GLOSSARY OF TERMS AND ACRONYMS
| AVHRR | Advanced Very High Resolution Radiometer |
| AWAR | Area Weighted Average Resolution |
| ABSORPTION | A process by which radiation is coverted to other types of energy (especially heat) by a material. |
| ACTIVE REMOTE SENSING | Remote sensing methods that provide their own source of electromagnetic radiation, e.g., Radar. |
| ADDITIVE PRIMARY COLOURS | The colours blue, green and red. Filters of these colours transmit the primary colour of the filter and absorb the other two colours. |
| ALBEDO | The ratio of the amout of electromagnetic energy reflected by a surface to the amout of energy incident upon it. The symbol is A. |
| ALTIMETER (ALT) | Instrument which determines the altitude of an object with respect to a fixed level such as sea level. |
| 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 represented by directly measurable quantities such as voltages or resistances. Analog computing methods contrast with digital methods in which values are treated numerically. |
| ANGLE OF INCIDENCE | (1) The angle between the direction of incoming EMR and the normal to the intercepting surface; |
| (2) In SLAR systems this is the angle between the vertical and a line connecting the antenna and the target. | |
| ANGSTROM (Å) | A measurement of length (10-10m). |
| ANGULAR FIELD OF VIEW | The angle subtended by lines from a remote sensing system to the outer margins of the strip of terrain that is viewed by the system. |
| ANTENNA | The device that transmits and/or receives microwave and radio energy. |
| ASPECT ANGLE | Same as angle of incidence in SLAR. |
| ATMOSPHERE | The layer of gases that surround some planets. |
| ATMOSPHERIC WINDOWS | Wavelength intervals at which atmosphere transmits most electromagnetic radiation. |
| ATTITUDE | The angle of orientation of a remote sensing system with respect to a geographic reference system. |
| AZIMUTH | The geographic orientation of a line given as an angle measured clockwise from north. |
| BACKSCATTER | (1) 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; |
| (2) In SLAR usage this refers to the portion of the microwave energy scattered by the terrain surface that is directed back towards the antenna. | |
| BAND | A wavelength interval in the electromagnetic spectrum. For example, in LANDSAT the bands designate specific wavelength intervals at which images are required. |
| BEAM | A focused pulse of energy. |
| BEAM WIDTH | In SLAR usage this is the angle subtended in the horizontal plane by the radar beam. |
| BINARY | A numerical system using the base 2. |
| BIT | In digital compute terminology, this is a binary digit that is an exponent of the base 2. |
| BLACKBODY | A substance that radiates energy at the maximum possible rate per unit area at each wavelength for any given temperature. A blackbody also absorbs all energy that falls on it. |
| BRIGHTNESS | Magnitude of the response produced in the eye by light. |
| BRUTE FORCE RADAR | See Real-aperture Radar. |
| BYTE | A group of eight bits of digital data. |
| CCT | See Compute Compatible Tape |
| CIR | Colour Infrared |
| CRT | See Cathode Ray Tube |
| CZCS | Coastal Zone Colour Scanner |
| CALIBRATION | The process of comparing measurements, made by an instrument, with a standard. |
| CALORIE | The amount of heat required to raise the temperature of 1 gm of water by 1°C. |
| CATHODE RAY TUBE | (CRT) A vacuum tube with a phosphorescent screen upon which images are displayed by an electron beam. |
| CLASSIFICATION | The process of assigning individual pixels of a digital image to categories, generally on the basis of spectral reflectance or radiometric characteristics. |
| COLOUR-COMPOSITE IMAGE | A colour image prepared by combining individual band images. Each band (up to a maximum of 3) is assigned one of the three additive primary colours: blue, green and red. |
| COMPUTER COMPATIBLE TAPE (CCT) | The magnetic tape upon which the digital data for remotely sensed images are distributed. |
| CONDUCTION | The transfer of electromagnetic energy through a material by molecular interaction. |
| CONTRAST | The difference between highlights and shadows in a photographic image. The larger the difference in density the greater the contrast. |
| CONTRAST RATIO | The ratio between the reflectance of the brightest and darkest parts of the image, commonly referred to as contrast. |
| 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 display device. |
| CONVECTION | The transfer of heat through the physical movement of heated matter. |
| DCS | Data Collecting System |
| DENSITY OF IMAGES | A measure of the opacity or darkness of an image. |
| DENSITY OF MATERIALS | The ratio of mass to volume of a material, typically expressed as gm . cm-3. |
