Which of the following is an example of a tidal datum?

Which of the following is an example of a tidal datum?

• A. Mean Sea Level (MSL)
• B. North American Datum (NAD)
• C. Geoid
• D. Ellipsoid

Answer: (A)

A tidal datum is a reference surface tied to the actual sea surface as it rises and falls with tides. Mean Sea Level fits this because it represents the average height of the ocean surface over a long period at a location, serving as a vertical reference for elevations in surveying. It is determined from tide observations, unlike the others: the North American Datum is a horizontal coordinate framework, the geoid is a gravity-based surface used to model mean sea level globally but not defined as a tidal average, and the ellipsoid is a mathematical shape used for coordinates, not sea level.

A tidal datum is a reference surface tied to the actual sea surface as it rises and falls with tides. Mean Sea Level fits this because it represents the average height of the ocean surface over a long period at a location, serving as a vertical reference for elevations in surveying. It is determined from tide observations, unlike the others: the North American Datum is a horizontal coordinate framework, the geoid is a gravity-based surface used to model mean sea level globally but not defined as a tidal average, and the ellipsoid is a mathematical shape used for coordinates, not sea level.