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Appendix B Glossary Mark Patterson NOTE: italicized terms in the definitions are defined in this glossary. Albedo. The ratio of the amount of electromagnetic radiation reflected by a surface to the amount falling on a surface. Lighter-colored surfaces, such as snow, have higher albedo ratios than do darker-colored surfaces, such as trees. Amazonia. A term denoting the legal boundary of several Brazilian states that encompass a portion of the Amazon River Basin in Brazil. ARC/INFO. Geographic information system software produced by the Environ- mental Research Systems Institute (ERSI). AVHRR: Advanced Very High Resolution Radiometer. A U.S. National Oceanic and Atmospheric Administration satellite that collects multispectral data. This satellite has a spatial resolution of 1.1 x 1.1 km and a temporal resolution of approximately 12 hours. Cadastral map. A map of the extent, value, and ownership of land, originally used as a basis for taxation. Census tract. A small areal unit used in collecting and reporting census data. Central business district. The location in an urban area where the concentration of commercial activity is most dense. Centrifugal forces. A term used to describe factors, such as crime and pollution, that push people and businesses away from the center of urban areas. Centripetal forces. A term used to describe factors, such as employment oppor 229
230 GLOSSARY "unities, that pull or attract people and businesses toward the center of urban areas. Commission error. A measure of classification accuracy, based on the number of pixels incorrectly assigned to a particular class that belong in other classes. It is the probability that a pixel in an image is not actually representative of a class in reality. Composite image. An image derived from multiple images of the same area. A false color composite is a common composite image in which different spec- tral bands of the same image are displayed simultaneously using different colors. DEM: Digital elevation model. A digital file in raster format in which each georeferenced pixel has an elevation value. Digital number. The numerical value assigned to a pixel in a digital image. Doppler radar. A radar system that measures the velocity of an object by recording the change in frequency of returning radar waves caused by the object's moving. ENSO: El Nino/Southern Oscillation. An atmospheric and oceanic phenom- enon that affects ocean currents. Cool ocean currents are replaced by warm ocean currents in the eastern tropical Pacific Ocean. The change in the temperature of ocean currents affects precipitation patterns on land, which in turn alters vegetation growth and agriculture. ENS O events occur roughly every 4 to 6 years. The Southern Oscillation refers to fluctuations in atmo- spheric pressure and rainfall across the Indo-Pacific region. Electromagnetic spectrum. A continuous sequence of electromagnetic radia- tion arranged according to wavelength. The spectrum also includes visible light. Epistemology. The study of knowledge. More specifically, it is the study of the nature of and grounds for knowledge, especially with reference to the limits and validity of knowledge. FEWS: Famine Early Warning System. A U.S. Agency for International Development progam that monitors a variety of social and physical variables in a country or region of Africa in order to identify populations at risk of food insecurity. Advance warning can then be provided to the U.S. government so it will be prepared to commit food-aid resources before a crisis occurs. Remote sensing is an integral part of FEWS, as it provides a composite indicator of vegetation growth and rainfall distribution. Fractal. Short for fractional dimension. A geometrical or physical structure that has an irregular or fragmented shape at all scales of measurement. Coast- lines are often depicted or represented by fractals. Fuzzy boundary. A boundary that is treated as a band of uncertainty.
