Absorption: The process by which radiant energy is absorbed and converted into other forms of energy.(A)
Absorption band: A range of wavelengths (or fre- quencies) in the electromagnetic spectrum within which radiant energy is absorbed by a substance.(A)
Absorption spectrum: The array of absorption lines and absorption bands that results from the passage of radiant energy from a continuous source through a selectively absorbing medium cooler than the source.(A)
Absorptivity: The capacity of a material to absorb incident radiant energy. A special case of absorp- tance, it is a fundamental property of material that has a specular (optically smooth) surface and is sufficiently thick to be opaque. It may be further qualified as spectral absorptivity. The suffix (-ity) implies a property intrinsic with a given material, a limiting value.(A)
Accuracy: The success in estimating the true value. The closeness of an estimate of a charac- teristic to the true value of the characteristic of the population.(D)
Active system: A remote sensing system that trans- mits its own electromagnetic emanations at an object(s) and then records the energy reflected or refracted back to the sensor.(A)
Active microwave: Ordinarily referred to as a ra- dar.(A)
Additive color process: A method for creating essen- tially all colors through the addition of light of the three additive color primaries (blue, green, and red) in various proportions through the use of three separate projectors. In this type of pro- cess, each primary filter absorbs the other two primary colors and transmits only about one- third of the luminous energy of the source. It also precludes the possibility of mixing colors with a single light source because the addition of a second primary color results in total ab- sorption of the light transmitted by the first color. (A)
Aerial photograph, vertical: An aerial photograph made with the optical axis of the camera approx- imately perpendicular to the Earth's surface and with the film as nearly horizontal as is practica- ble. (A)
Aerial reconnaissance: The securing of information by aerial photography or by visual observation from the air. (A)
Albedo: (1) The ratio of the amount of EMR re- flected by a body to the amount incident upon it, often expressed as a percentage, e.g., the albedo of the Earth is 34 percent. (2) The re- flectivity of a body as compared to that of a perfectly diffusing surface at the same distance from the Sun, and normal to the incident radia- tion. (A)
Algorithm: (1) A fixed step-by-step procedure to accomplish a given result, usually a simplified procedure for solving a complex problem, also a full statement of a finite number of steps. (2) A computer-oriented procedure for resolving a problem. (D)
Alphanumeric: A character set composed of letters, integers, punctuation marks, and special symbols. Usually the number of characters in a set varies between forty-eight and sixty-four. (D)
Analog: A form of data display in which values are shown in graphic form, such as curves. Also a form of computing in which values are repre- sented by directly measurable quantities, such as voltages or resistances. Analog computing meth- ods contrast with digital methods in which values are treated numerically. (A)
Ancillary data: In remote sensing, secondary data pertaining to the area or classes of interest, such as topographical, demographic, or climatological data. Ancillary data may be digitized and used in the analysis process in conjunction with the primary remote sensing data. (B)
Angle of depression: In SLAR usage, the angle be- tween the horizontal plane passing through the antenna and the line connecting the antenna and the target. (C)
Angle of incidence: (1) The angle between the di- rection of incoming EMR and the normal to the intercepting surface, (2) In SLAR systems this is the angle between the vertical and a line connect- ing antenna and target. (C)
Angle of reflection: The angle that EMR reflected from a surface makes with the perpendicular (normal) to the surface. (A)
Angle of view: The angle subtended by lines that pass through the center of the lens to diametri- cally opposite corners of the plate or film used. (A)
Angstrom (A)
: Unit of measurement, 10-10 m. (A)
Anomaly: An area on an image that differs from the surrounding normal area. For example, a concentration of vegetation within a desert scene constitutes an anomaly. (C)
Atmospheric windows: Those wavelength ranges in which radiation can pass through the atmo- sphere with relatively little attenuation; in the optical portion of the spectrum, approximately 0.3-2.5, 3.0-4.0, 4.2-5.0, and 7.0-15.0 micron. (B)
Attenuation: In physics, any process in which the flux density (or power, amplitude, intensity, illuminance) of a "parallel beam" of energy de- creases with increasing distance from the energy source. (A)
Attitude: The angular orientation of a remote sensing system with respect to a geographical reference system. (C)
Azimuth: The geographical orientation of a line given as an angle measured clockwise from north. (C)
Background: Any effect in a sensor or other appara- tus or system, above which the phenomenon of interest must manifest itself before it can be observed. (See background noise.) (A)
Background luminance: In visual-range theory, the luminance (brightness) of the background against which a target is viewed. (A)
Background noise: (1) In recording and reproduc- ing, the total system noise independent of whether or not a signal is present. The signal is not to be included as part of the noise. (2) In receivers, the noise in the absence of signal modulation on the carrier. Ambient noise detected, measured, or recorded with the signal becomes part of the background noise. Included in this definition is the interference resulting from primary power supplies, which separately is commonly described as hum. (A)
Backscatter: The scattering of radiant energy into the hemisphere of space bounded by a plane normal to the direction of the incident radiation and lying on the same side as the incident ray; the opposite of forward scatter. Also called backscattering. (A)
Band: (1) A selection of wavelengths. (2) Frequency band. (3) Absorption band. (4) A group of tracks on a magnetic drum. (5) A range of radar frequencies, such as X-band, Q-band, etc. (A)
Band-pass filter: A wave filter that has a single transmission band extending from a lower cutoff frequency greater than zero to a finite upper cutoff frequency. (A)
Bandwidth: (1) In an antenna, the range of fre- quencies within which its performance, with respect to some characteristic, conforms to a specified standard. (2) In a wave, the least fre- quency interval outside which the power spec- trum of a time-varying quantity is everywhere less than some specified fraction of its value at a reference frequency. (3) The number of cycles per second between the limits of a frequency band. (A)
Base-height ratio: Air base (ground distance be- tween centers of successive overlapping photos) divided by aircraft height. This ratio determines vertical exaggeration on stereo models. (C)
Batch processmg: A method whereby items are coded and collected into groups and then processed sequentially. (D)
Beam: A focused pulse of energy. (C)