| DENSITY SLICING | The process of converting the continuous grey tone of an image into a series of density intervals or slices, each corresponding to a specific digital range. |
| DEPOLARIZATION | Change in polarization of a radar pulse as a result of multiple reflections from the terrain surface. |
| DEPRESSION ANGLE | In SLAR usage this is the angle between the horizontal plane passing through the antenna and the line connecting the antenna and the target. |
| DETECTOR | The component of a remote sensing system that converts the electromagnetic radiation into a signal that is recorded. |
| DEVELOPMENT | The chemical processing of exposed photographic material to produce an image. |
| DIAZO FILM | A transparent material on which image transparencies may be reproduced in specific colours. |
| DICHORIC | A beam-splitting mirror that efficiently reflects certain wavelengths while it efficiently transmits others. |
| DIELECTRIC | A substance which contains few or no free charges and is consequently a poor electrical conductor. |
| DIELECTRIC CONSTANT | Electrical property of matter that influences radar returns; also referred to as complex dielectric constant. |
| DIFFRACTION | The propagation of EMR around the edges of opaque objects into the shadow region. |
| DIGITAL DATA | Data displayed, recorded or stored in binary notation. |
| DIGITAL IMAGE PROCESSING | Computer manipulation of the digital values for picture elements of an image. |
| DIGITIZATION | The process of converting an image into numerical format. |
| DIGITIZER | A device for scanning an image and converting it into numerical picture elements. |
| DISPERSION | Separation of EMR into its spectral components. |
| DISTORTION | On an image, this refers to change in shape and position of objects with respect to their true shape and position. |
| DOPPLER PRINCIPLE | Describes the change in observed frequency of electromagnetic or other waves caused by relative movement between the source of waves and the observer. |
| EM | Electromagnetic |
| EMR | See Electromagnetic Radiation |
| ERTS | Earth Resource Technology Satellite |
| ESA | European Space Agency |
| EKTACHROME | A Kodak colour-positive film. |
| ELECTROMAGNETIC RADIATION (EMR) | Energy propagated through space or through material media in the form of an advancing interaction between electric and magnetic fields. |
| EMISSION | With respect to EMR, the process by which a body emits EMR usually as a consequence of its temperature only. |
| EMISSIVITY | The ratio of radiant flux from a body to that from a blackbody at the same kinetic temperature. |
| EMULSION | A suspension of photosensitive silver halide grains in gelatin that constitutes the image- forming layer on photographic materials. |
| ENHANCEMENT | The process of altering the appearance of an image so that the interpreter can extract more information. Enhancement may be done by digital or photographic methods. |
| FLIR | Forward Looking Infrared |
| FALSE COLOUR IMAGE | A colour image in which the dye colour is not the same as the scene colour. |
| FILM ( PHOTOGRAPHIC ) | A transparent base having a light-sensitive photographic emulsion. |
| FILM SPEED | A measure of the sensitivity of photographic film to light. Larger numbers indicate higher sensitivity. |
| FILTER | Any physical device or mathematical function that is used to modify a spectrum. |
| FILTER, DIGITAL | A mathematical procedure for removing unwanted values from numerical data. |
| FILTER, OPTICAL | A material that, by absorption or reflection, selectively modifies the radiation transmitted through an optical system. |
| FLIGHT PATH | The line on the ground directly beneath a remote sensing aircraft or satellite. |
| FLUORESCENCE | The emission of light from a substance caused by exposure to radiation from an external source. |
| FOCAL LENGTH | In cameras, the distance measured along the optical axis from the optical centre of the lens to the plane at which the image of a distant object is brought into focus. |
| FOCUS | To adjust a remote sensing system to produce a sharp, distinct image. |
| FOOTPRINT | A definite patch of earth surface illuminated by a radar at any given instant of time. |
| FORMAT | The size scale of an image. |
| FRAMING CAMERA | A camera that observes and records the scene in sections (or frames) in contrast, for example, to a strip camera. |
| FREQUENCY | The number of wave oscillations per unit time or the number of wavelengths that pass a point per unit time. The symbol is |
| GOES | Geostationary Operational Environment Satellite |
| GAIN | An increase in signal power in transmission from one point to another and usually expressed in decibels. |
| GAMMA RAYS | High energy electromagnetic radiation emitted by radioactive decay. Gamma rays have wavelengths shorter than 1 Angstrom unit. |
