By: Tim Stagg, Vice President
Both Helicopter and Mobile LiDAR systems have a niche that they fulfill in high accuracy mapping. However, the biggest advantage to the Atlantic’s Low Level Mapping System or (LLMS) is its high accuracy capabilities coupled with platform cost savings. From my experience managing the transportation sector programs for one of the largest geospatial firms today, I understand that Survey and Design Firms are reaching for the highest accuracy possible from their mapping efforts. Yet the issue with mobile and helicopter LiDAR remains the same – they both have a very high operational cost, making the highest degree of accuracy possible, just out of reach from a budget standpoint. The second largest factor in firm reluctance to pay for this survey technology is that the sensor data is only as good as the base survey ground control. In order to achieve .05’ vertically from a helicopter or even .03’ from a mobile system, the amount of survey control required and the requirement for digital leveling makes this technology in all but the most demanding projects cost prohibitive.
Having had the opportunity to use all of these technologies, I have longed for the middle ground in which I could offer my clients a high degree of accuracy, (0.1’) and a large area collection from a vertical or nadir point of view, the best vantage point for elevation data, and deliver all of this at a price that they could afford — enter LLMS. The system offers all of the above and has exceeded my expectations.
LLMS collects data from a nadir view, which is more likely to reach the ground through dense vegetation. It can also provide much denser point spacing than normal higher altitude fixed-wing systems. This platform also shines with regard to swath width. LLMS, with normal GPS control, can provide 0.1’ vertically for up to an 800’ swath with a single pass. This would not be possible with a mobile system. If all of these advantages weren’t enough, perhaps the biggest advantage is the ability to map behind structures: like buildings, into ditches, even swales and deep vegetation. All of this at an operational cost one quarter that of mobile or helicopter systems.
Atlantic’s Low Level Corridor Mapping System (LLCMS)
Atlantic provides high-accuracy mapping services to meet specialized requirements for detailed corridor engineering analysis and design. Our STOL Cessna 210 and P68 Aircraft our equipped with Atlantic’s proprietary Low Level Corridor Mapping System or (LLMS). The LLMS was designed for low-altitude mapping where extreme accuracy is required for engineering design along with high-resolution digital photography for orthophotography and photogrammetric production. The system can obtain vertical accuracies as precise as 2 inches and is ideal for mapping projects such as highway corridors, transmission lines, and development sites. The LLMS includes a high-frequency ALS70-HP LiDAR sensor, high-resolution Leica RCD105, metric digital camera, dual frequency GPS and Applanix Inertial Measurement Unit (IMU).
Leica ALS70-HP LiDAR Sensor
Atlantic is one of only three (3) firms in North America that own and operate at least two (2) Leica ALS70-HP LiDAR systems. The ALS70-HP is a compact laser-based system designed for the acquisition of high-density topographic and return signal intensity data from a variety of airborne platforms, at flying heights up to 3500 m AGL. During our evaluation of sensors manufactured by Leica, Optech and Riegl, Atlantic conducted numerous tests for data accuracy, quality and efficiency of collection. Like many other large remote sensing companies, we ultimately determined that the Leica ALS70-HP offered the highest degree of flexibility, repeatability, and efficiency among the sensors evaluated.
Leica RCD105 Medium Format Imaging Sensor
The Leica RCD 105 camera offers high dynamic range and detailed image quality. It facilitates bi-directional communication with the flight management system (FMS) and an onboard computer, sending and receiving signals to trigger the camera and indicate the status of the capture sequence. Images are captured as fast as one per 1.25 seconds and are processed utilizing SimActive software suite and other Atlantic tools which perform file corrections on raw images to further enhance their quality.
Final Thoughts
All three technologies, LLMS, Helicopter, and Mobile systems are powerful tools and each has their role. The important thing is to realize where to best utilize their capabilities and choose the option that meets the needs of the specific project. However, in a world where accuracy and cost matter, I’m excited to have the LLMS system in the toolbox.