GPS elevations are referenced to which of the following?

GPS elevations are referenced to the ellipsoid, which is a mathematical representation of the Earth's shape. The ellipsoid provides a geometric model that simplifies the complexities of the Earth's surface and allows for consistent elevation calculations. When a GPS receiver calculates elevation, it typically uses the WGS84 (World Geodetic System 1984) ellipsoid model, which is a standard in geospatial data collection.

In contrast, mean sea level and NAVD88 are geodetic datums associated with physical measurements of the Earth. Mean sea level is a dynamic reference point influenced by tidal variations and other factors, while NAVD88 is a vertical datum based on precise leveling techniques. The geoid represents the theoretical mean sea level across the globe, accounting for gravitational variations due to Earth's terrain and density. All of these reference systems have distinct applications, but when it comes to GPS-derived elevations, the common reference is the ellipsoid.