| GEOID | The figure of the earth considered as a sea-level surface extended continuously over the entire earth's surface. |
| GELBSTOFFE | Dissolved yellow substances which absorb light in natural waters. |
| GREY BODY | A material that does not display strong absorption and emission features, but has an overall reduced emissivity (in comparison to a blackbody) which is practically constant over all wavelengths. |
| GREY SCALE | A calibrated sequence of grey tones ranging from black to white. |
| GROUND RANGE | The distance from the ground track to an object. |
| GROUND RECEIVING STATION | A facility that records image data transmitted by airborne or spaceborne sensors. |
| GROUND RESOLUTION CELL | The area on the terrain that is covered by the instantaneous field of view of a detector. Size of the ground resolution cell is usually determined by the altitude of the remote sensing system and the instantaneous field of view of the detector. |
| h | See Planck's Constant |
| HCMM | Heat Capacity Mapping Mission |
| HCMR | Heat Capacity Mapping Radiometer |
| HRVR | High Resolution visible Radiometer |
| HARMONIC | Refers to wave in which the component frequencies are whole number multiples of the fundamental frequency. |
| HERTZ ( Hz ) | Cycles per second. |
| HUE | The attribute of a colour that differentiates it from grey of the same brilliance and that allows it to be classed as blue, green, red or intermediate shades of these colours. |
| IFOV | See Instantaneous Field of View |
| IR | See Infrared |
| IMAGE | The representation of a scene as recorded by a remote sensing system. Although image is a general term, it is commonly restricted to representations acquired by non-photographic methods. |
| INFRARED(IR) | Portion of the electromagnetic spectrum lying between the red end of the visible spectrum and microwave radiation (0.7 to 1000 micrometres). |
| INSTANTANEOUS FIELD OF VIEW (IFOV) | The cone angle within which incident energy is focused on the detector. The instantaneous field of view is commonly expressed in milliradians. |
| INTEGER | Any positive or negative whole number or zero. |
| INTENSITY | A measure of energy reflected from a surface. |
| INTERACTIVE PROCESSING | The method of data processing by which the operator views preliminary results and can alter the instructions to the computer to achieve optimum results. |
| INTERPRETATION | The extraction of information from an image. |
| INTERPRETATION KEY | A characteristic or combination of characteristics that enable an object or materiel to be identified on an image. |
| IR COLOUR FILM | A colour film consisting of three layers in which the red-imaging layer responds to photographic IR radiation ranging in wavelength from 0.7 to 1.3 micrometres. The green-imaging layer responds to red light and the blue-imaging layer responds to green light. |
| IRRADIANCE | The radiant power density incident on a surface (watts/cm square). |
| K-BAND | Radar wavelength region from 0.8 to 1.1 cm. |
| 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 | 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. |
| KODACHROME | A normal colour-positive film manufactured by Kodak. |
| LASER | Light Amplification by stimulated Emission of Radiation |
| LIDAR | Light Detection and Ranging |
| LANDSAT | An unmanned earth-orbiting NASA satellite (formerly called ERTS) that transmits multispectral images in the 0.4 to 1.1 micrometre range to earth receiving stations. |
| L-BAND | Radar wavelengths region from 15 to 30 cm. |
| LENS | A piece or combination of pieces of glass or other transparent material that enables images to form by refraction of light. |
| LIGHT | EMR within 0.4 to 0.7 micrometres in wavelength that is detectable by the human eye. |
| LIGHT METER | A device for measuring the intensity of visible radiation to determine the appropriate exposure for acquiring photographs. |
| LINEAMENT | A linear topographic or tonal feature on the terrain and on images and maps that may represent a zone of structural weakness. |
| LINEAR | An adjective that describes the straight line nature of features on the terrain or on images and maps. |
| LINE-PAIR | A pair of light and dark bars of equal sizes. The number of such line-pairs that can be distinguished per unit distance is used to express resolving power of imaging systems. |
| LOOK DIRECTION | Direction in which pulses of microwave energy are transmitted by a radar system. Look direction is normal to the azimuth direction. Also called range direction. |
| LOW-SUN ANGLE PHOTOGRAPHS | Aerial photographs acquired in the morning, evening or winter when the sun is at a low elevation above the horizon. |
| LUMINANCE | A quantitative measure of the intensity of light from a source, measured with a device called a photometer. |
| MEIS | Multi-detector Electro Optical Imaging Scanner |