Blackbody, black body (symbol bb used as sub- script): An ideal emitter which radiates energy at the maximum possible rate per unit area at each wavelength for any given temperature. A blackbody also absorbs all the radiant energy incident upon it. No actual substance behaves as a true blackbody, although platinum black and other soots rather closely approximate this ideal. In accordance with Kirchhoff's law, a blackbody not only absorbs all wavelengths, but also emits at all wavelengths and does so with maximum possible intensity for any given temperature. (A)
Blackbody radiation: The electromagnetic radiation emitted by an ideal blackbody; it is the theoreti- cal maximum amount of radiant energy of all wavelengths that can be emitted by a body at a given temperature. The spectral distribution of blackbody radiation is described by Planck's law and related radiation laws. (A)
Brightness: (1) The attribute of visual perception in accordance with which an area appears to emit more or less light. (2) Luminance. (3) The luminous flux emitted or reflected per unit projected area per unit solid angle. The unit of brightness, the Zambert, is defined as brightness of a surface which emits or reflects one/pi lumen per square centimeter per steradian. (A)
Brightness temperature: (1) The temperature of a blackbody radiating the same amount of energy per unit area at the wavelengths under considera- tion as the observed body. Also called effective temperature. (2) The apparent temperature of a nonblackbody determined by measurement with an optical pyrometer or radiometer. (A)
Calibration: The act or process of comparing cer- tain specific measurements in an instrument with a standard. (A)
Camera, multiband: A camera that exposes differ- ent areas of one film, or more than one film, through one lens and a beam splitter, or two or more lenses equipped with different filters, to provide two or more photographs in differ- ent spectral bands. (A)
Category: Each unit is assumed to be of one and only one given type. The set of types is called the set of "classes" or "categories," each type being a particular category, The categories are chosen specifically by the investigator as being the ones of interest to him. (D)
Cathode ray tube (CRT): A vacuum tube capable of producing a black-and-white or color image by beaming electrons onto a sensitized screen. As a component of a data-processing system, the CRT can be used to provide rapid, pictorial access to numerical data. (B)
Cell: An area on the ground from which EMR is emitted or reflected. (A)
Change-detection images: Images prepared by digi- tally comparing two original images acquired at different times. The gray tones of each pixel on a change-detecdon image portray the amount of difference between the original images. (C)
Chopper: A device, usually one that rotates, used to interrupt a continuous wave signal in a trans- mitter, receiver, or sensor. (A)
Class: A surface characteristic type that is of in- terest to the investigator, such as forest by type and condition, or water by sediment load. (D)
Classification: The process of assigning individual pixels of a multispectral image to categories, generally on the basis of spectral reflectance characteristics. (C)
Clustering: The analysis of a set of measurement vecton to detect their inherent tendency to form clusters in multidimensional measurement space. (B)
Color: Tnat property of an object which is depend- ent on the wavelength of the light it reflects or, in the case of a luminescent body, the wave- length of light that it emits. If, in either case, this light is of a single wavelength, the color seen is a pure spectral color; but if light of two or more wavelengths is emitted, the color will be mixed. White light is a balanced mixture of all the visible spectral colors. (A)
Color balance: The proper intensities of colors in a color print, positive transparency, or negative, that give a correct reproduction of the gray scale (as faithful as can be achieved by phatographic representatian of the true colon of a scene.) (A)
Calor composite (multiband photography): A color picture produced by assigning a color to a particular spectral band. In Landsat, blue is ordinarily assigned to MSS band 4 (0.5-0.6 micron), green to band 5 (0.6-0.7 micron), and red to band 7 (0.8-1.1 micron), to form a picture closely approx- imating a color-infrared photograph. (A)
Color infrared film: Photographic film sensitive to energy in the visible and near-infrared wave- lengths, generally from 0.40.9 micron; usually used with a minus-blue (yellow) filter, which results in an effective film sensitivity of 0.5-0.9 micron. Color infrared film is especially useful for detect- ing changes in the condition of the vegetative canopy which are often manifested in the near- infrared region of the spectrum. Note that color infrared film is not sensitive in the thermal in- frared region and therefore cannot be used as a heat-senative detector. (B)
Color temperature: An estimate of the temperature of an incandescent body, determined by obsering the wavelength at which it is emitting with peak intensity (its color), determined by applying the Wien law. (A)
Computer-compatible tapes: Tapes containing digi- tal Landsat data. These tapes are standard 19-cm (7 1/2in) wide magnetic tapes in 9-track or 7- track format. Four tapes are required for the four-band multispectral digital data correspond- ing to one Landsat scene. (D)
Continuous spectrum:(l) A spectrum in which wavelengths, wavenumbers, and frequencies are represented by the continuum of real num- bers or a portion thereof, rather than by a discrete sequence of numbers. See absorption spectrum. (2) For EMR, a spectrum that exhibits no detailed structure and represents a gradual variation of intensity with wavelength from one end to the other, as the spectrum from an in- candescent solid. (A)
Contrast stretching: Improving the contrast of images by digital processing. The original range of digital values is expanded to utilize the full contrast range of the recording film or dis- Play device. (C)
Coordinates, geographical: A system of spherical coordinates for describing the positions of points on the Earth. The declinations and polar bearings in this system are the latitudes and longitudes, respectively. (A)
Covariance: The measure of how two variables change in relation to each other (covariability). If larger values of Y tend to be associated with larger values of X, the covariance will be positive. If larger values of Y are associated with smaller values of Y the covariance will be negative. When there is no particular association between X and Y, the covariance value will approach zero. (D)
Cultural features: All map detail representing man- made elements of the landscape. (D)
Cursor: Aiming device, such as a lens with cross- hairs, on a digitizer or an interactive computer display. (D)
Data acqulation system: The collection of devices and media that measures physical variables and records them prior to input to the data process- ing system. (B)
Data bank: A well-defined collection of data, usually of the same general type, which can be accessed by a computer. (B)
Data dimensionality: The number of variables (e.g., channels) present in the data set. The term "in- trinsic dimensionality" refers to the smallest number of variables that could be used to represent the data set accurately. (B)
Data processing: Application of procedures-me- chanical electrical, computation, or other- whereby data are changed from one form into another. (A)
Data reduction: Transformation of observed values into useful ordered, or simplified information. (A)
