Glossary of Satellite Meteorology Terms
Go to: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
A
- absorptance (or absorptivity)
- The fractional quantity of available radiant energy absorbed by a material such as an atmospheric layer, cloud layer, surface, or particle.
- absorption
- The process by which incident radiant energy is retained by a material due to the material's physical composition.
- absorption region
- A portion of the electromagnetic spectrum where radiation is absorbed and re-emitted by atmospheric gases such as water vapor, carbon dioxide, methane, and ozone.
- albedo (or reflectivity)
- The ratio of the amount of radiation reflected by a body to the amount incident upon it, commonly expressed as a percentage. Also defined as the reflectivity of a surface for a specified broad spectral range such as the visible or solar spectrums.
- attenuation
- Any process in which the intensity of radiation decreases due to scattering or absorption.
- atmospheric window
- A portion of the electromagnetic spectrum where radiation is allowed to pass through the atmosphere without absorption by atmospheric gases such as water vapor, carbon dioxide, and ozone.
B
- backscatter
- That portion of radiation scattered back toward the source.
- blackbody
- A theoretical body (or object) that absorbs all of the electromagnetic radiation striking it regardless of wavelength, and emits radiation determined only by the temperature of the blackbody.
- brightness temperature
- A measure of radiation in terms of the temperature of a hypothetical perfect emitter (or blackbody) that would emit the same amount of radiation at the same wavelength. Defined as the Planck temperature associated with the radiance for a given wavelength.
C
- carbon dioxide channel (or CO₂ channel)
- A spectral band in which the radiance is attenuated by carbon dioxide. In this module it refers to the 13.3 micrometer channel on board GOES-12 to -15.
- channel selection
- A spectral band to be included on a remote sensing instrument or to be selected for analysis.
- cloud streets
- Small fields of cumulus clouds. Often the vertical development and spacing of cloud streets are controlled by thermodynamic stratification and wind shear. Cloud streets are easily observed in daytime visible satellite imagery.
- cold cloud shield
- The portion of the clouds over a frontal zone or cyclone that form a well-defined pattern of uniform cold tops on infrared satellite imagery and an opaque appearance on visible imagery.
- Coordinated Universal Time (UTC)
- Same as Zulu (Z) and Greenwich Mean Time (GMT). The local mean solar time at the Royal Observatory in Greenwich, England, with the day starting at midnight, and incorporating adjustments according to Earth's changing rotation. A standard time commonly used in telecommunications, Internet standards, aviation, weather forecasts, astronomy, and military applications.
- cyclogenesis
- A body that absorbs all of the electromagnetic radiation striking it The formation and intensification of a low-pressure center.
- cyclone
- An area of low pressure around which winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
D
- divergence
- A measure of the expansion of a vector field. The fractional rate of increase of a horizontal area due to the outward spreading or the rate of decrease of mass in a specified volume.
- dryline
- A narrow zone of sharp moisture gradients separating warm, dry air from warm, moist air and usually found over the Plains region of the United States during spring or early summer. When dynamically active is often the site of thunderstorm development.
E
- electromagnetic (EM)
- Energy carried by electric and magnetic waves.
- emission
- The process by which a material generates electromagnetic radiation due to its temperature and composition.
- emissivity
- The ratio of emitted radiation of a surface at a given temperature and wavelength to that of a blackbody at the same wavelength and temperature.
- emittance
- The fractional quantity of available radiative energy emitted by a material.
- emitter
- Anything that radiates measurable electromagnetic radiation.
- energy
- The capacity to do work or transfer heat. Denoted by dQ and measured in MKS units as Joules (kg·m2·s-2).
F
- field of view (FOV)
- Generally associated with the ground resolution from the detector standard viewing location, directly below the satellite and on the equator in the case of a geostationary satellite. The field of view is the solid angle through which a detector observes radiation.
- frequency
- The number of recurrences of a periodic phenomenon per unit time. The frequency of electromagnetic energy is usually specified in Hertz (Hz), which represents one cycle per second.
