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Louisiana DOTD

Close Tolerance Elevation in Louisiana

Challenge

To better understand potential flood threats, Louisiana Department of Transportation and Development (LADOTD) required a high accuracy elevation survey of its highway system. Louisiana State University (LSU) had surveyed sections to a tolerance of 1.6 inches (4 cm) from absolute elevation.

LADOTD’s request to Fugro Roadware: Achieve or approach the same level of precision while surveying 35,288 miles (56,791 km) at highway speeds.

What We Did

Fugro Roadware:

  • Configured an ARAN vehicle with precision-grade inertial navigation and differential GPS equipment
  • Precisely positioned the instruments relative to the road surface, to eliminate any built-in bias
  • Used lasers to provide additional data on the ARAN’s vertical movement

This process uses LSU’s Real Time Network (RTN) and RTK corrections. To achieve desired results due to GPS outages and cell phone signal loss we post-processed the GPS using corrections downloaded from LSU’s RTN. During collection, two separate sources, Omnistar’s global navigation satellite system and LSU’s combination of physical and virtual base stations, were used to correct the GPS data received. The redundant correction systems enabled us to crosscheck results and to compensate for occasional gaps in satellite availability and the LSU base station network.

To align our data with results collected from LSU’s benchmark sections, we developed and applied sophisticated real time and post-collection processing algorithms.

Results

Initial results varied widely from the LSU test results. However, after refining the process, as of December 2012, results over multiple runs showed an average error of 2 inches (5 cm). This project is ongoing.

“Our team did a terrific job of surveying elevation—the z axis—with a precision not previously possible on a large scale. In the process, we also improved our achievable accuracy and repeatability on the x and y axes.” ~ Cory Hackbart, Project Manager

Technologies Used

The Louisiana highway elevation process leveraged Fugro Roadware’s:

  • ARAN state-of-the-art highway data collection vehicles
  • Experienced collection crews and new technologies
  • Experience with differential GPS and inertial navigation technology
  • Ability to combine multiple technologies and redundant inputs to improve accuracy and repeatability
  • Data processing and analysis capabilities
  • High accuracy benchmark locations provided by LADOTD

Similar Applications

In addition to enabling close tolerance elevation surveys in other flood-prone jurisdictions; this project enabled Fugro Roadware to achieve greater accuracy and repeatability of asset inventory and data referencing across all projects.

To read the entire case study, click here.

Copyright Fugro Roadware 2013.