Glossary

Some of the glossary was modified by NASA from the Virtual Nebraska web pages at http://www.scasde.unl.edu/vn/glossary/introfr.htm and can also be found at http://growsmart.gsfc.nasa.gov/glossary.html , NASA’s Educational Resource site for the Investigation of Urban Sprawl and Land Cover Change.

A-I | J-R | S-Z

Absorption: The process in which radiant energy is retained by a substance. A further process always results from absorption, that is, the irreversible conversion of the absorbed radiation into some other form of energy within and according to the nature of the absorbing medium. The absorbing medium itself may emit radiation, but only after an energy conversion has occurred.

Bandwidth: The total range of frequency required to pass a specific modulated signal without distortion or loss of data. The ideal bandwidth allows the signal to pass under conditions of maximum AM or FM adjustment. (Too narrow a bandwidth will result in loss of data during modulation peaks. Too wide a bandwidth will pass excessive noise along with the signal.) In FM, radio frequency signal bandwidth is determined by the frequency deviation of the signal.

Barrier: an environment that prevents or impedes the dispersal of a species from one location to another. A fast moving river may serve as a barrier for species that cannot fly or swim.

Canopy: The top layer of a forest formed naturally by the leaves and branches of trees and plants.

Census: It is the collection, compiling, and dissemination of demographic, economic, and social data pertaining to people living within a defined space at a specified time.

Choropleth map: It is a thematic map displaying data by area.  Color or shade intensities proportional to the magnitudes of values in given areas are used to map data.

Color Composites Images: The human eye is not sensitive to ultra-violet or infrared light. To build a composite image from remote sensing data that makes sense to our eyes, we must use colors from the visible portion of the EM spectrum–red, green, and blue. Three-band composites are created by using the measured reflected energy in each of three Landsat Thematic Mapper (TM) spectral bands to control the amount of blue, green, and red in a color output image. The way in which the seven TM bands are mapped to the three colors in the output image depends on what information is desired to be highlighted in the image. For some applications, it may be desirable that land cover classes be associated with familiar colors, e.g., grass is green. In other cases, contrasting colors are preferred to highlight objects of interest from the background. We give three examples of commonly used band combinations and describe how different features appear in each.

Note: The specific bands used in three-band composites are often identified by giving the band numbers used for red, green, and blue, respectively. Thus, an image using band seven for red, band four for green, and band two for blue would be designated (7,4,2). This unit uses the same convention.

Community: a collection of species that live in close proximity to one another, share the same habitat, or live in the same region.

Connectivity: the degree to which patches of habitat are linked to one another. It is easy for individuals to travel between patches that display a high degree of connectivity; perhaps because the patches are connected by corridors. Patches that are separated from one another have a low connectivity.

Core area: the central portion of a habitat patch; the core is surrounded by similar habitat, and is away from the edge of a patch.

Corridor: a connection between two patches of habitat that allows for the safe travel of individuals between the patches. The Isthmus of Panama served as a corridor between North and South America for many species of mammal; a hedgerow may serve as a corridor between forests for species that live in forest habitat.

Cosmopolitan: an adjective that describes a species that is widely dispersed; describes a species that is found all over the world, or has a wide range. See also pandemic.

Digital image: An analog image converted to numerical form so that it can be stored and used in a computer. The image is divided into a matrix of small regions called picture elements or pixels. At sub-satellite point each pixel represents a specific amount of area. For example, in Landsat each pixel represents 30 meters. Each pixel has a numerical value or data number value, quantifying the radiance of the image at that spot. The data number value of each pixel usually represents a value between black and white, i.e., shades of gray.

Dispersal: the movement of organisms to new locations, away from their parents. For example, dandelions disperse using seeds that catch the wind, while thistles will disperse by catching in the fur of a passing mammal. Animals tend to have an excellent capacity for dispersal, because they typically are able to walk, fly or swim to a new location.

