Question

Which of the following statement(s) is/are CORRECT?

• A. Mean sea level is defined as the long-term mean of the tide gauge measurements at a given location
• B. Mean sea level is the same as the mean tide level
• C. Mean sea level is defined as the monthly mean of the tide gauge measurements
• D. Mean sea level is an approximation of geoid

Hint:

Remember: {MSL} = long-term tide-gauge average (years), used to realize vertical datums; {mean tide level} = average of mean high & mean low water (a tidal statistic).

Answer 1

The Correct Option is A

(A) True. Mean Sea Level (MSL) is the long-term average of sea level observed at a tide gauge (typically many years; e.g., 19-year tidal epoch) at a fixed location.
(B) False. “Mean tide level” is the average of the mean high water and mean low water; it is not the same as the long-term mean sea level.
(C) False. A monthly mean is too short to define MSL; long-term averaging is required to remove periodic tidal and seasonal effects.
(D) True. MSL at gauges is often used as a practical realization/approximation of the geoid (zero-elevation surface) for vertical datums.