Definitions - C-Nav IALA Hardware Reference Manual

C-Nav Hardware Reference Guide

Definitions

1 Pulse Per Second (1PPS) is a precision electronic pulse output (at TTL levels) from the GPS
receiver that marks exact second intervals. It is used for precise timing and to synchronize
sensors and acquisition computers.
.yym files see meteorological files (where yy = two digit year data was collected).
.yyn files see navigation files (where yy = two digit year data was collected
.yyo files see observation files (where yy = two digit year data was collected).
Absolute Positioning is the ability of a GPS receiver to produce positional values without
another receiver for reference.
Accuracy is the degree of conformity of a measured or calculated quantity to a standard or true
value. Accuracy is therefore related to the quality of the results.
Almanac is found in subframe 5 of the Navigation Message. It is a data file that helps the
receiver track, and lock-on to satellites as it contains a summary of orbital parameters for all
GPS satellites. The almanac can be acquired from any GPS satellite.
Altitude is the vertical distance above the ellipsoid or geoid. It is always stored as height above
ellipsoid in the GPS receiver but can be displayed as height above ellipsoid (HAE) or height
above mean sea level (MSL).
Ambiguity is the unknown number of whole carrier wavelengths between satellite and receiver.
Antenna is a device used to collect and amplify the electromagnetic GPS signals broadcast by
a satellite. These electromagnetic waves are then converted into electrical currents that are
decoded by the receiver. Patch, or Microstrip antennas are most commonly used in GPS.
Antenna Phase Center (APC) is the point in an antenna where the GPS signal from the
satellites is received. The height above ground of the APC must be measured accurately to
ensure accurate GPS readings. The APC height can be calculated by adding the height to an
easily measured point, such as the base of the antenna mount, to the known distance between
this point and the APC.
Antispoofing (A/S) is an encryption technique developed by the US Department of Defense
(DoD) that when implemented, denies access to the P-Code by any unauthorized users. With
Antispoofing on, the user will need a DoD issued "key" in order to gain access to the P-Code.
Apogee is the point in the orbit of a satellite about the earth that is the greatest distance from
the center of the earth.
Autocorrelation in reference to code is a plot of the scalar product of the noise sequence with
a delayed copy of itself.
Autonomous positioning (GPS) is a mode of operation in which a GPS receiver computes
position fixes in real time from satellite data alone, without reference to data supplied by a
reference station or orbital clock corrections. Autonomous positioning is typically the least
precise positioning procedure a GPS receiver can perform, yielding position fixes that are
precise to 100 meters with Selective Availability on, and 30 meters with S/A off.
Average Deviation is a measure of variability in a data set but it is more robust than standard
deviation. It is not related to the bell-shaped curve. It is the average of the absolute deviations
of the values from the mean. The data values are subtracted from the mean producing a list of
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