Eliminate Calibration Flights For LIDAR Surveys

21 March 2008, 5:37pm

TopoSys has virtually eliminated the need for calibration flights or “Boresighting” for aerial LIDAR surveys with their line of LiDAR sensors which are highly stable, completely integrated, turn-key systems of IMU, GPS, LIDAR sensor and digital imaging systems.

"Calibration" and "boresighting" are two terms for the process to determine the offsets between the IMU coordinate axes and the Lidar coordinate axes. This is accomplished with a "patch test" flight over a suitable area in a clover-leaf, or figure eight, pattern (N-S, W-E and reverse). Most aerial LIDAR manufacturers recommend collecting "3D objects" on the terrain that are easily identifiable in the Lidar imagery, such as industrial buildings with flat roof tops or gabled roofs are even better. The results from this small patch flight are the roll, pitch and heading offsets between the IMU and the laser.

This relationship between the laser and IMU should not change unless the system is disassembled. However, the Lidar coordinate system changes significantly on systems based on an oscillating mirror to deflect the laser beam thus requiring frequent patch tests (boresights). The LIDAR technology based on an oscillating mirror that flips from side to side deflecting the laser pulse onto the ground needs to mechanically accelerate the mirror from side-to-side. This mechanical process of flipping the mirror from side to side, requires the mirror to start, speed up, then slow to a complete stop before reversing, speeding up and stopping again hundreds of times per second. This leads to mechanical wear-out causing the alignment with the IMU to drift and requiring a “boresight” before every mission.

A further consequence of the accelerating /decelerating mirror is that it paints the ground with a varying point density: More points are concentrated on the swath-ends than in the center where they are more useful for aerial LIDAR surveys.

Engineered in Biberach, Germany, the TopoSys line of Aerial LIDAR/Imaging Systems require a “boresight” before delivery of every system and then once a year for regularly scheduled maintenance. These are totally integrated, turn-key systems which include:

• Space-frame construction resulting in the most stable, durable and dependable LIDAR/Imaging system integrated with GPS, IMU, data storage, flight planning, LIDAR and RGB/CIR camera

• No Mechanical wear-out means no costly and time-consuming calibration flights or “Boresighting.”

• LIDAR Sensors:

• Falcon III: State-of-the-art, fibre optic LIDAR sensor does not require an oscillating mirror to deflect laser beam;

• Harrier 56 and Harrier 24: These systems use the Riegl Laser Scanner – the most reliable LIDAR sensors which use a polygon, continuous rotating mirror to deflect the beam which does not have mechanical wear-out.

• RGB/CIR Camera: Provides the ability to collect high-resolution, multispectral imagery and high-density, precise LIDAR datasets simultaneously.

• TopPIT, the pre-and-post processing software that streamlines the entire workflow from pre-flight planning to final deliverables.

The TopoSys line of sensors: Falcon III, Harrier 56/G3 and Harrier 24, are ideally suited for LIDAR applications ranging from precise, wide-area topographic mapping to high-density corridor mapping.

The Falcon III utilizes a unique, technologically advanced fibre-optic linear array LiDAR sensor with an effective measurement rate of 125kHz and an integrated four-channel (R, G, B, NIR) optical line scanner that can simultaneously acquire high-resolution, multi-spectral imagery plus elevation data. The fibre-based system of the Falcon III follows electronic distance measurement (EDM) guidelines resulting in the highest data quality, quick and sensitive echo detection, and outstanding production efficiency.

Harrier 56/G4 represents the leading edge in LiDAR scanning and digital image acquisition. Factors such as full waveform echo digitization and a Riegl LMSQ560 200kHz pulse-rate laser scanner are combined with a calibrated 39-megapixel camera to make this sensor the perfect tool for a variety of applications such as corridor, forestry, natural resource, flood and topographic mapping—as well as engineering site development. The full waveform digitization feature of the Harrier 56/G3 enables the user to extract the most comprehensive vertical information from the echo signal.

Harrier 24 is an optimized, entry-level system for helicopter-based mapping, combining a calibrated 39-megapixel camera with a low-cost 10kHz laser. The Harrier 24 is ready to use, allowing organizations to easily add LiDAR scanning to their existing business model, with the dual benefit of providing digital imaging as well as LiDAR for aerial surveys and remote sensing.

All three sensor systems are complemented by TopPIT, the LiDAR pre-and-post processing software that streamlines the entire workflow from pre-flight planning to final deliverables. The traditional deliverables include: Lidar data point clouds; Digital surface model (DSM); Digital terrain model (DTM); Intensity data: and, Image data RGB and NIR (true-ortho images).

About TopoSys
TopoSys Topographische Systemdaten GmbH was founded in 1995 as a spin-off of Dornier GmbH, one of the world’s leading air- and spacecraft manufacturers. Building on its long-standing expertise in the development and production of fibre-optic LiDAR scanners, TopoSys is committed to the manufacturing and worldwide marketing of turnkey LiDAR sensor systems, allowing its customers to deliver all LiDAR applications from precise, wide-area topographic mapping to high-density corridor mapping. In February 2007, TopoSys North America, Inc. was established as a wholly-owned subsidiary with North American headquarters in Denver, Colo.

For further information, please contact:
Roland Mangold
Director of Business Development
TopoSys North America Inc.
4600 South Ulster Street
Denver, CO 80237 USA
Toll-free: (888) 438-1208
Mobile: +1 (720) 934-2482
Fax: +1 (303) 740-6789

Article Source: LiDARcomm News (online)

http://www.lidarcomm.com/id25.html

Roland Mangold

Director of Business Development, TopoSys N.A.