Glossary
Appendix B
GSR2600
103
Occupation -
The period of recorded data for a site. For
example, a 1-hour period of data collection on a survey point is
considered an occupation. Occupation is usually
interchangeable with the term observation.
Orthometric elevation (orthometric height) -
The height of a
point above the geoid. Orthometric elevation is often equated
with mean-sea-level elevation.
P-Code (precise or protected) -
The protected or precise code
used on both LI and L2 GPS frequencies. This code is made
available by the DOD only to authorized users. The P code is a
very long (about 1014 bits) sequence of pseudo-random binary
biphase modulations on the GPS carrier at a chipping rate of
10.23 MHz which does not repeat itself for about 38 weeks. Each
satellite uses a one-week segment of this code which is unique to
each GPS satellite, and is reset each week.
Phase Center -
The phase center of a GPS antenna is the physical
location on the antenna where the raw GPS signals are observed.
This is the physical location where the computed position will
be determined. GPS antennas are manufactured to place the
phase center as closely as possible to the physical center of the
antenna housing. To determine the position of a survey marker
on the ground, the GPS antenna (and thus the phase center) is
centered over the marker and the HI is measured to the survey
marker for use during processing.
Precise Positioning Service (PPS) -
The GPS positioning,
velocity, and time service which will be available on a
continuous, worldwide basis to users authorized by the U.S.
Department of Defense (typically using P-Code).
PRN -
Pseudo Random Noise number. A number assigned by
the GPS system designers to a given set of pseudorandom codes.
Typically, a particular satellite will keep its PRN (and hence its
code assignment) indefinitely, or at least for a long period of
time. It is commonly used as a way to label a particular satellite.
Pseudolite -
An Earth-based transmitter designed to mimic a
satellite. May be used to transmit differential corrections.
Pseudorange -
The calculated range from the GPS receiver to
the satellite determined by taking the difference between the
measured satellite transmit time and the receiver time of
750-1-0093 Rev 1.book Page 103 Friday, June 28, 2002 4:02 PM