Ecosystem: a community of species and their physical environment. For example, a river ecosystem would include the fish, insects, plants, water, and sediment found in a river.

Edge: the outer boundary of a habitat patch.

Edge effect: a condition in which otherwise suitable habitat becomes less suitable for a species because it is adjacent to non-habitat land. This degradation of habitat may occur due to predation from species that live outside of the patch, or increased competition with species that live outside the habitat patch.

Electromagnetic radiation: Energy propagated as time-varying electric and magnetic fields. These two fields are inextricably linked as a single entity since time-varying electric fields produce time-varying magnetic fields and vice versa. Light and radar are examples of electromagnetic radiation differing only in their wavelengths (or frequency). Electric and magnetic fields propagate through space at the speed of light.

Electromagnetic spectrum: The entire ranges of radiant energies or waves frequencies from the longest to the shortest wavelengths--the categorization of solar radiation. Satellite sensors collect this energy, but what the detectors capture is only a small portion of the entire electromagnetic spectrum. The spectrum usually is divided into seven sections: radio, microwave, infrared, visible, ultraviolet, x-ray, and gamma-ray radiation.

Endemic, endemism: an adjective that describes species that occur only in a limited number of places. For example, the _______ is endemic to the Chesapeake Bay because it is only found in this one region of the world.

Extirpation: a process or condition in which a population has gone extinct from a particular patch of suitable habitat, or has been driven away from a region. In order for this region to support another population, it must be recolonized.

Exotic species: a recently introduced species, or a species that is living in a location that is outside of its 'normal' or historical range.

False color or false color composite image: Used to interpret radiance measurements in infrared portion of the EM spectrum, we assign colors to the bands of interest and then combine them into a "false color" composite image.

Fragmentation: the process whereby a large patch of habitat is broken down into many smaller patches of habitat, resulting in a loss in the amount and quality of habitat.

Geographic Information System (GIS): A system for archiving, retrieving, and manipulating data that has been stored and indexed according to the geographic coordinates of its elements. The system generally can utilize a variety of data types, such as imagery, maps. table, etc.

Geostationary: Describes an orbit in which a satellite is always in the same position (appears stationary) with respect to the rotating Earth. The satellite travels around the Earth in the same direction, at an altitude of approximately 35,790 km (22,240 statute miles) because that produces an orbital period equal to the period of rotation of the Earth (actually 23 hours, 56 minutes, 04.09 seconds).

Global Change Research Program (GCRP) The USGCRP is a government-wide program whose goal is "to establish a scientific basis for national and international policy-making relating to natural and human-induced changes in the global Earth system." The Global Change Research Program coordinates and guides the efforts of federal agencies. The program examines such questions as, is the Earth experiencing global warming? Is the depletion of the ozone layer expanding? How do we determine and understand the causes of global climate changes? Are they reversible? What are the implications for human needs and activities?

Global Learning and Observations to Benefit the Environment (GLOBE): is a worldwide network of students, teachers, and scientists working together to study and understand the global environment. Students and teachers from over 7,000 schools in more than 80 countries are working with research scientists to learn more about our planet.

Grayscale: Environmental satellite scanners, rather than photographing a scene, scan a scene line-by-line measuring light or heat levels and transmitting this information as a video image via an amplitude modulated (AM) sub carrier contained in the satellite's FM signal. The video image--a 2400 Hz tone--is amplitude modulated to correspond to the light and dark areas sensed, with the louder portion of the tone representing the lighter areas of the image and the lower portion of the tone representing the darker areas of the image. Intermediate volumes form the shades of the gray scale (up to 256 shades) needed to complete the image. This is an analog type of data transmission, and enables the assessment of such features as heat, light, temperature, and cloud heights.

Ground Validation: information collected at the same site that a remote sensing system collects the data. Ground validation data are used to interpret, accuracy access and calibrate remotely sensed observations.

Habitat: areas that meet the environmental requirements of a species.

Home range: the region in which an individual lives. See also range.

