Introduction To Hydrography

Question 0

Name the 4 main components of an echo-sounder system

Answer 0

Recording unit
Transducer
Heave compensator
A vertical datum

Question 1

What is mapping relief?

Answer 1

All the features of the seabed - natural and man made

Question 2

What does a transducer do?

Answer 2

Converts electrical energy into acoustic energy

Question 3

What are the installation considerations of a transducer system?

Answer 3

1. Vessel trim - third to half of way along vessel length - perpendicular to vertical
2. Vessel roll/pitch - as close to vessel centre line as possible.
3. Not to be obstructed by the hull.
4. Position should be considered in relation to other systems.
5. Away from noisy areas of the vessel.

Question 4

What is heave?

Answer 4

Up and down motion

Question 5

What is a vertical datum?

Answer 5

Where to measure the vertical depth from e.g. L.A.T – lowest astronomical tide

Question 6

Name 3 calibration considerations of a single beam echo-sounder

Answer 6

1. transducer draft (depth of transducer below water)
2. System index (electrical instrument delays)
3. average sound velocity of the water column.

Question 7

What is the calibration equation for a single beam echo-sounder?

Answer 7

D = (V*T/2) - K+Dr

Question 8

Break down the equation for echo-sounder calibration

Answer 8

D = depth from surface (m)
V = average sound velocity of water column (ms-1)
T = measures time from transmission to reception (s)
K = system index constant (m?)
Dr = transducer draft (m)