The mountain calls

Klöntalersee坐落在海拔848米，早在1655年苏黎世艺术家Conrad Meyer获得第一个现代高山全景。由岩石式古老的岩石队以前由2900米高的Mountain MassifGlärnisch侧翼而成，湖泊仍然是游客和艺术家的令人惊叹的吸引力。但不仅诗人和画家承认3.3平方公里的潜力只有3.3平方公里的潜力，由周围的山区布鲁克斯喂食，如klön。1908年，Klöntalersee在Rhodannberg和Sackberg之间的东边被地球土堆扣押，为周边村庄和公司发电。

Due to the new 220-m-long and 21.5-m-high earth bulk dam, the lake can carry about 39.8 million cubic meters of water, which can be used to generate electricity if demand fluctuates and during peak times.

From air to water

With their groundbreaking approach to combine hydrography and photogrammetry, the IngenieurTeam GEO GmbH planned to survey the area by using their sounding boat, Surveyor, Leica Geosystems industrial Unmanned Aerial Vehicle (UAV) solution as well as state-of-the-art positioning technology from Leica Geosystems in the Swiss canton of Glarus. The goal was to generate a 3D-model for accurate and inch-step precise calculation and simulation of the actual holding capacity.

毕竟筹备措施，批准进程和规划完成后，卡尔斯鲁厄的专家与他们的声纳装备的船只带到了220多公里的遥远的湖泊进入瑞士阿尔卑斯山，以将湖泊污染普通水表的污染情况。船舶和徕卡地质系统所做的所有测量都被记录在瑞士国家坐标系LV03中。

拥有172个计划的录音线，6米长的船只帆船使用其Reson Seabat 8​​101 Multibeam Echosounder创建湖泊土壤的详细信息。挡倒盘以150度的角度发射声信号，并通过测量回声的经过时间来计算水的深度。在每秒30平时的频率为101梁，水文照片通过每秒3,030个单点的晶粒接收高精度数据。通过每个测量轨道的三分之一重叠，专家确保在测量期间实现小于10厘米的精度。

But before data can be gathered, the measuring system must be calibrated precisely in order to avoid disturbance factors and to correctly determine the results. Therefore, the sensor technology must be adjusted before every deployment to subtract both linear movements of the vessel as well as rotation around its axles to impede any falsification. A further step for the hydrographs to get a clear and detailed view of the lakes ground is to factor the waters sound velocity into the calculation, which changes depending on temperature and suspended particles and becomes especially important in lentic water.

After the boat got launched and calibrated, the crew put out to sea on a two-and-a-half hour long first cruise to get a first impression of the lake’s character and began to create the first sonar data of the soil. Following the planned routes and under consideration of the lake’s depth and texture, the highly skilled hydrographs on the Surveyor collected enough information to create a point cloud of 134.837.653 X-Y-Z-coordinates. All in all, the crew of the observation boat made it in five days to record all 2,855,204 square meters of the Klöntalersee.

Beyond limits

Not only rapid changing weather conditions and bone-chilling cold pushed man and machine to its limits, with the glaciated massif Glärnisch building the south embankment, the environment put the technology to the test. With its 2,900 m, the massif literally threw its shadow ahead. Through the massifs steep slopes in close vicinity to the riverside, the experts feared they might lose their GPS-stream due to signal opacity on the south side of the Klöntalersee. In this case, the determination of the boat’s position would have been carried out by tachymeters placed on the northern and eastern shore of the lake. Because of the lake’s long-drawn-out kidney shape, this would have led to serious problems to get accurate details of the boat’s position.