MARK PATTERSON 231 GCM: general circulation model. A term used to describe a computer model that simulates large-scale features of atmospheric circulation by solving a set of equations governing atmospheric motion. Changes in temperature and precipitation are typical outputs of such a model. GIS: geographic information system. A computer system consisting of hard- ware and software used to store, manipulate, analyze, and display georeferenced data. Geometric correction. An image preprocessing procedure that corrects spatial distortions. Features in an image are repositioned so their locations are correct based on a known coordinate system, such as latitude/longitude. Georeferencing. The process of referencing elements in an image to a known coordinate system, such as latitude/longitude or Universal Transverse Mercator (UTM). GOES: Geostationary Operational Environmental Satellites. U.S. National Oceanic and Atmospheric Administration satellites that travel at the same speed and direction as the earth's rotation. They are used to collect weather data. Global carbon cycle. The global circulation of carbon. Carbon can be trans- ferred from the ground (by burning trees and fossil fuels, for example) to the atmosphere (in the form of the greenhouse gas carbon dioxide) and back to the earth (by photosynthesis). Both human actions and natural phenomena affect the amount of carbon in the atmosphere, mainly in the form of the carbon dioxide. GPS: Global Positioning System. A system of 24 satellites that orbit the earth and are used in computing a location on earth. A GPS receiver unit tracks these satellites and using geometry can compute the GPS receiver's location and elevation. GPS units are commonly used in collecting ground-refer- enced data. Ground-referenced data. Georeferenced data that are collected at the actual ground location of an area encompassed by imagery. A GPS unit is typically used to provide the georeferencing. Ground trothing. Also called ground referencing. In remote sensing, it is the exercise of field work to verify the interpretation of imagery. Human ecology. The study of humans' interaction with their physical and social environment. IRS: Indian Remote Sensing. A near-polar, sun-synchronous satellite system, developed by National Natural Resource Management Systems (India), that collects multispectral data of the earth with a spatial resolution of 72.5 x 72.5 m. Landsat. An unmanned satellite system initially operated by the U.S. National
232 GLOSSARY Aeronautics and Space Administration and now by the private firm, Earth Observation Satellite Company. These satellites collect Multispectral data. Presently, only Landsat 5 is still functioning. Landsat 6 failed to achieve orbit, and Landsat 7 is expected to be launched in 1998. Landsat MSS: Landsat Multispectral Scanner. An imaging system found on the first five Landsat satellites. The system collects Multispectral data in four nonthermal radiation bands with a spatial resolution of 79 x 79 m. On Landsat 1 to 3, data were also collected in a single thermal band with a spatial resolution of 250 x 250 m. Landsat TM: Landsat Thematic Mapper. A Multispectral scanner imaging system on board the Landsat 4 and 5 satellites. The imaging system collects Multispectral data in seven bands (six nonthermal and one thermal) ranging from visible radiation to thermal infrared radiation. The nonthermal bands have a spatial resolution of 30 x 30 m, whereas the thermal band has a spatial resolution of 120 x 120 m. The temporal resolution is 16 days. Latent heat flux. The increase in internal energy of a substance associated with a change in molecular configuration (e.g., liquid to gas) over a given period of time. Latent heat flux is critical for maintaining global energy balance as it transfers heat to and from the earth's surface. Markov chain analysis. A statistical analysis technique in which the probability of an event in a sequence of random events is affected by the outcome of the most recent event. Maximum likelihood classifier. A supervised classification technique based on the probability density function (distribution) of the spectral signatures of pixels, used to train the computer to assign pixels to classes. The probability of a pixel's belonging to each distribution is computed, and the pixel is assigned to the distribution (class) with the highest probability. Mesophyll reflectance. The reflectance of near-infrared radiation from the spongy mesophyll (internal cell structure) found in leaves. Metadata. The documentation associated with a data set, including a description of the data, the date the data were collected, and a source. Mid-infrared radiation. The portion of the electromagnetic spectrum spanning 1.55 to 3 micrometers (lam). Mid-infrared radiation is sensitive to the mois- ture content of features in an image. Monte Carlo simulation. A term used to describe the simulation or modeling of an event whose occurrence is random and not predicated on previous events. It alludes to games of chance, such as craps or roulette, played in Monte Carlo, in which the outcome of events is not dependent on previous out- comes. Monte Carlo simulation is often used to generate random numbers for use in computer modeling. Multispectral scanner. An imaging system, such as the Landsat Multispectral
