Feature: Surveyors to the Stars
Professional Surveyor Magazine - November 2010
NASA’s reputation for innovation and creativity is not limited to its engineers and scientists. At the Langley Research Center in Virginia, a team of surveyors and GIS professionals is pushing the technical envelope as well.
By John Stenmark, LS
For more than 90 years, NASA’s Langley Research Center
(LaRC) in Hampton, Virginia has played a leading role in America’s aviation and space research. As a premier location for U.S. aerospace research and testing, LaRC’s wind tunnels, laboratories, and test structures have seen a dizzying array of aircraft and space vehicles. LaRC’s work ranges from research that first enabled aircraft to fly at supersonic speeds through developing modern methods for orbital rendezvous and docking.
The country’s oldest civilian facility dedicated to aeronautical and aerospace research, LaRC was founded in 1917, when—to keep up with rapid aviation development in Europe—U.S. president Woodrow Wilson signed an order to establish a laboratory dedicated to aeronautical research. Because of its proximity to Washington, D.C., the existing Langley Airfield in Hampton was selected as the research center site. The center served as the initial home for Project Mercury, America’s first manned spaceflight program, and had the lead role in the Mars Viking Lander program. Langley was a key facility in development of the space shuttle orbiter and has participated in testing and development of virtually every type of aircraft flown by the U.S. military.
NASA Langley is a big, busy place. It is home to roughly 3,800 employees working in more than 290 buildings and structures spread over 788 acres (319 hectares). As the center grows and changes, it relies on accurate surveying and GIS data for planning, engineering, and operations. These services are provided by the NASA Langley GIS team, part of the Center Operations Directorate. This small group of surveyors, engineers, and GIS professionals provides positioning and related services to facilities managers and construction engineers. According to team lead Brad Ball, the group has the same passion for technology as the center’s aerospace scientists and engineers.
LaRC’s size and variety of needs has encouraged Ball and his group to investigate new ways of collecting and sharing precise surveying information. The LaRC GIS team uses a combination of real-time kinematic (RTK) GNSS, total stations, spatial imaging, and advanced data management to handle the workload. As part of the process of implementing new systems and methods, the team is helping other NASA and federal facilities move forward with current technology and equipment. LaRC is recognized as having the most advanced GIS of any NASA center.
The geodetic framework at NASA Langley dates to 1995, when Ball organized efforts to develop a control network for the base. That work established a handful of monuments on LaRC property and tied them to NAD83 High Accuracy Reference Network (HARN) points in the surrounding region. The team established a Continuously Operating GNSS Reference Station (CORS) on the roof of their building. The CORS uses a Trimble
NetR5 Reference Station and serves as the reference for all surveying and GIS work on the base. The CORS broadcasts RTK corrections that are used by the Langley surveyors and GIS teams as well as collecting data for post processing. To supplement the CORS, there are permanent survey markers at the center, and a new project has identified roughly 50 existing monuments that will be surveyed and added to the control network. As a result, every surveying and GIS project at Langley can be tied to the HARN.
In addition to the LaRC team, surveyors in the surrounding community use RTK corrections from the LaRC CORS, and the ties to the HARN help ensure that roads and utilities coming onto the base match well with the surrounding areas. When working in areas where control monuments for optical surveys are not convenient, surveyors use the CORS and RTK to set pairs of intervisible points for use with the total stations or scanner. Ball said the group has defined a vertical slope and offset for the facility that is built into the calibration file for their GNSS control network.
The control network serves more than just surveyors. John Meyer, an engineer on the Langley team, described a test of an unmanned Global Hawk aircraft that was to fly autonomously from California and land at the nearby Langley Air Force Base. “The Air Force needed a good set of coordinates for the runway here at Langley,” Meyer said, “We gave them coordinates based on our control network. We transformed our coordinates to International Terrestrial Reference Frame (ITRF) for the flight, and they landed the drone successfully.”
