Chapter E. Basic Gravity Measurement

1. Geoid Modeling

There is a lot that goes into creating a model of a surface that doesn't physically exist. Its configuration and location must be inferred through physics principles, geodynamics, celestial influence, dynamic forces, etc. Based on how they were created, neither NGVD 29 nor NAVD 88 are true representations of either MSL nor the geoid.

It all depends on gravity and the ability to measure and monitor it.

In the chapter on Earth surfaces we said the geoid changes over time due to the Earth's internal dynamics. Remeasuring and/or monitoring gravity as well as increasing the density of gravity measurements will ultimately lead to better geoid definition.

Expanded gravity measurements will be used to develop GEOID2022 which will be a critical component of the North American Terrestrial Reference Frame of 2022 (NATRF2022) and North American-Pacific Geopotential Datum of 2022 (NAPGD2022)

In this chapter we'll touch on some basic gravity measurement concepts to introduce terminology and some programs in progress. There is considerably more depth to this subject than covered here. As the lead agency NGS has many publications and presentations on gravity measurement and geoid modeling on its website. The reader is encouraged to explore their resources at the NGS website.