TERMS AND DEFINITIONS

absorbed photosynthetically active radiation (APAR)

The amount of solar radiation ranging from 400 -700 nanometers (0.4 - 0.7 micrometers) that gets absorbed by green vegetation during photosynthesis.

absorption

Assimilation and conversion of radiation from one form to another in a medium.

active sensor

A sensor that provides its own source of incident energy.

albedo

Ratio of the amount of electromagnetic radiation reflected by a surface to the amount of radiation incident upon it.

anthropogenic

Generated or made by humans.

asthenosphere

A zone of partial melting within Earth's upper mantle, upon which the rigid lithospheric plates can move.

atmosphere

The thin veil of gases surrounding Earth forming a protective boundary between outer space and the biosphere.

atmospheric absorption bands

Specific wavelengths or wavelength intervals of the electromagnetic spectrum where incident energy gets absorbed by the atmosphere.

atmospheric windows

The wavelength intervals or bands in the electromagnetic spectrum where solar radiation can be transmitted through the atmosphere without being absorbed. In the absence of clouds, sunlight gets through atmospheric windows to Earth's surface and Earth's radiative heat escapes back into space.

bandwidth

The width or range of the electromagnetic radiation being detected by a sensor, measured in wavelengths or frequencies. This fundamental parameter of imaging systems determines the spectral resolution of the data.

bidirectional

Referring to the interaction or consideration of both the illumination angle and the viewing angle of observed surface reflectance. Illumination and viewing angles affect the reflectance values recorded by a sensor.

biomass

The total dry organic matter or stored energy content of living organisms that is present at a specific time in a defined unit (community, ecosystem, crop, etc.).

biome

A large terrestrial ecosystem influenced in part by climate and characterized by specific plant communities and formations; usually named after the dominant vegetation inhabiting the biome.

biosphere

All of Earth's living organisms inhabiting and interacting with the physical environment (where the atmosphere, lithosphere, pedosphere and hydrosphere function together and support life).

calibration

Process of comparing an instrument's measurements with known standards.

channel

A specific wavelength or wavelength range selected from the electromagnetic spectrum in which data are measured.

classification

The process and results of ordering or categorizing data or phenomena into related groups.

classification (remote sensing)

The grouping of pixels of image data into categories based on spectral reflectance values or other characteristics.

climate

The persistent, relatively long-term manifestation of weather and weather patterns over time.

coefficient of variation

A relative measure of dispersion, calculated by dividing a distribution's standard deviation by its mean.

compositing

A technique to combine multiple images to create a single image, for example, the formation of a color composite by combining the images from 3 separate spectral bands of an instantaneous dataset, or the creation of a single image summarizing a particular time period from multitemporal imagery (such as a monthly composite).

deforestation

The practice of removing trees (cut and burn) from large areas typically for timber, forest products, and cleared land for agriculture and pasture.

desertification

The expansion of deserts worldwide, caused by a variety of factors and practices such as overgrazing, improper soil-moisture management, erosion, salinization, deforestation, and climate change.

density slice

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.

Earth systems science

An emerging science of Earth as a complete, systematic entity having many complex, interrelated, interacting processes.

ecosphere

Another name for the biosphere.

ecosystem

A self-regulating association of living plants, animals, and their nonliving physical and chemical environment.

electromagnetic radiation

Energy propagated as waves through space or through material media in accordance with basic wave theory.

electro-optical systems

Sensor systems using radiation detectors that transform electromagnetic radiation into electrical signals that can be recorded.

equal area projection

A map projection in which area can be accurately and consistently measured for any location.

evaporation

The phase change from liquid water to water vapor.

evapotranspiration

The uptake and release of water from plant foliage, also called transpiration.

false color

An imaging process that assigns visible colors to data values detected for a spectral band other than the assigned color; in other words, a color image is produced that does not represent the "true" color of the scene as it would naturally appear to the human eye.

field of view

The total instantaneous area or solid angle that can be viewed by a sensor.

fluorescence

Emission of electromagnetic radiation that is caused by the input of energy into the emitting body and which ceases abruptly when the excitation source is removed.

fractional PAR (fPAR)

Fractional photosynthetically active radiation; computes what fraction of the incident PAR (reaching the canopy top) is either intercepted (fIPAR) or absorbed (fAPAR).

fraction of absorbed PAR (fAPAR)

The fraction of photosynthetically active radiation absorbed by plant canopy layers, calculated by dividing APAR by the canopy top incident PAR.

fraction of intercepted PAR (fIPAR)

The fraction of photosynthetically active radiation intercepted by plant canopy layers, calculated by dividing IPAR by the canopy top incident PAR.

geographic coordinates

Coordinates based upon a geographic reference system, used to locate features on Earth.

geographic information system (GIS)

