Mapping buried fiber cable in Columbia County Georgia
The GIS Department in Columbia County, Ga., is mapping buried fiber cables as fast as its field crews can walk—even under tree canopy. The ability to collect accurate location data at walking speed is a four-fold improvement over what the GIS crews were able to achieve just two years ago, thanks to upgraded handheld GNSS units, a newly upgraded reference station and advanced data-editing software.
While the benefits of more-efficient mobile data collection are being experienced by several county departments that rely on the GIS Department’s GNSS technology and mapping expertise, one of the most dramatic impacts has been the benefit of inventorying the extensive broadband infrastructure backbone that was partially funded through a federal stimulus grant.
In 2010, Columbia County received $13 million from the U.S. government to fund 75 percent of a new broadband project. Part of the objective was to provide free Wi-Fi access to the county’s 125,000 (in 2010; 131,627 in 2013) residents when they visit public parks, libraries, schools and community centers. In addition, the broadband backbone would tie county buildings, utilities, schools, and even traffic control infrastructure into a common communications network.
The plan called for installation of 220 miles of buried fiber cable and five wireless relay towers spread across 307-square-mile county, located along the Savannah River in eastern Georgia. The network itself is considered a “middle mile” project, which means Columbia County is able to offer contracts with telecommunication and Internet service providers so that they can tap into the broadband for a fee and run private lines to homes and businesses, generating long-term revenue as well as savings for the county.
The county awarded construction contracts to 13 companies to build the towers and install the underground cable; the cable was buried either by trenching or boring. With each of the contractors responsible for a different geographic region of the county, the installation was a complicated job carried out quickly during 2010 and 2011.
Ernestine Phelps locates the broadband assets in Columbia County.
As a prolific user of geospatial technology, the county GIS department was prepared to handle the inventory during rapid construction of many different sites across the 220-mile route. Columbia County’s robust GIS asset inventory, developed using Trimble GPS products since 1998, allowed management to optimally assess collection areas and plan construction methodologies. In-house personnel use Trimble GNSS-based data collection tools to develop, populate and update the Esri-based GIS, according to Mary Howard, the county’s GIS manager. At the time of the broadband implementation, the GIS Department had just purchased several Trimble GeoXH 6000 handheld data collectors for existing projects such as sewer, water, storm water, fiber, and other utility inventory.
The efficiency of data collection received a boost when the county upgraded its GNSS capabilities. The GIS Department upgraded its Continuously Operating Reference Station (CORS) with the purchase of a Trimble NetR9 GNSS reference receiver. This permanent reference station now broadcasts real-time differential correction signals in three formats for use with the GeoXH 6000s as well as survey equipment. The big results: high-quality data.
“Our GIS technicians use real-time corrections during data collection, and we have found excellent return on investment for staffing time during collections as well as having a reliable end-product,” said Howard.
According to Howard, the new handheld data collectors and reference station were drivers that enabled the GIS Department to quickly map the entire broadband network with a high degree of confidence. Location accuracy was especially important during this work because the county is one of the fastest developing counties in the state of Georgia, and both residential and commercial construction are major activities.
Collecting Data Everywhere
The fiber-mapping crew typically consisted of two county employees, both on foot. A utility worker equipped with an underground-line-locating device went first, detecting the buried fiber and marking its location with florescent spray paint. Following close behind was the GIS technician carrying the handheld GeoXH unit running Esri ArcPad with Trimble GPScorrect™ data-collection software; the county later switched to Trimble Positions software. Prior to each day’s work, the unit was set to capture location points at one-second intervals.
This was among the first field projects in which the county GIS technicians used the new GeoXH units with Trimble Floodlight technology. The technicians were eager to put this technology to the test because their field-work productivity had long been sapped by a phenomenon called satellite shadow, which Floodlight was designed to overcome.
Satellite shadow is caused when tall buildings or dense tree canopies deflect or block the signals coming from GNSS satellites overhead. As a result, a GNSS receiver on the ground achieves a poor signal lock or can’t acquire signals from enough satellites, resulting in reduced accuracy for the collected location points. In Columbia County, the culprits were towering pine and hardwood trees that cover much of the terrain.
