CH Field Survey & Data Collection 4

Question 1

What is the significance of the Rayleigh criterion in the context of multibeam sonar resolution?

Accepted Answer

It establishes the minimum angular separation at which two targets can be distinguished

Answer

The Rayleigh criterion defines the minimum angular separation between two targets needed for them to be resolved as distinct objects by a sonar system.

Question 2

During a hydrographic survey in an area with strong currents, what effect does significant cross-track current have on a towed side-scan sonar towfish?

Accepted Answer

It causes the towfish to fly off to one side, creating asymmetric coverage

Answer

Cross-track currents push the towfish laterally, causing it to deviate from the vessel's track and creating unequal range coverage on port and starboard sides.

Question 3

Which IHO publication defines the minimum standards for hydrographic surveys, including accuracy requirements and feature detection specifications?

Accepted Answer

IHO S-44

Answer

IHO S-44 'Standards for Hydrographic Surveys' defines order categories (Special, 1a, 1b, 2) with associated depth accuracy, feature detection, and coverage requirements.

Question 4

What does a 'total propagated uncertainty' (TPU) calculation in hydrographic surveys account for?

Accepted Answer

The combined effect of all error sources contributing to the final depth uncertainty

Answer

TPU combines all individual error sources (positioning, heave, sound velocity, tides, draft, system noise) using error propagation to yield a single uncertainty estimate for each depth measurement.

Question 5

When planning survey lines for a coastal multibeam survey, what is the primary factor determining the spacing between adjacent lines?

Accepted Answer

The required bottom coverage relative to achievable swath width at the target depth

Answer

Line spacing is set so that adjacent swaths overlap sufficiently (typically ≥10%) to ensure complete bottom coverage, based on achievable swath width at the survey depth.

(CH) Certified Hydrographer Practice Test

(CH) Certified Hydrographer Practice Test

CH Field Survey & Data Collection 4