates to its landforms, and it can be used to search for thermal hotspots in the Martian subsurface.

THEMIS is managed from the Mars Space Flight Facility at Arizona State University and was built by the Santa Barbara Remote Sensing division of Raytheon. The instrument was named after the Greek goddess of justice.

Trou au Natron

Trou au Natron (French: "hole of natron") or Doon Orei (Teda: "big hole") is a volcanic caldera of the Tibesti Massif in the nation of Chad in Northern Africa. The volcano is extinct. It is unknown when it last erupted. Its volcano number is 0205–01. Trou au Natron is located just south-east of Toussidé, the westernmost volcano of the Tibesti Mountains. Its edge cuts into the nearby Yirrigue caldera.

The caldera sits at an elevation of 2,450 m (8,040 ft). It has an irregular diameter of approximately 6–8 km (4–5 mi) and is up to 1,000 m (3,300 ft) deep. Four smaller volcanic cones, made of scoria or andesitic tuff sit on the floor of the caldera. Numerous smaller vents and hot springs on the caldera's floor emit hot steam and mineral water.Because of its irregular shape, it has been theorized that the caldera was formed as a result of multiple massive explosions, each of which deepened the enormous pit. During these explosions, chunks of debris up to 5 m3 (180 cu ft) in size may have been hurled up to 10 km (6.2 mi) from the crater. Its exact period of formation is unconfirmed, although a Pleistocene formation has been suggested. It is known to be one of the youngest formations on the Tibesti Massif.


UNIFORM-1 or University International Formation Mission is a Japanese micro-satellite launched in 2014. The satellite is built around a wildfire detection camera and features the following instruments:

Microbolometer infrared camera with resolution 200m and swath width 100 km.

visible-light camera to assist in wildfire detectionAll instruments are powered by solar cells mounted on the spacecraft body and stub wings, with estimated electrical power of over 100W.


The visible and near-infrared (VNIR) portion of the electromagnetic spectrum has wavelengths between approximately 400 and 1400 nanometers (nm). It combines the full visible spectrum with an adjacent portion of the infrared spectrum up to the water absorption band between 1400 and 1500 nm.

Some definitions also include the short-wavelength infrared band from 1400 nm up to the water absorption band at 2500 nm.

VNIR multi-spectral image cameras have wide applications in remote sensing and imaging spectroscopy.Hyperspectral Imaging Satellite carried two VNIR instruments


Volcanology (also spelled vulcanology) is the study of volcanoes, lava, magma, and related geological, geophysical and geochemical phenomena. The term volcanology is derived from the Latin word vulcan. Vulcan was the ancient Roman god of fire.

A volcanologist is a geologist who studies the eruptive activity and formation of volcanoes, and their current and historic eruptions. Volcanologists frequently visit volcanoes, especially active ones, to observe volcanic eruptions, collect eruptive products including tephra (such as ash or pumice), rock and lava samples. One major focus of enquiry is the prediction of eruptions; there is currently no accurate way to do this, but predicting eruptions, like predicting earthquakes, could save many lives.

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