Protecting people and property with bathymetric LiDAR

Author:Renata BarradasGutiérrez

Japan is a large archipelago situated along an active convergent zone next to deep trenches on the Pacific side and many faults and canyons in the Japan sea. Due to its geography and complex topography, Japan is one of the most exposed countries on Earth to natural hazards, such as sea-level rise, flooding, earthquakes and tsunamis. Population growth, climate change and economic development, furthermore, are threatening people, infrastructure and the ecosystems located at the plains of several rivers and coasts.

Despite its great exposure to hazards, ranked by the 2016 World Risk Report as the 17^Thmost prone disaster risk country, Japan has lowered its vulnerability by adapting long-term preparedness strategies and taking actions to understand its topography and environment.

Aero Asahi Corp’s (AAC) mission is to protect life and property from any disaster or incident by using the latest hardware and software technologies. This aviation and spatial information services company is aware that data is required to mitigate the risks in the event of future disasters. To support disaster management and prevention, maintain infrastructure and map properties, AAC uses mobile mapping, aerial photo surveys, and LiDAR topographic and bathymetric surveys.

On a mission

日本直接由政府管理的河流的总长度约为8,800公里，其特征是陡峭的森林深处的V形冲洗。土地，基础设施，运输和旅游部（MLIT）管理并监视Nippon国家的河流。为了监测每200米的螺距每五年的MLIT监测河床变形，一次回声响应器每五年在主要河流上进行横断面地形调查。至prevent disasters and speed up any recovery efforts, AAC now provides bathymetric and topographic data and maps到MLIT的河流管理局。

AAC collects data precisely and safely using the Leica Chiroptera II bathymetric and topographic LiDAR sensor mounted in a helicopter, covering large areas in just minutes. The Chiroptera II’s near-infrared (NIR) wavelength for topographic and a green wavelength for bathymetric data collection allows the team to map and measure depth in shallow coastal zones and inland freshwater bodies, such as rivers and lakes and surrounding flood-plains.

“我们收集和分析所有公关的精确的数据ovide information ready to use, such as deformation, sediment, cross sections, erosions, and bank height for management authorities. Since the Chiroptera II combines a topographic and bathymetric lidar, we can seamlessly measure from water to land – this is particularly useful when rivers are running浅的，”said Hiroshi Isobe, deputy chief of airborne operations at AAC.

AAC通过用内部解决方案（一个回声声音“水下检查员”）补充了用Chiroptera II捕获的数据来改进过去使用的方法。该小组对日本政府控制的河流进行了测试。这项合并的调查帮助团队创建了一个无缝致密点云，无论河水的深度，浊度，颜色，温度和pH值如何。

将激光雷达传感器连接到直升机的特权

山脉覆盖了升起阳光的土地的73％。在山区进行空中调查时，AAC附加The Chiroptera II to the back of an AS350-B3 helicopter with a GNSS antenna on the top of the vertical stabiliser to obtain a georeferenced point cloud with higher density。AAC坚信可变的空速，灵活的基座位置，较短的转弯时间和可以用直升机飞行的非常低的高空比具有固定机翼平面提供的远距离飞行时间和延长的飞行时间比较安静的飞行更可取。

“在较慢的空速中获得的点云很密集。与直升机一起飞行，我们可以收集带有回声声音的船长船无法进入和控制日本陡峭地形的海拔高度的水深，”said Isobe.

Multiple applications

多种可交付成果，例如数字表面和terrain models, classified point clouds, orthophotos, and GIS layers可以使用Chiroptera II的收集数据来创建以开发水文模型分析水流，排水管理，洪水控制和支持土地规划活动。The team of experts uses Leica LiDAR Survey Studio (LSS) to understand the river’s topography and create accurate risks analysis.

The periodical cross-sectional survey AAC provides can be used for a wide variety of applications including:

• Flood mapping
• Environmental modelling and monitoring
• Visualise the riverbed deformation ground and underwater
• Deriving flow capacity
• Accuracy controls for water level applications.

Predicting the unpredictable

至protect populations living near water bodies authorities need to study the topography of a river and its surrounding area to monitor changes and predict the behaviour of a water body under different conditions. Airborne LiDAR bathymetry is an effective method to即使在危险区域和浑浊的水域进行调查，创建了沿海和内陆水体的准确而精确的模型。

“The detailed topographic data obtained from aerial laser surveys is used to simulate flooding and make hourly predictions of how floods spread. The simulation results and infrastructure information maps are analysed to provide optimum data for crisis management, such as evacuation routes, evacuation shelters and affected population. In addition, stereo matching of aerial photos during flooding is used to analyse surface flow rate and flow direction,”concluded Isobe.