User's Guide

75
D. Glossary
Terms
Description
Base Station
Also called reference station. A base station in
construction is a receiver placed at a known point on a
job site that tracks the same satellites as an RTK rover
and provides a real-time differential correction
message stream through the radio to the rover, to
obtain centimeter level positions on a continuous
real-time basis. A base station can also be a part of a
virtual reference station network or a location at which
GPS observations are collected over a period, for
subsequent postprocessing to obtain the most accurate
position for the location.
Carrier
A radio wave is having at least one characteristic (such
as frequency, amplitude, or phase) that can be varied
from a known reference value by modulation.
Carrier Frequency
It means the frequency of the unmodulated
fundamental output of a radio transmitter. The GPS L1
carrier frequency is 1575.42 MHz.
Carrier Phase
The time is taken for the L1 or L2 carrier signal
generated by the satellite to reach the GPS receiver.
Measuring the number of carrier waves between the
satellite and receiver is a very accurate method of
calculating the distance between them.
CMR
CMR+
Compact Measurement Record. A real-time message
format developed by Trimble for broadcasting
corrections to other Trimble mainboard receivers. CMR
is a more efficient alternative to RTCM.
DGPS
See real-time differential GPS.
Differential Correction
Differential correction is the process of correcting GPS
data collected on a rover with data collected