absorption band-Wavelength interval within which electromagnetic radiation is absorbed by the atmosphere or by other substances.

advanced very high resolution radiometer (AVHRR)-Crosstrack multispectral scanner on a NOAA polar-orbiting satellite that acquires five spectral bands of data (0.55 to 12.50 µm) with a ground resolution cell of 1.1 by 1.1 km.

aerial photograph-a photograph of the Earth's surface taken (either directly downward or obliquely) from an airplane.

airborne visible and infrared imaging spectrometer (AVIRIS)-Experimental airborne along-track multispectral scanner under development at JPL to acquire 224 images in the spectral region from 0.4 to 2.4 µm.

albedo (A)-Ratio of the amount of electromagnetic energy reflected by a surface to the amount of energy incident upon it.

altimeter-An instrument which indicates the vertical distance above a specified datum plane.

ancillary data-In remote sensing, secondary data pertaining to the area or classes of interest, such as topographic, demographic, or climatological data.

angular field of view-Angle subtended by lines from a remote sensing system to the outer margins of the strip of terrain that is viewed by the system.

aperture-Opening in a remote sensing system that admits electromagnetic radiation to the film in radar systems.

apogee- The farthest point in an elliptical orbit of a satellite from the body, e.g., the Earth, which it is orbiting.

artifact-A feature on an image which is produced by the optics of the system or by digital image processing, and sometimes masquerades as a real feature.

atmospheric correction-Image-processing procedure that compensates for effects of selectivity scattered light in multispectral images.

attitude-Angular orientation of remote sensing system with respect to a geographic reference system.

AVHRR-Advanced Very High Resolution Radiometer, a multispectral imaging system carried by the TIROS-NOAA series of meteorological satellites.

AVIRIS-Airborne visible and infrared imaging spectrometer.

background-Area on an image or the terrain that surrounds an area of interest, or target.

background noise-Ambient response of the recorder or receiver either independent of the signal or added to that signal.

backscatter-In radar, the portion of the microwave energy scattered by the terrain surface directly back toward the antenna.

backscatter coefficient-A quantitative measure of the intensity of energy returned to a radar antenna from the terrain.

band-A wavelength interval in the electromagnetic spectrum. For example, in Landsat images the bands designate specific wavelength intervals at which images are acquired.

bandwidth-The number of cycles per second between the limits of a frequency band; also the range of frequencies recorded by an antenna.

base-height ratio-Air base divided by aircraft height. This ratio determines vertical exaggeration on stereo models.

beam-A focused pulse of energy.

beam width-A measure of the concentration of power of a directional antenna.

calibration the process of quantitatively defining the system response to known, controlled signal inputs.

centerpoint-The optical center of a photograph.

charge-coupled device (CCD)-A device in which electron are stored at the surface of a semiconductor.

classification-Process of assigning individual pixels of an image to categories, generally on the basis of spectral reflectance characteristics.

clustering-The analysis of a set of measurements to detect their inherent tendency to form clusters in multispectral space.

contrast enhancement-Image-processing procedure that improves the contrast ratio of images. The original narrow range of digital values is expanded to utilize the full range of available digital values.

contrast filter-A color filter chosen to make a colored subject stand out sharply from surrounding objects.

contrast ratio-On an image, the ratio of reflectances between the brightest and darkest parts of an image.

contrast stretching-Expanding a measured range of digital numbers in an image to a larger range, to improve the contrast of the image and its component parts.

control point-Any station in a horizontal and/or vertical control system that can be identified on a photograph and used for correlating the data shown on that photo.

digital image-An image where the property being measured has been converted from a continuous range of analogue values to a range expressed by a finite number of integers, usually recorded as binary codes from 0 to 255, or as one byte.

digital image processing-Computer manipulation of the digital-number values of an image.

digital number (DN)-Value assigned to a pixel in a digital image.

digitization-Process of converting an analog display into a digital display.

distortion-On an image, changes in shape and position of objects with respect to their true shape and position.

