FS - Fundamentals of Surveying Hydrographic Surveying Flashcards
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What is the purpose of tide gauge readings during a hydrographic survey?
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.
What is a bar check in echo sounder calibration?
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.
What is the approximate velocity of sound in water used for echo sounder calculations?
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.
What is side scan sonar primarily used to detect in hydrographic surveys?
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.
What is a lead line in hydrographic surveying?
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.
What is the primary purpose of performing hydrographic surveys?
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.