The geoid matters because it's the reference surface used to define what counts as sea level and elevation. Gravity isn't uniform across the planet, so an ocean responding only to gravity, with no wind, tides or currents, would not sit at one flat height. Height and elevation systems, including the corrections applied to satellite and GPS altitude data, are ultimately referenced back to this uneven surface rather than to a perfect sphere. NASA's Scientific Visualization Studio published the new interactive 3D model on July 15 (NASA SVS). The geoid is the surface an ocean would take if it responded to gravity alone, and in this visualization that height is exaggerated by a factor of 10,000 so the variation is visible. The measured geoid height itself ranges from +85 meters near Iceland down to -106 meters over southern India, per NASA. The data behind the model comes from GOCO06s, a satellite-only global gravity field model built from more than a billion observations gathered over 15 years by 19 satellites, including NASA's GRACE mission and ESA's GOCE mission (NASA SVS / GOCO project). Combining that many independent orbital gravity measurements is what lets researchers resolve the small-scale gravity anomalies the model shows. The visualization is credited to Mark SubbaRao as visualizer and Scott Luthcke as science advisor, both at NASA Goddard, and includes a downloadable 3D model file that can be rotated and inspected directly. Open questions the announcement did not address: \- How often the GOCO06s model gets updated as new satellite gravity data comes in \- Whether other geodesy or navigation systems plan to adopt this specific model over existing geoid references \- What resolution limits remain in ocean regions with comparatively sparse satellite gravity coverage
I knew gravity was different based on altitude but somehow didnt connect that it was just different all over. The crazy implication of that is different levels of gravity means time passes differently as well. granted the difference is imperceptible, but wild to think about