Decision rule (or classification rule): The criterion used to establish discriminant functions for clas- sification (e.g., nearest-neighbor rule, minimum- distance-to-means rule, maximum-likelihood rule). (B)
Density (symbol, D): A measure of the degree of blackening of an exposed film, plate, or paper after development, or of the direct image (in the case of a printout material). It is defined strictly as the logarithm of the optical opacity, where the opacity is the ratio of the incident to the transmitted (or reflected) light or trans- missivity, T, as D = log (l/T). (A)
Density slicing: The process of converting the continuous gray tone of an image into a series of density intervals, or slices, each correspond- ing to a specific digital range. (C)
Detection: A unit is said to be "detected" if the decision rule is able to assign it as belonging only to some given subset of categories from the set of all categories. Detection of a unit does not imply that the decision rule is able to identify the unit as specifically belonging to one particu- lar category. (D)
Detector (radiation): A device providing an electri- cal output that is a useful measure of incident radiation. It is broadly divisible into two groups: thermal (sensitive to temperature changes), and photodetectors (sensitive to changes in photon flux incident on the detector), or it may also include antennas and film. Typical thermal detectors are thermocouples, thermopiles, and thermistors; the latter is termed a bolometer. (A)
Dielectric constant: Electrical property of matter that influences radar returns, also referred to as complex dielectric constant. (C)
Diffraction: The propagation of EMR around the edges of opaque objects into the shadow region. A point of light seen or projected through a circular aperture will always be imaged as a bright center surrounded by light rings of grad- ually diminishing intensity in the shadow region. Such a pattern is called a diffraction disk, Airy disk, or centric. (A)
Diffuse reflection: The type of reflection obtained from a relatively rough (in terms of the wave- length of the EMR) surface, in which the reflect- ed rays are scattered in all directions. (A)
Diffuse reflector: Any surface that reflects incident rays in many directions, either because of irregularities in the surface or because the material is optically inhomogeneous, as a paint, the opposite of a specular reflector. Ordinary writing papers are good examples of diffuse reflectors, whereas mirrors or highly polished plates are examples of specular reflectors in the visible portion of the EM spectrum. Almost all terrestrial surfaces (except calm water) act as diffuse reflectors of incident solar radiation. The smoothness or roughness of a surface depends on the wavelength of the incident EMR. (A)
Diffuse sky radiation: Solar radiation reaching the Earth's surface after having been scattered from the direct solar beam by molecules or suspensoids in the atmosphere. Also called skylight, diffuse skylight, sky radiation. (A)
Digitization: The process of converting an image recorded originally on photographic material into numerical format. (C)
Discriminant function: One of a set of mathemati- cal functions which in remote sensing are commonly derived from training samples and a decision rule, and are used to divide the meas- urement space into decision regions. (B)
Display: An output device that produces a visible representation of a data set for quick visual access; usually the primary hardware component is a cathode ray tube. (B)
Distribution function: The relative frequency with which different values of a variable occur. (D)
DN: Digital number. The value of reflectance recorded for each pixel on Landsat CCT's. (C)
Edge: The boundary of an object in a photograph or image, usually characterized by a rather drastic change in the gray shade value from the immediate interior of the boundary to the immediate exterior of the boundary. (D)
Edge enhancement: The use of analytical tech- niques to emphasize transition in imagery. (A)
Electromagnetic radiation (EMR): Energy propa- gated through space or through material media in the form of an advancing interaction between electric and magnetic fields. The term radiation alone, is commonly used for this type of energy, although it actually has a broader meaning. Also called electromagnetic energy. (A)
Electromagnetic spectrum: The ordered array of known electromagnetic radiations extending from the shortest cosmic rays, through gamma rays, X-rays, ultraviolet radiation, visible radia- tion, infrared radiation, and including microwave and all other wavelengths of radio energy. (A)
Element: The smallest definable object of interest in the survey. It is a single item in a collection, population, or sample. (D)
Emission: With respect to EMR, the process by which a body emits EMR usually as a cense- quence of its temperature only. (A)
Emissivity: The ratio of the radiation given off by a surface to the radiation given off by a black- body at the same temperature, a blackbody has an emlsslvlty of 1 other objects between 0 and 1. (B)
Emittance: The obsolete term for the radiant flux per unit area emitted by a body, or exitance. (A)
Environment: An external condition, or the sum of such conditions, in which a piece of equipment or a system operates, as in temperature environ- ment, vibration environment, or space environ- ment. The environments are usually specified by a range of values, and may be either natural or artificial. (A)
Ephemeral data: Data that: (1) help to characterize the conditions under which the remote sensing data were collected: (2) may be used to calibrate the sensor data prior to analysis; (3) include such information as the positioning and spectral stability of sensors, Sun angle, platform attitude, etc. (B)
Equivalent blackbody temperature: The tempera- ture measured radiometrically corresponding to that which a blackbody would have. Most natural objects including soil, plant leaves, and water have emissivities greater than 0.9 but less than 1.0. (A)
Exitance (symbol, M): The radiant flux per unit area emitted by a body or surface. (A)
False color: The use of one color to represent another, for example, the use of red emulsion to represent infrared light in color infrared film. (A)
Far range: Refers to the portion of an SLAR image farthest from the aircraft flight path. (C)
Feature: An n-tuple or vector with components which are functions of the initial measurement pattern variables or some subsequence of the measurement n-tuples. Feature n-tuples or vec- tors frequently have fewer components than the initial measurement vectors and are designed to contain a high amount of information about the discrimination between units of the types of cat- egories in the given category set. Features often contain information about gray shade, texture, shape or context. Also, a cartographic type in digital form appearing as part of the descriptor in coded form (Feature Code). (D)
Feature extraction: The process in which an initial measurement pattern or some subsequence of measurement patterns is transformed to a new pattern feature. (D)
Field of view: The solid angle through which an in- strument is sensitive to radiation. Owing to various effects, diffractions, etc., the edges are not sharp. In practice they are defined as the "half-power" points, i.e., the angle outwards from the optical axis, at which the energy sensed by the radiometer drops to half its on-axis value. (A)
