C-Nav 1000, Hardware Reference Manual

Page: 99 / 99

C-Nav Hardware Reference Guide
99
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.
Standard Deviation is a measure of how widely values are dispersed from the mean. The
larger the standard deviation is, the more spread out the values are from the mean. It is the
square root of the average squared deviations of each of the values from the mean.
Time Tag is when a time value is appended to an actual measurement.
Triple Difference between receivers, between satellites, and between epochs (time) is the
difference between a double difference at one epoch and the same double difference at the
following epoch.
Troposphere is the inner layer of the atmosphere, located between 6 and 12 miles above the
earth’s surface.
Twice Distance Root Mean Square (2dRMS) is a measurement that varies in its probability
from 95.4% to 98.2%, meaning that if 100 observations are taken, between 95 and 98 of those
observations will be withi
n the 2dRMS where approximation = 2ơ
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.
User Segment is the portion of the GPS system with major components that can be interfaced
by the user (e.g., GPS receivers).
Wide Area Augmentation System (WAAS) is a set of corrections for the GPS satellites, which
are valid for the Americas region. They incorporate satellite orbit and clock corrections.
Wide Area Differential GPS (WADGPS) is a set of corrections for the GPS satellites, which are
valid for a wide geographic area.
World Geodetic System 1984 (WGS84) is the current standard datum for global positioning
and surveying. The WGS-84 is based on the GRS-80 ellipsoid.
Y-code is the name given to encrypted P-code when the U.S. Department of Defense uses
selective availability.
Z-count Word is the GPS satellite clock time at the leading edge of the data subframe of the
transmitted GPS message.