McKim & Creed performed services for a bridge tunnel mobile scan project. The project included a mobile scan through the eastbound and westbound tunnels of this heavily traveled and congested corridor.
The scope of work for the project was to map the approach islands and show the profile of the existing tunnels so two new parallel tunnels could be designed. Mobile targets were set at 500-foot intervals in the tunnels to compensate for the lack of GPS. Also due to the lack of GPS, the IMU (Inertial Measurement Unit) and the wheel-mounted DMI (Distance Measurement Indicator) were used to position the scanner while we were surveying in the tunnels.
Mobile LiDAR was collected at 1 million points per second to provide sufficient density of the point cloud. The overall accuracy of the output control report was less than 0.05 foot. The surveys inside the tunnel were completed at night because a lane closure was required for traffic concerns and all surveys crews were required to follow the owner’s safety procedures. The islands were surveyed with a Leica P50 static scanner and processed with Leica Cyclone software. The tunnels were scanned with the Leica Pegasus 2 and the LiDAR was processed using Leica Pegasus Manager/Terrascan software. The island and tunnels were then mapped per the owner’s standards from the merged LiDAR point clouds.