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National Geodetic Survey


Of Seconds & Centimeters: How South Carolina Positioned Itself at the Forefront of Global Positioning

NOAA’s National Geodetic Survey (NGS) develops and maintains a national system of positioning data needed for a range of applications, from navigation to mapping and construction. NGS’s activities set the standards for other states to build their own statewide positioning networks. South Carolina is one state that is successfully pushing the limits of global positioning.

Tower used to transfer data within the SC Real Time Network

The 42 stations in the South Carolina Real Time Network transfer data either via a 24-foot self-supporting tower, like the one shown here, or a stainless-steel antenna that can be mounted on masonry buildings.

The South Carolina Real Time Network
In a modest building at the back of a small state-government complex in Columbia, SC, new horizons in global positioning are being explored and conquered. Here, the South Carolina Geodetic Survey (SCGS) is exploring the future of global positioning technology with its statewide Real Time Network (SC RTN) – the first of its kind in the nation and in the world.

It’s only fitting that this cutting-edge work requires little space and time from but a few SC state employees, because efficiency and tininess – in effort, costs, and scales of accuracy – are what this work is all about, as SCGS Chief Lewis Lapine, PhD, explains.

“We’re proud that our South Carolina Real Time Network is running at centimeter-level accuracy virtually round the clock,” says Lapine, who also happens to be a retired NOAA Corps Captain who served as the Director of NGS from 1992-1998. “With our Integrity Monitor, we can look at all 42 network control stations in the state and see at any time, in real time, how accurate the system is.”

In recent fieldwork to verify the Integrity Monitor, he visited 416 NGS benchmarks across the state and did a 60-second comparison with the SC RTN.  He found that the state system runs within a mean difference of two millimeters’ accuracy, far smaller than NGS’s Height Modernization standard of five centimeters.

Portable base station

The SC RTN portable “base station” essentially “follows” the surveyor around, making the new technology faster, cheaper, and more accurate than classical leveling techniques.

The Evolution of the Network
First, the state embraced NGS’s Height Modernization program. “We don’t do anything in South Carolina unless it conforms to NGS specifications and Height Modernization,” says Lapine. Then, with funding from federal Height Modernization grants over the past seven years, the SCGS’s three surveyors used the U.S. Global Positioning System (GPS) to determine approximately 2,500 accurate position and elevation points in 20 of South Carolina’s 46 counties.

Using Height Modernization stations as a basis, SCGS began the task of building a network of satellite receivers around the state that mimic NGS’s Continuously Operating Reference Station (CORS) network, only at a smaller scale. These receivers relay information back to SCGS, allowing surveying and engineering tasks to be accomplished in real time with an accuracy that approaches NGS Height Modernization standards.

The challenge was to find a place in every county that had reliable Internet and cell coverage, since a few portions of the state are rural and not well-connected. SCGS’s strong partnership with the SC Department of Transportation (DOT) proved valuable when the DOT agreed to let SCGS install a network station – basically a GPS antenna and receiver – at each of its 32 county maintenance lots.  Ten other stations are located at colleges and other agency facilities.

Next, the state’s surveyors, each equipped with a specially built portable “base station” that fits into the brass control-point marker, and a hand-held device that is essentially a large cell phone with specialized data-collecting functions, recorded the positioning coordinates (for latitude, longitude, and elevation) at each site.

Applications: Putting the Data to Use
Collected positioning data are continually sent back to the SCGS office via the Internet and several servers in real time, where they are made available for use in a myriad of global-positioning applications. Among the most common uses of the data are map production, GPS navigation via a hand-held receiver, verification and or redrawing of election districts, address verification, and state boundary surveys.

Some applications that may not instantly come to mind include the drawing of highway center lines, development of state standards for survey accuracy, precise automation of graders used in highway construction and tractors for farming activities, and the fast capture of deadly fugitives from the law.

“The potential of RTN is virtually limitless,” concludes Lapine, who has only just begun, together with his SCGS colleagues, to dream the future of global positioning into existence, one South Carolina county at a time.

Ocean sampling on a GLOBEC research cruise

Precision automation of highway construction, measurements of dam subsidence (sinking), and accurate elevations in tidal areas are only a few of the SC RTN’s practical applications.