通过在测量师上使用Leica Viva GS 16 GNSS天线，可以将Multibeam Sonar记录的数据分配给其坐标。凭借其内置的SmartLink-Technology，机组人员仍然能够录制高精度数据并接收GNSS校正数据，即使GSM网络的信号丢失。由于550个通道，最先进的测量引擎和超现实的RTK算法，可以精确地分配到测试结果的UAV和船只的数据。

Due their general design, bank situations are hard to capture for multibeam equipped vessels. In addition to that, the risk of damaging the sensitive and expensive sensor rapidly rises in shallow water and in the proximity of the shore. In order to still obtain exact results for the volume calculations and simulations, the engineers relied on their experience with their UAV and decided to capture the shores and embankments airborne via photogrammetry.

Precision from the sky

After the lake was measured at regular water level from the boat, the engineers began to plan the flights for the Leica Geosystems UAV solution. To capture the shore regions overlapping with the measurements taken by the boat, it was crucial to plan the following flights with the UAV at lower water levels. After the level of the Klöntalersee had been lowered seasonally, the survey with Leica Geosystems hexacopter began.

对于this purpose, the experts of the Ing.Team GEO planned the flight with the in-house built flight planning software, set the waypoints for the following flights, and determined the parameters suitable for the survey, such as height, ground sampling distance (GSD), flight speed and overlapping of the data. To record the often angled and steep terrain of the bank area as precisely as possible, the experts decided to survey each area several times to increase the validity of their data. After the flight planning on the PC had been completed and the waypoints were loaded onto the UAVs internal storage, the ground control points (GCP) around the lake were measured with the Viva GS16 so first flights could begin.

Once again, the surveying of the alpine reservoirs presented its very own challenges for man and machine. In addition to average temperatures of less than 0 degrees Celsius, rapid weather changes and low clouds, once again the southern bank of the Klöntalersee with its steeply sloping mountain walls was the biggest challenge. The UAV had to be started and landed on a separate boat because the steep walls and the dense vegetation of the shore made it impossible for the pilot to operate from the land. In addition to the sensitive and reliable technology, the skills and the steady hand of the pilot were particularly important.

尽管条件不利，但是来自Karlsruhe的团队能够在18个航班中收集高度精确的数据，因此在两天内覆盖了总长度超过12公里的干岸条。通过每两秒钟拍摄的照片和4 M / s的无人机移动，专家确保通过连接到飞行多传感器平台的相机以最高精度记录数据。

“Due to the fast data availability of the UAV, we were able to evaluate the first results on site,” said Benjamin Busse, IngenieurTeam GEO.

Combining technologies with accuracy

与测量船的录音一样，它对于基于UAV的结果来说是准确地引用的内在重要性。为此，Ingenieurteam Geo的专家用特殊的RTK / GNSS模块配备了UAV，另外使用了VIVA GS16 GNSS天线，这是在这些困难条件下工作的完美匹配，以实现1-3厘米的准确性在地理转移收集的数据中。

After all measurements had taken place, the surveying experts began to process the obtained data. The point clouds created by the multibeam sonar had to be fed into the PDS 2000 bearing software to manually edit and correct them from imprecision. In order integrate the data of the river banks into the volume calculation, all 4,400 high-resolution images created with the UAV had to be imported into flight planning software, where they were merged with the coordinates from the UAV’s log file. After that, the georeferenced data was edited in the post processing software AgiSoft PhotoScan Pro to create a 3D model as well as a point cloud. Subsequently, the two 3D models were combined in the Autodesk application AutoCAD® Civil 3D to generate an exact model of the lake's situation.

Using the data from the 3D model, the engineers generated a precise map with elevation lines for their client. By being able to generate such a precise result and to combine two completely different ways of surveying large and challenging areas, the engineers stood up to the game and used the most modern technology to get the job done. With the data generated by boat and UAV, the experts are able to fulfill their clients’ wishes of a detailed virtual 3D model and a metres long situation plan with contour lines printed out.

“我们现代多阵线系统和徕卡地质系统的测量结果的组合使我们能够非常快速地产生高精度数据，”Busse说。

Once again choosing the flying multisensory platform by Leica Geosystems to rethink conventional ways of working was the right choice for the professionals to achieve the best results.