Monitoring the World’s Forest Resources
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Advanced Very High Resolution Radiometer (AVHRR) — a sensor located on NOAA polar
orbiting satellites. NOAA receives AVHRR data at full resolution and archives them in two different formats: some data are recorded at full resolution and are known as LAC data with a 1km spatial resolution; all data are sampled down to a nominal resolution and are referred to a
GAC data with a 4-km spatial resolution.
Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) — a sensor developed by the
Jet Propulsion Lab (JPL) under a contract with NASA that produces hyperspectral data with
224 contiguous bands. The bands are 0.01 micrometers wide and cover the spectral range of
0.4 to 2.4 micrometers.
Attribute — the tabular information associated with a raster or vector layer.
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Band — a set of data file values for a specific portion of the EM spectrum (red, green, blue,
near-infrared, infrared, thermal, etc.), or some other user-defined information created by combining or enhancing the original bands, or creating new bands from other sources. Sometimes
called a channel.
Burn Area Mapping Methods — provide information about post-fire effects.
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Camera, Large Format — a mapping camera used in commercial and technical photography
designed to provide large-sized (commonly 230mm x 230mm) negatives that will cover as
large a footprint as possible. Photography from this type of camera is commonly used for
mapping large areas. The camera is housed in a specialized mount that compensates for the
aircraft tip, tilt, and roll.
Camera, Small Format — can be as simple as a handheld 35mm camera taking pictures out
of the window of an aircraft to a mounted 70mm camera. Most digital cameras fall into this
category.
Cell Size — the area that one pixel represents, measured in map units. Sometimes called
pixel size.
Change Detection—a comparison of two images over a specific period of time to detect
change.
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Channel — see Band
Classification — the process of assigning the pixels of a continuous raster image to discrete
categories.
Classification Scheme — a set of target classes or legend that serves as the basis of a classification or map, also known as a classification system.
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Digital Elevation Model (DEM) —a raster array of elevation values. In remote sensing,
DEM’s are frequently used as secondary data for image classification and accuracy assessment processes. Sometimes referred to as a Digital Terrain Model (DTM).
Digital Image — a representation consisting of many individual pixels arranged in a grid. Digital images can be used in computer image processing and GIS analysis.
Digital Number (DN) — the numerical value of a specific pixel. The DN corresponds to the
average radiance measured in each pixel. DN is expressed in a value—typically ranging from
0 to 255.
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Electromagnetic (EM) Spectrum — the range of energy transmitted through space in the
form of electric or magnetic waves, extending from cosmic waves to radio waves. Included in
this spectrum are visible and IR regions that are particularly important for land remote sensing
applications.
Energy, Emitted — mainly derived from visible and near IR (shortwave) energy that has
been absorbed by an object and then reradiated as thermal IR (long wave) energy
Energy, Reflected — energy in the visible and near IR portion of the EM spectrum that is a
result of solar radiation bouncing (or being reflected) off of an object.
Enhanced Thematic Mapper Plus (ETM+) — multispectral data acquired in eight spectral
bands ranging from visible to thermal IR with a spatial resolution of 30 meters, except the
panchromatic band (with a spectral range from visible to near-IR) which has a spatial resolution of 15 meters. This sensor is aboard the Landsat 7 satellite. See also Thematic Mapper.
Enhancement — the process of making an image more interpretable for a particular application. Enhancement can make important features of raw, remotely sensed data more interpretable to the human eye.
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False Color Composite — a method of displaying satellite or other multispectral data in
which the recorded near-IR and other “invisible” (to the human eyes) energies are shown as
colors. The colors in such an image are called “false” because they are not necessarily the
colors we might expect to see (e.g., vegetation can appear as magenta or orange).
Fire Detection Methods — provide information on the frequency and distribution of fire.
Footprint — the total area on the ground covered by the scanner. A footprint has a set width
and length.
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Galileo—A GNSS system proposed by the European Space Agency in March 2001, the Galileo system has been delayed by political and economical issues. The only fully commercial
system (the Russian and US versions are military controlled and can be disabled for commercial users in times of conflict), it is expected to be fully operational by 2018.
GeoEye — higher resolution satellite imagery commercially available from the company of
the same name. The data is acquired in multispectral format covering four spectral bands
ranging from the visible to the near IR with a 1.65 meter spatial resolution; also acquired in a
panchromatic format with a single band covering the visible to near IR with a 0.41 meter spatial resolution.
Geographic Information System (GIS) — the term frequently applied to geographically oriented computer technology. In its broadest sense, GIS is a system for capturing, storing,
checking, manipulating, analyzing, and displaying data that are spatially referenced to Earth.
