Inspecting dams for sustainable hydropower

Author: Anne Pitkaenen

当您接近Lai da Nalps时，瑞士的Tujetsch，Grisons市政当局的水库时，高度为127米的大坝结构，宽度为480米，宽度已经从远处雄伟地打开。大型拱形大坝是为海拔近2,000 m的水力发电生产而设计的。水电被认为是当今瑞士电力供应高安全性的骨干。

Lai Da Nalps is located close to the Gotthard tunnel, this and other dams nearby are monitored automatically for acute movements and changes. In addition to the detailed monitoring, an inspection of the dam construction is done visually to document the condition for long-term understanding of the dam’s health.

大坝由瑞士水力发电的最大电力生产商Axpo Group运营。该公司还负责使用道路，桥梁，水坝湖，发电厂和大坝的周围地区的检查和开发。

The concrete construction of the dam is designed to withstand extreme loads, which only occur every 10’000 years. This will ensure it won’t risk the lives and livelihood of the people in the valley. However strongly built, the behaviour of the dam and its surroundings and the state of the construction is intensively observed by Axpo personnel.

AXPO拥有一个由测量师组成的内部团队，其中三名培训用于使用Leica Aibot进行测量任务。AXPO的工程测量师Thorsten Zimmer负责Lai da Nalps的检查项目。

“Using a UAV has widened our toolbox of available equipment technologies we can use for our daily tasks. Total stations, GNSS rovers and smaller UAVs are as common tools for us as it is the Leica Aibot,”齐默说。

大坝检查中的游戏规则技术

Before surveying with UAVs, one option for dam inspection purposes was to take images from below the dam and from the mountain walls surrounding it. For a dam of the size of the Lai da Nalps, the surveyor occasionally had to climb the surrounding hills, have the camera positioned correctly and take the photos, finally covering the entire wall. Another option was to move up and down along the outside of the dam, standing inside a basket or a gondola, and document everything from there. Even with precise planning and the perfect locations, these methods were very time-consuming, sometimes even dangerous, and couldn’t deliver as highly detailed images and quality results as the ones taken with a UAV facing the dam from an approximate 10 m distance.

Before owning a Leica Aibot, the Axpo team had already been a user of Aibotix Aibot X6, which they used for several years for surveying. Now it was the time to upgrade because flight time is started to be a challenge with the previous Aibot. Previously during large inspections - due to much shorter achievable flight times - one person was responsible just for recharging the batteries. With the new Leica Aibot surveyors can use more time and energy focusing on the inspection and not just keeping the system in the air.

用莉卡·艾博特（Leica Aibot）进行调查

Every dam Axpo operates is planned to have a full UAV inspection every five years using the Aibot. The inspection of a large dam takes two to three days and approximately 10 hours of total flight time. During the flight, the Aibot takes automatic images every two seconds, enabling the pilot to focus just on flying the copter at a constant height and distance close to the wall. The inspection is a two-person job: one operates the UAV with a focus on the flying position, speed and height, while the other person observes the surroundings, focusing on the quality and overlap of the photos taken as well as the status of the batteries.

Axpo uses a Leica Aibot AX20 UAV solution equipped with Sony α7RII sensor and a 55 mm lens. The 42 MP and crisp clear images ensure that data and results are accurate. To create an accurate and reliable point cloud, Axpo uses a Leica Nova TS60 total station to measure control points for post-processing of the data. The dam has several visible elements that can be used as control points, to be able to position and scale the point cloud. Measuring and documenting the control points can be done before, in between or after the flights.

“The conditions at the dam are challenging because of the sheer size or the arching dam and limited access to GPS. We needed a stable UAV that the pilot can easily operate because sometimes one has to fly without the assistance of GPS yet still holding the UAV in a stable and safe position. We use Leica Aibot because it is easy and safe to operate along our large dams and because we are able to have high-resolution images of the outside faces of our dams, which are needed to achieve the level of detail we require for the end result and the final 3d-model”评论Zimmer。作为测量师，我们通常会选择适合该任务的解决方案：对于某些任务，例如，我们使用的某些任务，扫描仪或较小的无人机，尤其是室内检查，对于其他项目，AIBOT是正确的解决方案 - 甚至是所有人的组合”。

During the snowless time of the year surveyors are busy with the inspection on the dams. The collected data and images will be processed into a point cloud and analysed by geologists and surveyors during the winter. The results are part of the long-term analysis of the dam to plan if any preventative renovation is needed and when.

无限可能

测量无人机改变地理空间行业，并为测量师提供巨大的潜力。AXPO使用AIBOT检查几个活跃的大坝以及其他室内和室外测量项目。

1. 该公司使用Leica Aibot检查大坝的无法接近的部分。一旦水位较低，团队就会检查通常在水下的大坝结构。浸没结构的目视检查是通过将无人无人机检查技术和载人检查结合起来完成的。
2. Flood modelling is also an interesting project for UAVs to mitigate risks related to dam spilling. Geologists investigate potentially risky masses of land and rock that could slide into the dam lake. Volumes of those are calculated and then used in careful what-if analyses.
3. 建筑项目和支持他们的基础设施是AXPO的大型测量项目，也可以由无人机捕获的数据支持。
4. Axpo also uses the Aibot for documentation of river banks by flying along inaccessible areas and for certain planning purposes.

“The Leica Aibot is a solution that fits our purposes, especially for large and detailed inspections of major dams. It is interesting to see how versatile the Leica Aibot is and in how many ways it can be used by our team,”concludes Zimmer.