Fearless of high drop terrain, Hi-Cloud Airborne LiDAR will take you terrain-flollow flying

Introduction: To assist the construction of high-speed railway along the Yangtze River, Hi-Cloud airborne LiDAR is applied in terrain survey of high altitude mountainous areas

I. Project Background

In 2018, the Yangtze River Office of the People's Republic of China issued the Implementation Plan for Promoting the Construction of High-speed Railway Passageways along the Yangtze River Economic Belt. High-speed railways along the Yangtze River connect the Yangtze River Delta, the middle reaches of the Yangtze River and Chengdu-Chongqing city agglomerations, making them an important part of the eight vertical and eight horizontal main passageways of the national high-speed railway network.

II. Project Overview

Topographic survey is required for this project. The lowest altitude of the survey area is 300m and the highest altitude is 2000m. There are many scattered points in the survey area, but the survey area is distributed in the section with large drop, and the maximum height difference of the independent survey area is about 600m.

The project requires to obtain the ground points under the vegetation. The cloud density of the ground points under the vegetation is greater than 2 points / ㎡, and the elevation accuracy is better than 10cm.

III. Project Difficulties

The whole survey area is covered with mountains, deep valleys, steep terrain, high altitude and large elevation difference. Manual survey alone is not only difficult, long construction period, low efficiency, but also high risk.

IV. Solution

Since the maximum height difference in the survey area of the project is 600m and the vegetation is dense, if the route is planned according to the conventional operation mode, and the UAV is as high as 700m from the lowest point of the survey area, it will inevitably lead to too few laser penetrations through the vegetation and too few ground points.

In this project, we use the Long120 six rotor UAV, equipped with the ARS1000L laser measurement system, to reduce the distance between the UAV LiDAR system and the ground by means of terrain-follow flight, so as to ensure that the laser can penetrate the dense forest and obtain data that meet the accuracy requirements.

ARS1000L Laser Measurement System

System Advantages

1) Long measurement range, maximum 1350m;

2) Long endurance, the operation teime of UAV with load could reach 50mins;

3) Terrain-follow flight, especially suitable for long altitude and large drop terrain.

Technical specifications:

V. Technical Proposal

Pre-plan the route, select the route to enter the survey area, plan to select the takeoff and landing points, and select the high altitude position.

Height safety inspection: whether there are high towers, electric towers and other buildings within the survey area is investigated on site. Under the condition of ensuring safe flight, terrain-follow flight operation is carried out.

VI. Achievement

1) Accuracy verification

i. Compare the laser points with the verification points in the corresponding area, and count the height difference accuracy. The average elevation error is -0.021m, and the mean square error is 0.025m, both less than 10cm, meeting the requirements.

ii. The standard deviation of plane accuracy is 0.0896m, meeting the requirements.

2) Point density calculation

Before the classification of this project, the average point density is 40 points /m². After the classification, the average ground point cloud is 6 points/m² in lush vegetation coverage area and 15 points/m² in non-lush vegetation coverage area.

VII. Project Summary

According to the terrain characteristics of high altitude and high drop in the survey area, Long120 six rotor UAV equipped with ARS1000L LiDAR is used in this project for terrain-follow flight. Without dividing the survey area, the number of takeoff and landing sorties is reduced, the impact of height difference on data accuracy is reduced, and the field work is more efficient.