NavCom LAND-PAK Rev.N - Manual (Page 193)

Technical Reference Manual Rev. N
Glossary - 191
RTG Real Time GIPSY, a processing technique developed by NASA’s Jet Propulsion
Laboratory to provide a single set of real time global corrections for the GPS satellites.
S/A see Selective Availability.
SBAS (Satellite Based Augmentation System) this is a more general term, which
encompasses StarFire™, WAAS, EGNOS, MSAS, and GAGAN type corrections.
Selective Availability (S/A) is the deliberate degradation of the GPS signal by encrypting the
P-code and dithering the satellite clock. When the US Department of Defense uses S/A, the
signal contains errors, which can cause positions to be inaccurate by as much as 100 meters.
Signal-to-Noise Ratio (SNR) is a measure of a satellite’s signal strength.
single-frequency is a type of receiver that only uses the L1 GPS signal. There is no
compensation for ionospheric effects.
SNR see signal-to-noise Ratio.
StarFire a set of real-time global orbit and clock corrections for GPS satellites. StarFire
equipped receivers are capable of real-time decimeter positioning
(see Appendix C).
Spread Spectrum Radio (SSR) a radio that uses wide band, noise like (pseudo-noise) signals
that are hard to detect, intercept, jam, or demodulate making any data transmitted secure.
Because spread spectrum signals are so wide, they can be transmitted at much lower spectral
power density (Watts per Hertz), than narrow band signals.
SV (Space Vehicle) a GPS satellite.
Universal Time Coordinated (UTC) a time standard maintained by the US Naval Observatory,
based on local solar mean time at the Greenwich meridian. GPS time is based on UTC.
UTC see Universal Time Coordinated.
WAAS (Wide Area Augmentation System) a US satellite system that provides a set of
corrections for the GPS satellites, which are valid for the North American region. They
incorporate satellite orbit and clock corrections.
WADGPS (Wide Area Differential GPS) a set of corrections for the GPS satellites, which are
valid for a wide geographic area.
WGS-84 (World Geodetic System 1984) the current standard datum for global positioning and
surveying. The WGS-84 is based on the GRS-80 ellipsoid.
Y-code the name given to encrypted P-code when the U.S. Department of Defense uses
selective availability.