Glossary of Terms and Acronyms

The Canada Centre for Remote Sensing (CCRS) offers a very useful on-line Remote Sensing Glossary. Readers are referred to this for items not listed here.

Absorption	A process by which radiation is converted to other types of energy (especially heat) by a material. Reduction in strength of an electromagnetic wave propagating through a medium.
Absorptivity	Ratio of the absorbed to incident electromagnetic radiation on a surface.
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.
ADEOS	Advanced Earth Observing Satellite. A Japanese Earth observation satellite. Carries the OCTS sensor. See Chapter 3.
Adjacency effect	The change in the digital number of a pixel caused by atmospheric scattering of radiance that originates outside of the sensor element’s field of view.
Aerial photography	Photography from airborne platforms.
Albedo	The ratio of the amount of electromagnetic energy reflected by a surface to the amount of energy incident upon it.
Algorithm	A statement of predefined steps to be followed in the solution of a problem, such as a set of image processing steps (each a mathematical manipulation of the image data) to bring about a desired outcome.
Altimeter	Instrument which determines the altitude of an object with respect to a fixed level such as sea level.
All weather	Refers to the capability of a sensing system to operate under any weather condition.
AMS (Daedalus)	Airborne Multispectral Scanner. See Chapter 3
Analogue	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 of resistances. Analogue computing methods contrast with digital methods in which values are treated numerically.
Analogue recorder	Data recorder in which data are stored in continuous form as contrasted with digital data having discrete values.
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.
Ångstrom (Å)	A measurement of length (10^-10 m). Equivalent to 10 nm.
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.
API	Aerial photographic interpretation. The process of visually interpreting aerial photographs.
APT	Automatic Picture Transmission (TIROS, ATS, ESSA, NOAA-n).
ATM (Daedalus)	Airborne Thematic Mapper sensor. See Chapter 3.
Atmospheric absorption	The process whereby some or all of the energy of sound waves or electromagnetic waves is transferred to the constituents of the atmosphere. See Chapter 7.
Atmospheric reflectance	Ratio of reflected radiation from the atmosphere to incident radiation.
Atmospheric scattering	Process whereby part or all of the energy of electro magnetic radiation is dispersed when traversing the atmosphere. See Chapter 7.
Atmospheric windows	Wavelength intervals at which the atmosphere transmits most electromagnetic radiation.
ATSR	Along Track Scanning Radiometer. Sensor carried on the European Remote Sensing satellites. See Chapter 3.
AVHRR	Advanced Very High Resolution Radiometer. Carried on NOAA polar orbiting satellites. Spatial resolution 1.1 x 1.1 km.
AVI	Angular Vegetation Index. An index of vegetation cover. See Chapter 3.
AVIRIS	Airborne Visible/Infra-Red Imaging Spectrometer. Produces multispectral data with 224 narrow (10 nm) bands between 400 and 2400 nm. See Chapter 3.
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 sensors the bands designate specific wavelength intervals at which images are required.
BIL	Band Interleaved by Line. A format for data storage. See Chapter 5.
BIP	Band Interleaved by Pixel. A format for data storage. See Chapter 5.
Bit	In digital computer terminology, this is a binary digit that is an exponent of the base 2.
Brightness	Magnitude of the response produced in the eye by light.
Byte	A group of eight bits of digital data.
Calibration	The process of comparing measurements, made by an instrument, with a standard.
CASI	Compact Airborne Spectrographic Imager. A digital airborne multispectral sensor.
CCD	Charge Coupled Device. A light sensitive solid-state detector that generates a voltage which is proportional to the intensity of illumination. Arrays of CCDs make up pushbroom scanners.
CCRS	Canada Centre for Remote Sensing.
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 sometimes distributed.
Conformal	A map projection that has the property of true shape (conformality). See Chapter 6.
Contextual editing	The use of non-spectral information, e.g. location or depth, to improve classification of spectrally overlapping classes.
Contrast	The difference between highlights and shadows in a photographic image. The larger the difference in density the greater the 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.
CZCS	Coastal Zone Color Scanner. See Chapter 3
DEM	Digital Elevation Model. See Chapter 6.
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.
Descriptive resolution	The level of ecological/geomorphological detail to which a sensor can map a given area. Equivalent to habitat discrimination.
Detector	The component of a remote sensing system that converts the electromagnetic radiation into a signal that is recorded.
DGPS	Differential Global Positioning System.
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.
Digitizer	A device for scanning an image and converting it into numerical picture elements.
Electromagnetic Radiation (EMR)	Energy propagated through space or through material media in the form of an advancing interaction between electrical 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.
EMR	See Electromagnetic Radiation.
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.
Equidistance	The property of a map projection to represent true distances between points. See Chapter 6.
Equivalence	The property of a map projection to represent all areas in true proportion to one another. See Chapter 6.
EOSAT	Earth Observation Satellite Company. A private company contracted to the US government to market Landsat data. Now superseded by Space Imaging.