G
- geostationary orbit
- An orbit whose rotation period equals that of the Earth. The altitude of a geostationary orbit is approximately 35,800 km above the Earth's equator. Satellites in geostationary orbit appear stationary relative to a fixed point on the Earth, and in the case of weather satellites allows for continous monitoring of Earth's surface, clouds, and atmosphere for a given region.
- GOES
- Geostationary Operational Environmental Satellite.
The NOAA operated GOES series began with the launch of GOES-1 in 1975 and are designed to monitor Earth's weather and space environment from geostationary orbit above a fixed location along the equator.
- Greenwich Mean Time (GMT)
- Mean solar time of the meridian at Greenwich, England, used as the basis for standard time throughout most of the world. Also referred to as Zulu (Z) and Coordinated Universal Time (UTC) with the day starting at midnight.
- greybody
- A body that absorbs some constant fraction of all electromagnetic energy striking it regardless of wavelength.
H
- heat capacity
- The physical capacity of a material to store thermal energy. Typically measured in units of J/°C or J/K (which are equivalent).
I
- infrared (IR)
- Electromagnetic energy within the wavelength interval generally defined from 0.7 to 100 micrometers.
- irradiance
- The energy per unit time (or Watts) incident upon a unit area of a given surface, denoted by E = dQ/dt/dA and measured in MKS units as Watts/m2.
- isobaric
- An object or a process characterized by constant or equal pressure (i.e., an isobaric surface, an isobaric process.)
J
- jet streak
- An isotach (wind) maximum, often observed along the jet stream.
- Joule
- A unit of energy equal to 1 Watt second or 0.2389 calories. The energy (or work) exerted by the force of one newton acting to move a 1 kg object across a distance of one meter.
K
L
- longwave (LW)
- Electromagnetic energy in the infrared wavelength interval generally defined from 4.0 micrometers to just short of the microwave region starting around 1000 micrometers (1 mm).
M
- mesoscale convective system (MCS)
- Precipitation systems 20 to 500 km (11 to 270 n mi) wide that contain deep convection. Examples in mid-latitudes are large isolated thunderstorm complexes, squall lines, Mesoscale Convective Complexes (MCCs), and rainbands.
- MKS system
- Meter-Kilogram-Second system of physical units.
- monochromatic
- Of or pertaining to a single wavelength, or in practice, perhaps a very narrow spectral interval.
N
- nadir
- The satellite viewing angle directly downward (viewing zenith angle = 0 degrees). Also used to refer to the sub-satellite point location.
0
- opaque
- A physical description of a material which attenuates electromagnetic radiation.
- optical depth
- A measure of the cumulative attenuation of a beam of radiation as a result of its travel through the atmosphere.
- outflow boundary
- The boundary between an airmass that has been cooled by thunderstorm downdrafts and the unaffected surroundings.
P
- Polar Orbiting Environmental Satellite (POES)
- A satellite which has a polar orbit, such as the NOAA series or Defense Meteorological Satellite Program systems.
- polar orbit
- An orbit whose path crosses the polar regions. This type of orbit is located at an altitude generally between 200 and 1000 km, and can provide sun-synchronous observations.
- potential vorticity (PV)
- A quantity proportional to the product of vorticity and stratification that, following an air parcel, can only be changed by adiabatic or frictional processes. Baroclinic instability requires the presence of a potential vorticity gradient along which waves amplify during cyclogenesis.
- Planck's law
- An expression for the variation of monochromatic radiance as a function of wavelength for a blackbody at a given temperature.
Q
R
- radiance
- A measure of radiant intensity produced by a material in a given direction and per unit wavelength interval, denoted by Il = dQ/dt/dA/dl/dW and measured in MKS units as Watts/m2/steradian/micrometer. Can also be defined as the radiant flux per unit solid angle and wavelength interval.
- radiant flux
- The rate of energy transfer by electromagnetic radiation, in units of energy per unit time. Denoted by F = dQ/dt and measured in MKS units as Joules/second or Watts.
