|
Absorptance — 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.
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.
Applications Technology Satellite (ATS) — One of the early
geostationary satellites.
Attenuation — Any process in which the intensity of radiation
decreases due to scattering or absorption.
Advanced Very High Resolution Radiometer (AVHRR) — The
multispectral imaging sensor carried aboard the NOAA-series polar orbiting
satellites.
Backscatter — That portion of radiation
scattered back toward the source.
Blackbody — A body that absorbs all of the electromagnetic
radiation striking it regardless of wavelength.
Brightness Temperature — The Planck temperature associated
with the radiance for a given wavelength.
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).
Cyclogenesis — 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.
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.
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).
Field of View (FOV) — Generally associated
with the ground resolution from the detector standard viewing location,
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.
Geostationary Orbit — An orbit whose rotation
period equals that of the Earth. The altitude of a geostationary orbit
is approximately 35,800 km.
GOES — Geostationary Operational Environmental Satellite.
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).
Greybody — A body that absorbs some constant fraction of
all electromagnetic energy striking it regardless of wavelength.
Heat Capacity — The physical capacity of
a material to absorb incident thermal energy.
Infrared (IR) — Electromagnetic energy
within the wavelength interval generally defined from 0.7 to 100 microns.
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.
Jet Streak — An isotach (wind) maximum,
often observed along the jet stream.
Joule — A unit of energy equal to 0.2389 calories.
Longwave (LW) — Electromagnetic energy
lying in the wavelength interval generally defined from 4.0 microns
to an indefinite upper limit.
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.
Nadir — The satellite viewing angle directly
downward (viewing zenith angle = 0 degrees). Also used to refer to the
sub-satellite point location.
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.
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.
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/micron. 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 suffers a net loss of heat due to the emission of infrared radiation.
Reflectance — The fraction of incident radiation reflected
by a material.
Reflection — The process by which incident radiation is
scattered in the backward direction (backscattered).
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 microns.
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-micron
regions in which greater water vapor attenuation at 12 microns 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.
Tiros Operational Vertical Sounder (TOVS) —
A multichannel sounding instrument carried on the NOAA-series polar
orbiting satellites.
Transmission — The process by which incident radiation
propagates forward through a material.
Transmissivity (or transmittance) — The fractional quantity
of incident radiation transmitted by matter.
Ultraviolet (UV) — Electromagnetic radiation
of shorter wavelength than visible radiation but longer than x-rays
(approximately 0.03 to 0.4 microns)
VAS (or VISSR Atmospheric Sounder) — The
multichannel infrared sounding instrument aboard GOES satellites prior
to GOES-8.
Visible — The region of the electromagnetic spectrum which
is detectable to the human eye (approximately 0.4 to 0.7 microns).
VISSR — Visible and Infrared Spin-Scan Radiometer. The
visible and 11-micron infrared imaging sensor aboard 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.
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. This usually
refers to the 6.7 micron channel in this module.
Weighting Function — A mathematical expression representing
the relative radiance contribution provided from a given level of the
atmosphere (usually a function of atmospheric pressure).
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 clocktime at GMT and
UTC. See Greenwich Mean Time (GMT), or Coordinated Universal Time (UTC).
|