The following are some general GPS field survey procedures that should be performed at each station, observation, and/or session on a GPS survey.
A. Receiver setup : GPS receiver shall be set up in accordance with manufacturer’s specification prior to beginning any observation. To eliminate any possibility of missing the beginning of the observation session, all equipment should be set up with power supplied to the receivers at least 10 minutes prior to the beginning of the observation session. Most receivers will lock-on to satellites within 1-2 min of powering up.
B. Antenna setup : All tribrachs used on a project should be calibrated and adjusted prior to beginning each project. Dual use of both optical plummets and standard plumb bobs is strongly recommended since centering errors represent a major error source in all survey work, not just GPS surveying.
C. Height of instrument measurements : Height of instrument (HI) refers to the correct measurement of the distance of the GPS antenna above the reference monument over which it has been placed. HI measurements will be made both before and after each observation session. The HI will be made from the monument to a standard reference point on the antenna .These standard reference point for each antenna will be established prior to the beginning of the observation so all observers will be measuring to the same point. All HI measurements will be made in meters. HI measurements shall be determined to the nearest millimeter in metric units. It should be noted whether the HI is vertical or diagonal.
D. Field GPS observation recording procedures : Field recording books, log sheet, or log forms will be completed for each station and/or session. Any acceptable recording media may be used. For archiving purpose, standard bound field survey books are preferred. However, USACE Commands may require specific recording sheet/forms to be used in lieu of a survey book. The amount of record keeping detail will be project-dependent. Low-order topographic mapping points need not have as much descriptive information as would have for permanently marked primary control points . The following typical data may be included on these field log records:
1) Project, construction contract, observer(s) name(s), and/or contractor firm and contract number.
2) Station designation.
3) Station file number.
4) Date, weather conditions, etc.
5) Time, start/stop session (local and UTC).
6) Receiver, antenna, data recording unit, and tribrach make, model, and serial numbers.
7) Antenna height: vertical or diagonal measure in inches (or feet) and meters.
8) Space vehicle designations (satellite number).
9) Sketch of station location.
10) Approximate geodetic location and elevation.
11) Problems encountered.
E. Field processing and verification : It is strongly recommended that GPS data processing and verification be performed in the field where applicable. This is to identify any problem that may exist which can be corrected before returning from the field.