FS FS - Fundamentals of Surveying Hydrographic Surveying 2 — Questions and Answers
Question 1: What is the purpose of tide gauge readings during a hydrographic survey?
- To measure wave heights and storm surge
- To reduce soundings to a common chart datum (Correct answer)
- To determine water current direction
- To calibrate the echo sounder frequency
Correct answer: To reduce soundings to a common chart datum
Tide gauge readings record water level changes so that soundings collected at various tidal states can be reduced to a common chart datum like MLLW.
Question 2: What is a bar check in echo sounder calibration?
- Checking for sand bars in the survey area
- Lowering a plate to known depths to verify sounder accuracy (Correct answer)
- Testing signal propagation through different water densities
- Verifying the sounder's output frequency against a standard
Correct answer: Lowering a plate to known depths to verify sounder accuracy
A bar check involves lowering a metal plate to known depths and comparing the echo sounder's readings to verify its accuracy and account for sound velocity variations.
Question 3: What is the approximate velocity of sound in water used for echo sounder calculations?
- 343 m/s
- 1,500 m/s (Correct answer)
- 5,000 m/s
- 3,000 m/s
Correct answer: 1,500 m/s
The standard velocity of sound in seawater used for echo sounder calculations is approximately 1,500 m/s, though actual velocity varies with temperature and salinity.
Question 4: What is side scan sonar primarily used to detect in hydrographic surveys?
- Water current velocity and direction
- Submerged objects and seafloor texture (Correct answer)
- Water temperature gradients with depth
- Sediment chemical composition
Correct answer: Submerged objects and seafloor texture
Side scan sonar emits acoustic energy to the sides of the survey vessel, producing image-like data that reveals submerged objects, wreckage, and bottom characteristics.
Question 5: What is a lead line in hydrographic surveying?
- An electrical cable connecting survey instruments on a vessel
- A weighted rope marked at intervals for manually measuring water depth (Correct answer)
- The survey vessel's primary navigation control line
- The boundary line separating adjacent survey zones
Correct answer: A weighted rope marked at intervals for manually measuring water depth
A lead line is a weighted rope or wire marked at regular intervals, historically used to manually measure water depth before electronic instruments were available.
Question 6: What is the primary purpose of performing hydrographic surveys?
- Water quality and pollution monitoring
- Supporting safe navigation and maritime infrastructure planning (Correct answer)
- Flood insurance rate map production
- Environmental impact assessment only
Correct answer: Supporting safe navigation and maritime infrastructure planning
Hydrographic surveys primarily support safe navigation by mapping underwater topography for nautical charts, and they also support port design, dredging, and marine construction.
FS FS - Fundamentals of Surveying Hydrographic Surveying 2
What is the purpose of tide gauge readings during a hydrographic survey?