A password will be e-mailed to you.
Surveying Solutions Inc. used a Riegl VMX-250 LiDAR system mounted on an SUV to collect survey data in New Orleans’ Ninth Ward.

On Aug. 29, 2005, Hurricane Katrina ravished southern Louisiana and Mississippi. The impact and destruction is still evident today, nearly six and a half years after the storm. While the devastation left in the wake of the deadliest hurricane in history was unimaginable, new innovative technologies are being deployed to help a vital region of the United States recover and rebuild.

Project
Topographic Utility Survey, New Orleans

Participants
Surveying Solutions Inc.
Dale Stockstill & Associates
U.S. Army Corps of Engineers

Product application
LiDAR survey using a Riegl VMX-250 mobile mapper rapidly provides a 3D model with engineering design tolerances over a 120-acre site.

The reconstruction process will continue for years to come, but with the help of new technologies, surveyors, engineers, and contractors are able to expedite reconstruction and redesign projects that are desperately needed in the post-Katrina Gulf South Region.

One of the newest technologies for civil engineering design surveys is mobile LiDAR. While airborne LiDAR has been available in the commercial world for about 20 years, mobile LiDAR just became readily available about four years ago. Many types of mobile LiDAR systems are available from an abundance of manufacturers around the world, but only a few of these systems are capable of achieving engineering design tolerances. In addition to utilizing the proper mobile LiDAR system, the data acquisition must be completed by a specialized firm that is strong in the technical understanding of LiDAR, as well as conventional and traditional survey principles and practices. To be successful as an engineering tool, many important considerations have to be made.

LiDAR point clouds were registered, stitched together, and merged with high-resolution digital imagery that is captured simultaneously by the mobile mapping system.

In September 2011, the U.S. Army Corps of Engineers (USACE) New Orleans District tasked Dale Stockstill & Associates (DS&A) to provide a detailed Topographic Utility Survey for major drainage canal improvements in the Ninth Ward of New Orleans. The high-priority project was the fourth and final phase of a large drainage project named the Southeast Louisiana Urban Flood Control Project, Florida Ave Ph. IV. Since other phases of the project are already under construction, completing the full topographic survey in a timely manner was the highest priority.

In early discussions with USACE, officials indicated an initial interest in using airborne LiDAR for the collection of the ground data. However, following some initial research and technical briefings from airborne LiDAR service providers on the published accuracies of this method (10 cm), the focus shifted to mobile mapping and mobile LiDAR. DS&A’s owner, Alan Chavers, had met previously with Surveying Solutions Inc. (SSI) of Standish, Mich. During these initial meetings, discussions about using mobile LiDAR as an alternative for consideration by USACE offered many foreseeable advantages to the proposed project. Discussions regarding equipment manufacturers, procedures, relative and positional accuracies, software programs, etc. helped USACE determine that mobile LiDAR would be a satisfactory method for obtaining the information that was needed by its engineers, and the technology could yield acceptable tolerances for design. In addition, there were many other benefits of utilizing mobile LiDAR on the project that were attractive for USACE. SSI was invited to submit a bid for the proposed work and the project moved forward from there.

Setting control
After the project was negotiated and the Notice to Proceed obtained, DS&A’s field crews began to set primary and secondary control throughout the project area with guidance and targeting plans from SSI. The primary control utilized three permanent monuments set at locations specified by USACE; the coordinates were collected by static GPS observations on multiple days. The secondary control consisted of 103 survey points spread throughout the approximate 120-acre work area. These control points were painted and labeled. The coordinates were collected horizontally using multiple RTK GPS locations; vertical values were established through digital leveling.

The final control point values were used by SSI’s surveyors to constrain the LiDAR data collected with SSI’s Riegl VMX-250 mobile mapper. The system incorporates Riegl’s latest in mobile LiDAR sensor technology generating 600,000 laser pulses per second while maintaining a relative accuracy of 8 mm and a precision of 5 mm. The control network is a vital step for mobile LiDAR systems to be able to achieve engineering design tolerances.

Data collection for the entire 120-acre urban area, containing approximately 4 miles of city streets, only took four hours from start to finish.