Doppler principle-Describes the change in observed frequency that electromagnetic or other waves undergo as a result of the movement of the source of waves relative to the observer.

Earth Science Enterprise (ESE)-An ongoing NASA program that will use space platforms with several multipurpose sensors to gather information about the Earth System.

edge enhancement-Image-processing technique that emphasizes the appearance of edges and lines.

electromagnetic radiation (EMR)-Energy propagated in the form of and advancing interaction between electric and magnetic fields. All electromagnetic radiation moves at the speed of light.

electromagnetic spectrum-Continuous sequence of electromagnetic energy arranged according to wavelength or frequency.

element-The smallest definable object of interest in the survey; it is a single item in a collection, population, or sample.

enhancement-Process of altering the appearance of an image so that the interpreter can extract more information.

EROS Data Center (EDC)-Facility of the U.S. Geological Survey at Sioux Falls, South Dakota, that archives, processes, and distributes images.

false color image-A color image where parts of the non-visible EM spectrum are expressed as one or more of the red, green, and blue components, so that the colors produced by the Earth's surface do not correspond to normal visual experience. Also called a false-color composite (FCC). The most commonly seen false-color images display the very-near infrared as red, red as green, and green as blue.

false color photograph-Another term for IR color photograph.

far infrared- Extends through the thermal or emissive infrared region (5.6 - 1000 µm).

feature-Has several meanings, depending on context: 1) overall appearance; 2) a set of measurable properties diagnostic of a class or material; 3) referring to geometric or geomorphic entities, such as a hill, stream, on anything found on a natural or manmade surface.

field of view-The solid angle through which an instrument is sensitive to radiation.

film-Light-sensitive photographic emulsion and its base.

filtering-In analysis, the removal of certain spectral or spatial frequencies to highlight features in the remaining image.

flight path-Line on the ground directly beneath a remote sensing aircraft or space craft. Also called flight line.

focal length-In cameras, the distance from the optical center of the lens to the plane at which the image of a very distant object is brought into focus.

Fourier Analysis-A mathematical procedure that breaks complex sinusoidal curves into the sets of different harmonics that cause the observed variations.

gain-Denotes an increase in signal power or amplification.

Gaussian-A statistical term that refers to the normal distribution of values.

GCP-Ground-control point: a geographic feature of known location that is recognizable on an image and can be used to determine geometrical corrections.

geocoding-Geographic referencing or coding of the location of data items.

geoid-The figure or shape of the Earth as generalized by extending mean sea level continuously through the continents.

geometric correction-Image-processing procedure that corrects spatial distortions in an image.

Geostationary Operational Environmental Satellite-a NOAA satellite that acquires visible and thermal IR images for meteorologic purposes.

geostationary orbit-An orbit at 41 000 km in the direction of the Earth's rotation, which matches speed so that a satellite remains over a fixed point on the Earth's surface.

Goddard Space Flight Center (GSFC)-The NASA facility at Greenbelt, Maryland, that is also a Landsat ground receiving station.

GMT-Greenwich mean time. This international 24-h system is used to designate the time at which Landsat images are acquired.

GOES-Geostationary Operational Environmental Satellite.

gray scale-A sequence of gray tones ranging from black to white.

ground-control point-A geographic feature of known location that is recognizable on images and can be used to determine geometric corrections.

ground receiving station-Facility that records data transmitted by a satellite, such as Landsat.

ground resolution cell-Area on the terrain that is covered by the IFOV of a

ground truth-Jargon coined for data, information, and observations obtained on the surface or subsurface about features or classes, used to aid in interpretation of remotely sensed data; ground data is a preferred term.

GSFC-Goddard Space Flight Center

high-pass filter-A spatial filter which selectively enhances contrast variations with high spatial frequencies in an image. It improves the sharpness of images and is a method of edge enhancement.

histogram-A means of expressing the frequency of occurrence of values in a data set within a series of equal ranges or bins, the height of each bin representing the frequency at which values in the data set fall within the chosen range. A cumulative histogram expresses the frequency of all values falling within a bin and lower in the range. A smooth curve derived mathematically from a histogram is termed the probability density function (PDF).

hue-In the IHS system, represents the dominant wavelength of a color.

hyperspectral-Refers to sensors that measure radiation in very narrow bandwidths (typically, around 0.02 µm), from which a quasi-continuous spectral curve can be produced.