Image: Pictorial representation of data acquired by satellite systems, such as direct readout images from environmental satellites. An image is not a photograph. An image is composed of two-dimensional grids of individual picture elements (pixels). Each pixel has a numeric value that corresponds to the radiance or temperature of the specific ground area it depicts. See gray scale.

Image resolution: The area represented by each pixel of a satellite image. The smaller the area represented by a pixel, the more accurate and detailed the image. For example, if a U.S. map and a world map are printed on identically sized sheets of paper, one square inch on the U.S. map will represent far less area and provide for more detail than one square inch on the world map. In this example the U.S. map has higher resolution. Landsat satellites have a resolution of 30 meters, AVHRR has a resolution of 1 km and Spot resolution is 10 meters.

Imperviousness: The inability of a surface, such as those covered by asphalt or concrete, to allow water to infiltrate into the underlying soil.

Individual: a single plant or animal; a separate organism.

Infrared radiation (IR): Infrared is electromagnetic radiation whose wavelength spans the region from about 0.7 to 1000 micrometers (longer than visible radiation, shorter than microwave radiation). Remote sensing instruments work by sensing radiation that is naturally emitted or reflected by the Earth's surface or from the atmosphere, or by sensing signals transmitted from a satellite and reflected back to it. In the visible and near-infrared regions, surface chemical composition, vegetation cover, and biological properties of surface matter can be measured. In the mid-infrared region, geological formations can be detected due to the absorption properties related to the structure of silicates. In the far infrared, emissions from the Earth's atmosphere and surface offer information about atmospheric and surface temperatures and water vapor and other trace constituents in the atmosphere. Since IR data are based on temperatures rather than visible radiation, the data may be obtained day or night.

Introduction: to establish a population in a new location where it has never before existed.

IR See infrared.

Landsat Land Remote-Sensing Satellite, operated by the U.S. Earth Observation Satellite Company (EOSAT). Commercialized under the Land Remote-Sensing Commercialization Act of 1984, Landsat is a series of satellites (formerly called ERTS) designed to gather data on the Earth's resources in a regular and systematic manner. Objectives of the mission are: land use inventory, geological/mineralogical exploration, crop and forestry assessment, and cartography. Landsat has a spatial resolution of 28.5 meters.

Restructured Federal agency responsibilities for the Landsat program are effective for the acquisition and operation of Landsat 7. New operating policy specifies that NOAA will be responsible for satellites after they are placed in orbit, NASA will be responsible for the development and launch of Landsat 7, and that the U.S. government will provide unenhanced data to users at no cost beyond the cost of fulfilling their data request.

Latitude (AKA the geodetic latitude): The angle between a perpendicular at a location, and the equatorial plane of the Earth.

Light: 1. Form of radiant energy that acts upon the retina of the eye, optic nerve, etc., making sight possible. This energy is transmitted at a velocity of about 186,000 miles per second by wavelike or vibrational motion. 2. A form of radiant energy similar to this, but not acting on the normal retina, such as ultraviolet and infrared radiation.

Interplay between light rays and the atmosphere cause us to see the sky as blue, and can result in such phenomena as glows, halos, arcs, flashes, and streamers.

Longitude: The angular distance from the Greenwich meridian (0 degree), along the equator. This can be measured either east or west to the 180th meridian (180 degrees) or 0 degree to 360 degrees W.

Middle infrared: Electromagnetic radiation between the near infrared and the thermal infrared, about 2-5 micrometers.

MultiSpec: MultiSpec is being developed at Purdue University, West Lafayette, IN, by David Landgrebe and Larry Biehl from the School of Electrical and Computer Engineering and LARS. It results from an on-going multiyear research effort that is intended to define robust and fundamentally based technology for analyzing multispectral and hyperspectral image data.

National Aerial Photography Program (NAPP) was a program to photograph the entire United States in infrared and black and white photography. The US Geological Survey sponsored this effort.

