C-Nav 2050, User Manual

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2050 User Guide
ellipsoid a mathematical figure approximating the earth’s surface, generated by rotating an ellipse
on its minor axis. GPS positions are computed relative to the WGS-84 ellipsoid . An ellipsoid has a
smooth surface, which does not match the earth’s geoidal surface closely, so GPS altitude
measurements can contain a large vertical error component. Conventionally surveyed positions
usually reference a
geoid , which has an undulating surface and approximates the earth’s surface
more closely to minimize altitude errors.
epoch literally a period of time. This period of time is defined by the length of the said period.
geoid the gravity-equipotential surface that best approximates mean sea level over the entire
surface of the earth. The surface of a geoid is too irregular to use for GPS readings, which are
measured relative to an ellipsoid . Conventionally surveyed positions reference a geoid . More
accurate GPS readings can be obtained by calculating the distance between the geoid and ellipsoid
at each position and subtracting this from the GPS altitude measurement.
GIS (Geographical Information Systems) a computer system capable of assembling, storing,
manipulating, updating, analyzing and displaying geographically referenced information, i.e. data
identified according to their locations. GIS technology can be used for scientific investigations,
resource management, and development planning. GIS software is used to display, edit, query and
analyze all the graphical objects and their associated information.
Global Positioning System (GPS) geometrically, there can only be one point in space, which is the
correct distance from each of four known points. GPS measures the distance from a point to at least
four satellites from a constellation of 24 NAVSTAR satellites orbiting the earth at a very high altitude .
These distances are used to calculate the point’s position .
GMT see Greenwich Mean Time
GPS see Global Positioning System .
GPS time a measure of time. GPS time is based on UTC , but does not add periodic ‘leap seconds’
to correct for changes in the earth’s period of rotation. As of September 2002 GPS time is 13
seconds ahead of UTC .
Greenwich Mean Time ( GMT ) the local time of the 0° meridian passing through Greenwich,
England.
HAE see altitude , and ellipsoid .
JPL Jet Propulsion Laboratory
Kbps kilobits per second
L-Band the group of radio frequencies extending from approximately 400 MHz to approximately
1600 MHz. The GPS carrier frequencies L1 (1575.4 MHz) and L2 (1227.6 MHz) are in the L-Band
range.
L1 carrier frequency the primary L-Band carrier used by GPS satellites to transmit satellite data.
The frequency is 1575.42MHz. It is modulated by C/A code , P-code or Y-code, and a 50 bit/second
navigation message.
L2 carrier frequency the secondary L-Band carrier used by GPS satellites to transmit satellite data.
The frequency is 1227.6MHz. It is modulated by P-code or Y-code, and a 50 bit/second navigation
message.
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