Unloading technology development
The development of no-load technology begin from NASA in the 1970s and 1980s. with the Global Positioning System (GPS) and Inertial Navigation System(INS) become common, causing high-precision real-time positioning method can be achieved.
DEM or DSM and other terrain data collection used to be in two main ways : The most common way is to measure in the field, through the artificial sampling of the ground features of the mapping. Another way is to take aerial photogrammetry or satellite imagery telemetry technology. However, although the first method is more corrective, but still can not be used in large-scale ground mapping.
In recent years, due to active remote sensing detection technology has been quite mature, especially LiDAR with thigh-frequency laser light transmission speed scanning which can collect large position information in short time ,offering a wide range of high-precision high-resolution between DEM and DSM production system.
LiDAR Three - Dimensional Numerical Topographic Model (DTM) for the Songzoushan Area of Dayun Mountain Group from 2005 to.
(Source: Geology, Vol. 25, No. 3). (Measured by geological survey)
Taiwan no-load light course
Numerical terrain is the core of the national spatial information infrastructure, the United States and other advanced countries have the numerical terrain into the federal disaster relief mechanism. The Ministry of Economic Affairs of China's Central Geological Survey, under the special regulations on the reconstruction of Typhoon Typhoon in the Ministry of Economic Affairs, promoted the "Geographical Sensitive Area Investigation and Analysis Project for Land Conservation" to produce LiDAR high-resolution numerical terrain.
2002 Taiwan has introduced two models to test : Optech 2033 and Leica ALS40,which laser pulse repetition rate up to 38kHz; 2004 Taiwan by the private sector have introduced ALTM3070 and ALS50 , these two models began commercial operation, and the laser pulse repetition is up to the rate of 83kHz. Since 2005, Multi-pulse in Air and Full Wave laser scanning technology has matured, and four new systems have been introduced by the domestic civil company in 2009 after the Mora Morris Wind Project. With this new function, and the laser pulse repetition rate has been able to reach 200kHz, the maximum flight up to 4,500 meters, and are equipped with a medium format (medium format) of the aerial camera, can provide the integration of image fusion products (Liu Jinjin, Xu Weicheng, Geology, Vol. 31, No. 2).
Introduction of no - load technology
The broad definition of LiDAR (Light Detection And Ranging) refers to the technique of measuring the target with laser light, and what is now known as the use of laser light to carry out high-density scanning of the target. The three-dimensional topography of the target technology can now be divided into three categories: Airborne LiDAR, Bathymetric LiDAR and Terrestrial LiDAR, the fastest growing Is the aircraft to be as a carrier for the surface of the no-load technology.
Unloading mainly includes: POS, Position and Orientation System, Laser Scanner and SystemController , among them, the positioning orientation system is based on "Direct Georeferencing" technology. The integration of dynamic GPS positioning technology is to obtain the three-dimensional coordinates, and precision inertial attitude meter (IMU) Inertial Measurement Unit measured the three-axis deflection angle and Acceleration and other information, which directly in the flight process to provide 200Hz frequency precision track positioning; and laser scanning device is up to 60,000 ~ 150,000Hz per second frequency, recording the pulse of the laser launch angle and the time difference between the received and echo . That can converted to the measured distance and the intensity of the reflection; the controller can not only be the operator of the man-machine interface, recording the two devices of the time stamp (time stamp) but also can accurately link positioning and laser measurement information The (Xu Weicheng 2007) Idle light of the operating principle as shown below:
Unloading Each pulse of the emitted laser can be echoed, and each message is recorded as a separate three-dimensional coordinate point on the scanner, so the structure of the forest can be obtained. In addition to the coordinates of the ground, you can get accurate terrain.
The original data generated by Light Detection And Ranging (LiDAR) is called point cloud, which contains three-dimensional spatial coordinates , reflection intensity (E, N, h, I), and multi-return (Multi-return) ) Information. The amount of information is very large. The company has advanced optical data processing technology, including Leica ALS, Riegl, Optech ALTM and other no-load light laser scanner produced by the data, can be classified cloud classification and output DEM, DSM and other numerical terrain model.
LiDAR point cloud data of Shenlan Mountain
Comparison of Light Achievements and Aerial Images