Survey Equipment Operation and Calibration
Survey Equipment Operation and Calibration
Candidates must know how to operate and calibrate key survey equipment: echosounders (single and multibeam), GNSS receivers, motion sensors (IMU, MRU), gyrocompasses, sound velocity sensors, tide gauges, and side-scan sonar. Understand calibration procedures: patch test for MBES (roll, pitch, heading, timing), bar check for single-beam echosounders, GNSS antenna offset measurements, and sound velocity calibration. Know the importance of integration and time synchronization between sensors. Be familiar with quality control checks: cross-lines, overlap, repeatability, and comparison with independent data.
Traps: Questions may ask about the order of patch test adjustments; typically roll, pitch, heading, then timing. Another trap is bar check procedure: lower a bar to known depths and compare echosounder readings; correct for index error and sound velocity. Also, motion sensor misalignment causes depth biases that vary with vessel heading. Be careful with GNSS height vs water level; ensure vertical datum consistency.
Rule of thumb: Perform a patch test after any major equipment change or mobilization. Worked example: If a bar check shows a consistent 0.3 m offset at all depths, apply an index correction of −0.3 m to all soundings. If the offset varies with depth, check sound velocity and transducer draft. Always document calibrations and maintain calibration logs.
Key terms: patch test, bar check, index error, motion sensor, MRU, gyrocompass, sound velocity, time synchronization, cross-lines, overlap.