.: Overview

LiDAR (Light Detection and Ranging) is a laser mapping technique for measuring distance.

LiDAR systems can be Terrestrial or Airborne. Terrestrial LiDAR systems are either stationery or land-vehicle mounted and used for small area or building surveys. Airborne LiDAR systems are mounted on helicopters or fixed wings aircraft and survey for large areas. LiDAR system consists of a laser ranging and scanning unit together with a Position and Orientation System (POS), which includes integrated Differential Global Positional System (DGPS) and an Inertial Measurement Unit (IMU). The laser unit measures the distance while onboard GPS/IMU components give the position and orientation of the platform.

Airborne LiDAR systems satisfy the needs of several mapping applications and made it as a preferred technology compared to any others. The advantages include:

• Higher accuracy than satellite imagery and other remote sensing techniques

• Ability to capture data much faster and more cost effectively than conventional survey methods for medium to large areas

• Ability to accurately measure ground elevations underneath dense forest canopy without interpolation

• No ground intrusion so no environmental or social impact

• Robust against human error, which can be rife in conventional survey

GDS and our partners have been building LiDAR systems since the 1980s and our latest LiDAR systems are called DVG-HELIX.

The DVG-Helix is a unique modular Airborne LiDAR system, which can be fitted with a variety of digital frame or video cameras, scanning lasers together with DGPS and POS. It also allows for mounting to several different types of aircraft, fixed wing or helicopter. Thus, the DVG-Helix is fully adaptable to local conditions and clients’ requirement. DVG-Helix is a proprietary system from GDS and its partners only.

.: Airborne Laser Scanner

GDS uses Riegl LMS-Q560 digital waveform scanners with high infrared laser pulse repetition rates up to 240 kHz. They meet the most challenging requirements in airborne laser scanning as they provide full waveform analysis for unlimited numbers of target echoes.

Waveform laser scanner provides continuous pulse return without apparent dead time. The waveform is analyzed with respect to echo and amplitude where all returns are digitized, producing the highest density of points, including ground points.

 Conventional LiDAR scanners are inferior because they have an inherent sensor dead time of 8nsec (equivalent to 1.2m distance in height), which leads to non-measurement of elevation points. In particular, ground returns will be missed in densely vegetated areas such as long grass and low shrub areas. In contrast, waveform laser scanners do not have any sensor dead time and much more detailed data of targets could be captured. In the case of forest application for instance, detailed canopy structure could be captured thus facilitating tree characterization and classification.

 GDS’s waveform LiDAR systems also allow for return waveform to be analyzed, giving insight into the slope, surface roughness and composition at each point measured.

.: Inertial Measurement Unit (IMU)

Inertial Measurement Unit, or IMU, is an electronic device that measures sensor orientation in roll, pitch and heading/yaw. GDS uses three types of IMUs such as iMAR 1, iMAR 2 and DMARS-1. These values are used in calculation, together with the DGPS positional information and the laser altimetry data to produce the X, Y, Z values of the points.

.: Camera

GDS’s DVG-HELIX survey system uses Canon EOS 1D Mark III high resolution digital camera which captures images at average of 11cm pixel resolution and resample the final orthorectified images at 13cm pixel resolution. The camera imagery system designed uniquely where each of the frames contains the time coordinated with the GPS references time stamps. It acquires the imagery at 600m above ground level or lower and produces better quality high resolution imagery because there is not much cloud, smoke and haze at that level.

Canon EOS 1 D Mark III Camera