The interior of Earth in 3D

Special to the Reporter from the European Space Agency

小时候，3D洞穴映射的Speleists兼专家Tommaso Santagata从未想象过他会测试一些最新，最具创新性的3D扫描技术，以进行未来的太空探索。2017年，他在欧洲航天局（ESA）太空飞行模拟现场活动的Pangea-X（行星模拟地质和天文学演习）期间在西班牙的Lanzarote度过了五天的密集映射。虽然该开创性课程的第一个结果一直在流入，但冒险的洞穴学家已经产生了largest 3D scan of a lava tube on Earth.

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

Pangea-X探险队冒险进入西班牙Lanzarote岛的“ La Cueva de Los Verdes”熔岩，这是世界上最大的火山洞综合体之一，总长度约为8公里。该洞穴既有干燥的部分也有水。

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.

These formations are similar to those found on Mars and on the moon. Being underground structures, they offer good shelters from radiation. This similarity makes Lanzarote a great environment to train astronauts and simulate space exploration.

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为什么在洞穴内进行3D映射？

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.

熔岩管是具有恒定温度的环境，免受宇宙辐射的屏蔽，并免受微量历史的保护，为人类提供了安全的栖息地。

精确测量熔岩洞穴的几何形状将使科学家能够改善其模型，并更好地了解他们对其他天体的演变。

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移动映射团队在短短20分钟内就如何操作Pegasus：背包进行了培训。

宇航员走过困难的地形，并通过平板电脑当场检查了结果。他通过沿着试管行走并返回以比较数据的准确性来执行洞穴映射任务。

“Hiking and performing geological mapping with the high-tech backpack was easy and efficient. I can perfectly see it integrated in our spacesuits for future exploration missions to the Moon or Mars,”莫勒说。

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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任务

该团队使用Pegasus：背包进行了两次不同的收购，以测试该解决方案中嵌入的所有定位技术。这两个任务均使用Leica Pegasus Manager软件处理。

1.The fused Simultaneous Localisation and Mapping (SLAM) mission

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.

The Pegasus:Backpack, the first position-agnostic solution, could track Maurer’s movements during the data acquisition, and the IMU recorded them 125 times per second. This way, the team obtains a first good trajectory with greatest accuracy at both the beginning and the end of the mission. The team needed to re-enforce the calculation for the part with zero satellites coverage using SLAM. At this stage, no pictures or point clouds are created. The part of the mission without any GNSS information used the trajectory obtained in the previous step as an input value to process the SLAM algorithm. The result is an improved trajectory with an estimation of the positioning error where point clouds, pictures orientation and spherical views are generated.

2.The pure SLAM mission

纯粹的大满贯任务通常是在诸如建筑物，洞穴和隧道之类的GNSS贬低环境中的任务。用于此类任务的主要定位传感器是指南针，IMU和SLAM仅激光雷达（SO LIDAR）。正确放置参数，完整的任务可能是processed in one single click. A basic trajectory of the Pegasus:Backpack was processed using information from the compass and the IMU. The complete mission uses this first trajectory as an input value to process the SLAM algorithm. Point cloud and pictures orientation and spherical views are generated with this trajectory.

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3D激光扫描

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.

As part of the CAVES 2016 training course, the team used photogrammetry – getting precise measurements and 3D data from at least two photographs – as a good alternative. However, photogrammetry cannot always guarantee good results, especially without the right light conditions.

To solve these problems, the PANGEA-X campaign tested the BLK360, the smallest and lightest imaging scanner on the market. The Leica Geosystems team operated it in set positions, obtaining360° images of the environment in just three minutes通过按下一个按钮并通过平板电脑应用直接对齐扫描。

Inless than three hours, data from both instruments obtained a complete 3D model of a1.3 km section of the lava tube.

The PANGEA-X campaign used two of the latest Leica Geosystems technologies for a demanding mission. Both technologies provided valuable information and accurate data to map areas in a short period of time where satellite navigation was unavailable.

A version of this story first appeared in the European Space Agency blog.