Filter: (1, noun) Any material which, by absorp- tion or reflection, selectively modifies the radia- tion transmitted through an optical system. (2, verb) To remove a certain component or compo- nents of EMR, usually by means of a filter, although other devices may be used. (A)
Filtering: In analysis, the removal of certain spec- tral or spatial frequencies to highlight features in the remaining image. (A)
Focus: The point at which the rays from a point source of light reunite and cross after passing through a camera lens. In practice, the plane in which a sharp image of any scene is formed. (A)
Format: The arrangement of descriptive data in descriptors, identifiers, or labels. The arrange- ment of data in bit, byte, and word form in the CPU. (D)
Frame: Complete tape of a single or multidate Landsat frame covering roughly an area about 100 nautical miles square. (D)
Frequency: Number of oscillations per unit time or number of wavelengths that pass a point per unit time. (D)
Frequency response: (1) Response of a system as a function of the frequency of excitations. (2) The portion of the frequency spectrum that can be sensed by a device within specified limits of amplitude error. (A)
Gain: (1) A general term used to denote an increase in signal power in transmission from one point to another. Gain is usually expressed in decibels. (2) An increase or amplification. (A)
Gamma: A numerical measure of the extent to which a negative has been developed, indicating the proportion borne by the contrast of the negative to that of the subject on which it was exposed. The numerical figure for gamma is the tangent of the straight-line (correct exposure portion of the curve resulting from plotting exposure against density. (A)
GCP: Ground control point. A geographical feature of known location that is recognizable on images and can be used to determine geometrical correc- tions. (C)
Geocoding: Geographical referencing or coding of location of data items. (D)
Geometrical transformations: Adjustments made in the image data to change its geometrical charac- ter, usually to improve its geometrical consistency or cartographic utility. (B)
Gray body: A radiating surface whose radiation has essentially the same spectral energy distribution as that of a blackbody at the same temperature, but whose emissive power is less. Its absorptivity is nonselective. Also spelled grey body. (A)
Gray scale: A monochrome strip of shades ranging from white to black with intermediate shades of gray. The scale is placed in a setup for color photograph and serves as a means of balancing the separation negatives and positive dye images. (A)
Grid line: One of the lines in a grid system; a line used to divide a map into squares. East-west lines in a grid sytem are x-lines, and north-south lines are y-lines. (A)
Ground data:Supporting data collected on the ground, and information derived therefrom, as an aid to the interpretation of remotely recorded surveys, such as airbome imagery, etc. Generally, this should be performed concurrently with the airborne surveys. Data as to weather, soils and vegetation types and conditions are typical. (A)
Ground range: The distance from the ground track (nadir) to a given object. (A)
Ground resolution cell: The area on the terrain that is covered by the instantaneous field of view of a detector. The size of the ground resolution cell is determined by the altitude of the remote- sensing system and the instantaneous field of view of the detector. (C)
Ground track: The vertical projection of the actual flight path of an aerial or space vehicle onto the surface of the Earth or other body. (A)
Ground truth (jargon): Term coined for data and information obtained on surface or subsurface features to aid in interpretation of remotely sensed data. Ground data and ground information are preferred terms. (A)
H-D (Hurter-Driffield) Curve: A graph showing the relationship of exposure to (photo) density, where the density is plotted against the loga- rithm of the exposure (also known as charac- teristic curve). (A)
Hardware: The physical components of a computer and its peripheral equipment. Contrasted with software. (D)
Histogram: The graphical display of a set of data which shows the frequency of occurrence (along the vertical axis) of individual measurements or values (along the horizontal axis); a frequency distribution. (B)
Hue: That attribute of a color by virtue of which it differs from gray of the same brilliance, and which allows it to be classed as red, yellow, green, blue, or intermediate shades of these colors. (A)
Illumination: The intensity of light striking a unit surface is known as the specific illumination or luminous flux. It varies directly with the intensity of the light source and inversely as the square of the distance between the illuminated surface and the source. It is measured in a unit called the lux. The total illumination is obtained by multiplying the specific illumination by the area of the sur- face covered by the light. The unit of total illumination is the lumen. (A)
Image: (1) The counterpart of an object produced by the reflection or refraction of light when focused by a lens or mirror. (2) The recorded representation (commonly as a photo-image) of an object produced by optical, electro- optical, optical mechanical, or electronic means. It is generally used when the EMR emitted or reflected from a scene is not directly recorded on film. (A)
Image Enhancement: Any one of a group of opera- tions that improve the detectability of the targets or categories. These operations include, but are not limited to, contrast improvement, edge en- hancement, spatial filtering, noise supression, image smoothing, and image sharpening. (D)
Image Processing: Encompasses all the various op- erations that can be applied to photographic or image data. These include, but are not limited to, image compression, image restoration, image enhancement, preprocessing, quantization, spa- tial filtering and other image pattern recognition techniques. (D)
Image Restoration: A process by which a degraded image is restored to its original condition. Image restoration is possible only to the extent that the degradation transform is mathematically invertible. (D)
Incident ray: A ray lmpinging on a surface. (A)
Infrared: Pertaining to energy in the 0.7-100 microns wavelength region of the electromagnetic spectrum. For remote sensing, the infrared wavelengths are often subdivided into near infrared (0.7-1.3 microns), middle infrared (1.3-3.0 microns) and far infrared (7.0-15.0 microns). Far infrared is sometimes referred to as thermal or emissive infrared. (B)
Infrared, photographic: Pertaining to or designating the portion of the EM spectrum with wavelengths just beyond the red end of the visible spectrum; generally defined as from 0.7 to about 0.1 microns, or the useful limits of film sensitivities. (A)
Insolation: Incident solar energy. (C)
Instantaneous field of view: (IFOV) A term specif- ically denoting the narrow field of view designed into detectors, particularly scanning radiometer systems, so that, while as much as 1200 may be under scan, only EMR from a small area is being recorded at any one instant. (A)
Interactive image processing: The use of an operator or analyst at a console that provides the means of assessing, preprocessing, feature extracting, classifying, identifying, and displaying the original imagery or the processed imagery for his subjective evaluations and further inter- actions. (D)