| MESSR | Multispectral Electronic Self Scanning Radiometer |
| MOS | Marine Observation Satellite |
| MSR | Microwave Scanning Radiometer |
| MSS | See Multispectral Scanner |
| METEOSAT | A European geostationary satellite used for meteorological observations and communications. The major instrument onboard is a scanning radiometer which has three spectral bands: visible 0.4 to 1.1 micrometres, thermal infrared 10.5 to 12.5 micrometres and infrared water vapour absorption 5.7 to 7.1 micrometres. |
| MICROWAVE | The region of the electromagnetic spectrum in the wavelength range from 1 mm to beyond 1 m. |
| MIE SCATTERING | Multiple reflection of light waves by atmospheric particles that have the approximate dimensions of the wavelength of light. |
| MULTISPECTRAL CAMERA | A system that simultaneously acquires photo- graphs at different wavelengths of the same scene. Also called multiband camera. |
| MULTISPECTRAL SCANNER(MSS) | A scanner system that simultaneously acquires images of the same scene in various wavelength bands. |
| NASA | National Aeronautical and Space Administration (U.S.A.) |
| NOAA | National Oceanic and Atmospheric Administration (U.S.A) |
| NADIR | The point on the ground vertically beneath the centre of a remote sensing system. |
| NEAR RANGE | Refers to the portion of a radar image closest to the flight path. |
| NEGATIVE PHOTOGRAPH | A photograph on film or paper in which the tones are reversed from the brightness of the features on the terrain. |
| NOISE | Random or repetitive events that obscure or interfere with the desired information. |
| NORMAL COLOUR FILM | A film in which the colours are essentially true representations of the colour of the terrain. |
| OBLIQUE PHOTOGRAPH | A photograph acquired with the camera axis intentionally directed between the horizontal and vertical orientations. |
| ORBIT | The path of a satellite around a body under the influence of gravity. |
| OVERLAP | The extent to which adjacent images or photographs cover the same terrain, expressed in percentages. |
| PANCHROMATIC | Sensitive to entire visible part of EMR spectrum. |
| PARALLEL POLARIZED | Radar returned pulse in which the polarization is the same as the transmitted pulse. Images recorded with parallel-polarized energy may be HH (horizontal transmit, horizontal return) or VV (vertical transmit, vertical return). |
| PASS | In digital filters this 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 REMOTE SENSING | Remote sensing of energy naturally reflected or radiated from the terrain. |
| PATTERN | The regular repetition of tonal variation on an image or photograph. |
| PHOTODETECTOR | A device for measuring energy in the photographic band. |
| PHOTOGRAPH | A representation of targets formed by the action of light on silver halide grains of an emulsion. |
| PHOTON | The elementary quantity of radiant energy. |
| PICTURE ELEMENT | In a digitized image this is the area on the ground represented by each digital value. Because the analog signal from the detector of a scanner may be sampled at any desired interval, the picture element may be smaller than the ground resolution cell of the detector. Commonly abbreviated as 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 | A contraction of picture element. |
| PLANCK'S CONSTANT (h) | The ratio of the energy of a photon to its frequency; it is equal to 6.62620±0.00005 × 10-34 Joules-seconds. |
| PLANCK'S LAW | A fundamental law of quantum theory stating that energy associated with electromagnetic radiation is emitted or absorbed in discrete amounts which are proportional to the frequency of radiation. |
| POLARIZATION | The direction of vibration of the electrical field vector of electromagnetic radiation. In radar systems polarization is either horizontal or vertical.1 |
| PULSE | A short burst of electromagnetic radiation transmitted by a radar antenna. |
| QUANTIZATION | Division of the range of values of a wave into a finite number of subranges, each of which is represented by an assigned or quantized value within the subrange. |
| RADAR | Radio Detection and Ranging |
| RBV | See Return Beam Vidicon |
| RUFAS | Remote Underwater Fishery Assessment System |
| RADAR-ROCK UNITS | Rock units characterized by distinctive signatures on radar images. The signatures are determined by surface roughness of the rocks. |
| 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 intercepts the radar beam. |
| RADIANT TEMPERATURE | Concentration of the radiant flux from a material. Radiant temperature is the product of the kinetic temperature multiplied by the emissivity to the one-fourth power. |
| RADIATION | The propagation of energy in the form of electromagnetic waves. |
| RANGE DIRECTION | For radar images, this is the direction in which energy is transmitted from the antenna and is normal to the azimuth direction. Also called look direction. |
