b. Antenna Setup. All tribrachs should be calibrated and adjusted before to beginning each project.
Since centering errors represent a major error source in all survey work (not just GPS surveying), use
both optical plummets and standard plumb bobs.
c. Height of Instrument. HI refers to the correct measurement of the distance of the GPS antenna
above the reference monument over which it is placed. HI measurements should be made before and
after each observation session. The HI should be made from the monument to a standard reference point
on the antenna. The standard reference points for each antenna should be established before to the
beginning of the observations. All measurements should be made both in meters and feet for
redundancy and blunder detection. Determine the measurement to the nearest millimeter in metric units
and the nearest 0.01 foot in US units. Note whether the HI is vertical or diagonal.
d. Field Global Positioning System Observation Recording Procedures. Field-recording books, log
sheets, or log forms should be completed for each station and session. Any acceptable recording media
may be used. Recording sheets or forms will be used for archiving purposes. The amount of recording
detail will depend on the project. Low-order geographic mapping points do not need as much
descriptive information as permanently marked, primary control points. Unit commands may require
that additional data be recorded. These requirements are contained in the project instructions. The
following data may be included on the field log records:
Project name, directive number, observer name(s), and unit name.
Station designation number.
Station file number.
Date and weather conditions.
Session start and stop time (local and universal time, coordinated [UTC]).
Receiver; antenna; data-recording unit; and tribrach make, model, and serial number.
Antenna height (vertical or diagonal measurements in metric or US units).
Satellite vehicle (SV) designation and number.
Geodetic location and elevation (approximate).