Irradiance: The measure, in power units, of radiant flux incident upon a surface. It has the dimen- sions of energy per unit time (e.g., watts). (A)
Irradiation: The impinging of EMR on an object or surface. (A)
Kelvin: A thermometer scale starting at absolute zero (-273C approximately) and having degrees of the same magnitude as those of the Celsius thermometer. Thus, OC = 273K; 100C = 373K; etc.; also called the absolute scale, thermo- dynamic temperature scale. (A)
Kinetic temperature: The internal temperature of an object, which is determined by the molecular motion. Kinetic temperature is measured with a contact thermometer and differs from radiant temperature, which is a function of emissivity and internal temperature. (C)
Kirchhoff's Law: The radiation law which states that at a given temperature the ratio of the emissivity to the absorptivity for a given wave- length is the same for all bodies and is equal to the emissivity of an ideal blackbody at that temperature and wavelength. This important law asserts that good absorbers of a given wavelength are also good emitters of the wavelength. (A)
Lambertian surface: An ideal, perfectly diffusing surface, which reflects energy equally in all directions. (B)
Large scale: (1) Aerial photography with a repre- sentative fraction of 1:500 to 1:10,000. (2) Maps with a representative fraction (scale) greater than 1:100,000. (A)
Layover: Displacement of the top of an elevated feature with respect to its base on the radar image. The peaks look like dip-slopes. (A)
Light: Visible radiation (about 0.4-0.7 microms in wavelength) considered in terms of its luminous efficiency, i.e., evaluated in proportion to its ability to stimulate the sense of sight. (A)
Line, flight: A line drawn on a map or chart to represent the track over which an aircraft has been flown or is to fly. The line connecting the principal points of vertical aerial photographs. (A)
Lineament: A linear topographical or tonal feature on the terrain and on images and maps, which may represent a zone of structural weakness. (C)
Linear feature: A two-dimensional, straight to somewhat curved (usually) line, linear pattern, or alignment of discontinuous patterns evident in an image, photo, a map, which represents the expression of some degree of linearity of a single or diverse grouping of natural or cultural ground features. (Definition by N.M. Short.) Look direction: Direction in which pulses of micro- wave energy are transmitted by an SLAR system. Look direction is normal to the azimuth direc- tion. Also called range direction. (C)
Luminance: In photometry, a measure of the in- trinsic luminous intensity emitted by a source in a given direction, the illuminance produced by light from the source upon a unit surface area oriented normal to the line of sight at any dis- tance from the source, divided by the solid angle subtended by the source at the receiving surface. Also called brightness (luminance is preferred). (A)
Map: A representation in a plane surface, at an established scale, of the physical features (nat- ural, artificial, or both) of a part of the Earth's surface, with the means of orientation indicated. (A)
Map, large-scale: A map having a scale of 1:100,000 or larger. (A)
Map, medium-scale: A map having a scale from 1:100,000, exclusive, to 1:1,000,000, inclusive. (A)
Map, small-scale: A map having a scale smaller than 1:1,000,000. (A)
Map, thematic: A map designed to demonstrate particular features or concepts. In conventional use this term excludes topographical maps. (D)
Maximum likelihood rule: A statistical decision criterion to assist in the classification of over- lapping signatures; pixels are assigned to the class of highest probability. Mie scattering: Multiple reflection of light waves by atmospheric particles that have the approxi- mate dimensions of the wavelength of light. (C)
Micrometer (abbr. micron): A unit of length equal to one-millionth (10-6) of a meter or one-thou- sandth (10-3) Of a millimeter. (A)
Micron (abbr. micron): Equivalent to and replaced by micrometer, 10-6 m. (A)
Microwave: Electromagnetic radiation having wave- lengths between 1 m and 1 mm or 300-0.3 GHz in frequency, bounded on the short wave- length side by the far infrared (at 1 mm) and on the long wavelength side by very high-frequency radio waves. Passive systems operating at these wavelengths are sometimes called microwave systems. Active systems are called radar, although the literal definition of radar requires a distance-measuring capability not always includ- ed in active systems. The exact limits of the microwave region are not defined. (A)
Minimum distance classifier: A classification tech- nique that assigns raw data to the class whose mean falls the shortest Euclidean distance from it. Mosaic: An assemblage of overlapping aerial or space photographs or images whose edges have been matched to form a continuous pictorial representation of a portion of the Earth's surface. (A)
Mosaic, controlled: A mosaic that is laid to ground control and uses prints that have been rectified as shown to be necessary by the control. (A)
Mosaicking: The assembling of photographs or other images whose edges are cut and matched to form a continuous photographic representa- tion of a portion of the Earth's surface. (A)
Multiband system: A system for simultaneously observing the same (small) target with several filtered bands, through which data can be re- corded. Usually applied to cameras; may be used for scanning radiometers that use dispersant optics to split wavelength bands apart for viewing by several filtered detectors. (A)
Multichannel system: Usually used for scanning systems capable of observing and recording several channels of data simultaneously, prefer- ably through the same aperture. (A)
Multispectral: Generally used for remote sensing in two or more spectral bands, such as visible and IR. (A)
Multispectral (line) scanner: A remote sensing de- vice that operates on the same principle as the infrared scanner, except that it is capable of recording data in the ultraviolet and visible portions of the spectrum as well as the infrared. (A)
Multivariate analysis: A data-analysis approach that makes use of multidimensional interrelations and correlations within the data for effective discrimination. (B)
Nadir: (1) That point on the celestial sphere ver- tically below the observer, or 1800 from the zenith. (2) That point on the ground vertically beneath the perspective center of the camera lens. (A)
Nautical mile (abbr. knot): A unit of distance used principally in navigation. For practical naviga- tion it is usually considered the length of one minute of any great circle of the Earth, the meridian being the great circle most commonly used. Also called sea mile. (A)
Near range: Refers to the portion of an SLAR Image closest to the aircraft flight path. (C)
Noise: Random or regular interfering effects in the data which degrade its information-bearing quality. (B)
Orbit: The path of a satellite around a body under the influence of gravity. (C)
Overlap:The area common to two successive photos along the same flight strip; the amount of overlap is expressed as a percentage of photo area. Also called endlap. (A)
Overlay: (1) A transparent sheet giving information to supplement that shown on maps. When the overlay is laid over the map on which it is based, its details will supplement the map. (2) A tracing of selected details on a photograph, mosaic, or map to present the interpreted features and the pertinent detail. (A)