Georeferencing — the process of assigning map coordinates to image data and resampling
the pixels of an image to conform to the map projection grid.
Geospatial — a term used to describe a class of data that has a geographic reference or position.
Global Navigation Satellite System — an array of space satellites and ground receivers
that use geometry to provide information about the precise latitude, longitude, and elevation
of a particular point. Previously known as GPS, which is name of the United States system,
GNSS is now accepted as the generic term for such navigation systems.
Global Positioning System — a GNSS system developed and operated by the United
States, it is the first and longest operating of such systems in use.
GLONASS—the Russian GNSS system, expected to have global coverage by the end of
2011.
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Ground Sample Distance — the representation of a pixel as projected on the ground.
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Hyperspectral — sensors (or images) that record (or display) data from tens to hundreds of
contiguous bands of the EM spectrum.
IKONOS — higher resolution satellite imagery commercially available from Geoeye; acquired
in multispectral format covering four spectral bands ranging from the visible to the near IR
with a four-meter spatial resolution; also acquired in a panchromatic format with a single band
covering the visible to near IR with a one-meter spatial resolution.
Image — a picture or representation of an object or scene on paper, or a display screen. Remotely sensed images are digital representations of the Earth.
Image Classification — the process of assigning the pixels of an image to discrete categories or classes.
Image Extent — the amount of area covered by an image
Image Processing — a general term referring to the manipulation of digital image data. Processing includes image enhancement, image classification, and rectification operations.
Infrared—the range of the electromagnetic spectrum measured from the nominal edge of visible red light (0.74 micrometers) to 300 micrometers. This range includes thermal radiation,
usually referred to as thermal-IR.
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Land Cover Map — a map of the visible ground features of a scene, such as vegetation,
bare land, pasture, urban areas, etc.
Landsat — name for a series of Earth-observing satellites first launched in 1972 by NASA
(originally named ERTS, for Earth Resource Technology Satellite). Landsat satellites serve as
platforms for several sensors including Landsat TM and Landsat ETM+.
LIDAR (Light Detection and Ranging) — an active remote sensing system used for Earth
resource observations as well as land surveying. It uses the transmission of short pulses of
EM energy in the ultraviolet, visible, or near infrared (typically 0.6—1.0 nanometers) through
the atmosphere to a target and then recording the amount of energy backscattered from the
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terrain. Due to the wavelengths used, LiDAR cannot penetrate clouds or similar obstructions
as RADAR can.
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Modeling — the process of creating a new GIS layer by combining or operating on existing
layers. Modeling creates an image (or images) that contains several types of information
comprised of several GIS variables (e.g., a scene could be considered in terms of its vegetation, elevation, water, and climate at the same time).
MODIS — acronym for the Moderate Resolution Imaging Spectroradiometer onboard NASA’s
Earth Observation System (EOS) satellites. This sensor acquires imagery in 36 spectral band
ranging from the visible to the far IR with a spatial resolution that varies from 250-meters up to
1,000-meters.
MODIS Land Rapid Response — a system producing daily active fire detection products
from its data feed in near-real time (typically less than four hours from acquisition).
Multispectral — sensors (or images) that record (or display) data from two up to 15 discrete
bands of the EM spectrum.
Multispectral Scanner (MSS), Landsat—Landsat satellite data acquired in four spectral
bands ranging from the visible to the IR, with a spatial resolution of 80 meters.
Multitemporal—data from two or more dates, also known as multidate.
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Nadir — the Earth’s surface point directly below the sensor.
National Oceanic and Atmospheric Administration (NOAA) Satellites — a series of
American satellites first launched in 1979. The NOAA-6 through NOAA-12 missions contain
the AVHRR sensors used in land remote sensing applications.
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Oblique — a photograph taken with the camera axis directed between the horizontal and vertical.
Off-nadir — capacity of a sensor to collect data regarding an area not directly beneath the
sensor. In the SPOT satellite sensors, off-nadir pointing increases the revisit capability and
allows for stereoscopic views of the ground. The off-nadir viewing is provided by SPOT’s
pointable optics.
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Orthophotograph — a continuous-tone photo image depicting terrain features in their true
planimetric position (i.e., in a map-like form).
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Panchromatic — monochromatic or single-band imagery. Most satellites can record panchromatic data as well as multispectral data.
Pixel — abbreviated from “picture element” (picture+element=pixel).