IFOV-Instantaneous field of view; that recorded from a small area in a very brief interval of time.

IHS-Intensity, hue, and saturation system of colors.

image-pictorial representation of a scene recorded by a remote sensing system. Although image is a general term, it is commonly restricted to representations acquired by non-photographic methods.

image enhancement-Any of a group of operations (e.g., contrast stretch, spatial filtering) that improve the detectability and presentation of targets or categories in an image.

image processing-Encompasses all the various operations that can be applied to producing the final photographic or computer-based image rendition.

image swath-See ground swath.

incidence angle-In radar, the angle formed between an imaginary line normal to the surface and another connecting the antenna and the target.

index of refraction (n) -Ratio of the wavelength or velocity of electromagnetic radiation in a vacuum to that in a substance.

infrared-Pertaining to EMR in the 0.7 to 100 µm region of the spectrum.

instantaneous field of view (IFOV)- Solid angle through which a detector is sensitive to radiation. In a scanning system, the solid angle subtended by the detector when the scanning motion is stopped.

intensity-In the IHS system, brightness ranging from black to white.

interpretation-The process in which a person extracts information from an image.

interpretation key-Characteristic or combination of characteristics that enable an interpreter to identify an object on an image.

IR-Infrared region of the electromagnetic spectrum that includes wavelengths from 0.7µm to 1 mm.

Johnson Space Flight Center (JSC)-A NASA facility in Houston, Texas, home of the manned spacecraft program.

JPL-Jet Propulsion Laboratory, a NASA facility at Pasadena, California, operated under contract by the California Institute of Technology.

Ka band-Radar wavelength region from 0.8 to 1.1 cm.

kernel-Two-dimensional array of digital numbers used in digital filtering.

kinetic energy-The ability of a moving body to do work by virtue of its motion. The molecular motion of matter is a form of kinetic energy.

kinetic temperature-Internal temperature of an object determined by random molecular motion. Kinetic temperature is measured with a contact thermometer.

Kirchhoff's Law-The radiation law which states that at a given temperature the ratio of the emissivity to the absorptivity for a given wavelength is the same for all bodies and is equal to the emissivity of an ideal blackbody at that temperature and wavelength.

KSC-Kennedy Space Center, NASA's main launch facility at Cape Canaveral.

Lambertian surface-An ideal, perfectly diffusing surface, which reflects energy equally in all directions.

large scale-Aerial photography with a representative fraction of 1:500 to 1:10000; maps with a RF (scale) greater than 1:100000.

L band-Radar wavelength region from 15 to 30 cm.

lens-One or more pieces of glass or other transparent material shaped to form an image by refraction of light.

lidar-Light intensity detection and ranging, which uses lasers to stimulate fluorescence in various compounds and to measure distances to reflecting surfaces.

light-Electromagnetic radiation ranging from 0.4 to 0.7µm in wavelength that is detectable by the human eye.

look angle-The angle between the vertical plane containing a radar antenna and the direction of radar propagation. Complementary to the depression angle.

look direction-Direction in which pulses of microwave energy are transmitted by a radar system. The look direction is normal to the azimuth direction. Also called range direction.

look-up table (LUT)-A mathematical formula used to convert one distribution of data to another, most conveniently remembered as a conversion graph.

low-sun-angle photograph-Aerial photograph acquired in the morning, evening, or winter when the sun is at a low elevation above the horizon.

map projection-A systematic drawing of lines on a plane surface to represent the parallels or latitude and the meridians or longitude of the Earth.

median filter-A spatial filter, which substitutes the median value of DN from surrounding pixels for that recorded at an individual pixel. It is useful for removing random noise.

medium scale-Ranging between 1:100000 to 1:1000000.

microwave-Region of the electromagnetic spectrum in the wavelength range of 0.1 to 30 cm.

mid-infrared (MIR)-The range of EM wavelengths from 2.5 to 5.6 µm.

