Protecting people and property with bathymetric LiDAR

Author:Renata BarradasGutiérrez

日本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米的螺距每五年使用的MLIT，每五年在主要河流上进行横截面地形调查。到prevent disasters and speed up any recovery efforts, AAC now provides bathymetric and topographic data and mapsto MLIT’s river management bureau.

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.

“We collect and analyse all the precise data to provide 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 runningshallow,”AAC空降行动副局长Hiroshi Isobe说。

AAC improved the approach used in the past by complementing the data captured with Chiroptera II with an in-house solution – an echo sounder “Underwater Inspector.” The team tested this approach on the government-controlled rivers in Japan. This combined survey helped the team to create aseamless dense point cloud regardless of the water depth, turbidity, colour, temperature and PH of the river。

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。

“Point clouds obtained in slower airspeed are denser. Flying with a helicopter allows us to collect water depth where a swath boat with an echo sounder cannot enter and control the altitude along the Japanese steep terrains,”Isobe说。

Multiple applications

多种可交付成果，例如数字表面和terrain models, classified point clouds, orthophotos, and GIS layerscan be created using Chiroptera II’s collected data to develop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
• 可视化河床变形地面和水下
• Deriving flow capacity
• Accuracy controls for water level applications.

Predicting the unpredictable

为了保护生活在水体附近的人群，需要研究河流及其周围地区的地形，以监测变化并预测在不同条件下水体的行为。空气传播的激光雷达测深是一种有效的方法survey even in hazardous areas and turbid waters, creating accurate and precise models of coastal and inland water bodies。

“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.