MARK PATTERSON 233 Scanner (MSS), that simultaneously collects data from the same scene at different wavelengths in the electromagnetic spectrum. NDVI: Normalized Difference Vegetation Index. A measure of vegetation vigor computed from multispectral data. It is computed by subtracting the red band from the near-infrared band and dividing the result by the sum of the red and near-infrared bands. Nearest neighbor resampling. The reassignment of a digital number to a pixel by assigning the value of the pixel nearest to the location of the resampled pixel. In geometric corrections of images, values must be assigned to the pixels in the new coordinate system. This process is known as resampling. Near-infrared radiation. The portion of the electromagnetic spectrum span- ning 0.7 to 1.55 micrometers (mm). This radiation is reflected by vegetation and hence is a good indicator of vegetation content in an image. Nonthermal radiation. Radiation that is reflected by an object and is found in the visible to the mid-infrared (0.45-3.00 mm) portion of the electromag- netic spectrum. Omission error. A measure of classification accuracy based on the number of pixels incorrectly excluded from a particular class. It is the probability of a ground reference pixel's being classified incorrectly. Orthophotograph. A digital aerial photograph that has been geometrically cor- rected for distortions. Panchromatic (pan) scanner. An imaging system that records all visible light in a single band. This type of scanner is found on board the SPOT satellites. Phenology. The study of the timing of recurring natural phenomena in the life cycle of plants. The different stages of the annual cycle of a plant have implications for vegetation classification from remotely sensed data and change detection analysis. Photogrammetry. The science and technology of procuring reliable measure- ments using aerial photographs. Pixel. The smallest unit of spatial resolution in a photo or remotely sensed image. It refers to the area on the ground (spatial resolution) represented by a digital number. A remotely sensed digital image may be composed of millions of pixels. Pixel size varies in accordance with the type of sensor used. Polygon. A closed-plane feature formed by a bounded series of straight lines. A polygon may be any shape. RADARSAT. A Canadian Space Agency satellite that collects C-band active microwave imagery. C-band microwaves have longer wavelengths than visible and infrared waves and range from 3.8 to 7.5 centimeters. They are
234 GLOSSARY useful for penetrating features such as clouds, tree canopies, and sand to record what lies underneath. Radiometric correction. An image processing procedure in which corrections are made to inaccurate digital numbers resulting from sensor degradation or malfunctioning. Radiometry. The science and techniques involved in using radiometers. A radiometer is a device capable of detecting electromagnetic radiation. Raster. A spatial data model in which features are represented by pixels. Each pixel is assigned a value that corresponds to a feature. Data from remotely sensed images are stored in raster format. Reflectance. The ratio of energy reflected by a surface to the total amount of energy striking the surface. Remote sensing. The use of electromagnetic radiation sensors to record images of an environment. Black-and-white photographs and satellite imagery are types of remotely sensed data. Rent theory. A theory according to which land use will be such that it returns the highest possible amount of profit. Semivariogram. A geostatistical graph that displays similarities (or differences) between two or more spatially discrete phenomena by measuring the vari- ance between the phenomena. Variance is assumed to be represented by the distance between the phenomena, so that phenomena closer to one another have a smaller variance. Senescence cycle. The phases of plant growth from maturity to death that are characterized by an accumulation of metabolic products (leaves, seeds, and fruit), increase in respiratory rate, and loss in dry weight (especially in the leaves). The spectral signature of a plant will vary depending on the phase of the cycle. Sensible heat flux. A measure of the kinetic energy of the molecular motion of a substance (e.g., air) over a given time period. A thermometer is used to measure sensible heat (i.e., air temperature). Sensitivity analysis. A type of analysis that accounts for the dependence of an outcome variable on a causal factor by providing a range of possible out- comes based on changes in the value of the causal factor. For example, a range of precipitation values may be computed in a general circulation model by changing the amount of carbon dioxide (causal factor) in the atmo- sphere each time the model is executed. Solar insolation. Energy in the form of electromagnetic waves from the sun that are intercepted by the earth. Spatial dependency. A condition arising when a strong relationship exists be- tween an event at one place and events in other places.