NASA See National Aeronautics and Space Administration

NASA Centers The ten major NASA Centers are:

• Ames Research Center (ARC): Located at Moffett Field, California. ARC is active in aeronautical research, life sciences, space science, and technology research. The Center houses the world's largest wind tunnel and the world's most powerful supercomputer system.

• The Dryden Flight Research Center: Edwards Air Force Base, California, formerly part of ARC, became a separate entity March 1994. Since the 1940s, this Mojave Desert site has been a testing ground for high-performance aircraft and is one of two prime landing sites for the Space Shuttle.

• Goddard Space Flight Center (GSFC): Goddard was NASA's first major scientific laboratory devoted entirely to the exploration of space. Located in Greenbelt, Maryland, GSFC's responsibilities include design and construction of new scientific and applications satellites, as well as tracking and communication with existing satellites in orbit. GSFC is the lead center for the Earth Observing System, a key element of Mission to Planet Earth. GSFC also directs operations at the Wallops Flight Facility on Wallops Island, Virginia, which each year launches some 50 scientific missions to sub-orbital altitudes on small sounding rockets.

• Jet Propulsion Laboratory (JPL): Located in Pasadena, California, JPL is operated under contract to NASA by the California Institute of Technology. Its primary focus is the scientific study of the solar system, including exploration of the planets with automated probes. Most of the lunar and planetary spacecraft of the 1960s and 1970s were developed at JPL. JPL also is the control center for the worldwide Deep Space Network, which tracks all planetary spacecraft.

• Lyndon B. Johnson Space Center (JSC): Johnson Space Center, located between Houston and Galveston, Texas, is the lead center for NASA's manned space flight program. JSC has been Mission Control for all piloted space flights since 1965, and now manages the Space Shuttle program. JSC's responsibilities include selecting and training astronauts; designing and testing vehicles and other systems for piloted space flight; and planning and executing space flight missions. The center has a major role in developing the Space Station. In addition, JSC directs operations at the White Sands Test Facility in New Mexico, which conducts Shuttle-related tests. The nearby White Sands Missile Range also serves as a backup-landing site for the Space Shuttle.

• Kennedy Space Center (KSC): Located near Cape Canaveral, Florida, KSC is NASA's primary launch site. The Center handles the preparation, integration, checkout, and launch of space vehicles and their payloads. All piloted space missions since the Mercury program have been launched from here, including Gemini, Apollo, Skylab, and Space Shuttle flights. KSC is the Shuttle's home port, where orbiters are serviced and outfitted between missions, and then assembled into a complete Shuttle "stack" before launch. The Center also manages the testing and launch of unpiloted space vehicles from an array of launch complexes, and conducts research programs in areas of life sciences related to human spaceflight.

• Langley Research Center (LaRC): Oldest of NASA's field centers, LaRC is located in Hampton, Virginia, and focuses primarily on aeronautical research. Established in 1917 by the National Advisory Committee for Aeronautics, the Center currently devotes two-thirds of its programs to aeronautics, and the rest to space. LaRC researchers use more than 40 wind tunnels to study improved aircraft and spacecraft safety, performance, and efficiency.

• Lewis Research Center (LeRC): Lewis Research Center, located outside Cleveland, Ohio, conducts a varied program of research in aeronautics and space technology. Aeronautical research includes work on advanced materials and structures for aircraft. Space-related research focuses primarily on power and propulsion. Another significant area of research is in energy and power sources for spacecraft, including the Space Station, for which LeRC is developing the largest space power system ever designed.

• George C. Marshall Space Flight Center (MSFC): The MSFC, located in Huntsville, Alabama, is responsible for developing spacecraft hardware and systems, and is perhaps best known for its role in building the Saturn rockets that sent astronauts to the Moon during the Apollo program. It is NASA's primary center for space propulsion systems and plays a key role in the development of payloads to be flown on the shuttle (such as Spacelab). MSFC also manages two other NASA sites: the Michoud Assembly Facility in New Orleans where the Shuttle's external tanks are manufactured, and the Slidell Computer Complex in Slidell, Louisiana, which provides computer support to Michoud and to NASA's John C. Stennis Space Center.

