Definitions and Keywords
- Active Remote Sensing
- Remote sensing that involves emitting a signal and then measuring
that signal when it is backscattered (or reflected) back to the
instrument. Examples include radars and lidars (LIght Detection
And Ranging Radars - similar to Radar but uses a laser).
- This can refer to either a narrow spectral channel (see below)
selected out of the electromagnetic spectrum, or to a larger
portion of the spectrum.
- A discrete portion of the spectrum measured by a satellite
instrument, defined by a filter function (vs. wavelength). Satellite
channels have a finite width, typically ranging from around 0.2
micrometers to greater than 1.0 micrometers in the infrared,
or to greater than 10 micrometers for sounder infrared channels.
- El Nino
- A name given to the event when abnormally warm surface waters
appear near the coast of equatorial South America.
- Sometimes called geosynchronous - a characteristic of a satellite
orbit in which the satellite circles the globe, over the equator,
in synchronization with the earth's rotation. These satellites
remain over the same earth location, allowing images of the scene below
the satellite to be taken continuously, with little or no perceived
- Geostationary Operational Environmental Satellites (GOES) are the
North American series of geostationary weather satellites. Currently
there are two operational GOES satellites, GOES-8 (75W) and GOES-10 (135W),
and two in-orbit replacements, GOES-11 and GOES-12. The GOES
satellites provide almost continuous viewing of the Americas and
surrounding oceans with spatial resolution up to 1 km in the visible
channel, and 4 km in the infrared channels. The GOES have
separate imaging and sounding systems to better suit the needs
of the atmospheric science community for both their operational
and research needs. The current imager provides routine coverage in five
spectral channels (a visible, a shortwave window, a split window pair,
and a mid-tropospheric water vapor band). The sounder provides a
visible channel and 18 infrared channels for temperature and moisture
profiling and cloud applications. This is a substantial improvement
over the previous GOES VAS instrument which had 12-channels for
all applications. Changes in channel locations and spatial resolutions
will be in effect starting with GOES-12 onward.
- Hydrologic Cycle
- The movement of water among the reservoirs of the ocean, the atmosphere,
and the land.
- As applied to GOES satellites: a 5-channel instrument designed
to measure the visible and infrared portions of the electromagnetic
spectrum. Normal scheduling of the imager provides operational images
every 15 minutes over most of the U.S.
- The portion of the electromagnetic spectrum with wavelengths
ranging from longer than visible radiation, starting around 0.7
micrometers, to wavelengths shorter than those in the microwave
portion of the spectrum. Satellite instruments typically measure
infrared radiation between wavelengths of about 3 micrometers
and 20 micrometers.
- Long wave
- When referring to the infrared portion of the electromagnetic
spectrum, longwave is the region above about 10 micrometers.
- Medium wave
- When referring to the infrared portion of the electromagnetic
spectrum, medium wave is the region between about 5 and 10 micrometers.
- Meridional Wind
- The wind, or wind component, in the north-south direction.
- The Meteosat series of geostationary satellites is the European
Communitys (operated by Eumetsat) equivalent to the U.S. GOES satellites
and provides similar imaging capabilities in three channels.
- The portion of the electromagnetic spectrum with much longer
wavelengths than infrared radiation, typically above about one
- Moderate Resolution Imaging Spectroradiometer (MODIS) is the key
instrument aboard the Terra (EOS AM-1) satellite.
Terra MODIS is viewing the entire Earth's surface every to 2 days,
acquiring data in 36 spectral bands, with spatial resolution of 250 m and
1 km for the visible and infrared channels, respectively.
- The process of using combinations of imagery taken at different
wavelengths to generate a product. (eg. vegetation classification,
vertical temperature, moisture sounding, etc.)
- Outgoing Longwave Radiation - A type of radiation emitted
by the earth. Although the atmosphere obsorbs only a small percentage
of the short-wave solar radiation, it absorbs much of the long-wave
terrestrial radiation. Only when the earth's surface temperature
is fairly high does the radiational loss through the transparent
bands and from the top of the atmosphere equal the amount absorbed
from the sun. This heat-retaining behavior is similar to that
of a greenhouse.
- Passive Remote Sensing
- Remote sensing that involves measuring the natural emission
of radiation. An example is weather satellites.
- A characteristic of a satellite orbit that allows the satellite
to circle the globe approximately over the poles of the earth.
Polar-orbiting satellites have orbital inclinations, with respect
to the equator, of close to 90 degrees. Typically, polar-orbiting
weather satellites are also sun-synchronous.