ERDAS	Earth Resources Data Analysis System. An image processing and GIS software package now called ERDAS Imagine and produced by ERDAS Inc.
ERS	European Remote Sensing Satellite.
ESA	European Space Agency.
ETM	Enhanced Thematic Mapper. Sensor carried on Landsat 7. See Chapter 3.
EXABYTE	A tape format on which satellite imagery may be supplied.
Fluorescence	The emission of light from a substance caused by exposure to radiation from an external source.
Gain	An increase in signal power in transmission from one point to another and usually expressed in decibels.
GCP	Ground Control Point. A point on the ground whose position is accurately known and which can be used with other GCPs to geometrically correct an image. See Chapter 6.
Gelbstoffe	Dissolved yellow substances which absorb light in natural waters.
GEMI	Global Environment Monitoring Index. An index of vegetation cover. See Chapter 13.
Geoid	The figure of the earth considered as a sea-level surface extended continuously over the entire earth’s surface.
Geometric correction	The correction of errors of skew, rotation, and perspective in raw, remotely sensed data. See Chapter 6.
GIS	Geographic Information System
GPS	Global Positioning System. A network of 24 radio transmitting satellites (NAVSTAR) developed by the US Department of Defense to provide accurate geographical position fixing.
Grey scale	A calibrated sequence of grey tones ranging from black to white.
Groundbusters	Elite SWAT team of groud-truthing professionals with total accuracy dedication: reaching the habitats that other survey teams can’t. Motto: Groundbusters are go!
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. Sixe 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.
Hertz (Hz)	Cycles per second. Measure of frequency.
HRV	Haute Resolution Visible. The visible and very near infra-red pushbroom sensor carried by SPOT 1-3.
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
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.
IMU	Inertial Measurement Unit. See Chapter 6.
Infra-red (IR)	Portion of the electromagnetic spectrum lying between the red end of the visible spectrum and microwave radiation (700 nm to 1000 mm).
INS	Inertial Navigation System. See Chapter 6.
Instantaneous Field Of View (IFOV)	A measure of the area viewed by a single detector on a scanning system at a given moment in time.
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.
IR	See Infra-red.
IR colour film	A colour film consisting of three layers in which the red-imaging layer responds to photographic infra-red radiation ranging in wavelength from 700 1300 nm. 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 (W cm^-2).
IRS	Indian Remote Sensing satellite. IRS-1A to 1D and IRS-P2 to P4 have been launched since 1988. See Chapter 3.
ISODATA	Iterative Self-Organizing Data Analysis Technique. A method of clustering used in image classification.
ITRES	A Canadian company who developed the Compact Airborne Spectrographic Imager (CASI).
LAI	Leaf Area Index. Single-side leaf area per unit ground area: a unit-less measure. See Chapter 17.
Landsat	A series (6 successfully launched since 1972) of unmanned earth-orbiting NASA satellites (formerly called Earth Resources Technology Satellite – ERTS).
Laser	Light Amplification by Stimulated Emission of Radiation.
L-Band	Radar wavelengths region from 15 to 30 cm.
Lidar	Light Detection and Ranging.
Light	EMR within 400-700 nm in wavelength that is detectable by the human eye.
LISS	Linear Imaging self-Scanning Sensor. A type of sensor carried on Indian Remote Sensing satellites. IRS-1c and 1d carry the LISS-III sensor. See Chapter 3.
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. See Chapter 7.
MOS	Marine Observation Satellite. MOS-1 was launched by Japan in 1987.
MSS	See Multispectral Scanner
Multispectral Scanner (MSS)	A scanner system that simultaneously acquires images of the same scene in various wavelength bands. Landsat MSS was one such system which was operational on Landsat series satellites from 1972-1993.
Nadir	The point on the ground vertically beneath the centre of a remote sensing system.
NASA	National Aeronautics and Space Administration (USA).
NDVI	Normalised Difference Vegetation Index. An index of vegetation biomass. See Chapter 13.
NIR	Near Infra-Red. Wavelengths around 700-3000 nm.
NOAA	National Oceanic and Atmospheric Administration (USA).
Noise	Random or repetitive events that obscure or interfere with the desired information.
NRSC	National Remote Sensing Centre (UK).
Oblique photograph	A photograph acquired with the camera axis intentionally directed between the horizontal and vertical orientations.
OCTS	Ocean Color and Temperature Scanner. Sensor carried on the Advanced Earth Observing Satellite (ADEOS). See Chapter 3.
Okta	Unit of measurement for cloud cover. One okta = 1/8 or 12.5 % cover.
Orbit	The path of a satellite around a body under the influence of gravity.
Overall accuracy	The overall probability that pixels on the image have been classified properly.
Overlap	The extent to which adjacent images or photographs cover the same terrain, expressed in percentages.
Panchromatic	Sensitive to entire visible part of ERM spectrum.
Passive remote sensing	Remote sensing of energy naturally reflected or radiated from the terrain.