• John C. Stennis Space Center (SSC): This Center, located on Mississippi's Gulf Coast, is NASA's prime test facility for large liquid propellant rocket engines and propulsion systems. The main mission of the Center is to support testing, on a regular basis, of the Space Shuttle's main propulsion system. SSC is responsible for a variety of research programs in the environmental sciences and the remote sensing of Earth resources, weather, and oceans, and is the lead NASA Center for the commercialization of space remote sensing.

National Aeronautics and Space Administration (NASA): U.S. Civilian Space Agency created by Congress. Founded in 1958, NASA belongs to the executive branch of the Federal Government. NASA's mission to plan, direct, and conduct aeronautical and space activities is implemented by NASA Headquarters in Washington, D.C., and by nine major centers spread throughout the United States. Dozens of smaller facilities, from tracking antennas to Space Shuttle landing strips to telescopes are located around the world. The agency administers and maintains these facilities; builds and operates launch pads; trains astronauts; designs aircraft and spacecraft; sends satellites into Earth orbit and beyond; and processes, analyzes, and distributes the resulting data and information. See NASA Centers.

NASA shares responsibility for aviation and space activities with other federal agencies, including the Departments of Commerce, Transportation, and Defense. Much of the work on major projects such as the Space Shuttle and the Space Station is done in the private sector by aerospace companies under government contract.

From its inception, NASA has been directed to pursue the expansion of human knowledge of phenomena in the atmosphere and space. NASA's programs of basic and applied research extend from microscopic sub-atomic particles to galactic astronomy. In addition to enhancing scientific knowledge, thousands of the technologies developed for aerospace have resulted in commercial applications. Science offices at NASA Headquarters carry out a wide range of research activities to fulfill NASA's science goals.

Near Infrared Composite (4,3,2) Adding a near infrared (NIR) band and dropping the visible blue band creates a near infrared composite image. Vegetation in the NIR band is highly reflective due to chlorophyll, and an NIR composite vividly shows vegetation in various shades of red. Water appears dark, almost black, due to the absorption of energy in the visible red and NIR bands.

Normalized Difference Vegetation Index (NDVI): There are various forms of combining satellite bands to monitor vegetation; a vegetation index is the term used to describe these ratio combinations. The vegetation indices that is used in this project is the Normalized Difference Vegetation Index (NDVI), which is defined by a very simple algebraic formula.

(Near IR – red band) / (Near IR + red band) NDVI = ______________________.

Simply put, vegetation indices are used to isolate vegetation’s presence and condition from other factors.

"Delta" Normalized Difference Vegetation Index (D NDVI): The reason the created image is called D NDVI is that the new image is showing the change in NDVI pixel values between two NDVI images. The Greek letter delta notation is used to show a change in quantity between the two NDVI images. Imagine that in one area in the satellite coverage was forest in an older image and has since been changed into another non-vegetated form of land cover. In the older image the NDVI pixel values will for vegetation range from a low of 0.05 to a high of 0.66. In the more recent image the bright nonvegetated surfaces will have a NDVI value of less than zero. Using a simple algebraic transformational formula the D NDVI can be created. Below is the formula, the C1 represents the older image always and the C2 always represents the newer image.

C1-C2 x 1

1

If the C1 value is 0.54 (remember when the NDVI image was created using MultiSpecÓ the NDVI value needed to be multiplied by 255 for display reasons. If the true NDVI value is needed all that is required is to divide the pixel value by 255) and the C2 value is 0.0, the D NDVI will be 140. This will be displayed as white. The brighter the pixel the greater the change between the two images, old to new.