- The total atmospheric water vapor contained in a vertical
column of unit cross-sectional area extending from the surface
to the top of the atmosphere.
- The process of measuring a parameter (such as temperature,
moisture, or rainfall) from a distance (such as from space, or
by using a radar). This is done by measuring natural emission
of radiation or backscattered radiation (i.e. radiation that
was reflected or bounced back to the observing instrument) from
an emission source.
- The size of the field-of-view (FOV) of a satellite picture
element, often called a pixel, as measured on the earth in kilometers.
Resolution can have a second meaning: as the distance between
the centers of adjacent picture elements. The two resolutions
can be different, resulting in either overlap of individual FOVs,
or gaps between them.
- As applied to GOES satellites: a 19-channel instrument designed
to provide visible and infrared spectral radiances, used to vertically
probe, or sound, the atmosphere. This is done by employing spectral
bands with different amounts of atmospheric absorption, in order
to measure temperatures and moisture at different depths in the
atmosphere. Sounder data is typically available from GOES every
hour, over the same locations.
- A characteristic of a satellite orbit that allows the satellite's
path to precess, or rotate slowly in synchronization with the
earth's revolution about the sun. Sun-synchronous satellites
view the earth at the same local time each pass; and, by necessity,
are polar-orbiting, viewing the earth below during both a day-time
and a night-time overpass, approximately twelve hours apart.
- Television and InfraRed Observation Satellite - an old term
used for the first polar-orbiting weather satellites. Currently,
satellites in the series are called NOAA satellites.
- The portion of the electromagnetic spectrum viewable by the
naked eye, with wavelengths ranging from approximately 0.43 micrometers
to 0.69 micrometers.
- Water Vapor Transport
- The movement or transport of moisture by the wind is an important
aspect of the hydrologic cycle. Traditionally this transport
has been calculated with the use of rawinsonde data. The availability
of global atmospheric models has allowed for the calculations
to be made over the globe with the initialized or forecasted
modeled variables. Recent applications of satellite data allow
for the determination of both wind and moisture fields, which,
like the rawinsonde and model data, can be used to calculate
the transport of water vapor in the atmosphere.
- Water Vapor Winds
- The application of a time sequence of co-registered satellite
images can be used to estimate the motion of features in the
images. When applied to cloud imagery, cloud motion vectors,
or cloud drift winds, are generated. These winds capture the
relative movement of the clouds with respect to the Earth. When
applied to mid- and upper-tropospheric water vapor imagery, the
winds are referred to as water vapor (tracked) winds. Water vapor
winds are generally thought to represent the large-scale flow
patterns in the mid- and upper-troposphere.
- What is the wind and why is it important? Sunlight striking
the earth's surface heats the air above, producing pressure differences.
In an attempt to equalize these differences, the atmosphere responds
by moving masses of air,which causes the wind. Additional forces
come in to play that can influence the wind speed and direction
as well. The distribution of the wind can tell us a great deal
about the state of the atmosphere. The wind transports water
vapor, heat, greenhouse gases, and aerosols, which interact with
clouds and incoming/outgoing radiation. All of these factors
work together to produce our weather and climate.
- Zonal Wind
- The wind, or wind component, in the east-west direction.
- AVHRR - Advanced Very High Resolution
- CAMEX - Convection and Moisture Experiment
- CaPE - Convection and Precipitation/Electrification
- ENSO - El Nino Southern Oscillation
- GMS - Geosynchronous Meteorological
- GOES - Geostationary Operational Environmental
- IWC - Integrated Water Content (same
- LST - Land Surface Temperature
- MAMS - Multispectral Atmospheric Mapping
- MAS - MODIS Airborne Simulator
- MODIS -
Moderate Resolution Imaging Spectroradiometer
- NCAR - National Center for Atmospheric
- NCEP - National Centers for Environmental
- NDVI - Normalized Difference Vegetation
- NVAP - NASA Water Vapor Project
- PW - Precipitable Water
- TIROS - Television and InfraRed Observation
- SSM/I - Special Sensor Microwave/Imager
- SSM/T - Special Sensor Microwave/Temperature
- SST - Sea Surface Temperature
- STORMFEST - Storm-scale Operational
and Research Meteorology-Fronts Experiment Systems Test
- UTH - Upper Tropospheric Humidity
- VISSR - Visible Infrared Spin Scan
Radiometer (an instrument aboard GOES-1 through 7)
- VAS - VISSR Atmospheric
Sounder (an instrument aboard GOES-4 through 7)
- WVTI - Water Vapor Transport Index
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Last updated on: January 17, 2002