Panchromatic: Used for films that are sensitive to broadband (e.g., entire visible part of spectrum) EMR, and for broadband photographs. (A)
Passive system: A sensing system that detects or measures radiation emitted by the target. Com- pare active system. (A)
Pattern: (1) In a photo image, the regularity and characteristic placement of tones or textures. Some descriptive adjectives for patterns are reg- ular, irregular, random, concentric, radial, and rectangular. (2) The relations between any more-or-less independent parameters of a response, e.g., the pattern in the frequency domain of the response from an object. (A)
Pattern recognition: Concerned with, but not limited to, problems of: 1. pattern discrimination, 2. pattern classification 3. feature selection, 4. pattern identification 5. cluster identification 6. feature extraction, 7. preprocessing, 8. filtering, 9. enhancement, 10. pattern segmentation, 11. screening. (D)
Perspective: Representation, on a plane or curved surface, of natural objects as they appear to the eye. (A)
Photogrammetry: The art or science of obtaining reliable measurements by means of photogra- phy. (A)
Photograph: A picture formed by the action of light on a base material coated with a sensitized solu- tion that is chemically treated to fix the image points at the desired density. Usually now taken to mean the direct action of EMR bn the sensi- tized material. Compare Image. (A)
Photographic interpretation: The act of examining photographic images for the purpose of identi- fying objects and judging their significance. Photo interpretation, photointerpretation, and image interpretation are other widely used terms. (A)
Pitch: Rotation of an aircraft about the horizontal axis normal to its longitudinal axis, which causes a nose-up nose-down attitude. (C)
Picture: Representation of a scene by a photo- graphic positive print or transparency, made from a negative, produced by the direct action of actinic (visible) light or EMR outside the visible part of the spectrum and converted into visible EMR by an optical-mechanical or wholly electronic scanner. (A)
Pixel: (Derived from "picture element.") A data element having both spatial and spectral aspects. The spatial variable defines the apparent size of the resolution cell (i.e., the area on the ground represented by the data values), and the spectral variable defines the intensity of the spectral response for that cell in a particular channel. (B)
Planck's Law: An expression for the variation of monochromatic emittance (emissive power) as a function of wavelength of blackbody radiation at a given temperature; it is the most fundamen- tal of the radiation laws. (A)
Polarization:The direction of vibration of the electrical field vector of electromagnetic radia- tion. In SLAR systems polarization is either horizontal orvertical. (C)
Precision:A measure of the dispersion of the values observed when measuring a characteristic of elements of a population. The clustering of sample values about their own average. (D)
Pulse: (1) A variation of a quantity whose value is normally constant, this variation is characterized by a rise and a decay, and has a finite duration. (2) A short burst of EMR transmitted by the radar. (A)
Radar: Acronym for radio detection and ranging. A method, system or technique, including equip- ment components, for using beamed, reflected, and timed EMR to detect locate, and (or) track objects, to measure altitlde and to acquire a terrain image. In remote sensing of the Earth's or a planetary surface, it is used for measuring and, often, mapping the scattering properties of the surface. (A)
Radar beam: The vertical fan-shaped beam of EM energy produced by the radar transmitter. (A)
Radar shadow: A dark area of no return on a radar image that extends in the far-range direction from an object on the terrain that mtercepts the radarbeam. (C)
Radiance: The accepted term for radiant flux in power units (e.g., W) and not for flux density per solid angle (e.g., W cm-2 sr-l ) as often found in recent publications. (A)
Radiant flux: The time rate of the flow of radiant energy;radiant power. (B)
Radiant power: Rate of change of radiant energy with time. May be further qualified as spectral radiant power, at a given wavelength. (A)
Radiant temperature: Concentration of the radiant flux from a material. Radiant temperature is the product of the kinetic temperature multiplied by the emlsslvlty to the one-fourth power. (C)
Radiation: The emission and propagation of energy through space or through a material medium in the form of waves; for example, the emission and propagation of EM waves, or of sound and e3astic waves. The process of emitting radiant energ. (A)
Radiometer: An instrument for quantitively meas- uring the intensity of EMR in some band of wavelengths in any part of the EM spectrum. Usually used with a modifier, such as an IR radiometer or a microwave radiometer. (A)
Radiometric correction: Correcting gain and offset variations in MSS data. Procedure calibrates and corrects the radiation data provided by the Landsat sensor detectors. Range direction: For radar images this is the direc- tion in which energy is transmitted from the antenna and is normal to the azimuth direction. Also called look direction. (C)
Rayleigh-Jeans Law: An approximation to Planck's Law for blackbody radiation valid in the longer (microwave) wavelengths. It is almost always of sufficient accuracy for calculations in the radio and microwave regions of the spectrum. (A)
Rayleigh scattering: The wavelength-dependent scat- tering of electromagnetic radiation by particles in the atmosphere much smaller than the wave- lengths scattered. (B)
Real-aperture radar: SLAR system in which azi- muth resolwtion is determined by the physical length of the antenna and by the wavelength. The radar returns are recorded directly to pro- duce images. Also called brute-force radar. (C)
Real time: Time in which reporting on events or recording of events is simultaneous with the events. For example, the real time of a satellite is the time in which it simultaneously reports its environment as it encounters it; the real time of a computer is the time during which it is accept- ing data and performing operations on it. (A)
Reflectance: The ratio of the radiant energy re- flected by a body to that incident upon it. The suffix (-ance) implies a property of that particu- lar specimen surface. (A)
Reflection (EMR theory): EMR neither absorbed nor transmitted is reflected. Reflection may be diffuse when the incident radiation is scattered upon being reflected from the surface, or specular, when all or most angles of reflection are equal to the angle ofincidence. (A)
Reflectivity: A fundamental property of a material that has a reflecting surface and is sufficiently thick to be opaque. One may further qualify it as spectral reflectivity. The suffix (-ity) implies a property intrinsic with a given material, a limiting value. (A)
Refraction: The bending of EMR rays when they pass from one medium into another having a different index of refraction or dielectric co- efficient. EMR rays also bend in media that have continuous variations in their indices of refraction or dielectric coefficients. (A)