• C1 pixel value Low - C2 pixel value High = D NDVI pixel value Vegetation gain
• C1 pixel value High - C2 pixel value Low = D NDVI pixel value Vegetation loss
• C1 pixel value Equal - C2 pixel value Equal = D NDVI pixel value Vegetation same

Near infrared Electromagnetic radiation with wavelengths from just longer than the visible (about 0.7 micrometers) to about two micrometers.

Panchromatic Sensitive to all or most of the visible spectrum.

Passive system: A system sensing only radiation emitted by the object being viewed or reflected by the object from a source other than the system. See active system.

Photosynthetically active radiation (PAR) Electromagnetic radiation in the part of the spectrum used by plants for photosynthesis.

Photo interpretation: the process of examining aerial photographs and images for the purpose of identifying objects and judging their significance. (NASA Observatorium: Remote Sensing in History)

Polar orbit: An orbit with an orbital inclination of near 90 degrees where the satellite ground track will cross both polar regions once during each orbit. The term is used to describe the near-polar orbits of spacecraft such as the USA's NOAA/TIROS and Landsat satellites.

Radiation: Energy transfer in the form of electromagnetic waves or particles that release energy when absorbed by an object.

Regionalization: It is a form of classification whereby places or areas are grouped into a larger contiguous unit according to specific attributes or criteria.

Remote sensing: The technology of acquiring data and information about an object or phenomena by a device that is not in physical contact with it. In other words, remote sensing refers to gathering information about the Earth and its environment from a distance, a critical capability of the Earth Observing System.

For example, spacecraft in low-Earth orbit pass through the outer thermosphere, enabling direct sampling of chemical species there. These samples have been used extensively to develop an understanding of thermospheric properties. Explorer-17, launched in 1963, was the first satellite to return quantitative measurements of gaseous stratification in the thermosphere. However, the mesosphere and lower layers cannot be probed directly in this way--global observations from space require remote sensing from a spacecraft at an altitude well above the mesopause. The formidable technological challenges of atmospheric remote sensing, many of which are now being overcome, have delayed detailed study of the stratosphere and mesosphere by comparison with thermospheric research advances.

Some remote-sensing systems encountered in everyday life include the human eye and brain, and photographic and video cameras.

Resolution: A measure of the ability to separate observable quantities. In the case of imagery, it describes the area represented by each pixel of an image. The smaller the area represented by a pixel, the more accurate and detailed the image. See Digital image

Satellite: A free-flying object that orbits the Earth, another planet, or the sun.

Sensor: Device that produces an output (usually electrical) in response to stimulus such as incident radiation. Sensors aboard satellites obtain information about features and objects on Earth by detecting radiation reflected or emitted in different bands of the electromagnetic spectrum. Analyzing the transmitted data provides valuable scientific information about Earth.

Weather satellites commonly carry radiometers, which measure radiation from snow, ice, clouds, and bodies of water. Spaceborne radars are used for Earth observations, bouncing radar waves off land and ocean surfaces to study sea-surface conditions, ice thickness, and land surface features. A wind scatterometer is a special type of radar designed to measure ocean surface winds indirectly by bouncing signals off the water and measuring them from various angles. Infrared (IR) detectors measure heat generated by Earth features in the IR band of the spectrum.

Photographic reconnaissance sensors in their simplest form are large telescope-camera systems used to view objects on Earth's surface. The bigger the lens, the smaller the object that can be detected. Camera-telescope systems now incorporate all sorts of sophisticated electronics to produce better images, but even these systems need cloudless skies, excellent lighting, and good color contrast between objects and their surroundings to detect objects the size of a basketball. Some of the satellites produce film images that must be returned to Earth, but a more convenient method is to record the image as a series of digital code numbers, then reconstruct the image from the electronic code using a computer at a ground station.

Shortwave Infrared Composite (7,4,3 or 7,4,2) A shortwave infrared composite image is one that contains at least one shortwave infrared (SWIR) band. Reflectance in the SWIR region is due primarily to moisture content. SWIR bands are especially suited for camouflage detection, change detection, disturbed soils, soil type, and vegetation stress.

