AIRBORNE LIDAR SURVEY
1.AIRBORNE LASER SCANNER
GDS has five Riegl digital waveform scanners, which have infrared laser pulse repetition rates that go up to 400 kHz, capable of meeting the most challenging requirements in airborne laser scanning as they provide full waveform analysis for an unlimited number of target echoes. Waveform LiDAR, as acquired from waveform scanners, provide a continuous pulse return without an apparent dead time. The waveform is then analyzed with respect to echo and amplitude when all returns are digitalized, producing the optimum density of points. Conventional LiDAR scanners are inferior as there is a sensor dead time of 8 nanoseconds, which is the equivalent of 1.2m distance in height, leading to the non-measurement of elevation points.
2. INERTIAL MEASUREMENT UNIT (IMU)
An Inertial Measurement Unit, or IMU, measures the orientation of the sensors, in roll, pitch and heading/yaw. GDS uses three types of IMUs: the iMAR iNAV-FMS-E, iMAR iDIS and DMARS. These values are used in the calculations together with the DGPS positional information and the laser altimetry data to produce the XYZ values of the points.
3.GLOBAL POSITIONING SYSTEM (GPS)
GDS uses a Differential Global Positioning System (DGPS) with NovAtel’s DL-4 data logger, which is a high performance GPS receiver with fast data update rates. The GPS antenna receiver is mounted in the aircraft’s tail, away from aircraft’s rotor and other obstructions which can prevent GPS signal interruptions, resulting in consistency in the data’s accuracy.
Phase One iXR-180 (80 Megapixel Metric camera)
4. HIGH RESOLUTION CAMERA
GDS’s MATRIX survey system uses either the Phase One iXA-R 180 (an 80MP Metric Camera) or one of five Canon EOS 5D Mark III (21MP) digital cameras. The camera imagery system is uniquely designed where each of the frames contains the time coordinated with the GPS reference time stamps. The acquired imagery produces better quality high resolution imagery as there is less cloud, smoke and haze at lower flying heights.