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QuickBird — high resolution satellite image imagery commercially available from Digital
Globe; acquired in multispectral format covering four spectral bands ranging from the visible
to the near IR with a 2.4-meter spatial resolution; also acquired in a panchromatic format with
a single band covering the visible to near IR with a 0.6-meter spatial resolution.
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RADAR (Radio Detection and Ranging) — an active microwave remote sensing system
used for Earth resource observations. It is based on the transmission of long-wavelength
(e.g., 3 to 25 cm) microwaves through the atmosphere and then recording the amount of energy backscattered from the terrain.
Radiometric Resolution—a measure of how many bits of computer memory are used to
store the information for a single pixel in a raster image. Current technology typically uses
anywhere from 8 bits to 12 bits, which equates to values of 0—255 for 8-bit data and 0—4095
for 12-bit data. Higher radiometric data allows for improved differentiation of objects.
Raster Data — data that is organized in a grid of columns and rows. Raster data usually represents a planar graph or geographic area.
Raster Image — a digital array of pixels
Reflectance — the total solar energy incident on a given feature minus the energy that is either absorbed or transmitted by the feature. Reflectance is dependant upon the material type
and condition, and permits us to distinguish different features in a visual image.
Remote Sensing — the collection and interpretation of information about objects from a distance (remotely) based on reflected or emitted energy from those objects.
Revisit Time — how often a sensor can collect information about the same target.
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Sensor — a device that records EM radiation or other data about an object and presents it in
a form suitable for obtaining information about the environment.
Spatial Resolution — a measure of the smallest object that can be resolved by the sensor, or
the area on the ground represented by each pixel.
Spectral Band — an interval in the EM spectrum delineated by two wavelengths or frequencies.
Spectral Reflectance Curve — a graph of spectral reflectance of an object as a function of
wavelength.
Spectral Resolution — the dimension and number of specific bands (wavelength intervals) in
the EM spectrum that a sensor can detect.
Spectral Response Curve—see Spectral Reflectance Curve.
SPOT (Systeme Probatoire d’Observation de la Terre) — a multispectral and panchromatic
remote sensing satellite system with pointable HRV sensors. This French satellite was first
launched in 1986.
SPOT Multispectral — satellite data acquired in three spectral bands ranging from visible to
near-IR with a spatial resolution of 20 meters.
SPOT Panchromatic — satellite data acquired in a single spectral band covering portions of
the visible and near-IR with a spatial resolution of 10 meters.
Swath Width — the total width of the area on the ground covered by the scanner. A swath
has a set width but can have a variable height/length.
Synthetic Aperture Radar (SAR) — a radar system which employs a short physical antennae
that can simulate the effect of a very long antennae through modified data recording and processing techniques. SAR has been effectively used in vegetation mapping projects.
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Temporal Resolution — a measure of how often a given sensor obtains imagery of a particular area, also called coverage. For satellite data, temporal resolution depends upon the satellite’s orbit schedule and off-nadir pointing capability. Temporal resolution is important for projects requiring multitemporal imagery (such as change detection projects).
Thematic Mapper (TM) — multispectral satellite data acquired in seven spectral bands ranging from visible to thermal IR with a spatial resolution of 30 meters (120 meters for the thermal
band). This sensor is aboard the Landsat 5 spacecraft. See also Enhanced Thematic Mapper
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Plus.
Thermal Infrared — the portion of the EM spectrum that is perceived as heat; emitted energy
as opposed to reflected energy normally measured by remote sensing systems.
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Vector Data — data that represent physical forms (elements) such as points, lines, and polygons. In terms of GIS, vectors typically represent a boundary between spatial objects.
The definitions provided in this glossary were adapted in part from the following sources:
Avery, T. E. and Berlin, G. L. 1985. Interpretation of Aerial Photographs, fourth edition.
Minneapolis, MN: Burgess Publishing.
Colwell, R. N., editor-in-chief. 1983. Manual of Remote Sensing, Volumes I and II, second edition. Falls Church, VA: American Society of Photogrammetry.
Jensen, J. R. 1996. Introductory Digital Image Processing: A Remote Sensing Perspective, second edition. Englewood Cliffs, NJ: Prentice-Hall, Inc.
Leica Geosystems. 2003. ERDAS Field Guide, seventh edition. Atlanta, GA: Leica Geosystems, Inc.
Lillesand, T. M. and Keifer, R. W. 1994. Remote Sensing and Image Interpretation. New
York, NY: John Wiley & Sons, Inc.
Star, J. and Estes, J. 1990. Geographic Information Systems: An Introduction. Englewood Cliffs, NJ: Prentice-Hall, Inc.