Together with geologists Umberto Del Vecchio and Marta Lazzaroni, they mapped most of the lava tube system as part of a project supported by the Cabildo of Lanzarote and the University of Padua, Italy. The resulting map is presented in great detail and helps local institutions to protect this underground environment. It also provides scientific data to study the origin of the tube and its particular formations.
The PANGEA-X expedition dared to jump into the lava tube “La Cueva de los Verdes” on the Spanish island of Lanzarote, one of the world’s largest volcanic height complexes with a total length of around 8 kilometres. The cave has both dry and water-filled areas.
The 6 kilometre long, dry part of the lava tube has natural open roof windows aligned along the cave path. Some of the caves are large enough to accommodate residential streets and houses.
These formations are similar to those on Mars and the Moon. As underground structures, they provide good protection from radiation. This similarity makes Lanzarote a great environment to train astronauts and simulate space exploration.
Why 3D mapping in a cave?
When a new environment is discovered, the mapping of the area is always a first starting point for exploration. This is also true for missions to other planets, where one of the main objectives will be to choose locations to build the base camp.
Lava tubes are constant temperature environments, shielded from cosmic rays and protected from micrometeorites, and could provide safe habitats for humans.
Accurate measurement of the geometry of lava caves will allow scientists to improve their models and better understand their evolution in other celestial bodies.
For these reasons, learning how to map lava tubes on Earth helps to explore the Earth. ESA astronaut Matthias Maurer participated in the expedition to test two different instruments developed by Leica Geosystems, the Leica Pegasus:Backpack and the Leica BLK360.
Leica Geosystems’ mobile mapping team trained Maurer to use the Pegasus:Backpack in just 20 minutes.
The astronaut walked through the difficult terrain and checked the results on site using a tablet. He performed his cave mapping mission by walking along the tube and back to compare the accuracy of the data.
“Hiking and geological mapping with the high-tech backpack was simple and efficient. It can be perfectly used in our space suits for future exploration missions to the Moon or Mars,” Maurer said.
The Pegasus:Backpack synchronizes images collected by five cameras and two 3D imaging LIDAR profiles, the laser equivalent of radar. It enables accurate mapping when satellite navigation is not available, such as in caves.
The team has made two different acquisitions with the Pegasus:Backpack to test all positioning technologies integrated in this solution. Both missions were completed with Leica Pegasus Manager software.
- The Merged Simulaneous Localisation and Mapping (SLAM) Mission
From the outdoor area with good GNSS conditions over the indoor area under difficult GNSS conditions with very little or no satellite coverage to the completion of the outdoor mission with good GNSS conditions. For this type of mission, the team uses several positioning technologies: GNSS + Inertial Measurement Unit (IMU) + SLAM. The processing software automatically detected the different phases of the mission.
The Pegasus:Backpack, the first position-agnostic solution, could track the movements of bricklayers during data acquisition and the IMU recorded them 125 times per second. In this way, the team gets a first good trajectory with the highest accuracy both at the beginning and end of the mission. The team had to reinforce the calculation for the part with zero satellite coverage using SLAM. No images or point clouds are created at this point. The part of the mission without GNSS information used the trajectory obtained in the previous step as input value for processing the SLAM algorithm. The result is an improved trajectory with an estimate of the positioning error where point clouds, image orientation and spherical views are generated.
A pure SLAM mission is typically a mission in GNSS limited environments such as buildings, caves and tunnels. The main position sensors used for this type of mission are the compass, the IMU and SLAM Only LiDAR (So LiDAR). If the parameters were set correctly, the entire mission could be processed with a single click. A basic Pegasus trajectory: backpacks were processed with information from the compass and IMU. The whole mission uses this first trajectory as input value for the processing of the SLAM algorithm. This trajectory is used to generate point cloud and image orientation and spherical views.
3D laser scanning.
On Lanzarote, lava tubes usually develop along tunnels at different levels, as the lava flows over several eruptions and cracks and fissures follow from previous eruptions. It is not always possible to reach the upper levels without climbing equipment.
As part of the CAVES 2016 training course, the team used photogrammetry – precise measurements and 3D data from at least two photos – as a good alternative. However, photogrammetry cannot always guarantee good results, especially without the right lighting conditions.
To solve these problems, the PANGEA-X campaign tested the Leica BLK360, the smallest and lightest image scanner on the market. The Leica Geosystems team operated it in adjustment positions and created 360° images of the surroundings in just three minutes at the touch of a button, aligning the scans directly via a tablet app.
In less than 3 hours, the data from both instruments received a complete 3D model of a 1.3 km long 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 time where satellite navigation was not available.