User's Manual

Page 57
X360 GIS Reference Receiver User Guide
D. Glossary
ephemeri
s /
ephemerid
es
A list of predicted (accurate) positions or locations of satellites as a function
of time. A set of numerical parameters that can be used to determine a
satellite’s position.
Available as broadcast ephemeris or as postprocessed precise ephemeris.
epoch
The measurement interval of a GPS Receiver. The epoch varies according to the
measurement type: for real-time measurement it is set at one second; for
postprocessed measurement it can be set to a rate of between one second and
one minute. For example, if data is measured every 15 seconds, loading data
using 30-second epochs means loading every alternate measurement.
firmware
The program inside the Receiver that controls Receiver operations and
hardware.
GNSS
Global Navigation Satellite System.
GSOF
General Serial Output Format. A Trimble proprietary message format.
HDOP
Horizontal Dilution of Precision. HDOP is a DOP value that indicates the
accuracy of horizontal measurements. Other DOP values include VDOP
(vertical DOP) and PDOP (Position DOP).
Using a maximum HDOP is ideal for situations where vertical precision is not
particularly important, and your position yield would be decreased by the
vertical component of the PDOP ( for example, if you are collecting data under
canopy).
L1
The primary L-band carrier used by GPS satellites to transmit satellite data.
L2
The secondary L-band carrier used by GPS satellites to transmit satellite data.
L5
The third L-band carrier used by GPS satellites to transmit satellite data. L5
will provide a higher power level than the other carriers. As a result,
acquiring and tracking weak signals will be easier.
multi-
frequency
GPS
A type of Receiver that uses multiple carrier phase measurements (L1, L2, and
L5) from different satellite frequencies.
multipath
Interference, similar to ghosts on a television screen that occurs when GPS
signals arrive at an antenna having traversed different paths. The signal
traversing the longer path yields a larger pseudorange estimate and increases
the error. Multiple paths can arise from reflections off the ground or off
structures near the antenna.
NMEA
National Marine Electronics Association. NMEA 0183 defines the standard for
interfacing marine electronic navigational devices. This standard defines a
number of 'strings' referred to as NMEA strings that contain navigational details
such as positions. Most CHC GPS Receivers can output positions as NMEA
strings.
PDOP
Position Dilution of Precision. PDOP is a DOP value that indicates the accuracy of