Mie scattering-The scattering of EM energy by particles in the atmosphere with comparable dimensions to the wavelength involved.

mixed pixel-A pixel whose DN represents the average energy reflected or emitted by several types of surface present within the area that it represents on the ground.

mosaic-Composite image or photograph made by piecing together individual images or photographs covering adjacent areas.

MSS-Multispectral scanner system of Landsat that acquires images of four wavelength bands in the visible and reflected IR regions.

multispectral-Refers to use of two or more bands in remote sensing.

multispectral classification-Identification of terrain categories by digital processing of data acquired by multispectral scanners.

multispectral scanner-Scanner system that simultaneously acquires images of the same scene at different wavelengths.

multivariate analysis-A data-analysis approach that makes use of multidimensional interrelations and correlation within the data for effective discrimination.

nadir-Point on the ground directly in line with the remote sensing system and the center of the earth.

NASA-National Aeronautical and Space Administration.

near infrared (NIR)-The shorter wavelength range of the infrared region of the EM spectrum, from 0.7 to 2.5 µm. It is often divided into very-near infrared (VNIR) covering the range accessible to photographic emulsions (0.7 to 1.0 µm), and the short-wavelength infrared (SWIR) covering the remainder of the NIR atmospheric window from 1.0 to 2.5 µm.

near range-Refers to the portion of a radar image closest to the aircraft or satellite flight path.

negative photograph-Photograph on film or paper in which the relationship between bright and dark tones is the reverse of that of the features on the terrain.

NHAP-National High Altitude Photography program of the U.S. Geological Survey.

NOAA-National Oceanic and Atmospheric Administration.

noise-Random or repetitive events that obscure or interfere with the desired information.

nondirectional filter-Mathematical filter that treats all orientations of linear features equally.

non-selective scattering-The scattering of EM energy by particles in the atmosphere which are much larger than the wavelengths of the energy, and which causes all wavelengths to be scattered equally.

non-spectral hue-A hue which is not present in the spectrum of colors produced by the analysis of white light by a prism of diffraction grating. Examples are brown, magenta, and pastel shades.

nonsystematic distortion-Geometric irregularities on images that are not constant and cannot be predicted from the characteristics of the imaging system.

oblique photograph-Photograph acquired with the camera intentionally directed at some angle between horizontal and vertical orientations.

orbit-Path of a satellite around a body such as the earth, under the influence of gravity.

orthophotograph-A vertical aerial photograph from which the distortions due to varying elevation, tilt, and surface topography have been removed, so that it represents every object as if viewed directly from above.

overlay-A transparent sheet giving information to supplement that shown on maps; a tracing of selected details on a photograph.

overlap-Extent to which adjacent images or photographs cover the same terrain, expressed as a percentage.

panchromatic film-Black and white film that is sensitive to all visible wavelengths.

panorama-A photograph of a wide expanse of terrain, taken from on or near the surface; a series of overlapping photographs.

parallax-Displacement of the position of a target in an image caused by a shift in the observation system.

parallax difference-The difference in the distance on overlapping vertical photographs between two points, which represent two locations on the ground with different elevations.

parameter-Any quantity in a problem or equation that is not an independent variable; can be assigned arbitrary values in solution of problem.

pass-In digital filters, refers to the spatial frequency of data transmitted by the filter. High-pass filters transmit high-frequency data; low-pass filters transmit low-frequency data.

passive microwaves-Radiation in the 1 mm to 1 m range emitted naturally by all materials above absolute zero.

passive remote sensing-Remote sensing of energy naturally reflected or radiated from the terrain.

path-and-row index-System for locating Landsat MSS and TM images.

pattern-Regular repetition of tonal variations on an image or photograph.

