Mapping underwater terrain with bathymetric LiDAR

Author:Reka Vasszi

用于航海目的的水深度可以追溯到古代文明。随着技术的发展，几个世纪以来，除了基于船舶的回声外，对水体的远程监控和映射越来越多，通过机载系统进行的激光雷达测深量调查，可以使用。

Bathymetric surveys allow professionals to measure water depth, map the underwater terrain, classify submerged vegetation and habitat as well as study marine ecology, water-quality, contaminant spills and hydrodynamics.

With the 4X bathymetric product line, Leica Geosystems introduced an innovative high-resolution technology for shallow water and coastal mapping and increased point density by a factor of four compared to previous airborne systems versions. TheLeica Chiroptera 4x, bathymetric and topographic LiDAR system, captures每秒140,000点and covers shallow water regions down to a25 metre depth。This efficient coastal survey LiDAR sensor, designed to offer more accurate data for environmental monitoring, research and surveying even in turbid water demonstrated its efficiency mapping Cape John peninsula in Canada and the Tonga islands in the Pacific.

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Improving shallow water detection

新斯科舍省社区学院的应用地理研究小组（AGRG）的研究科学家蒂姆·韦伯斯特（Tim Webster）是最早使用新的Chiroptera 4X调查加拿大约翰·半岛沿海地区的人之一。

使用传统的映射浅水和沿海地区itional aerial photography or boat-based echo sounder methods can be costly, time consuming and challenging due to water clarity and unforeseen weather conditions. To overcome these challenges and increase productivity and data accuracy, Webster decided to use the Chiroptera 4X bathymetric and topographic LiDAR in his geomatics research.

这purpose of the geomatics research was twofold. First, the team mapped the底栖栖息地海湾现有的水产养殖，包括贝类基础设施的地图和浮​​标，以估计正在生长多少生物质。

研究的第二个目标是develop a hydrodynamic modelto help the lease of new oyster farms and propose the appropriate locations around the bay without damaging the sensitiveZostera码头or so-called eelgrass. The eelgrass beds are important for sediment deposition and nursery grounds for many species of fish and shellfish, thus it is used as an ecosystem health indicator by Fisheries and Oceans Canada (DFO).

Webster has carried out similar research in the region of Maritime Canada in 2014 on how to optimise data collection and post-processing of shallow water topographic-bathymetric LiDAR survey using the Leica Chiroptera II. This time, the professor and his team had the chance to deploy the new Chiroptera 4X and compare the captured data with results from 2014. Toquantify the improvement of the point cloud density and target identification在新的Chiroptera 4X中，该团队比较了三种测量工具的捕获数据：

• Chiroptera II
• Chiroptera 4X
• Multibeam echo sounder.

This geomatics experiment involved the target surveying of four 1 cubic metre cubes at different water depths to determine the level of detail and data provided by the three different sensors.

Flying the Chiroptera 4X over the bay, the research team collected information on the surveying targets and compared the captured data of the terrain and seabed from 2014 with the data from this experiment carried out in 2018. Using the four cubes and other flat targets captured with the three different survey methods, researchers compared:

• 点云密度
• 正射马赛克
• Digital Elevation Model
• LiDAR amplitude.

使用从波形数据得出的离散点完成了捕获数据的分析Leica LiDAR Survey Studio用于点云生成和清洁原始LIDAR数据的后处理软件。

“这个特殊的实验是量化Chiroptera 4X的细节的准确性和水平，我们对结果感到非常满意，”报告了韦伯斯特。“The results show a significant increase in point density comparing to other equipment, improved target detail, detection limits, and potential for more direct benthic point classification.”

Taking advantage of the Chiroptera 4X’s near-infrared laser for topographic data collection combined with a green laser for bathymetric data collection, the research team precisely captured underwater features and generated virtual reality elevation models to study the benthic habitat. Additionally, researchers proposed sustainable locations for oyster farming without damaging the eelgrass habitat.

“ Chiroptera 4X的这种进步是在点密度方面显着突破and it improved the resolution of our coastal zone mapping,”年代aid Webster.“在目标检测很重要的任何应用中，我都会看到，脊髓翅目4X在水文和考古等行业中的好处增加。”

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安全可靠地通过太平洋水域

这Pacific is an extremely culturally diverse region, as exemplified by the more than 1,000 languages spoken and, yet, what connects them is the water. The ocean and coastal seas have long been integral to the Pacific way of life. The economy, transportation and culture of those sharing the Pacific waters is based on the naval and marine infrastructure and ecosystem this ocean provides. Even though marine navigation plays a key role in the archipelago, theSouth Pacific is inadequately charted。

浅水深度范围数据对于安全海洋航行以及港口，管道和沿海地区或浅离岸区域的任何其他基础设施的建设至关重要。如果没有有关水深的精确信息以及水下特征和潜艇峡谷的确切位置，则经济和可持续发展会受到负面影响。

iXBlue together with project partners Geomatics Data Solutions (now Woolpert, Inc.) and EOMAP Australia were requested to map the Tongan archipelago and surrounding areas to provide the 3D water depth information and improve the nautical chart of the region.

这project was part of the Pacific Regional Navigation Initiative (PRNI), an overarching programme geared towards the safe and reliable passage through the Pacific Ocean while protecting the environment and allowing Pacific island economies to develop. The project was sponsored by the New Zealand Ministry of Foreign Affairs and Trade (MFAT) in partnership with the Land Information New Zealand (LINZ).

这Kingdom of Tonga, a Polynesian archipelago comprising of169岛, stretches across approximately800公里在南太平洋。在汤加，农业，捕鱼和林业提供了大部分就业，因此，关于土地和浅水特征的详细数据可以支持该岛集团的可持续发展。

Considering the relatively large area in need of high-resolution survey and charting, LINZ required a smart solution to bring the most out of the tight budget. iXBlue, together with EOMAP Australia and Geomatics Data Solutions, applied amulti-sensor approach to collect topographic and bathymetric data， 包含：

• Satellite-Derived Bathymetry (SDB)
• Airborne Laser Bathymetry (ABL)
• Multibeam Echosounder (MBES)
• 潮汐量表安装和基准计算。

SDB surveys are very effective tools in mapping large areas to the visible water depth, however tocapture high-resolution data on land and underwater使用了r翅目4X ALB。

Chiroptera 4X安装在Cessna 441中，以获取汤加和尼埃的数据，包括贝弗里奇礁，覆盖了大约633-square-kilometre area。Geomatics Data Solutions experts collected both high-resolution bathymetric and topographic data on- and offshore and compared the results of the Chiroptera 4X to SDB.

“Having the extra density of the Chiroptera 4X, compared to the Chiroptera II, allows us to run spatial algorithms while reducing the risk that we are accidentally removing seabed objects from the dataset. In other words, it improves our target recognition probability,”年代aid Carol Lockhart of Geomatics Data Solutions.

除了海底的测深数据外，通过使用Chiroptera 4X获得的意外好处数据解决方案之一是改善了土地上密集的测深量激光数据的渗透率，即使在较密的植被上也提供了完全覆盖，在该植被上，TOPO激光器没有渗透。

“Local stakeholders will receive full imagery and the topo-bathy dataset, so they can also benefit from the high-resolution data provided with the new Chiroptera 4X, and can use the data for other purposes in addition to improving the nautical charts,”洛克哈特解释了。

这不同测量设备的结合方法provided the complete knowledge of allnavigational-significant features and additional topographic informationof the islands. Thanks to the 4X technology of the newly-released Chiroptera,experts surveyed at four times the sounding density than it was previously possible。