Registration: The process of geometrically aligning two or more sets of image data such that resolu- tion cells for a single ground area can be digitally or visually superposed. Data being registered may be of the same type, from very different kinds of sensors, or collected at different times. (B)
Remote sensing: In the broadest sense, the measure- ment or acquisition of information of some property of an object or phenomenon, by a recording device that is not in physical or inti- mate contact with the object or phenomenon under study, e.g., the utilization at a distance (as from an aircraft, spacecraft, or ship) of any device and its attendant display for gathering information pertinent to the environment such as measurements of force fields, electromagnetic radiation, or acoustic energy. The technique employs such devices as the camera, lasers, and radio frequency receivers, radar systems, sonar, seismographs, gravimeters, magnetometers, and scintillation counters. (A)
Resolution: The ability of an entire remote sensor system, including lens, antennae, display, ex- posure, processing, and other factors, to render a sharply defined image. It may be expressed as line pairs per millimeter or meter, or in many other ways. In radar, resolution usually applies to the effective beam-width and range measure- ment width, often defined as the half-power points. For infrared line scanners the resolution may be expressed as the instantaneous field of view. Resolution may also be expressed in terms of temperature or other physical property being measured. (A)
Resolution cell: The smallest area in a scene con- sidered as a unit of data. For Landsat-l and -2 the resolution cell approximates a rectangular ground area of 0.44 hectares or 1.1 acres (see pixel, instantaneous field ofview). (B)
Reststrahlen (residual) rays: The difference in intensities or radiance at certain frequencies (wavelengths) between the special signatures for the ideal (perfect blackbody) and actual emission curves of a substance. Return beam vidicon (RBV): A modified vidicon television camera tube, in which the output sig- nal is derived from the depleted electron beam reflected from the tube target. The RBV can be considered as a cross between a vidicon and an orthicon. RBVs provide highest resolution TV imagery, and are used in the ERTS (Landsat) series. (A)
Roll: Rotation of an aircraft about the longitudinal axis to cause a wing-up or wing-down attitude. (C)
Roughness: For radar images this term describes the average vertical relief of small-scale irregular- ities of the terrain surface. (C)
Sample: A subset of a population selected to obtain information conceming the characteristics of the population. (D)
Sampling rate: The temporal, spatial, or spectral rate at which measurements of physical quan- tities are taken. Temporally, sampling variables may describe how often data are collected or the rate at which an analog signal is sampled for conversion to digital format; the spatial sampling rate describes the number, ground size, and position of areas where spectral measurements are made, the spectral sampling rate refers to the location and width of the sensor's spectral channels with respect to the electromagnetic spectrum. (B)
Scale: The ratio of a distance on a photograph or map to its corresponding distance on the ground. The scale of a photograph varies from point to point because of displacements caused by tilt and relief, but is usually taken as f/H, where f is the principal distance (focal length) of the camera and H is the height of the camera above mean ground elevation. Scale may be expressed as a ratio 1:24,000; a representative fraction, 1/24,000; or an equivalence, 1 in. = 2,000 ft. (A)
Scan line: The narrow strip on the ground that is swept by the instantaneous field of view of a detector in a scanner system. (C)
Scanner: (1) Any device that scans, and thus pro- duces an image. See scanning radiometer. (2) A radar set incorporating a rotatable antenna, or radiator element, motor drives, mounting, etc. for directing a searching radar beam through space and imparting target information to an indicator. (A)
Scanning radiometer: A radiometer, which by the use of a rotating or oscillating plane mirror, can scan a path normal to the movement of the radiometer. (A)
Scattering: (1) The process by which small particles suspended in a medium of a different index of refraction diffuse a portion of the incident radiation in all directions. (2) The process by which a rough surface reradiates EMR incident upon it. (A)
Scene: In a passive remote sensing system, every- thing occurring spatially or temporally before the sensor, including the Earth's surface, the energy source, and the atmosphere, that the energy passes through as it travels from its source to the Earth and from the Earth to the sensor. (B)
Sensitivity: The degree to which a detector re- sponds to electromagnetic energy incident upon it. (c) Sensor: Any device that gathers energy, EMR or other, converts it into a signal and presents it in a form suitable for obtaining information about the environment. (A)
Sidelap:The extent of lateral overlap between images acquired on adjacent flight lines. (C)
Signal: The effect (e.g., pulse of electromagnetic energy) conveyed over a communication path or system. Signals are received by the sensor from the scene and converted to another form for transmission to the processing system. (B)
Signal-to-noise ratio: The ratio of the level of the information-b earing signal power to the level of the noise power. Abbreviated as S/N. Signature: Any characteristic or series of character- istics by which a material may be recognized in an image, photo, or data set. See also spectral signature. (A)
Signature analysis techniques: Techniques that use the variation in the spectral reflectance or emit- tance of objects as a method of identifying the objects. (A)
Signature extension: The use of training statistics obtained from one geographical area to classify data from similar areas some distance away; in- cludes consideration of changes in atmosphere, and other geographical and temporal conditions that can cause differences in signal level for single classes of interest (see spectral signature). (B)
Smoothing: The averaging of densities in adjacent areas to produce more gradual transitions. (A)
Slant range: For radar images this term represents the distance measured along a line between the antenna and the target. (C)
Software: The computer programs that drive the hardware components of a data processing sys- tem; includes system monitoring programs, programming language processors, data handling utilities, and data analysis programs. (B)
Spatial filter: An image transformation, usually a one-to-one operator used to lessen noise or enhance certain characteristics of the image. For any particular (x, y) coordinate on the transformed image, the spatial filter assignsa gray shade on the basis of the gray shades of a particular spatial pattern near the coordinates (x,y). (D)
Spatial information: Information conveyed by the spatial variations of spectral response (or other physical variables) present in the scene. (B)
Spectral band: An interval in the electromagnetic spectrum defined by two wavelengths, fre- quencies, or wavenumbers. (A)
Spectral intewal: The width, generally expressed in wavelength or frequency of a particular portion of the electromagnetic spectrum. A given sensor (e.g., radiometer or camera film) is designed to measure or be sensitive to energy received at the satellite from that part of the spectrum. Also termed spectralband. (A)