“Before Floodlight technology, it would take 30 minutes to an hour just to collect a point under canopy, even with the Zephyr external antenna,” said Howard.
“Depending on the satellite availability, some days we had only small windows of time that we could collect data,” added Ernestine Phelps, a county GIS/GPS technician.
Now the technicians rarely need to use external antennas to supplement their data collectors. Floodlight technology minimizes or eliminates the satellite-shadowing effect through advanced tracking algorithms and altitude-constrained positioning. In addition, the GeoXH is able to acquire signals from both GPS and GLONASS constellations, nearly doubling the total number of satellites the receiver can lock onto.
“You don’t have to stand there and wait,” Howard explained. “It’s amazing to see how quickly you’re receiving four-inch accuracy.”
The county has set four inches as the location accuracy required for all features mapped into its GIS. This parameter was entered in ArcPad when the data collection menu was set up for the fiber mapping. Trimble GPScorrect, an ArcPad extension, monitored data being captured by the GeoXH units as well as the correction information streaming into the device wirelessly from the Trimble NetR9 reference station. If the accuracy of collected points fell outside the 4-inch limit, the unit emitted an audible chirp.
“This let the user know to slow down or stop until signal quality improved,” said Howard, explaining that the technician could look at the display screen on the GeoXH unit to determine the point accuracy at any time.
According to Phelps, it was the Floodlight technology, combined with the real-time NetR9 differential correction broadcast, which allowed the field technicians to keep moving and collect data almost continuously regardless of canopy cover. The GIS technicians collected fiber-location data on foot in the field at a rate of about one mile every 15 minutes. Previously, similar linear mapping projects required about one hour to cover the same distance.
Although the Zephyr antenna was used only rarely in the broadband project, Phelps still carries the pole-mounted antenna with her to the field on utility mapping projects. She uses it under extremely dense tree canopies and in those parts of the county that are outside of cell signals.
Back in the office after a day of mapping fiber, the GIS technician uploaded the location data onto a desktop computer, where the points were edited using the new Trimble Positions software. The data editing process in the office had already been made easier thanks to real-time correction in the field, but the office saw a “huge boost” in workflow efficiency with new software.
The software displayed a graph onscreen showing the point locations for the fiber. Bad coordinate points appeared skewed from the otherwise straight line of broadband fiber. The technician could examine the accuracy of each individual point and, if needed, delete it with a click of the mouse. Once the data was reviewed for accuracy, Trimble Positions checked the new fiber location points into the Esri GIS layer representing the broadband network. As a result, time spent editing data in the office has been greatly reduced.
“For every hour we spent mapping in the field, we spent 15 minutes editing the data,” said Howard. “It was wonderful, and we are thrilled with how easy and user friendly the Trimble Positions software is! It has added to our efficiency in the office and has cut down on the time required to process the data by half.”
Serving Multiple Applications
Mapping the buried fiber served both short- and long-term purposes for the county. The first was determining precisely where and how far the fiber meandered across public property lines and utility easements onto privately owned land as well as locations where fiber is located for future growth projects such as road widening projects, commercial area development and subdivision development.
When encroachments or areas of future development are determined by GIS analysis, the county can accurately forecast the scope of work for relocations or property area needed for acquisition.
The second advantage of mapping the fiber as a layer in the GIS is to safeguard the integrity of the broadband connections as Columbia County grows. Federal facilities are being built nearby and, as a result, new homes and roads are being constructed at record rates. As the development companies excavate to install new infrastructure, they need to know precisely where fiber is buried to avoid severing it. The county has already relocated lines in several areas to accommodate construction of roundabouts on busy secondary roads.
Growth and development will continue in the county; although that will likely mean that portions of the broadband network will have to be relocated, the GIS Department is ready to update the asset inventory in a highly productive and accurate manner. Howard and her team can quickly show where the lines are buried and management can determine the best new locations thanks to an accurate GIS map that can be updated with a quick walk in the woods.