| RASTER LINES | The individual lines swept by an electron beam across the face of a CRT, that constitute the image display. |
| RATIO IMAGE | An image prepared by processing digital multispectral data. For each pixel the value for one band is divided by that of another. The resulting digital values are displayed as an image. |
| RAYLEIGH CRITERION | For radar images, this is the relationship between surface roughness, depression angle and wavelength that determines whether a surface will respond in rough or smooth fashion to the radar pulse. |
| REAL-APERTURE RADAR | SLAR system in which azimuth resolution is determined by the physical length of the antenna and by the wavelength. The radar returns are recorded directly to produce images. Also called brute-force radar. |
| REAL TIME | Time in which reporting of events or recording of events is simultaneous with the event. |
| REFLECTANCE | The ratio of the radiant energy reflected by a body to that incident upon it. |
| REFLECTANCE, SPECTRAL | Reflectance measured at a specific wavelength interval. |
| REFLECTIVITY | The ability of a surface to reflect incident energy. |
| REFRACTION | The bending of electromagnetic rays as they pass from one medium into another. |
| REMOTE SENSING | The collection of information about an object or event without being in physical contact with the object or event. Remote sensing is restricted to methods that record the electromagnetic radiation reflected or radiated from an object, which excludes magnetic and gravity surveys that record force fields. |
| RESOLUTION | The ability to distinguish closely spaced objects on an image or photograph. Commonly expressed as the spacing, in line-pairs per unit distance, of the most closely spaced lines that can be distinguished. |
| RESOLVING POWER | A measure of the ability of individual components and of remote sensing systems to define closely spaced targets. |
| RETURN-BEAM VIDICON (RBV) | A little-used imaging system on LANDSAT that consists of three cameras operating in the green, red and photographic IR spectral regions. Instead of using film, the images are formed on the photosensitive surface of a vacuum tube. The image is scanned with an electron beam and transmitted to an earth receiving station. |
| REVERSAL FILM | A photographic film in which the negative image is converted to a positive image during the developing process. |
| ROLL | Rotation of an aircraft about the longitudinal axis to cause a wing-up or wing-down attitude. |
| SAR | Synthetic Aperture Radar |
| SASS | SEASAT-A Satellite Scatterometer |
| SLAR | Side-Looking Airborne Radar |
| SMMR | Scanning Multichannel Microwave Radiometer |
| SMS | Synchronous Meteorological Satellite |
| SPOT | Satellite Pour l'Observation de la Terre |
| SST | Sea Surface Temperature |
| SATELLITE | An object in orbit around a celestial body. |
| SCALE | The ratio of the distance on an image to the equivalent distance on the ground. |
| SCAN LINE | The narrow strip on the ground that is swept by the instantaneous field of view of a detector in a scanner system. |
| SCAN SKEW | Distortion of scanner images caused by forward motion of the aircraft or satellite during the time required to complete a scan. |
| SCANNER | (1) Any device that scans, and thus produces an image; |
| (2) A radar set incorporating a rotatable antenna for directing a searching radar beam through space and imparting target information to an indicator. | |
| SCANNER DISTORTION | The geometric distortion that is characteristic of scanner images. The scale of the image is constant in the direction parallel with the aircraft or spacecraft flight direction. At right angles to this direction, however, the image scale becomes progressively smaller from the nadir line outward toward either margin of the image. Linear features, such as roads, that trend diagonally across a scanner image are distorted into S-shaped curves. Distortion is imperceptible for scanners with a narrow angular field of view but becomes more pronounced with a larger angular field of view. Also called panoramic distortion. |
| SCATTERING | Multiple reflection of electromagnetic waves by gases or particles in the atmosphere. |
| SCATTEROMETER | A non - imaging radar device that records backscatter of terrain as a function of incidence angle. |
| SCENE | The area on the ground that is covered by an image or photograph. |
| SENSITIVITY | The degree to which a detector responds to electromagnetic energy incident upon it. |
| SENSOR | A device that receives electromagnetic radiation and converts it into a signal that can be recorded and displayed as numerical data or as an image. |
| SIGNATURE | A characteristics, or combination of characteristics, by which a material or an object may be identified on an image or photograph. |
