The Karakoram Highway (KKH), whose north end is located at Kashgar, China and south end was situated at Thakot, Pakistan is aliased as China-Pakistan friendship highway or Pamir Highway. It is regarded as the arterial road connecting north part of Pakistan, the capital city Islamabad (ISB) as well as coastal areas in the south part of the country. At the meantime, KKH is the unique land access from China to Pakistan, the port city Karachi in the south, the South Asian sub-continent as well as the Middle East, which contributes to its high significance in strategic and military aspects. The overall length of KKH is 1,032 km with 416 km located within Chinese territory and 616 km situated within Pakistan. The location makes KKH a cross-borders road with the highest latitude in the world, entitling it the highest and most beautiful highway and one of the ten tough highways around the world, as well as the world’s eighth wonder due to its extremely difficult construction.
The construction of KKH started at 1960’s, completed in 1979, and officially opened to the public in May of 1986. KKH crosses collision zone of the Indian and Eurasian plate, where there are tough topography and complex geology condition. Geologic hazards including snow slide, landslide, rock fall, collapses, snow cover, ice deposit and earthquake happen regularly, which destructed road surface and bridge facilities along the highway. As the consequence, there were traffic interruptions regularly. In July of 2010, KKH was significantly destroyed by the flood in Pakistan. The Chinese government implemented “Pakistan national road network N35 and N55 (North Section) repair project”, and the repairing of N35 focused on the middle part of KKH - the THAKOT-RAIKOT section. In spite of sections which need to be repaired, there was 136.4 km of road in the middle of N35 remained not reconstructed, and its condition became worsening year by year. In addition, the rate of hazards including collapse, landslide, debris flow and rock fall was worryingly high which led to frequent traffic interruption.
“Surveying is the first task of the construction”. In order to speed up the progress of the project, ensure the completion of surveying and drawing of 1:2000 strip tropospheric map at the beginning, and overcome difficulties such as steep mountain, tough environment and less efficiency of manual operation at the survey areas, AS100 airborne laser scanning system produced by CHC Navigation was introduced into the project, and the equipment successfully completed the acquiring of data along the highway and generated relevant results at a high speed.
Geographical Location of The Surveying Area
The survey area was located at east longitude 73°13′ to 74°05′, north latitude 35°13′ to 35°31′. The following figure expresses the geographical location of the survey area:
The majority part of the survey area was situated in a mountainous region where there were complex terrains with giant fluctuation in elevation. There was a serious problem on the reconstructing of a section around 10 km, and the traffic interruption within the area caused a lot of inconvenience to the survey group.
Given the situation, the whole data acquiring task using UAV was operated manually. The operating worker used remote controlling to guide UAV operating along the highway. Meanwhile, other workers assisted in monitoring the ground station and transported real-time information about the UAV to the operating worker. For survey area where the road was passable, operating worker did the control work inside the vehicle, otherwise, the job was done by walking.
CHC AS100 airborne laser scanning system is launched by CHC Navigation which is based on light UAV. The UAV platform for AS100 is CHC P560 which is a six-rotor UAV.
AS100 is an all-in-one device with Velodyne VLP-16 laser scanner, positioning & orientation (GNSS&IMU) system, synchronous control unit as well as CCD camera. These made AS100 able to efficiently acquire real-time 3D spatial information about terrain surface as well as its images. Therefore, the features of AS100 include high accuracy, high density, high efficiency and a wide range of products. As a new method of 3D data acquiring, AS100 could be used in city surveys and digital city construction, terrain mapping, power line, road and channel reconnaissance and design mission, highway and railway monitoring and constructing management.
Preprocessing includes POS calculating, laser processing and coordinate transforming. The POS calculating produces PosT file which can output carrier's location and attitude information. The laser processing step decodes raw data and operates coordinate transforming, and as a consequence, LAS point cloud in WGS-84 coordinate system is produced. Coordinate transforming is based on requirements from User, and this step transforms point cloud result into an independent coordinate system of the project.
● Point Cloud Post-processing
Point cloud post-processing includes vacuation of laser point cloud, excluding of noisy point as well as filtering and classification. After elaborate classification of the laser data, precise ground points without vegetation point, noisy point and construction point will be produced, and then, elevation points remain terrain features can be extracted.
● Topographic Mapping
This process includes the generation of elevation point and contour line, as well as the drawing of surface features. Contour lines are generated based on ground points. Then, after modification, DEM products with high accuracy can be generated. After that, input point cloud into CAD software and draw relevant surface objects depend on the environment of the survey area. And at the end of the procession, we can get the 1:2000 strip tropospheric map as the final result.
Airborne LIDAR technique, as an advanced integration measurement technique, has overwhelming advantages over traditional aero-photogrammetry on data acquisition. And it is regarded as an attractive technique especially in the field of 3D geospatial information acquisition.
In this project, the efficiency of data acquisition of KKH highway was dramatically improved by AS100 airborne LIDAR system. This equipment helped operators conquer the elevation fluctuations, tough environment and danger for manual surveying. Using self-developed point cloud post-processing software, which includes point cloud transformation, noisy point vacuation, filtering and classification can be successfully achieved without influencing the speed of operation and acquiring conditionally amount of point cloud within a short time. The success of this project proved that it is an efficient method with high accuracy to do 1:2000 tropospheric mapping using airborne LIDAR scanning system. With the popularity of LIDAR technique, geomatics work will become more and more efficient.