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.
geo-data 지리정보
geo data subset 지리정보 일부분
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.
geological 지질학
geometry 기하
geophisical 지구물리학
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, 지리정보시스템 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.
GKS Graphic Kernel System, API standard, device independence and logical input device
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.
GLONASS/GPS Russian Global Navigation Satellite System
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.
GNSS Global Navigation Satellite System
Graphic representation 그래픽 표현
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.