The interior of Earth in 3D

Special to the Reporter from the European Space Agency

As a child, Tommaso Santagata, speleologist and expert in 3D cave mapping, would have never imagined that he would test some of the newest and most innovative 3D-scanning technologies for future space exploration. In 2017, he spent five days of intense mapping in Lanzarote, Spain, during the PANGEA-X (Planetary ANalogue Geological and Astrobiological Exercise for Astronauts) an European Space Agency (ESA) Spaceflight Analog field campaign. While the first results from that pioneering course keep flowing in, the adventurous speleologist has produced the地球上熔岩管的最大3D扫描。

Along with geologists Umberto Del Vecchio and Marta Lazzaroni, he mapped most of the lava tube system as part of a project supported by the Cabildo of Lanzarote and the University of Padova, Italy. The resulting map comes alive in great detail, helping local institutions to protect this subterranean environment. It also provides scientific data to study the origins of the tube and its peculiar formations.

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The terrain

The PANGEA-X expedition ventured into the “La Cueva de los Verdes” lava tube in the Spanish island of Lanzarote, one of the world’s largest volcanic cave complexes with a total length of about 8 kilometres. The cave has both dry and water-filled sections.

The 6-km dry portion of the lava tube has natural open skylights, orjameosas the locals call them, that are aligned along the cave pathway. Some of the caves are large enough to accommodate residential streets and houses.

这些地层与火星和月球上的地层相似。作为地下结构，它们提供了辐射的良好避难所。这种相似性使Lanzarote成为训练宇航员并模拟太空探索的绝佳环境。

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Why 3D mapping inside a cave?

When a new environment is discovered, mapping the area is always a first starting point of exploration. This also applies to missions to other planets, where one of the main objectives will be to choose places to setup base camp.

Lava tubes are environments with a constant temperature, shielded from cosmic radiation and protected from micrometeorites, providing safe habitats for humans.

Precisely measuring the geometry of lava caves will allow scientists to improve their models and better understand their evolution on other celestial bodies.

For these reasons, learning how to map lava tubes on Earth is helping exploration off Earth. ESA astronaut, Matthias Maurer, joined the expedition to test two different instruments developed by Leica Geosystems, the Leica Pegasus:Backpack and the Leica BLK360.

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Mobile mapping

Leica Geosystems mobile mapping team trained Maurer on how to operate the Pegasus:Backpack in just 20 minutes.

The astronaut walked through the difficult terrain and checked the results on the spot through a tablet. He performed his cave-mapping mission by walking along the tube and back to compare the accuracy of the data.

“使用高科技背包远足和执行地质映射非常容易有效。我可以完美地看到它在我们的航天服中融合在一起，以供未来的月球或火星探索任务。”said Maurer.

The Pegasus:Backpack synchronises images collected by five cameras and two 3D imaging LIDAR profilers, the laser equivalent of radar. It enables accurate mapping where satellite navigation is unavailable, such as in caves.

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The missions

The team did two different acquisitions with the Pegasus:Backpack to test all the positioning technologies embedded in this solution. Both missions were processed with the Leica Pegasus Manager software.

1.The fused 同时本地化和映射（SLAM）任务

Starting from the outdoor with good GNSS conditions then going indoor in challenging GNSS conditions with very low or zero satellites coverage and finishing the mission outdoor with good GNSS conditions. For this type of mission, the team used multiple positioning technologies: GNSS + Inertial Measurement Unit (IMU) + SLAM. The processing software recognised automatically the different phases of the mission.

Pegasus：Backpack是第一个位置不足的解决方案，可以在数据采集期间跟踪Maurer的动作，IMU每秒记录了125次。这样，团队在任务的开始和结束时都获得了最高准确性的第一个良好轨迹。该团队需要使用SLAM覆盖零卫星的零件来重新强加计算。在此阶段，没有创建图片或点云。没有任何GNSS信息的任务部分使用上一步中获得的轨迹作为输入值来处理SLAM算法。结果是改进的轨迹，并估计了位置误差，在该误差中生成点云，图片方向和球形视图。

2.纯粹的大满贯任务

A pure SLAM mission is typically a mission in GNSS-denied environments, like buildings, caves and tunnels. The main positioning sensors used for this type of mission are the compass, the IMU and SLAM Only LiDAR (So LiDAR). Putting the parameters correctly, the complete mission could beprocessed in one single click。PEGASUS：背包的基本轨迹是使用Compass和IMU的信息处理的。完整的任务使用第一个轨迹作为输入值来处理SLAM算法。点云和图片方向和球形视图是通过此轨迹生成的。

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3D laser scanning

In Lanzarote, lava tubes generally develop along tunnels on different levels due to lava flowing over multiple eruptions and following cracks and crevasses left from previous eruptions. It is not always possible to access the upper levels without climbing equipment.

作为洞穴2016培训课程的一部分，该团队使用了摄影测量法 - 从至少两张照片中获得精确的测量和3D数据 - 作为一个很好的选择。但是，摄影测量法不能总是保证良好的结果，尤其是没有正确的光条件。

为了解决这些问题，Pangea-X活动测试了BLK360，这是市场上最小，最轻的成像扫描仪。Leica Geosystems团队以固定位置进行操作，获得仅三分钟内的360°环境图像by pressing one button and aligning the scans directly through a tablet app.

In少于三个小时, data from both instruments obtained a complete 3D model of a1.3 km section of the lava tube.

Pangea-X活动使用了两种最新的Leica Geosystems Technologies进行苛刻的任务。这两种技术都提供了有价值的信息和准确的数据，以在不可用的卫星导航的短时间内绘制区域。

这个故事的一个版本首先出现在欧洲航天局博客中。