Computer based systems designed to efficiently organize, manipulate, analyze and display all types of geographically or spatially referenced data stored as layers of information.

geosphere

A broad term that loosely refers to an earth spherical shell or layer.

geostationary or geosynchronous

Refers to satellites traveling at the angular velocity at which Earth rotates; as a result, they remain above the same point on Earth at all times.

greenhouse effect

The absorption of outgoing terrestrial infrared radiation by atmospheric gases such as carbon dioxide, water vapor and methane; this process traps heat in the atmosphere, analogous to a greenhouse trapping heat within its glass walls.

gross primary production (GPP)

The total amount (mass or weight) of organic matter created by photosynthesis over a defined time period (total product of photosynthesis).

histogram

The graphical display of dataset values showing the frequency of occurrence (on the vertical axis) of individual measurements or values grouped by interval bins along the horizontal axis; also referred to as a frequency distribution.

hydrosphere

An abiotic open system that includes all of Earth's water.

image coordinates

Coordinates for denoting a position or location on an image. The coordinate units are usually pixels and the origin (unless otherwise specified) is the upper left corner of the image display. A particular location is given in "x" (pixel location as measured across a horizontal line) and "y" (row or line) coordinates. The coordinate value of the origin in some image processing systems is "0,0" and in others "1,1".

incident

The light or energy that falls on an object or surface.

incidence angle

Angle at which radiative energy hits an object or surface.

incident photosynthetically active radiation

The amount of photosynthetically active radiation (PAR) incoming at the top of the vegetation canopy (or other surface of interest).

infrared radiation

Electromagnetic radiation defined by wavelengths ranging from about 0.7 micrometers to about 1000 micrometers (1 millimeter), which includes the near-infrared, mid-infrared and thermal infrared.

insolation

Solar radiation incoming to Earth.

intercepted PAR (IPAR)

The amount of photosynthetically active radiation (PAR) caught by various canopy layers as PAR incident at the canopy top travels down through canopy layers to the ground surface.

joule

The term for 1 newton-meter, the unit of work in the metric system. One joule equals approximately 0.7 foot-pounds.

land cover

Material at the surface of Earth; basic land cover types include rock, sand, soil, vegetation, water, ice, and manmade materials.

land use

Human activities and structures associated with various parcels of land.

latitude

The angular distance in degrees north or south of the equator. Lines of latitude are also referred to as "parallels."

leaf area index (LAI)

The total one-sided area of all leaves above a given ground area divided by that given ground area.

leaf water potential

A measure of how tightly or strongly a leaf holds moisture.

lidar

An acronym for Light Detection and Ranging. Active optical sensor systems that emit short duration pulses of laser light at specific wavelengths.

light use efficiency (LUE)

The ratio of net primary production (NPP) to absorbed photosynthetically active radiation (APAR).

lithosphere

The rigid outer surface of the earth consisting of the crust and the top part of the upper mantle.

longitude

The angular distance in degrees east or west of the Greenwich Prime Meridian. Lines of longitude are also referred to as "meridians".

map projection

A systematic conversion of geographic locations from spherical to planar coordinates.

microwave

Electromagnetic radiation having wavelengths ranging from 1 millimeter to 1 meter.

mid-infrared (MIR)

The range of wavelengths from about 1.3 to 3 micrometers.

multispectral

A term referring to the presence of multiple spectral bands or channels.

multispectral scanner (MSS)

A multichannel sensor system on Landsat satellites 1 through 5.

nadir

In remote sensing, refers to a view from a sensor that is looking straight down at the surface.

near infrared (NIR)

Infrared radiation having wavelengths extending from approximately 0.7 to 1.3 micrometers.

near polar orbit

A satellite orbit that encircles Earth in nearly north-south directions, passing just to the side of the poles.

net primary productivity (NPP)

The part of gross primary production that remains stored in the producer organism (primarily green plants) after deducting the amount used during the process of respiration.

noise

Extraneous responses or disturbances that add to or subtract from a sensor's data signal in random or systematic fashion.

normalized difference vegetation index (NDVI)

A spectral vegetation index calculated from reflectances measured in the visible and near infrared channels.

orbit

Path of a satellite around a spherical body such as Earth.

panchromatic band

A spectral channel ranging over the entire visible part of the electromagnetic spectrum.

passive sensor

Refers to an instrument that depends on an external radiation generator (usually the Sun) as the source of surface reflection or emission.

pedon

An individual soil unit with unique properties, formed by processes interacting between the lithosphere, atmosphere, hydrosphere, and biosphere.

pedosphere

The shell or layer of Earth where soil-forming processes occur.

pixel

Term derived from "picture element." The smallest resolved area of information on an image display, representing an element from a data array.

pixel coordinates

See image coordinates.

