Geoid height N represents which quantity?

• A. The separation between the geoid and the reference ellipsoid
• B. The height above mean sea level
• C. The height of the ellipsoid above the geoid
• D. The distance from Earth's center to the ellipsoid

Answer: (A)

Geoid height is the separation between the geoid and the reference ellipsoid at a given location, measured along the normal to the ellipsoid. This quantity, called the geoid undulation, tells you how far the geoid sits above or below the smooth ellipsoid used for calculations. Positive values mean the geoid is above the ellipsoid, negative values mean it is below. It’s the bridge between ellipsoidal height and height above mean sea level: h = H + N, so the orthometric height H (height above the geoid/mean sea level) can be found from the ellipsoidal height h by subtracting N.