- radiational cooling
- Accomplished mainly at night, the cooling of the earth's surface and adjacent air or whenever the earth's surface experiences a net loss of heat due to the emission of infrared radiation.
- reflectance (or reflectivity)
- The fraction of incident radiation reflected by a material.
- reflection
- The process by which incident radiation is scattered in the backward direction (backscattered).
- retrieval
- The process or end result of a process where physical quantities such as water vapor, temperature, cloud top pressure, and cloud amount, are extracted from measurements of total upwelling radiance to space; here involving the GOES imager and sounder instruments.
S
- scattering
- The process by which a material interacts with and redirects incident radiation (in any given direction).
- selective absorber
- A substance in which absorption varies with the wavelength of incident radiation.
- selective emitter
- A substance in which emissivity varies with wavelength.
- shortwave (SW)
- Electromagnetic radiation generally defined as having a wavelength shorter than 4.0 micrometers.
- skin temperature
- The equivalent blackbody temperature of a material which has a high emissivity, such that the observed radiance is representative of the sensible temperature of the material surface region ("skin") that faces the instrument.
- spectral
- A descriptor for radiometric quantities or measurements which have a limited wavelength range.
- split window
- A pair of regions of the electromagnetic spectrum which are closely located in wavelength, but have slightly different attenuation characteristics. Used to denote the 11- and 12-micrometer regions in which greater water vapor attenuation at 12 micrometers causes slightly different brightness temperatures.
- steradian
- The unit of measure of solid angles, equal to the angle subtended at the center of a sphere.
- storm relative wind
- The wind that would be measured by an observer traveling with the storm. It is the vector obtained by subtracting the storm motion vector from a wind vector measured with respect to a fixed ground location.
- storm system motion
- The direction and speed of a moving storm or storm system. For multicell thunderstorms, this motion is the result of cell motion and discrete propagation associated with new cell formation. For supercell thunderstorms, the motion is the result of forcing by the environmental wind field and transverse propagation normal to the mean wind shear of the environment.
- sun-synchronous
- Used to describe an orbit where the orbital plane is near polar (satellite crosses Earth's polar regions) and the altitude (typically 600-800 km) is such that the satellite ascends or descends over any given point of the Earth's surface at the same local solar time twice daily.
T
- transmission
- The process by which incident radiation propagates forward through a material.
- transmissivity (or transmittance)
- The fractional quantity of incident radiation transmitted by matter.
U
- ultraviolet (UV)
- Electromagnetic radiation of shorter wavelength than visible radiation but longer than x-rays (approximately 0.03 to 0.4 micrometers)
V
- visible
- The region of the electromagnetic spectrum that is detectable to the human eye (approximately 0.4 to 0.7 micrometers).
- VISSR
- Visible and Infrared Spin-Scan Radiometer. The visible and 11-micrometer infrared imaging sensor on board GOES satellites prior to GOES-8.
- vorticity
- A vector measure of the local rotation in a fluid flow. This can be evidenced by upper air parameter fields as well as the relative circulation observed in satellite imagery.
W
- wavelength
- The distance a wave will travel in the time required to generate 1 cycle. A length measured along the direction of propagation, usually from the midpoint of a crest (or trough) to the midpoint of the next crest (or trough).
- water vapor channel (or water vapor IR channel)
- A spectral band in which the radiance is attenuated by water vapor. In this module it refers to the 6.7 (GOES-8 to -11) and 6.5 (GOES-12 to -15) micrometer channels.
- weighting function
- A mathematical expression representing the relative radiance contribution from a given level of the atmosphere. Usually described as a function of atmospheric pressure.
X
Y
Z
- Z
- Used to represent radar Zulu time (i.e. GMT), Coordinated Universal Time (UTC), a vertical (height) coordinate, or radar reflectivity factor.
- Zulu
- Used to represent the same clock time as GMT and UTC. See Greenwich Mean Time (GMT), or Coordinated Universal Time (UTC).