Mobile Mapping for Colorado Highway Tunnel Inspections

Mobile LiDAR

Earlier this year, SAM completed a project with the Colorado Department of Transportations as a sub-consultant to assist in exploring technologies to develop new procedures for engaging in Non-Destructive Testing (NDT) and monitoring of the highway tunnels it manages and operates. The objectives of the project were to explore the application of thermography and LiDAR for NDT, create a truly mobile solution collecting data at speeds as close to posted speeds as possible, and create deliverables that are acceptable to CDOT for their data workflows. Ultimately, SAM was tasked with assisting CDOT and the Federal Highway Administration (FHWA) in finding and implementing technology to better serve the traveling public by being safer and more efficient than traditional means of tunnel inspection.

"SAM regularly performs research and development of new technologies." said Mark Treon, Project Manager based in SAM's Denver office, "And this project was an example of the how our expertise can be brought-to-bear in an applied way to deliver efficient new solutions for our clients." SAM's Denver-area office was responsible for performing all testing, data collection, and management of data processing on this project. A wide range of imaging and LiDAR scanning options were available to SAM, but Mobile LiDAR was the choice platform for this project.

Initially, SAM performed extensive research into available technologies, as well as testing a series of cameras and other equipment added to its existing mobile mapping system. In the first phase, data was collected from a single tunnel using a test platform and a workflow was established to produce deliverables for CDOT that included:

  • LiDAR point cloud colored by thermal
  • LiDAR point cloud with intensities
  • Tunnel Triangulated Irregular Network (TIN) from one-foot contour profiles
  • Flattened thermal tunnel image

Although this was successful, SAM identified several opportunities to enhance the process and improvements were made in the next phase that included seven additional tunnels. In this phase SAM continued to evaluate other technologies and techniques to improve, supplement, and verify data collected by the cameras. Thermal imaging was of particular interest and both new RGB and HD thermal cameras were incorporated into the mobile mapping system. Thermocouple data loggers also proved to be an effective means of determining the best times during which to collect data in tunnels.

During phase two, SAM continued to assess the expanded platform of tools that had been identified, tested, and improved upon. By utilizing equipment in new ways and integrating different technologies, SAM was able to identify the best pairings of cameras, lenses, sensors, processing software, and other components to most efficiently deliver a robust NDT solution for CDOT. This ultimately led to a further improved process and workflow that was used to complete the final phases of data processing from phase two. The final package of deliverables provided included:

  • LiDAR with intensity values
  • LiDAR colorized by corresponding normalized thermal metadata
  • Contours of tunnel created every two feet
  • Mesh of tunnel liner surface and roadway
  • FLIR self-viewing files
  • Flattened high-resolution normalized thermal tunnel liner PDFs
  • RAW FLIR video in .MP4 format
  • Normalized thermal image frames
  • Proof of concept Virtual Reality environment to review project data

After completion of both phases of this project, and working through a variety of tunnels with differing factors, SAM developed an expert level of understanding about the tunnel monitoring process as a whole, and the potential for highly efficient application of surveying, scanning, and imaging technologies to support it. The capabilities SAM have in place to ensure accurate measurements, positioning, and calculations transferred readily to the technologies and equipment used to develop this new approach. The data and images gathered, including the spatial components, and processed through our workflows, were fully compatible with industry standard tools used by our clients.

Due to SAM's extensive experience with transportation surveying practices, leading technologies, and DOT procedures, SAM was well prepared to engage in the research and development necessary for new NDT methods to support CDOT tunnel monitoring needs. SAM can bring this same skill and experience with research and development to help develop efficient new approaches for many other client needs. Please see our Geospatial Services webpage, or contact us for more information.