Measurement Technology and Field Procedures
What this domain tests
Questions probe whether you know what corrections apply to your instruments, how to design a field procedure that can be checked, and where modern GNSS fails.
Core rules
- EDM distances require atmospheric correction and prism-constant agreement; a mismatch in the prism constant is a systematic error, not a random one.
- Total station work should be closed: closed traverses, redundant shots, or a check to a known azimuth at the end of the run.
- GNSS: static or rapid-static for control, RTK or RTN for topographic and stakeout work. Check against an independent control point and watch PDOP, canopy, and multipath.
- Magnetic declination in New Mexico is on the order of 7°–8°E and changes annually; compute it for the date and location, never assume a printed value.
- Record field notes that would let another surveyor reproduce your work: instrument and serial number, HI and target heights, weather, control used, and who did what.
Worked example
A distance of 2,500.00 ft is measured at 95°F against a 68°F instrument standard, 27°F warmer (about 15°C). The rule of thumb is roughly 1 ppm per °C, so about 15 ppm: 15 × 0.0025 ft = 0.0375 ft. The air is thinner, so the instrument over-measures; apply the correction as a subtraction and report 2,499.96 ft. Reasoning: sign matters - heat makes the raw distance too long.
Traps that cost marks
- Mixing metric and imperial ppm factors.
- Forgetting to change the prism constant between two prism types.
- Trusting RTK in heavy canopy or near reflective surfaces.
- Bookkeeping errors in HI or target height that survive into the final coordinates.
- Running a base station too far from the rover for the accuracy claimed.