| As a proactive detection technology, Light Detection and Ranging, also known asAirborne Lidar, is more popular in recent years in the three-dimensional data acquisition.Compared to regular measuring methods, the aerial photogrammetry technology andmicrowave radar, Airborne Lidar systems are faster in speed, higher precision in largeamounts of data acquising. Therefore, Light Detection and Ranging technology has arousedwidespread concern. But the situation of domestic technical researches and developmentpresent is relatively backward. The domestic market mainly relys on the applications ofimporting commercial system products from the overseas.According to various researches, this paper made a lot of work on the feasibility of thedomestic production of Airborne Lidar systems as well as the technical difficulties in programdesigning, and proposed a preliminary design scheme finally.Based on the market investigation and study, it is found that the accuracy of the domesticIMU/DGPS positioning and navigation system products does not meet the needs of therequirements of Airborne Lidar systems. Therefore, the design philosophy of this paper is todesign an airborne laser scanner——the main sensor of the system independently and topurchase a set of POS products, which can provide the flying platform the positioncoordinates and posture information, to integrate a set of radar system at last. The design ofthe airborne laser scanner is the core content of this study.The designed system is placed on the low-altitude remote sensing platform, relativeflying height:300to1000m approximately, no more than1500m in principle, to cruise at thespeed of160to220km/h. The scan bandwidth is300to800m. Using Navigator1064-5, oneof the NavigatorTMseries laser products as the system light source, which is manufactured byUnited States Spectra-Physics (Newport Corporation) company. The laser scanner may sendout20000to50000bunches of lasers each second, with the wave length of1064nm. The laser beam divergence angle is0.55mrad after the collimation of the scattering beam mirror. Thecube mirror scanning mode is applied. The maximum scanning angle is±30°and field ofview angle30°to60°adjustable.45to60scan lines are received per second, which can besaid to be the scanning frequency45to60Hz. The interval between the two adjacent scans isless than1m. Two detectors are introduced, one PIN detector works as the primary wavedetector, and the other APD works for echo detecting. The time interval between the primarywave and the echo is measured by the FPGA digital logic circuits. At the same time FPGAalso can gain the information from anther sensors, such as the rotational speed of the electricalmachinery, the echo-strength, monitors information, and so on. FPGA transmits theinformation to the ARM embedded system through an interface. ARM is the main controllerof the scanner, who is allowed to access control directives through a keyboard or hostcomputers. FPGA is responsible to carry out these specific measurement operations.The paper also combines distances, angles, coordinates and attitude obtained by variouscomponents in the system for a model to locate laser points cloud according to thepolar-coordinate method. Moreover, the theory precision of the designed system is derivedand each kind of factors who influence precision is analyzed.At the end of the paper, the problems found in system designing are summarized. Andseveral reasons for the lag of the domestic products research and development have beenanalyzed. It is certern that mature products homemade under this technology will appear inthe near future. |
PDF Full Text Request