Gravity's Importance

摘要

As the country moves toward the adoption a new vertical datum based entirely on the determination of Earth's gravity field, surveyors will need to better understand the foundational aspects of how these data have been collected and managed as well as the relationship of gravity observations to the traditional and classical efforts of leveling. In this month's issue, Kelly Bellis, a land surveyor from Maine, has done an outstanding job of piecing together an overview of the development of gravity observations, especially as they have been performed and continue to develop in the United States by the National Geodetic Survey and its predecessor agencies. The study of Earth's gravity field is one of the most important aspects of physical geodesy. While seldom mentioned in land surveying text books or discussed at local surveying, mapping, and GIS conferences, it is nonetheless one of the most important issues that surveyors deal with on a daily basis. Two fundamental issues come to mind.