|
|
Earth Imaging Glossary
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
" G "
GAC--Global Area Coverage
GAC data are derived from a sample averaging of the full resolution AVHRR data. Four out
of every five samples along the scan line are used to compute one average value and the data
from only every third scan line are processed, yielding 1.1 km by 4 km resolution at the
subpoint.
GAIN COEFFICIENT
Gain coefficient is a measurement to denote an increase in signal power in transmission from
one point to another.
GAMMA
This is a unit of magnetic intensity.
GAMMA-RAY DATA
Gamma-ray data are high frequency, penetrating radiation emitted from the nucleus of a
radioactive atom.
GAMMA-RAY SPECTROSCOPY
This non-destructive analytical technique is used to determine concentrations of specific
chemical elements such as potassium, thorium, and uranium. These elements have naturally
occuring radioactive isotopes based on their normal radioactive decay and the associated
emission of gamma-rays at specific wavelengths.
GAUSS-SEIDEL
The Gauss-Seidel method is a technique for interpolating irregularly spaced data points, such
as spot elevations, onto a regular grid (e.g., Digital Elevation Models). Unlike simple
interpolation methods which assume only correlation, the Gauss-Seidel method is used when
some characteristics of the system are known, such as the local value of a derivative. This
method, which must be solved iteratively, takes the form of an implicit equation.
The Successive Over Relaxation (SOR) method, a refinement to the Gauss-Seidel method,
causes the system to converge more rapidly so fewer iterations are required to achieve the
same result.
GCP--Ground Control Point
GCPs are physical points on the ground whose positions are known with respect to some
horizontal coordinate system and/or vertical datum. When mutually identifiable on the
ground and on a map or photographic image, ground control points can be used to establish
the exact spatial position and orientation of the image to the ground. Ground control points
may be either horizontal control points, vertical control points, or both.
GCTP--General Cartographic Transformation Package
The official U.S. Geological Survey (USGS) map projection software library, the GCTP is a
system of software routines designed to permit the transformation of coordinate pairs from
one map projection to another. The GCTP is the standard computer software used by the
National Mapping Division for map projection computations.
GEODETIC
Of or determined by geodesy; that part of applied mathematics which deals with the
determination of the magnitude and figure either of the whole Earth or of a large portion of
its surface. Also refers to the exact location points on the Earth's surface.
GEODETIC ACCURACY
The accuracy with which geographic position and elevation of features on the Earth's surface
are mapped. This accuracy incorporates information in which the size and shape of the Earth
has been taken into account.
GEOREGISTERED
An image that has been geographically referenced or rectified to an Earth model, usually to a
map projection. Sometimes referred to as geocoded or geometric registration.
GIRAS--Geographic Information Retrieval and Analysis System
GIRAS reflects the judgement of the USGS concerning the presentation and format of
polygonal data. The GIRAS data structure was designed to handle large quantities of data for
a map area. With the data structure, the basic topological elements (arcs, nodes, and
polygons) are all uniquely identified and cross-referenced to one another.
GIS--Geographic Information System
A system, usually computer based, for the input, storage, retrieval, analysis and display of
interpreted geographic data. The data base is typically composed of map-like spatial
representations, often called coverages or layers. These layers may involve a three-
dimensional matrix of time, location, and attribute or activity. A GIS may include digital line
graph (DLG) data, digital elevation models (DEM), geographic names, land-use
characterizations, land ownership, land cover, registered satellite and/or aerial photography
along with any other associated or derived geographic data.
GISS--Goddard Institute of Space Studies
Based out of New York, New York, GISS, one of NASA's Goddard Space Flight Center
research facilities, institutes activities involving research and analysis in specialized subjects,
including climate, biogeochemical cycles, remote sensing, and planetary atmospheres.
GLOBAL CHANGE MASTER DIRECTORY
The Master Directory (MD) is an online computer-based system designed to enable rapid
identification and location of data of interest to earth and space science researchers. It
provides brief, high level data set information from which the user should be able to identify
data of potential interest. The Master Directory has remote linking capabilities to a number of
other online data directories.
The MD resides on a VAX at the National Space Science Data Center (NSSDC) and may be
reached from GLIS by selecting the Remote Option (6) on the GLIS Main Menu screen.
GMT--Greenwich Mean Time
GMT is the mean solar time of the meridian of Greenwich used as the prime basis of
standard time throughout the world.
GPS--Global Positioning System
The GPS is a worldwide satellite navigation system that is funded and supervised by the U.S.
Department of Defense. GPS satellites transmit specially coded signals. These signals are
processed by a GPS receiver that computes extremely accurate measurements, including 3-
dimensional position, velocity, and time on a continuous basis. [Woods Hole Field Center]
GRASS--Geographic Resources Analysis Support System
GRASS is a product of the U.S. Army Corps of Engineers Construction Engineering
Research Laboratories (USACERL) in Champaign, Illinois. It is an integrated set of
programs designed to provide digitizing, image processing, map production, and geographic
information system capabilities to its users.
DISCLAIMER: Any use of trade, product, or firm names is for descriptive purposes only and
does not imply endorsement by the U.S. Government.
GRAVIMETRIC
Relating to weight measurement. A GRAVIMETER is an instrument used for determining
the specific gravity of bodies, solid or liquid.
GSFC--Goddard Space Flight Center
The NASA GSFC was established in 1959 just northeast of Washington, D.C. Goddard's
mission is to expand knowledge of the Earth, its environment, the solar system and the
universe through the development and use of near-Earth orbiting spacecraft. The GSFC is
responsible for supporting NASA's leadership role in space and Earth sciences; research and
application of technology for sensors, instruments and information systems; planning and
executing space flight projects for scientific research; and for tracking of manned and
unmanned Earth satellites through worldwide ground and space communication systems.
GUEST
A GLIS guest user is one who has not registered as a fully functional GLIS user. The guest
user has full search capabilities and may request that data be ordered, but does not have the
capability to save session information or search results, have a GLIS electronic mailbox, or
use some of the system's advanced features. A guest may register by selecting the
USERINFO option from the MAIN_MENU screen.
NOTE: A registered user who has signed on as a guest cannot switch to a "registered user"
status within the same session. The user must exit GLIS and login as a registered user.
GVI--Global Vegetation Index
The GVI is a specific AVHRR application that uses global area coverage (GAC) data to
produce a vegetative index called the normalized difference vegetation index (NDVI). GAC
data are processed daily and then composited on a weekly basis to produce a global map
portraying vegetation vigor.
GZIP
Gzip reduces the size of the named files using Lempel-Ziv coding (LZ77). Whenever
possible, each file is replaced by one with the extension .gz, while preserving the same
ownership modes, access, and modification times. The gzip programs for UNIX, Macintosh,
and DOS environments are available at the following websites.
UNIX gzip:
ftp://prep.ai.mit.edu/pub/gnu
Macintosh gzip:
ftp://mirrors.aol.com/pub/mac/util/compression
macgzip0.3b2.sit.hqx
DOS gzip:
ftp://prep.ai.mit.edu/pub/gnu
gzip-1.2.4.tar
ftp://ftp.uu.net/systems/ibmpc/msdos/pcroute
Did we miss something?
Send your submission to imaging@geocomm.com
Glossary Home
Initial content for this Glossary of terms has been graciously supplied by RADARSAT International - www.rsi.ca
|
|
Sponsored by:
For information
regarding
advertising rates
Click Here!
|