PCA	Principal Components Analysis. A statistical technique for reducing the number of bands in an image by generating a series of components, each of which is an uncorrelated combination of raw bands. The first few components will contain most of the information found within all the raw bands.
PCI EASI/PACE	An image processing and GIS software package produced by the PCI Remote Sensing Corporation.
Photogrammetry	The making of maps using aerial photographs.
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 analogue signal form the detector of a scanner may be sampled at any desired interval, the picture element may be smaller that 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.
Producer accuracy	The probability that a pixel in a given habitat category will have been classified correctly on the image.
Pushbroom scanner	An imaging system consisting of a linear array of many detectors (CCDs) that record the brightness of a line of pixels directly below the sensor in the across-track direction.
Radar	Radio Detection and Ranging.
RADARSAT	A Canadian radar satellite launched in 1995.
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.
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 scattering	Selective scattering of light in the atmosphere by particles that are small compared to the wavelength of light. See Chapter 7.
RBV	See Return Beam Vidicon.
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.
Refraction	The bending of elecrtomagnetic rays as they pass from one medium to 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.
Return Beam Vidicon (RBV)	A little-used imaging system on Landsat that consists of three cameras operating in the green, red and photographic infra-red 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.
RGB	Red, green blue. The primary additive colours which are used on most display hardware (computer monitors) to display images.
RMS error	Root Mean Square error. The distance between the input (source) location of a GCP and the retransformed location for the same GCP. Measure used to assess the accuracy of geometric correction. See Chapter 6.
Roll	Rotation of an aircraft about the longitudinal axis to cause a wing-up or wing-down attitude.
SAR	Synthetic Aperture Radar. A radar imaging system in which high resolution in the azimuth direction is achieved by using Doppler shift of backscattered waves to identify waves from ahead and behind the platform, thereby simulating a very long antenna. Available on both satellite (ERS, RADARSAT) and airborne platforms.
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.
Scene	The area on the ground that is covered by an image or photograph.
SeaWiFS	Sea-viewing Wide Field-of-view Sensor carried on the SeaStar satellite. See Chapter 3.
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 characteristic, or combination of characteristics, by which a material or an object may be identified on an image or photograph.
Skylight	The component of light that is scattered by the atmosphere and consists predominantly of shorter wavelengths of light.
SLAR	Side-Looking Airborne Radar. Airborne systems that use real-aperture radar to generate images. Cheaper than synthetic aperture radar (SAR).
Spectral envelope	Boundaries of the spectral properties of a feature, expressed as the range of brightness values in a number of spectral bands.
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.
SPOT	Satellite Pour l’Observation de la Terre. A French satellite carrying two pushbroom imaging systems. (Originally Système Probatoire de l’Observation de la Terre).
SST	Sea Surface Temperature.
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 heliosychronous.
Supervised classification	A classification method whereby thematic classes are defined by the spectral characteristics of pixels within an image that correspond to training areas in the field chosen to represent known features (e.g. habitats). Each pixel within the image is then assigned to a thematic class using one of several decision rules. See Chapter 10.
Surface phenomenon	Interaction between electromagnetic radiation and the surface of a material.
Swath width	The linear ground distance in the across-track direction which is covered by a sensor on a single overpass.
Synthetic Aperture Radar (SAR)	A radar imaging 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.
Tau coefficient (accuracy)	A coefficient which describes the accuracy of a thematic map. See Chapter 4.
Thermal capacity	The ability of a material to store heat, expressed in J Kg^-1 K^-1.
Thermal conductivity	The measure of the rate at which heat passes through a material, expressed in W m^-1 K^-1
Thermal IR	The portion of the infra-red region from approximately 3-15 mm wavelength that corresponds to heat radiation. This spectral region spans the radiant power peak of the Earth.
TIROS	Television Infrared Observational Satellite.
TM	Thematic Mapper.
Ultraviolet (UV) radiation	The region of the electromagnetic spectrum consisting of wavelengths from 1 to 400 nm.
UNDP/GEF	United Nations Development Programme/Global Environment Facility.
Unsupervised classification	Using a computer to automatically generate a thematic map from digital remotely sensed imagery by statistically clustering pixels on the basis of spectral similarity. The clusters may then be assigned labels (e.g. habitat names) using the operator’s field knowledge.
User accuracy	The probability that a pixel classified as a particular habitat on the image is actually that habitat.
UTM	Universal Transverse Mercator. A widely used geographic coordinate system. See Chapter 6.
Visible radiation	Energy at wavelengths from 400 700 nm that is detectable by the eye.
Wavelength	The distance between successive wave crests or other equivalent points in a harmonic wave.
X-Band	Radar wavelength region from 2.4 to 3.8 cm.
XS	Multispectral SPOT imagery from the HRV sensor. See Chapter 3.
Yaw	Rotation of an aircraft about its vertical axis that causes the longitudinal axis to deviate from the flight line.

Start		Introduction		Activities	Publications	Search
		Wise Practices	Regions		Themes