The History

The facility experienced two rockslide events on the banks of a medium sized dam. The dam is part of critical infrastructure for the regions utility provider and a specialist geotechnical engineering team was contacted to evaluate stability, safety, and make recommendations for bank reinforcement approaches. The engineering team obtained conventional manned fixed wing aerial LIDAR data early in their evaluation. An aerial approach was necessary because of the steep and heavily wooded terrain surrounding the facility.

The Problem

The conventional aerial LIDAR scan was delivered and was quickly found to be completely unsuitable for the evaluation needed. With the time sensitive nature of this project our client needed better data in a hurry, and having already paid for unusable data, cost control was also high priority.

The conventional aerial LIDAR collection was scanned from a few thousand feet above the site. This altitude resulted in lower density and shadowing leading to poor coverage of the most important areas.

The Solution

Using a LIDAR scanning system capable of scan coverage in excess of 270° around the UAV we were able to fly from ground level below the dam and rock slides all the way up to 500ft above the highest point of the area of interest. As a result there is almost no shadowing of the data in the area of interest. In addition the UAV platform was flown in a slow pattern for less than 12 minutes resulting in a point density in excess of 320 points per square meter. This is five to ten times greater than the density achieved from most manned aerial LIDAR flights. As an added benefit the UAV system also includes a high resolution digital camera system, which can be combined with the LIDAR results for accurate color reproduction of the scan data, orthorectified aerial photos, and visual inspection.

The Process

1. Prior to arriving for the scan, Fight Evolved worked with the engineering survey team to place ground control points throughout the area of interest for accuracy confirmation.
2. Flight Evolved coordinated with the local authorities to ensure adequate crowd control for safety in this popular tourist stop.
3. On arriving for the flight an RTK base station was placed over one of the previously placed ground control points.
4. Flight operations were conducted without incident and only a single flight was necessary to capture all the needed data with flight time around 12 minutes. The LIDAR technician used a live processing program to visualize the scan results in real-time while the UAV was in flight to ensure coverage and point density was sufficient to meet the client’s specification.
5. RTK and inertial corrections were applied to the data on the scene after the flight to ensure an accurate trajectory had been recorded, and variables like wind motion or turbulence didn’t adversely impact the data.
6. Back at the office, the precise trajectory was combined with the raw scanning data. The resulting point cloud was classified to meet client specifications.
7. The associated photographs were then orthorectified using the LIDAR data.
8. The final data was evaluated for global accuracy and delivered with a detailed accuracy report.

The Results

• Point Density: 326.1 points per square meter
• RMS Global Accuracy: 5.7 centimeters
• Relative Accuracy: 1.5 centimeters