CH Tides, Water Levels & Vertical Datums

Question 1

What is the primary cause of ocean tides on Earth?

Accepted Answer

Gravitational forces of the moon and sun

Answer

Earth's rotation

Answer

Wind patterns

Answer

Ocean currents

Question 2

What is Mean Lower Low Water (MLLW)?

Accepted Answer

Average of the lower low tides each day over 19 years

Answer

Average sea level over a year

Answer

Average of daily low tides

Answer

Lowest recorded tide

Question 3

Which instrument is commonly used to measure water levels over time?

Accepted Answer

Tide gauge

Answer

Echo sounder

Answer

GPS receiver

Answer

CTD profiler

Question 4

Why are vertical datums important in hydrography?

Accepted Answer

They provide a height reference for soundings

Answer

They reduce water pollution

Answer

They determine water temperature

Answer

They improve sonar resolution

Question 5

Which vertical datum is used for referencing water depths in U.S. nautical charts?

Accepted Answer

Mean Lower Low Water

Answer

Mean Sea Level

Answer

Ellipsoidal Height

Answer

Mean High Water

Question 6

How do tides influence hydrographic survey data?

Accepted Answer

They require depth corrections to a vertical datum

Answer

They alter water temperature

Answer

They change sediment composition

Answer

They affect GPS accuracy