Bench mark—A permanent monument established by any federal, state, or local agency, whose location and/or elevation are referenced to a specified datum.

Carrier frequency—The frequency used by a radio signal to carry information and to which a receiver must be precisely tuned to isolate that signal from the radio signals at other frequencies.

Celestial reference frame—The inertial (un-accelerated) non-rotating reference frame associated with the distant stars.

Co-location—Two or more geodetic techniques or systems occupying simultaneously or subsequently very close locations.

Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC)—A joint Taiwan/U.S. mission providing atmosphere profiles using GPS occultation measurements.

Continuously Operating Reference Stations (CORS)—A NGS-coordinated network of GNSS receivers to support positioning activities throughout the United States and its territories.

Coordinates—A set of N numbers designating the location of a point in N-dimensional space. Horizontal coordinates are two-dimensional coordinates, normally expressed as x, y coordinates, eastings and northings, or longitude and latitude (geographic coordinates).

Coordinated Universal Time (UTC)—A modern continuation of Greenwich Mean Time, the standard “clock time.”

Corner cube—A combination of reflecting surfaces that always reflect light parallel to the incoming direction.

Crustal deformation—The deformation of the Earth’s crust in response to stress.

Crustal Dynamics Data Information System (CDDIS)—A NASA system for space geodetic data archiving and distribution.

Cryosphere—The Earth’s glaciers and ice sheets.

Datum—A set of constants specifying the coordinate system used for geodetic control (i.e., for calculating coordinates of points on the Earth).

  • Horizontal datum (geometric reference frame)—A geodetic datum specifying the coordinate system in which horizontal control points are located. The North American Datum of 1983 (NAD83) is the official horizontal datum of the United States. For horizontal datums, at least eight constants are needed to form a complete datum: three to specify the location of the origin of the coordinate system, three to specify the orientation of the coordinate system, and two to specify the dimensions of the reference ellipsoid (NRC, 2007b).

  • Mean sea level—A tidal datum computed as the arithmetic mean of hourly heights observed over a specific 19-year Metonic cycle. Shorter series are specified by name (for example, monthly mean sea level, yearly mean sea level).

  • Vertical datum—A set of constants defining a height (elevation) system containing a coordinate system and points that have been consistently determined by observations, corrections, and computations. The North American Vertical Datum of 1988 (NAVD88) is the official vertical datum of the United States.

Decadal Survey—The common name for the National Research Council report Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond (NRC, 2007a).

Deformation, Ecosystem Structure and Dynamics of Ice (DESDynI)—A proposed NASA InSAR and LiDAR mission optimized for studying hazards and global environmental change.

Distributed Active Archive Centers (DAAC)—NASA centers for archiving, documenting, and distributing data from past and current Earth-observing satellites and field measurement programs.

Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS)—A French geodetic technique in which transmitters on the ground communicate with receivers on satellites to provide precise orbit determination required by ocean altimeter satellites.



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