Final answer:
The statement is true; differences in Earth's geoid are measured relative to a perfect ellipsoid, representing deviations from the gravitational field.
Step-by-step explanation:
The statement that differences in the height of Earth's geoid are measured relative to a perfect ellipsoid is True. The geoid represents an equipotential gravitational surface and is shaped by the Earth's mass distribution and rotation, causing it to be irregular and undulating. On the other hand, an ellipsoid is a mathematically defined, smooth surface that approximates the shape of the Earth. These ellipsoids are often used as a reference surface from which the deviations are measured to create a geoid. The differences between the geoid and the ellipsoid represent the irregularities in Earth's gravitational field due to uneven mass distributions such as mountain ranges, valleys, and other geological structures.