P-band-A frequency band used in radar extending from 225 to 390 Hz.

perigee-The orbital point nearest the body about which a satellite is orbiting.

periodic line dropout-Defect on Landsat MSS or TM images in which no data are recorded for every sixth or sixteenth scan line, causing a black line on the image.

periodic line striping-Defect on Landsat MSS or TM images in which every sixth or sixteenth scan line is brighter or darker than the others. Caused by the sensitivity of one detector being higher or lower than the others.

perspective-Representation on a plane or curved surface of objects as they appear to the eye.

photograph-Representation of targets on film that results from the action of light on silver halide grains in the film's emulsion.

photographic IR-Short-wavelength portion (0.7 to 0.9 µm) of the IR band that is detectable by IR color film or IR black-and-white film.

photographic UV-Long-wavelength portion of the UV band (0.3 to 0.4 µm) that is transmitted through the atmosphere and is detectable by film.

photomosaic-Mosaic composed of photographs.

picture element-In a digitized image, the area on the ground represented by each digital number. Commonly contracted to pixel.

pitch-Rotation of an aircraft about the horizontal axis normal to its longitudinal axis that causes a nose-up or nose-down attitude.

pixel-Contraction of picture element; the spatial variable defines the apparent size of the resolution cell and the spectral variable defines the intensity of the spectral response (at specified wavelength[s]) for that cell.

point spread function (PSF)- The image of a point source of radiation, such as a star, collected by an imaging device. A measure of the spatial fidelity of the device.

polarization-The direction of orientation in which the electrical field vector of electromagnetic radiation vibrates.

polar orbit-An orbit that passes close to the poles, thereby enabling a satellite to pass over most of the surface, except the immediate vicinity of the poles themselves.

polarized radiation-Electromagnetic radiation in which the electrical field vector is contained in a single plane, instead of having random orientation relative to the propagation vector. Most commonly refers to radar images.

precision-A (statistical) measure of the dispersion of the values observed when measuring a characteristic of elements in a population; a clustering of values about their average.

primary colors-A set of three colors that in various combinations will produce the full range of colors in the visible spectrum. There are two sets of primary colors, additive and subtractive.

principal component analysis-The analysis of covariance in a multiple data set so that the data can be projected as additive combinations on to new axes, which express different kinds of correlation among the data.

principal point-Optical center of an aerial photograph.

probability density function (PDF)-A function indicating the relative frequency with which any measurement may be expected to occur. In remote sensing it is represented by the histogram of DN in one band for a scene.

pushbroom system-An imaging device consisting of a fixed linear array of many sensors which is swept across an area by the motion of the platform, thereby building up an image. It relies on sensors whose response and reading is nearly instantaneous, so that the image swathe can be segmented into pixels representing small dimensions on the ground.

quantization-The process of converting from continuous values of information to a finite number of discrete values.

radar-Acronym for radio detection and ranging. Radar is an active form of remote sensing that operates in the microwave and radio wavelength regions.

radial relief displacement-The tendency of vertical objects to appear to learn radially away from the center of a vertical aerial photograph. Caused by the conical field of view of the camera lens.

radian-Angle subtended by an arc of a circle equal in length to the radius of the circle 1 rad = 57.3¡.

radiance-Radiant flux in power units (e.g. Watts) leaving an extended source in some direction.

radiant temperature-Concentration of the radiant flux from a material. Radiant temperature is the kinetic temperature multiplied by the emissivity to the one-fourth power.

raster-The scanned and illuminated area of a video display, produced by a modulated beam of electrons sweeping the phosphorescent screen line by line from top to bottom at a regular rate of repetition.

raster format-A means of representing spatial data in the from of a grid of DN, each line of which can be used to modulate the lines of a video raster.