Following the collection of coordinate values throughout the control network, engineers from the USACE specified that all of the survey data was to be moved from the NGVD88 datum to Cairo Datum. The Cairo datum is more than 100 years old and unique to New Orleans. Since nearly the entire city of New Orleans is below sea level, this datum helps surveyors and engineers raise the elevation value of the coordinates nearly 22 feet. This translation brought all of the elevation values back to positive numbers. The actual average ground elevation for the work site was 5 feet below mean sea level.

Data collection for the entire 120-acre urban area, containing approximately 4 miles of city streets, only took four hours from start to finish. The four hours included install and uninstall times associated with operating a mobile mapping system. The project area consisted of several areas of interest that included streets, overpasses, multiple train tracks, train trestles, several drainage canals, and an extensive network of overhead utilities. To collect the data on all of these features using conventional survey methods would have taken several months. By using mobile LiDAR on this project, the field time needed to complete the entire data collection was done in a half day.

In addition to the obvious reasons why fast and efficient data collection is important, there often are unforeseen circumstances that validate the use of new technologies. While all of the above-ground information was collected using LiDAR, the subsurface information still had to be collected utilizing conventional practices. Just during the time that it took DS&A field crews to conduct these subsurface surveys, there were police activities that severely limited access to and from the 120-acre site. The ability for survey crews to complete the full data collection in less than one day without having to stop and go because of limited access had a very positive impact for everyone involved.

Once the data was collected and all of the initial processing completed, the LiDAR point clouds were registered, stitched together, and merged with the high-resolution images that are captured simultaneously by the mobile mapping system. The two firms divided the feature extraction processing. SSI was responsible for tracing all of the asphalt and concrete edges, fences, buildings, power poles, and the lowest elevations on overhead features. In addition, SSI also modeled the overpasses, train tracks, and train trestles, providing DS&A a “bare earth” point cloud gridded off to one point every 3 feet. Additional work was done with the LiDAR data set to generate and process a Bentley InRoads digital terrain model (DTM), reducing the LiDAR point cloud further to create a gridded surface with one point every 5 feet.

All of the underground utilities were located by DS&A field crews and this data was merged with the mapping produced from the LiDAR data collection. These field crews were responsible for tracing water lines, gas pipelines, locating valves, hydrants, manholes, inlets, etc. Every manhole that was located in the project area was opened and data was collected on all of the inverts. Using record drawings provided by the New Orleans Sewage and Water Board and the data that was collected by the field crews, technicians were able to properly model the underground data connecting sewer, gas, and drainage lines.

Conventional survey practices also were used to supplement the LiDAR data collection in some areas of the project. Technicians were able to model the concrete drainage canals by integrating both the conventional and LiDAR data. A surface DTM of the drainage canals was generated by technicians integrating the data from both survey methods.

The final deliverable was a 3D model in Bentley’s Microstation V8i.
It would have taken several field crews a minimum of three months to collect all of the necessary survey data using conventional methods.

Lastly, the final deliverable to USACE was a 3D Bentley Systems V8i Select Series 1 file. The files were set up per USACE MVD CADD standards using specified seed files, Units def file, and USACE A/E/C Defined Levels. The existing USACE levels were modified slightly to indicate the size of specific features.

The entire project from start to finish benefited from the use of mobile LiDAR. It would have taken several field crews a minimum of three months to collect all of the necessary survey data using conventional methods. In addition, extra time would still have been needed to process the deliverable files into the proper formats. However, because the project team elected to deploy a mobile LiDAR system, the entire project was completed and delivered in six weeks while achieving the tolerances set forth by the USACE. Safety for the field crews was maximized by minimizing the time that surveyors were needed in the field on the project site.

In addition, because of the higher resolution and density of the survey points collected by the mobile LiDAR system, compared with conventional surveys, the models created from the LiDAR data sets were more complete. With the substantial overall cost savings of the project, taxpayers also are able to benefit from the use of mobile LiDAR and other innovative technologies.

Brian Bailey is the Geospatial Services director for Surveying Solutions Inc., a provider of mobile LiDAR services. Prior to SSI, Bailey worked for a LiDAR manufacturing company as the U.S. sales manager for the company’s mobile mapping solutions. He can be contacted at bbailey@ssi-mi.com.

X