Just below the surface at NASA Langley, a warren of tunnels and passageways contains steam lines, water pipes, electrical conduits and other utilities serving the center’s buildings. Like many large facilities, LaRC’s utility systems have been modified and upgraded over the years, and recent work on the steam system exposed serious problems. Done without the benefit of a survey, the work resulted in numerous low points in the steam lines. “The operations contractor was experiencing a water hammer effect,” Ball said. “It occurs where a layer of water builds up in the steam lines and creates a wave. The wave collects at a low point and closes off the entire steam line, causing a huge hammering effect. When you get a 10-inch (25 centimeter) line full of 350 psi (24 atm) steam jumping around in a narrow tunnel, it’s pretty exciting.” The GIS team needed to survey
the steam lines to find all the low points so that condensate drains could be installed to eliminate the water.
The survey covered four tunnels with a combined length of nearly 2.7 miles (4.3 km). In addition to collecting horizontal and vertical locations of the steam lines, the surveyors were asked to capture the location of all valves, pumps, and other items that carried maintenance identification tags. “The water and high-pressure air systems are in the tunnels,” Ball said, “and some utilities haven’t been viewed for 50 years. This was an opportunity to find out where all this equipment is located.”
Working in the tunnels presented an array of challenges. To get started, the team used RTK and optical methods to establish control points in the tunnels. They used a Trimble R8 GNSS system for the GNSS work and a Trimble VX Spatial Station for the optical portions, connecting the sensors to a Trimble TSC2 Controller running Trimble Survey Controller software. “We moved control down manholes or access hatches using 20-foot (6-meter) poles with a prism or GNSS receiver on the top,” said GIS analyst Jason Hall. “Then we used a conventional traverse to move through each tunnel and closed to a control point at the other end. In one tunnel, we needed 24 stations to traverse 3,700 feet” (1,130 meters). That traverse closed vertically to 0.04 feet (1 cm), and Hall said other traverses achieved similar or better closures.
The strong results didn’t come easily. Hall and his colleague, Dana Torres, were working in tunnels six feet tall by three feet wide (1.8 by 0.9 meters) that were filled with pipes, conduits, and machinery. Work in the tunnels was further complicated by the presence of maintenance and construction crews working on the various utility and communications systems. It was hot, wet, and dirty work made more difficult by the presence of the steam pipes.
“One of the most difficult things we encountered was the temperature gradient coming from the steam lines,” Meyer said. “Cold air comes into these tunnels in several locations, and we’ve got steam leaks in other places. We had to develop a technique to get very close to the floor—below the heat blanket emanating from the steam lines. Jason and Dana were literally wading around in the muck on their knees to make the shots.” The abrupt temperature variations created heat shimmer that affected distance measurements and made sighting on targets nearly impossible. The crew determined that they could keep errors within specified tolerances by staying low and making short shots. They used SECO
mini tripods for the instrument and a cut-down traverse rod to hold the prism. In the tunnels, the typical instrument setup height was roughly two feet (0.6 meters).
When making measurements, Hall frequently used the video capability of the Trimble VX. It saved him from lying on his stomach to look through the eyepiece and helped the crew to detect obstructions in the line of sight. In the congested passages, many features were obstructed or out of the instrument’s view. To measure these objects, Hall and Torres used the dual-prism routine in Trimble Survey Controller and a SECO dual-prism pole to obtain accurate 3D positions. The Trimble VX automatically points to target prisms, and—with two prisms on the pole—Hall said the video display was invaluable in making sure that the instrument was aimed at the desired target.
By the time the fieldwork was finished, Hall and Torres had spent nearly 40 days in the tunnels, completed 2.44 miles (3.9 km) of traverses, and collected nearly 3,200 points. While in the field, the surveyors checked the traverse closures onboard the Trimble TSC2. From there, the information was downloaded into Trimble Geomatics Office software and then output to ESRI
ArcGIS and spreadsheet software for additional analysis. In addition to capturing locations for the utilities, the survey corrected some old errors. “Jason and Dana thoroughly surveyed the sides and the corners of the utility tunnel,” Ball said. “They found parts of this massive tunnel system that were four feet off compared to earlier surveys.”
