Spectra Precision ProMark 800 Reference Manual - Manual (Page 69)

57
Precise Surveying - Field Applications & Concepts
Phase Center Location (1)
This is a virtual point that represents the spatio-temporal
origin of the antenna. It is usually inside the antenna and
often on, or close to, the vertical axis of the antenna.
The phase center location is accurately determined by the
antenna manufacturer or the United States National Geodetic
Survey after a long series of tests. The location of the phase
center is usually indicated on the antenna itself (see also 4.
below).
A dual-frequency antenna usually has two different phase
centers instead of one. In this case, the antenna
manufacturer should mention the exact locations of the two
phase centers.
Phase Center Offset (2)
Vertical distance that separates the phase center from the
bottom of the antenna (see also ARP below).
SHMP (3)
(SHMP=Slant Height Measurement Point) Point located on
the edge of the antenna radome into which a tape measure
can be inserted to perform a slant measurement.
SHMP Offset (4)
Vertical distance that separates the SHMP from the base of
the antenna. This parameter is needed by the system to
determine the real height of the antenna over the landmark
after a slant measurement has been entered into the system.
Antenna Radius (5)
Horizontal distance from the geometrical center to the edge
of the antenna. This parameter is needed by the system to
determine the real height of the antenna over the landmark
after a slant measurement has been entered into the system.
ARP (6)
Antenna Reference Point located at the bottom of the
antenna receiving the 5/8” adaptor of the antenna pole.
Why is GNSS
Antenna Height so
Important
The basic measurement giving centimeter accuracy is the
vector from the phase center of the base antenna to the phase
center of the rover antenna. Usually, the real position of
interest is not the phase center of the antenna, but the survey
mark (or other landmark) over which the antenna is set up.