phenology

The study of periodic biological phenomena with relation to climate, particularly seasonal changes.

photosynthesis

The process by which plants use sunlight, carbon dioxide and water to manufacture carbohydrates and release oxygen.

photosynthetically active radiation (PAR)

Radiation with wavelengths ranging from 400 to 700 nanometers (0.4 to 0.7 micrometers) used by green vegetation in the photosynthetic process.

platform

The vehicle or structure on which sensors are housed or mounted.

polar orbit

An orbit that passes very close to the poles.

primary production

The rate of production of new organic matter by plants.

production efficiency models (PEMs)

Statistical models of primary production using remotely sensed observations and light use efficiencies.

radar

Acronym for Radio Detection and Ranging. Active microwave systems emitting radiation with wavelengths in the range of 1 millimeter to 1 meter.

radiation

See electromagnetic radiation.

radiometic calibration or correction

Adjustment of measurements detected by a sensor to produce radiance values comparable to standards of known radiance.

reflectance

Ratio of the radiant energy reflected by an object or surface to the energy incident upon it.

reflection

A process in which incident radiation is immediately turned away or back from an object or surface without being converted into heat or performing any work.

refraction

The bending effect that occurs when electromagnetic waves travel from one medium to another with different properties.

remote sensing

Technique of acquiring information about an area or an object without being in physical contact with the area or object.

resolution

Resolution refers to the level of detail at which data are measured. The smallest individual unit or degree of detail associated with the information that can be discerned by a sensor. Resolution can refer to spatial, spectral and temporal characteristics of the data.

respiration

Abiochemical process by which living organisms obtain energy for maintenance and formation of cell material.

satellite (artificial satellite)

Any man-made object placed in a near-periodic orbit in which it moves mainly under the gravitational influence of one celestial body, such as Earth, the Sun, another planet, or a planet's moon.

senescence

The process of dying or going into dormancy.

sensor

An instrument, usually consisting of optics, detectors, and electronics, that collects radiation and converts it into recordable information.

simple ratio (SR)

A simple vegetation index (same as ratio vegetation index, RVI), calculated by dividing values from a NIR band by values from a red or visible band.

spatial analysis

The examination of spatial elements, interactions, patterns, and variations over an imaged area.

spectral band

An interval in the electromagnetic spectrum defined by two bounding wavelengths.

spectral reflectance

The reflectance measured within a specific wavelength interval.

spectral signature

The reflectance of a particular object or surface material plotted against increasing spectral wavelength. The resulting patterns can be used to identify objects or materials if they differ from those of other objects or materials.

spectral vegetation index (SVI)

A numerical measure generated by reducing data from multiple spectral bands into a single value, designed to take advantage of the spectral signature of live green vegetation to enhance the vegetation signal in remotely sensed data.

standard deviation

An absolute measure of dispersion or spread of a set of data points (a distribution) around the data set's mean value, derived by calculating the root mean square of individual deviations from the mean.

stomata

Small openings or pores on the undersides of leaves, through which gases and water pass.

stratosphere

A layer of Earth's atmosphere between the troposphere and the ionosphere.

Sun-synchronous orbit

An orbit timed for a satellite to proceed over any given point on the landscape at roughly the same local sun time, providing repeatable sun illumination conditions during specific seasons.

swidden agriculture

Slash and burn agricultural practices where land is used to grow crops until the soil's nutrient supply is exhausted, at which time the land is abandoned.

temporal profile

The graphical display of a dataset showing pixel values at a given image location through time. For example, the pixel values for the upper-left-most pixel for ten images collected on different days could be plotted to illustrate any variations in those values over time.

terrestrial ecosystem

A self-regulating association of living organisms and the physical environment in which they live, can be characterized by specific plant formations.

thermal infrared

Infrared radiation with wavelengths ranging from 3 to 1000 micrometers.

transmission

The complete passage of radiation through a medium.

transparency

The characteristic of a medium that allows radiation to easily pass through it.

transpiration

The uptake and release of water from plant foliage, also called evapotranspiration.

troposphere

The lowest atmospheric layer next to Earth's surface in which temperature generally decreases rapidly with altitude, clouds form, and convection is active.

ultraviolet radiation

Electromagnetic radiation having wavelengths ranging from 4 - 400 nanometers.

vapor pressure deficit (VPD)

The difference between the actual vapor pressure and the saturation vapor pressure at the existing temperature. For plants it is the difference in vapor pressure inside and outside a leaf, an index of the drying capacity of the outside air that varies with temperature and humidity.

vegetation index (VI)

See spectral vegetation index.

visible light

Radiation having wavelengths ranging from 0.4 - 0.7 micrometers. The human eye is sensitive to this region.

wavelength

The measure of the distance between successive wave crests.