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Question 1

Why is it important to know if the application of the hydrographic survey is aimed for
“navigation safety” or “hydrographic project accountability” ?

Answer 1

Navigation safety: Ensures safe vessel passage by providing accurate data on water depths and hazards.important because influence the survey’s methodology, the level of detail required, and the interpretation of the data.
* Navigation safety: Ensures safe vessel passage by providing accurate data on water depths and hazards.
* Hydrographic project accountability: Supports legal, environmental, or project goals, like monitoring dredging or infrastructure progress.

Question 2

Give a classification of positioning methods in function of the time

Answer 2

• Before 1940: Manual methods (compass, sextant, rod-based speed measurement).
• After 1950: introduction of acoustic waves (radar) and satellite positioning, plus atomic clocks.
• 1985-2005: GPS becomes standard, GNSS developed, and methods like PPP, DGPS, and RTK improve GPS accuracy.
• After 2005: Development of inertial systems integrated with GNSS, marine robotics (USVs, AUVs), and LIDAR (laser scanning).

Question 3

Give a classification of positioning methods in function of the measuring principle

Answer 3

• Passive : Optical sextant, theodolite
• Active Optical : total station, laser scanner
• Terrestrial radio-positioning : radio waves from terrestrial emitters
• Satellite positioning : radio waves sent by satellites.
• Inertial navigation : Measures acceleration, calculates speed, then distance.
• Doppler sonar (waves and acoustic waves) : Measures relative speed with acoustic waves, calculates distance.
• Acoustic positioning : Uses sound waves to measure distance and/or directions.

Question 4

Give a classification of positioning methods in function of the frequencies of the radio systems

Answer 4

Low Frequency (LF): 1–10 km (30-300 kHz), max range ~1500 km.
Medium Frequency (MF): 100 m–1 km (300 kHz–3 MHz), max range ~600 km.
Ultra-High Frequency (UHF): 10 cm–1 m (0.3–3 GHz), max range ~110 km.
Super High Frequency (SHF): 1–10 cm (3–30 GHz), max range ~70 km.

Question 5

Explain: short/medium/long range systems

Answer 5

• Short Range (S): < 30 km
• Medium Range (M): 30-80 km
• Long Range (L): > 80 km

Question 6

Explain: single user/multi user restricted multi user systems.

Answer 6

• Single User systemen (SU) only 1 user at a time
• Multi User systemen (MU) infinite number of users at any time
• Restricted Multi User systemen (RMU) finite number of simultaneous users

they define how users can share or acces network resources

Question 7

What kind of hydrographic projects need hydrographic surveying ?

Answer 7

• Prospection/Exploitation of Natural Resources
• Construction of New Harbors (e.g., capital dredging)
• Maintenance Dredging (for harbors and river access)
• Reclamation Works
• Wreck and Mine Removal
• Coastal Land Protection (e.g., dikes, dams)
• Pipeline Projects
• Off-shore Projects