A dominant structure at LaRC is the 1297 gantry. Constructed in 1963 for lunar landing simulations, the gantry is now used for drop and crash tests on a variety of air- and spacecraft. It’s an enormous structure: 240 feet (73 meters) tall, 265 feet (81 meters) wide, and 400 feet (122 meters) long. As part of work to install a new crane atop the gantry, engineers called on the GIS team to measure the deflection of the gantry as loads were applied to the crane. To make the measurements, Hall needed to set up the Trimble VX directly under the gantry and measure straight up to the structure.
In planning the measurements, Hall used experience gained from a similar monitoring project at the gantry a few years earlier. During that work, the surveyors had struggled to obtain measurements to the points that were directly overhead. Hall said that the video and automatic pointing capabilities of the Trimble VX made a big difference in the new measurements. “We were monitoring the gantry in real time and didn’t want any surprises when they applied loads to the crane,” he said. “With the Trimble VX video, I could control it from the data collector and didn’t have to look through the eyepiece. It made things a lot easier.” Ball noted that there was a safety issue involved as well. By using the video, the crew did not need to stand under the structure.
As part of the project, the GIS team brought in control from the LaRC NAD83 coordinate system and tied the elevations to the NAVD88 datum. They also established a coordinate system orthogonal to the gantry itself, which enabled the structural engineers to compute deflections with respect to the gantry axis.
Following the initial deflection study, NASA engineers wanted to obtain data over multiple locations on the gantry structure. For that work, the GIS team used the Trimble VX to measure 29 prism targets that were attached to the gantry along the crane rails, which would again be loaded with weights. Anticipating a lengthy test, LaRC engineers had arranged for weights and support personnel to be available at the gantry for several days of testing and measurement. Hall said that by using the automated pointing and measurement functionality in the Trimble VX, they completed the test in one day.
The LaRC GIS team continues to find new applications for their advanced surveying technology. For most of its GIS work, the team uses the base CORS and Trimble R8 GNSS systems to obtain centimeter accuracy. On a recent project to validate existing aerial photos of the base, the team used RTK to survey roughly 1,000 points on the base that were visible in the photos. The work revealed enough inaccuracy to justify creating new high-resolution images of the base. To provide control for the new photos, the team surveyed and marked valve covers visible in the new images. Because many of the valves were located close to buildings, the surveyors used integrated surveying techniques to combine RTK with measurements from their Trimble S6 Total Station.
The LaRC GIS team deals with not only the infrastructure and exterior features. Meyer said that they carry GIS inside the building as well, where it plays a major role in operations, space planning, and facilities management. The team uses their Trimble GX 3D Scanner to scan the interior of buildings and ties the scans to the LaRC coordinate system.
The Langley GIS team’s accomplishments have not gone unnoticed. In 2009, the team received a Special Achievement in GIS award from ESRI in recognition of the team’s innovation and leadership in GIS and spatial data.
In addition to work at Langley, members of Ball’s team often travel to NASA or Air Force facilities to share technology or processes developed at LaRC. As part of their work to support engineering and research, the Langley GIS team traveled to NASA’s Dryden Research Center
in California to conduct a survey of a NASA DC-8 research aircraft. The plane was equipped with a lidar unit in its belly and had a GPS antenna mounted on the top of the fuselage, and NASA researchers needed to know the vector relationship between the two sensors.
To make the measurements, the Langley team oriented their Trimble S6 to an arbitrary coordinate system in the aircraft’s hangar and took shots to the GPS antenna and lidar data point as well as along the aircraft’s axis. Then they developed a transformation between the aircraft and hangar and computed the vector based on the plane’s axis. The team’s other work includes scanning wind tunnels with their Trimble GX 3D Scanner and surveys to support upgrades at Langley’s vacuum spheres.
Ball is convinced that the key to success is integrating surveying with GIS and in putting advanced technology into the hands of creative people. The investment pays off in letting them do things that are difficult or nearly impossible without the new approaches. Torres agreed. “It is interesting that there is no set formula for most of our jobs,” she said. “We do a lot of improvising to make things work. There is always some obstacle popping up, but the people and equipment are flexible enough to handle the problem.”
John Stenmark, LS, is a writer and consultant working in the AEC and technical industries. He has over 20 years’ experience in applying advanced technology to surveying and related disciplines.
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