Building a Better Geoid
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Some early illustrations amassed by NOAA’s National Geodetic Survey (NGS)—the oldest part of NOAA, with historic roots in President Thomas Jefferson’s 1807 Survey of the Coast—now reside in the Treasures of the NOAA Library Collection in Silver Spring, Maryland. These hand-drawn renderings are intriguing, informative, and evoke an exciting era when scientific inquiry came to the fore.
This slideshow compares our predecessors’ plodding, yet determined, scientific methods with today’s high-tech tools. There is much to be learned (and marveled at) by viewing the past and the present side-by-side.
The evolution of surveying from the optical methods depicted in the 17th century Dutch drawing (left) to today's global positioning system (GPS) technology (right) began at least as far back as ancient Egypt, where Pharoah's accountants kept careful track of changes to property boundaries caused by the annual flooding of the Nile.
In the illustration, the chief surveyor uses a predecessor of the modern theodolite—a precision instrument for measuring angles—to sight on a rod and take a measurement. At his feet lie surveying and drafting instruments, including a surveyor's chain for measuring distances. In the background, a cannon and its target illustrate the use of angles and distances for artillery. Various other surveying principles are scattered across the drawing, including a globe topped by a mountain to indicate elevation measurements.
In the photo, an NGS surveyor sets up a Trimble GPS antenna over a tidal bench mark, while another crew member ensures that the receiver that will be recording the GPS data is ready for observations. The observations were part of a survey to determine the elevations of hurricane evacuation routes in Louisiana.
The measurement of distances is an integral part of surveying, and people have wanted to figure out “How far from here to there?” since the dawn of civilization. The 1728 sketch (left) shows English surveyors using an odometer to measure a distance, with surveying formulas scribbled around the drawing. One of today’s tools of the trade is the Laser Scout 1000 (right), a hand-held electronic distance measurement instrument (EDMI) made by Riegl.
Around 23 BC, the Roman architect and engineer Vitruvius described an odometer that was based on the number of times a chariot wheel of four feet in diameter turned during one Roman mile. The arrangement of wheel, handles, and gears led to this contraption being called a "clock on a wheelbarrow." The same arrangement was used in 19th century America to measure rural roads.
The Laser Scout EDMI in the photo provides distances in a digital display. Since 1996, NGS’s Airport Surveys Program has used the “pistol grip” instrument to consistently measure accurate distances to the tops of tree branches from as far away as 4,000 feet (1,200 meters). The data is used to verify the locations and heights of potential obstructions at airports nationwide.
Also unearthed in ancient Egypt were the earliest known surveying instruments: the plumb board, A-level, T-level, and plum square, all in use by 2600 BC. These simple rope-and-board creations inspired millennia of innovation, including the early 19th-century double repeating circle (left). U.S. Coast and Geodetic Survey Founding Superintendent Ferdinand Hassler owned two of these instruments. Even today’s sophisticated GPS antennas (right) can be said to derive from the tools that gave rise to the pyramids.
Mary Caroline Hassler, Ferdinand’s granddaughter, was a gifted artist who enjoyed sketching her grandfather’s equipment, including the repeating circle shown here, around 1815. The instrument, which measured angles, employed two telescopes and was designed to reduce errors by repeated observations taken from all points of the circumference of the circle. With the advent of GPS, traditional line-of-sight techniques to measure distances and angles have given way to modern satellite positioning. Survey projects that once took weeks to perform can now be completed in a few short hours. In the present-day photo, an Alaskan shoreline is the backdrop for the antenna of a Novatel DL4 GPS system used by a private hydrographic survey company. The antenna receives signals that are broadcast from GPS satellites orbiting overhead.