Rayleigh scattering-Selective scattering of light in the atmosphere by particle that are small compared with the wavelength of light.

real time-Refers to images or data made available for inspection simultaneously with their acquisition.

rectification-The process of projecting or transforming a tilted or oblique photograph onto a horizontal reference plane, the angular relation between the photograph and the plane being determined by ground reconnaissance.

reflectance-Ratio of the radiant energy reflected by a body to the energy incident on it. Spectral reflectance is the reflectance measured within a specific wavelength interval.

registration-Process of superposing two or more images or photographs so that equivalent geographic points coincide.

relief-Vertical irregularities of a surface; local difference in elevations.

relief displacement-Geometric distortion on vertical aerial photographs. The tops of objects appear in the photograph to be radially displaced from their bases outward from the photograph's centerpoint.

remote sensing-collection and interpretation of information about an object without being in physical contact with the object.

resampling-The calculation of new DN for pixels created during geometric correction of a digital scene, based on the values in the local area around the uncorrected pixels.

resolution-Ability to separate closely spaced objects on an image or photograph. Resolution is commonly expressed as the most closely spaced line-pairs per unit distance that can be distinguished. Also called spatial resolution.

roughness-In radar, the average vertical relief of a small-scale irregularities of the terrain surface. Also called surface roughness.

sample-A subset of a population selected to obtain information concerning the characteristics of the entire population.

saturation-In the IHS system, represents the purity of color. Saturation is also the condition where energy flux exceeds the sensitivity range of a detector.

scale-Ratio of distance on an image to the equivalent distance on the ground.

scan line-Narrow strip on the ground that is swept by IFOV of a detector in a scanning system.

scanner-An imaging system in which the IFOV of one or more detectors is swept across the terrain.

scanner distortion-Geometric distortion that is characteristic of cross-track scanner images.

scattering-Multiple reflections of electromagnetic waves by particles in the atmosphere or from surfaces.

sensor-Device that receives electromagnetic radiation and converts it into a signal that can be recorded and displayed as either numerical data or an image.

sidelap-Extent of lateral overlap between images acquired on adjacent flight lines.

side-looking airborne radar (SLAR)-An airborne side scanning system for acquiring radar images.

signal-Information recorded by a remote sensing system; the effect of a pulse of EMR conveyed over a communication path onto a sensor.

signal to noise radio (S/N)-The ratio of the level of the signal carrying real information to that carrying spurious information as a result of defects in the system.

signature- Any characteristic or series of characteristics by which a material or object may be recognized in an image, photo, or data set.

SLAR-Side-looking airborne radar.

small-scale-For aerial photos, those with a representative fraction smaller than 1:40000; for maps, RF less than 1:1,000,000.

smoothing-The averaging of densities in adjacent areas to produce more gradual transitions.

spectral band- An interval in the electromagnetic spectrum defined by two end wavelengths.

spectral hue-A hue which is present in the spectral range of white light analyzed by a prism or diffraction grating.

spectral interval-The width, generally expressed as wavelength or frequency, of a particular portion of the EM spectrum.

spectral reflectance-Reflectance of electromagnetic energy at specified wavelength intervals.

spectral sensitivity-Response, or sensitivity, of a film or detector to radiation in different spectral regions (designated ranges of wavelengths).

spectral signature-Quantitative measurement of the properties of an object or material over one to several wavelength intervals; the diagnostic spectral response for that entity.

spectral vegetation index-An index of relative amount and vigor of vegetation. The index is calculated from two spectral bands of AVHRR imagery.

spectrometer-Device for measuring intensity of radiation absorbed or reflected by a materiel as a function of wavelength.

spectrum-Continuous sequence of electromagnetic energy arranged according to wavelength or frequency.

SPOT-Systeme Probatoire d'Observation del la Terre. Unmanned French remote sensing satellite orbiting in the late 1980s.

Stefan-Boltzmann constant- 5.68 x 10 ^-12 W . cm^-2 .K^-4; appropriate to Law of same name stating that the amount of energy radiated per unit time from a unit surface of an ideal blackbody is proportional to the fourth power of the absolute temperature (in units of K) of that body.