Spectral reflectance:The reflectance of electro- magnetic energy at specified wavelength inter- vals. (C)
Spectral regions: Conveniently designated ranges of wavelengths subdividing the electromagnetic spectrum, for example, the visible region, X-ray region, infrared region, middle-infrared region. (B)
Spectral response: The response of a material as a function of wavelength to incident electromag- netic energy, particularly in terms of the measur- able energy reflected from and emitted by the material. (B)
Spectral signature: Quantitative measurement of the properties of an object at one or several wave- length intervals. (A)
Spectrometer: A device to measure the spectral distribution of EMR. This may be achieved by a dispersive prism, grating, or circular interference filter with a detector placed behind a slit If one detector is used, the dispersive element is moved so as to sequentially pass all dispersed wavelengths across the slit. In an interferometer- spectrometer, on the other hand, all wavelengths are examined all the time, the scanning effect being achieved by rapidly oscillating two, partly reflective, (usually parallel) plates so that inter- ference fringes are produced. A Fourier transform is required to reconstruct the spectrum. Also called spectroradiometer. (A)
Specular reflection: The reflectance of electromag- netic energy without scattering or diffusion, as from a surface that is smooth in relation to the wavelengths of incident energy. Also called mirror reflection. (B)
Stefan-Boltzmann Law: One of the radiation laws stating that the amount of energy radiated per unit time from a unit surface area of an ideal blackbody is proportional to the fourth power of the absolute temperature of the blackbody. (B)
Steradian: The unit solid angle that cuts unit area from the surface of a sphere of unit radius centered at the vertex of the solid angle. There are 4pi steradians in a sphere. (A)
Subtractive color process: A method of creating essentially all colors through the subtraction of light of the three subtractive color primaries (cyan, magenta and yellow) in various propor- tions through use of a single white light source. (A)
Supervised classification: A computer-implemented process through which each measurement vector is assigned to a class according to a specified decision rule, where the possible classes have been defined on the basis of representative train- ing samples of known identity. (B)
Swath width (total field of view): The overall plane angle or linear ground distance covered by a multispectral scanner in the across-track direc- tion. (B)
Synchronous satellite: An equatorial west-to-east satellite orbiting the Earth at an altitude of 34,900 km, at which altitude it makes one revolution in 24 h synchronous with the Earth's rotation. (A)
Synoptic view: The ability to see or otherwise measure widely dispersed areas at the same time and under the same conditions; e.g., the overall view of a large portion of the Earth's surface which can be obtained from satellite altitudes. (B)
System: Structured organization of people, theory, methods and equipment to carry out an assigned set of tasks. (D)
Target: (1) An object on the terrain of specific interest in a remote sensing investigation. (2) The portion of the Earth's surface that produces by reflection or emission the radiation measured by the remote sensing system. (B,C) Thermal band: A general term for middle-infrared wavelengths which are transmitted through the atmosphere window at 8-14 micron. Ocasionally also used for the windows around 3-6 micron. (A)
Thermal capacity (symbol, C): The ability of a material to store heat, expressed in cal g-l C-l (C)
Thermal conductivity (symbol K): The measure of the rate at which heat passes through a material, expressed in cal cm-l s-l C-1. (c) Thermalcrossover: On a plot ofradiant temperature versus time, this refers to the point at which the temperature curves for two different materials intersect. (C)
Thermal inertia (symbol, P): A measure of the response of a material to temperature changes, expressed in cal cm-2 C-1 s-1/2. (C)
Thermal infrared: The preferred term for the middle wavelength range of the IR region, extending roughly from 3 micron at the end of the near infrared, to about 15 or 20 micron, where the far infrared begins. In practice the limits represent the envelope of energy emitted by the Earth behaving as a gray body with a surface temperature around 290"K (27 "C). (A)
Threshold: The boundary in spectral space beyond which a data point, or pixel, has such a low probability of inclusion in a given class that the pixel is excluded from that class. (D)
Tone: Each distinguishable shade of gray from white to black on an image. (C)
Training: Informing the computer system which sites to analyze for spectral properties or signa- tures of specific land cover classes; also called signature extraction. Training samples: The data samples of known iden- tity used to determine decision boundaries in the measurement or feature space prior to class- ification of the overall set of data vectors from a scene. (B)
Training sites: Recognizable areas on an image with distinct (spectral) properties useful for identifying other similar areas. Transmissivity: Transmittance for a unit thickness sample. One may further qualify it as spectral transmissivity. The suffix (ity) implies a prop- erty intrinsic with a given material. (A)
Transmittance: The ratio of the radiant energy transmitted through a body to that incident upon it The suffix (-ance) implies a property of that particular specimen. (A)
Ultraviolet radiation: EMR of shorter wavelength than visible radiation but longer than X-rays, roughly, radiation in the wavelength interval between 10 and 4000 A. Variance: Variance of a random variable is the expected value of the square of the deviation between that variable and its expected value. It is a measure of the dispersion of the individual unit values about their mean. (D)
Vidicon: (1) A storage-type electronically scanned photoconductive television camera tube, which often has a response to radiations beyond the limits of the visible region. Particularly useful in space applications, as no film is required. (2) An image-plane scanning device. See return beam vidicon. (A)
Vignetting: A gradual reduction in density of parts of a photographic image caused by the stopping of some of the rays entering the lens. (A)
Visible wavelengths: The radiation range in which the human eye is sensitive, approximately 04- 0.7micron. (B)
Wavelength (symbol h): Wavelength velocity/fre- quency. In general, the mean distance between maxima tor minima) of a roughly periodic pattern. Specifically, the least distance between particles moving in the same phase of oscillation in a wave disturbance. Optical and IR wave- lengths are measured in nanometers (10-9 m), micrometers (l0-6 m) and Angstroms (lO-l0 m). (A)
Wiens Displacement Law: Describes the shift of the radiant power peak to shorter wavelengths with Increasmg temperature. (C)
Window: A band of the electromagnetic spectrum which offers maximum transmission and minimal attenuation through a particular medium with the use ofa specific sensor. (D)
Yaw: Rotation of an aircraft about its vertical axis, causing the longitudinal axis to deviate from the flightline. (C)
Zenith: The point in the celestial sphere that is exactly overhead: opposed to nadir. (A)