![]() Geodetic leveling differs from ordinary spirit leveling in that it requires more sensitive instruments, specific techniques, and more care in making observations. ![]() Called a “spirit level,” this bubble floating in a vial of fluid is at the core of both the common carpenter’s level readily found in hardware stores today and the precision equipment used by NGS and its predecessor agencies, as well as other surveyors and engineers, to determine elevations by leveling. Image courtesy of Dieter Schmid Fine Tools, Berlin, Germany.Įventually, the alcoholic “spirit” ethanol replaced the use of water in the vials because of ethanol’s lower freezing point. Their lower freezing point minimizes the variations in measurements due to changes in temperature and prevents freezing. A surveyor's level combines a telescope having cross-hairs with a level vial.Ī “spirit level” uses fluids such as ethanol and sulphuric ether in the leveling vial rather than water. This vial provided the basis for the surveyor’s level developed 100 years later. Early leveling methods used water in a container to obtain sightings that were parallel with the ground, or “level.” In the mid-1600s, Melchisedech Thevenot sealed water in a vial in such a way as to form a bubble. The science of leveling goes back to the ancient Greeks, Egyptians, and Romans and their massive construction projects. This article is a brief journey through the history of leveling and its applications. These benchmarks are a fundamental component of the National Spatial Reference System.Īs a leader in providing data and developing and using surveying technologies, NOAA continues to update elevation data across the country. ![]() NGS has been in the business of leveling since the 1800s, and has placed hundreds of thousands of benchmarks across the U.S. Level lines are marked by periodically placing benchmarks in the ground along the line. Building off of known elevations and carrying elevations forward from point to point with a level and rods, surveyors construct a “ level line.” Leveling involves determining differences in elevation between survey points following a “leap frog” approach. Called a level, the instrument is used to read values from a set of specially constructed and marked rods. The most accurate elevation data are collected through a process called “ spirit leveling,” which is performed with an instrument that is a combination of a telescope and a spirit level vial. ![]() This party is using a Fischer level to leap frog its way into Glen Canyon in 1921. NGS responds to these changes and to changes in technology by working to develop and refine fast and accurate methods of data collection and to transfer new knowledge and techniques to the surveyors with whom the agency works in partnership. However, sea level rise, subsidence (i.e., land sinking), and geological events such as earthquakes are among the many forces constantly changing the surface of the Earth. NOAA’s National Geodetic Survey (NGS) provides a great deal of the accurate elevation data needed by these groups to do their work successfully. Knowledge of elevations is critical to surveyors, engineers, coastal managers, developers, and those who make resource or land-use management decisions. ![]()
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