Stereo base-Distance between a pair of correlative points on a stereo pair that are oriented for stereo viewing.

stereo pair-Two overlapping images or photographs that may be viewed stereoscopically.

subscene-A portion of an image that is used for detailed analysis.

subtractive primary colors-Yellow, magenta, and cyan. When used as filters for white light, these colors remove blue, green and red light, respectively.

sun-synchronous-Earth satellite orbit in which the orbit plane is nearly polar and the altitude is such that the satellite passes over all places on earth having the same latitude twice daily at the same local sun time.

supervised classification-Digital-information extraction technique in which the operator provides training-site information that the computer uses to assign pixels to categories.

swath width-The overall plane angle or linear ground distance covered by a scanner in the across-track dimension.

synchronous satellite-An equatorial west to east satellite orbiting the Earth at 34,900 km, at which altitude it makes one revolution in 24 hours synchronous with the Earth's rotation.

synoptic view-The ability to see or otherwise measure widely dispersed areas at the same time and under the same conditions.

systematic distortion-Geometric irregularities on images that are caused by known and predictable characteristics.

terrain-Surface of the earth.

texture-Frequency of change and arrangement of tones on an image.

thematic map-A map designed to demonstrate particular features or concepts.

Thematic Mapper (TM)- A cross-track scanner deployed on Landsat that records seven bands of data from the visible through the thermal IR regions.

thermal band-Generally, refers to thermal IR intervals associated with atmospheric windows, at 3-5 and 8-14 *micro;m wavelengths.

thermal IR-Generally, the IR region from 3 to 1000µm; specifically connotes the two intervals employed in remote sensing (3-5 and 8-14 &micr;m) This spectral region spans the radiant power peak of the earth.

tie-point-A point on the ground which is common to two images. Several are used in the co registration of images.

tilt-The angle between the optic axis of the camera or sensor and the plumb line to a given photo or image.

tone-Each distinguishable shade of gray from white to black on an image.

topographic inversion-An optical illusion that may occur on images with extensive shades. Ridges appear to be valleys, and valleys appear to be ridges. The illusion is corrected by orienting the image so that the shadows trend from the top margin of the image to the bottom.

topographic reversal-A geomorphic phenomenon in which topographic lows coincide with structural highs and vice versa. Valleys are eroded on crests of anticlines to cause topographic lows, and synclines form ridge, or topographic highs.

tracking-The process of following the movement of a satellite or rocket by radar, radio, or photographic observations.

as Landsat.

training site-Area of terrain with known properties or characteristics that is used in supervised classification.

transmissivity-Property of a material that determines the amount of energy that can pass through the material.

transmittance-The ratio of the radiant energy transmitted through a body to that incident upon it.

transparency-Image on a transparent photographic material, normally a positive image.

uncontrolled mosaic-A mosaic made without correction for any type of distortion.

unsupervised classification-Digital information extraction technique in which the computer assigns pixels to categories with no instructions from the operator.

UV-Ultraviolet region of the electromagnetic spectrum ranging in wavelengths from 0.01 to 0.4m.

Validation the process of assessing by independent means the quality of the data products derived from the system outputs.

Vandenberg AFB-military and civilian rocket launch facilities, including the Landsats.

variance-A measure of the dispersion of the actual values of a variable about its mean. It is the mean of the squares of all the deviations from the mean value of a range of data.

vector format-The expression of points, lines, and areas on a map by digitized Cartesian coordinates, directions, and values.

Verification the process of proving that the system performance is within specification.

vertical exaggeration-In a stereo model, the extent to which the vertical scale appears larger than the horizontal scale.

volume scattering-In radar, interaction between electromagnetic radiation and the interior of a material.

wavelength-Distance between successive wave crests or other equivalent points in a harmonic wave.

window-A band of EMR which offers maximum obtainable transmission and minimal attenuation through a particular medium with use of a specific sensor; wavelengths of optimum sensing.

X band-Radar wavelength region from 2.4 to 3.8 cm.

yaw-Rotation of an aircraft about its vertical axis so that the longitudinal axis deviates left or right from the flight line.

ERS-1 Calibration and Validation, ESA bulletin no 65, February 1991, by E. Attema and R. Francis.

Manual of Remote Sensing, Leonard Bowden, American Society Photogrammetry and Remote Sensing, Falls Church VA, copyright 1975.