NOAA News || NOAA Home Page

August 18, 1999 — A group of government scientists is taking the expression 'get to the point' to new heights. Geodesists from NOAA will get to the point, literally, when they conduct a precise three-dimensional positioning survey at the top of the Washington Monument this month. These NOAA surveyors are the first in nearly 65 years to "occupy the apex" of the monument. They will measure the exact height and gain valuable information on the stability of the famous structure. (Click Image for larger view.)

"You might think of this new technology as a satellite tape measure that survey experts from NOAA will use to learn the exact height of this treasured monolith," NOAA administrator D. James Baker said of the effort to pinpoint the exact height of the Washington Monument, historically said to be 555 feet, 5 and one-half inches. "Engineers will also use this information to monitor the monument's stability, measuring any shifting, settling, or other movement of the structure. The same precise positioning capabilities used in this project are essential for a wide range of survey work, navigation, and the operation of safe, reliable transportation and communications systems," he said.

The preliminary figure from the GPS readout for the height of the Washington Monument is 555 feet, 5.9 inches. The final figures will be available in a week.

Using state-of-the-art Global Positioning System (GPS) receivers and other specialized gear, geodesists and technicians from NOAA's National Geodetic Survey (NGS) will take hundreds of measurements at the top of the monument and at several other nearby Washington D.C. landmarks, such as the "meridian stone of 1890" and "Zero Milestone" at the Ellipse, and the "Jefferson Pier" on the west side of the Washington Monument, during the week of August 16.

The last official geodetic measurements from the top of the Washington Monument were made by the U. S. Coast and Geodetic Survey (USC&GS), the National Geodetic Survey's predecessor agency, in November 1934. At that time, manual observations were made with instruments such as Parkhurst Theodolites spirit levels, and leveling rods. When NOAA was formed in 1970 the USC&GS became part of the new environmental science agency and now consists of two branches, the Coast Survey and National Geodetic Survey, within NOAA's National Ocean Service.

(Click image below for larger view and caption)

The USC&GS survey crew that perched atop the monument in 1934 on a wooden platform and made their measurements by eye and hand, recording the information with fountain pens, would probably marvel at the new tools and high tech equipment now being used to grab satellite signals and turn them into precise coordinates and heights. Seven manufacturers of GPS receivers will provide equipment for this month's measurements. The NOAA project is being coordinated with the National Park Service, which cares for and operates the Washington Monument. One of NOAA's sister agencies in the Department of Commerce, the National Institute of Standards and Technology, also contributed to the project by designing and building a special mounting bracket to hold the GPS equipment atop the Washington Monument.

Baker added that a survey of the famous landmark will help raise public awareness of GPS, and the National Spatial Reference System (NSRS) maintained by NOAA's National Geodetic Survey. NSRS is the foundation for all types of surveys and allows government, industry, and researchers to measure the position of objects in three-dimensional space. NSRS is also a key component of the National Spatial Data Infrastructure --a critical element of the "information superhighway."

The monument measuring project also helps exercise NOAA's "GPS height modernization" project to demonstrate, test and refine new ways of analyzing GPS signals to determine height—a vital third dimension to the already valuable GPS technology. And height does matter—for example, NOAA uses the same survey techniques used on the monument project to survey areas around airports for obstructions and other possible hazards to aircraft, and more accurate height measurements mean safer air travel.

"Our predecessors did a spectacular job of laying a foundation of survey data necessary to build our great country," said Charles Challstrom, Director of NOAA's National Geodetic Survey. "They used the best equipment of their day and achieved a remarkable level of accuracy through skill, hard work, attention to detail and quality control. Today our people have the same spirit and devotion to the public service but they're working with remarkable new tools to give us an even better more accurate system of measurements and surveys," he said.

A large scaffolding structure completely surrounds the monument and serves as a support for workers repointing and maintaining the exterior of the structure. Because there is a metal framework surrounding the structure NOAA geodesy experts are also eager to test the accuracy of the survey equipment within the scaffolding. GPS and the NSRS are vital tools for engineers and public safety officials who monitor structural movements and stresses on bridges, buildings, utility lines, and other sites where metal or other materials could cause interference with GPS signals. Measuring the monument with several different types of equipment over several days will allow experts to analyze any variations or discrepancies in position readings.

(Click image for larger view.)

Although the structure surrounding the monument is strong and appears quite substantial, riding the temporary exterior elevator, and then climbing a 60-foot ladder to the top of the monument is not for the faint of heart. Mounting and securing the survey gear atop the monument, with only a safety belt and a few metal bars between you and the ground some 555 feet below, takes skill and concentration.

"It is an awesome experience to touch the top of the monument," said Dave Zilkoski, Deputy Director of NOAA's NGS who has tested some of the equipment at the apex. "It's a feat that only a few people will ever experience. I'm proud to be involved with this important work and consider it a privilege to participate in the project," he said.

Zilkoski and others involved in the project must temper their enthusiasm with a healthy dose of caution and skill to safely install the surveying gear to the top of the monument. Due to their unique responsibilities, NGS personnel often find themselves in unusual locations. In the past, that meant building and climbing 100-foot towers at night to determine precise positions. Today it means walking on beams and crawling underneath expansion bridges to measure movement, floating on GPS-equipped buoys in bays to measure water levels, and working on huge container ships to measure the movement of these vessels.

Preliminary results of the monument height measurement will be announced at a demonstration of the NOAA GPS height survey project on Wednesday, August 18, at 10:00 a.m. at the "Meridian Stone of 1890" at the center of the Ellipse. NOAA Administrator Dr. D. James Baker will be on hand along with NOAA survey experts and a National Park Service representative to explain the measurement project and answer questions.