| SILVER HALIDE | Silver salts that are sensitive to electromagnetic radiation and convert to metallic silver when developed. |
| SKYLAB | The United States' earth-orbiting workshop that housed three crews of three men in 1973 and 1974. |
| SKYLIGHT | The component of light that is scattered by the atmosphere and consists predominantly of shorter wavelengths of light. |
| SLANT RANGE | For radar images this term represents the distance measured along a line between the antenna and the target. |
| SOFTWARE | The programs that control computer operations. |
| SPECIFIC HEAT | The ratio between thermal capacity of a substance and thermal capacity of water. |
| SPECTRAL REFLECTANCE | See Reflectance, Spectral |
| SPECTRAL SENSITIVITY | The response or sensitivity of a film or detector to radiation in different spectral regions. |
| SPECTROMETER | Device for measuring intensity of radiation absorbed or reflected by a material as a function of wavelength. |
| SPECTRUM | (1) In physics, any series of energies arranged according to wavelength (or frequency); |
| (2) The series of images produced when a beam of radiant energy is subject to dispersion. A rainbow-coloured band of light is formed when white light is passed through a prism or a diffraction grating. This band of colours results from the fact that the different wavelengths of light are bent in varying degrees by the dispersing medium and is evidence of the fact that white light is composed of coloured light of various wavelengths. | |
| SUBTRACTIVE PRIMARY COLOURS | Yellow, cyan and magenta. When used as filters for white light these colours remove blue, red, and green, respectively. |
| SUN SYNCHRONOUS | An earth satellite orbit in which the orbit plane is near polar and the altitude such that the satellite passes over all places on earth having the same latitude twice daily at the same local sun time. Also known as heliosynchronous. |
| SUPERVISED CLASSIFICATION | A computer-implemented process through which each measurement vector is assigned to a class according to a specified decision rule, when the possible classes have been defined on the basis of representative training samples of known identity. |
| SURFACE PHENOMENON | Interaction between electromagnetic radiation and the surface of a material. |
| SYNTHETIC-APERTURE RADAR | SLAR system in which high resolution in the azimuth direction is achieved by utilizing the Doppler principle to give the effect of a very long antenna. |
| SYSTEMATIC DISTORTION | Predictable geometric irregularities on images that are caused by the characteristics of the imaging system. |
| THIR | Temperature Humidity Infrared Radiometer |
| TIROS | Television Infrared Observational Satellite |
| TM | Thematic Mapper |
| THERMAL CAPACITY | The ability of a material to store heat, expressed in cal . g-1 . °C-1. The symbol is C. |
| THERMAL CONDUCTIVITY | The measure of the rate at which heat passes through a material, expressed in cal . cm-1 . sec-1 . °C-1. The symbol is K. |
| THERMAL INERTIA | A measure of the response of a material to temperature changes, expressed in cal . -2 . °C-1 . sec-1/2. The symbol is P. |
| THERMAL IR | The portion of the IR region from approximately 8 to 14 micrometres that corresponds to heat radiation. This spectral region spans the radiant power peak of the earth. |
| THERMAL IR IMAGE | An image acquired by a scanner that records radiation within the electromagnetic band that ranges from approximately 8 to 14 micrometres in wavelength. |
| TRADE OFF | The compensating change that occurs in a remote sensing system as a result of changing one factor elsewhere in the system. For example, an increase in altitude increases the lateral coverage of an imaging system but the trade off is a decrease in scale and resolution of the image. |
| ULTRAVIOLET (UV) RADIATION | The region of the electromagnetic spectrum consisting of wavelengths from 10 to 4000 Angstroms. |
| VAS | VISSR Atmospheric Sounder |
| VIRR | Visible Infrared Radiometer |
| VISSR | Visible Infrared Spin Scan Radiometer |
| VTIR | Visible and Thermal Infrared Radiometer |
| VISIBLE RADIATION | Energy at wavelengths from 0.4 to 0.7 micrometres that is detectable by the eye. |
| WATT | Unit of electrical power equal to the rate of work done by one ampere under a pressure of one volt. The symbol is W. |
| WAVELENGTH | The distance between successive wave crests or other equivalent points in a harmonic wave. |
| WIEN'S DISPLACE- MENT | Describes the shift of the radiant power peak to shorter wavelengths with increasing temperature. |
| X-BAND | Radar wavelength region from 2.4 to 3.8 cm. |
| YAW | Rotation of an aircraft about its vertical axis that causes the longitudinal axis to deviate from the flight line. |