Spectral band: A finite segment of wavelengths in the electromagnetic spectrum. See electromagnetic spectrum

Spectrum: 1. The series of colored bands diffracted and arranged in the order of their respective wave lengths by the passage of white light through a prism or other diffracting medium and shading continuously from red (produced by the longest visible wave) to violet (produced by the shortest visible wave). 2. Any of various arrangements of colored bands or lines, together with invisible components at both ends of the spectrum, similarly formed by light from incandescent gases or other sources of radiant energy, which can be studied by a spectrograph. 3. In radio, the range of wavelengths of radio waves, from 3 centimeters to 30,000 meters, or of frequencies of radio waves, from 10 to 10,000,000 kilocycles. 4. The entire range of radiant energies. See electromagnetic spectrum.

Sprawl: It is a pattern of land use/land cover conversion in which the growth rate of urbanized land (land rendered impervious by development) significantly exceeds the rate of population growth over a specified time period, with a dominance of low-density impervious surfaces.

Suburban: Relating to lower density developments beyond central cities.

Suburbanization: It is the process of lower-density residential, commercial, and industrial development beyond the central city. According to Berry and Kasarda it “is the enlargement and spread of a functionally integrated population over an increasingly wider expanse of territory” (1997,180).

Thematic Mapper (TM): A Landsat multispectral scanner designed to acquire data to categorize the Earth's surface. Particular emphasis was placed on agricultural applications and identification of land use. The scanner continuously scans the surface of the Earth, simultaneously acquiring data in seven spectral channels. Overlaying two or more bands produces a false color image. The ground resolution of the six visible and short wave bands of the Thematic Mapper is 30 meters, and the resolution of the thermal infrared band is 120 meters. Thematic Mappers have been flown on Landsats-4 and -5.

Thermal infrared: Electromagnetic radiation with wavelengths between about 3 and 25 micrometers.

Tract: It is a small geographic unit used to aggregate and report census data. In the United States tracts are broken down into blocks, but not all census data is aggregated at the block level.

Training Data: Land cover data collected at Land Cover Sample Sites to help identify or label unknown clusters on the unsupervised classification of the TM image and/or to help in the manual interpretation of the TM image. These data can be collected using qualitative or quantitative data collection methods. Training data should never be used to assess the accuracy of the map because they have been used in the training process and you cannot use the same data to train as well as validate your results. GLOBE Program

True-color composite images: These images approximate the range of vision for the human eye, and hence these images appear to be close to what we would expect to see in a normal photograph. True-color images tend to be low in contrast and somewhat hazy in appearance. This is because blue light is more susceptible than other bandwidths to scattering by the atmosphere. Broad-based analysis of underwater features and land cover are representative applications for true-color composites.

Unsupervised Clustering: A computer identifies and clusters together pixels in the image that have the most similar spectral properties. The software assigns each cluster an arbitrary color.

Urban: Relating to towns and cities. Urban places are those that exceed a population size or density threshold as defined according to the census.

Urbanization: Becoming urban, specifically the concentration of population into towns and cities. Associated with this process is the replacement of pervious surfaces with impervious materials such as asphalt and concrete.

Validation Data: Land cover data collected at Land Cover Sample Sites to assess the accuracy of the classified map created using manual interpretation or unsupervised classification of your local TM scene. These data can be collected using qualitative or quantitative data collection methods (quantitative is preferred whenever possible). Collect as many samples as possible for each land cover type present on the map because many samples are needed in the accuracy assessment process. These data should be used only for accuracy assessment. GLOBE Program

Visible: That part of the electromagnetic spectrum to which the human eye is sensitive, between about 0.4 and 0.7 micrometers. See spectrum

Wave: 1. In electricity, a periodic variation of an electric current or voltage. 2. In physics, any of the series of advancing impulses set up by a vibration, pulsation, or disturbance in air or some other medium, as in the transmission of heat, light, sound, etc.

Wavelength: Physical distance of one period (wave repeat).

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