MARK PATTERSON 235 Spatial distortion. Changes in the position and shape of features in an image with respect to their true position and shape. Spatial resolution. The level of detail that can be detected by a sensor, often measured simply by the dimensions of a pixel in an image. The finer the spatial resolution, the more information can be discerned from an image. Landsat TM has a spatial resolution of 30 x 30 m, while SPOT PAN has a spatial resolution of 10 x 10 m. SPOT: Systeme pour l' Observation de la Terre. A French commercial satel- lite program designed to collect high-spatial-resolution panchromatic (10 x 10 m) and multispectral (20 x 20 m) images. SPOT HRV: SPOT High Resolution Visible. The scanner system used on board the SPOT satellites. SPOT MX (usually referred to as SPOT XS). SPOT multispectral scanner imaging system that collects data in the green, red, and near-infrared por- tions of the electromagnetic spectrum. SPOT XS images have a spatial resolution of 20 x 20 m. SPOT PAN: SPOT Panchromatic. A SPOT imaging system that collects data in a single spectral band. SPOT PAN images have a spatial resolution of 10 x tom. Stereoscopic imagery. Imagery or aerial photographs composed of two partially overlapping images that appear three-dimensional when viewed through ste- reoscopic glasses. Supervised classification. A classification technique in which the operator pro- vides classification information used by the computer to assign pixels to classes. Swidden cultivation. Also known as swidden agriculture or more colloquially as slash-and-burn agriculture. It is a form of agriculture that involves clear- ing forests or bushland for agricultural purposes. When soil fertility has decreased after a few years, the land goes to fallow of variable length before being cleared again. Temporal resolution. The time it takes for a satellite to return to or revisit the same location. Landsat TM, for example, has a temporal resolution of 16 days. TIR: thermal infrared radiation. The portion of the electromagnetic spectrum spanning 3 to 14 micrometers (lam). Objects that emit heat can be detected in this portion of the spectrum. TIGER file: Topologically Integrated Geographic Encoding Reference file. A digital geographic coding system developed by the U.S. Bureau of the Census. TIN: triangulated irregular network. A network of triangular facets drawn among points on a surface. The coordinates and elevations of the points
236 GLOSSARY forming the vertices of each triangular facet are used to compute the slope and aspect (direction) of the terrain. Topographic distortions. Distortions in reflectance readings by a satellite caused by topographic variability. Shadows are the most common form of topo- graphic distortions. Unsupervised classification. A computer algorithm that assigns pixels to classes with no prior instructions from the operator. Classes are defined such that differences among them are maximized, while differences within them are mlmmlzecl. USGS Level I class. A U.S. Geological Survey hierarchical land-use classifica- tion scheme based on a level of spatial resolution that can be achieved by satellite imagery, such as Landsat (scale less than 1:250,000~. An example of a USGS Level I class is urban land use. USGS Level II class. A U.S. Geological Survey hierarchical land-use classifica- tion scheme based on a level of spatial resolution that can be achieved by high-altitude imagery (scale 1:80,000 to 1:250,000~. An example of a USGS Level II class is residential land use. USGS Level III class. A U.S. Geological Survey hierarchical land-use classifi- cation scheme based on a level of spatial resolution that can be achieved by medium-altitude imagery (scale 1:20,000 to 1:80,000~. An example of a USGS Level III class is single-family-dwelling land use. USGS Level IV class. A U.S. Geological Survey hierarchical land-use classifi- cation scheme based on a level of spatial resolution that can be achieved by low-altitude imagery (scale greater than 1:20,000~. Vector. A spatial data model in which features are represented by points, lines, and polygons. A point could represent a city, a line could represent a road, and a polygon could represent a forest. Visible radiation. The portion of the electromagnetic spectrum spanning 0.4 to 0.7 micrometers (lam). Radiation in this portion of the spectrum is visible to the human eye in the form of different colors. Wetness Vegetation Index. A feature produced by the Kauth-Thomas linear transformation (also called the tasseled cap transformation) that displays vegetation and soil moisture content.