使用3D激光扫描来检测盐和冰洞的结构变化

作者：Tommaso Santagata

陆地激光扫描（TLS）已被用于地下调查超过十年，越来越多地用于洞穴中的探索和研究。来自虚拟地理机构的Tommaso SantagataVigea最近使用过Leica Geosystems laser scanning solutions在两个洞穴调查中：智利莱科扎盐洞和意大利自然井冰洞的形态（形式和结构）变化的调查。

Santagata explains how detailed scanning at intervals can offer insight into physical changes in cave environments, “Although most processes occurring in caves are relatively slow, some can be fast, such as erosion caused by flooding. These geological changes can be monitored by terrestrial laser scanning surveys and measured by comparing ‘before and after’ 3D models. It’s an interesting tool for making comparisons over time and is therefore increasingly being used in the study of climate change.”

Measuring changes caused by flooding in the Lechuza cave (Cordillera de La Sal)

靠近智利村的圣佩德罗德阿阿塔卡马是一个重要的洞穴，由寡核苷酸矿床岩石组成，称为Cordillera de la Sal。Two surveys carried out in 2015 and 2018 allowed Santagata’s team to verify and measure small topographical changes in the cave due to a flood in 2017, which caused the river in the cave to flow and dissolve a measurable amount of halite - commonly known as rock salt.

In 2015, a complete 3D survey of the cave was organised byLa Venta Esplorazioni Geografiche和里雅斯特委员会博罗特·埃巴尼奥布勒。该团队使用Leica HDS7000相激光扫描仪进行大约50个扫描。2018年，La Venta团队与博洛尼亚大学使用过徕卡Scanstation P40to perform 68 scans, including about 200-metres surveyed in the external canyon upstream of the cave as part of the research project “Reading the salt caves of Atacama” supported by the National Geographic Society.

Lechuza data obtained in point cloud file format was subsequently analysed to identify areas where changes had occurred. Santagata explains, “Since very limited variations were found, it was necessary to recognise points in common and position the point clouds in the same origin and orientation to make comparisons. In at least three areas of the cave, collapses from the ceiling and erosion on the floor were recognised and digitised to obtain detailed sections of these parts of the cave. The comparison between these two surveys has shown that in this case, it was possible to accurately document the areas where detachments or torrential erosion occurred.”

The natural well ice-rock cave monitoring project: measuring ice collapses

The second study concerns the underground ice deposit in the Cenote Abyss, one of the deepest and most voluminous caves of the Italian Dolomites. The 280metre-deep ice cave was discovered in 1994 after the entrance opened as a result of the abrupt emptying of a small lake in the Regional Park of Fanes, Sennes and Braies. The cave’s vertical entrance consists of a massive 130metre-thick layered ice deposit; at the lower limit of the ice-filled entrance part a shaft opens – ice-free and 165 metres deep – leading into a dome-shaped chamber occupied by a cave rock glacier.

2015年，2016年的激光扫描调查，2018年，允许Santagata的团队估算由于崩溃和获取完整监控项目的数据而估算变化。2015年10月的第一次远征包括使用基于HDS7000相激光扫描仪的最终室的完整3D激光扫描调查。本调查提供了腔室（420,000m³）的详细体积以及冰块悬挂在天花板和底部的岩石冰川位置的第一次记录。在2016年和2018年的随后的探险期间，洞穴的其他部分是使用ScanStation P40扫描的3D。

SantAdata解释说：“由于冰填充了一些段落在接下来的几年中，不可能重复最终会议室的调查（这将是未来探险的目标）。然而，在洞穴的上半年里，这些年来的数据使我们能够研究入口附近的前两个房间所发生的变化。特别地，在一个区域中突出显示崩溃，这导致了2016年之后发生的通道的放大。该区域是在崩溃之前和之后扫描的3D，并且所获取的数据允许我们验证分离并量化岩石的岩石的体积。“

使用两种不同的方法进行比较点云：首先，我们在两个数据集之间进行快速比较，以便了解要重点的何处进行更详细的分析。其次，我们提取了兴趣领域的几个“切片”。我们将这些领域导出为完整的数字化，更好地估计岩石体积倒塌，大约61m³。“

Ongoing studies: Using 3D models to understand geological processes

The studies show that 3D laser scanning is a useful measuring technique for highlighting changes to natural structures. The data obtained can be used to help interpret other geological information, Santagata says, “For example, the variations highlighted by comparing the Lechuza cave studies provided interesting data that can easily be correlated to the rainfall that occurred in this area between the two survey campaigns.”

“In the case of the Cenote Abyss, the collapses probably occurred due to temperature variations, considering that the area is subject to oscillations between surface and cave temperatures recorded by temperature and air pressure sensors installed in the cave. A detailed environmental monitoring of this area of the cave is ongoing and the repeated 3D models will allow us to understand if these processes are important for the origin and development of ice caves in the Alps.”

探索3D项目：
阿塔卡马盐洞穴
阿塔卡马3D模型
Cenote 2018 Expedition
Cenote 3D Models

Key people involved in the surveys: Tommaso Santagata (Vigea - Virtual Geographic Agency andLa Venta Esplorazioni Geografiche), Umberto Del Vecchio (Vigea - Virtual Geographic Agency andLa Venta Esplorazioni Geografiche），Jo de Waele（博洛尼亚大学和La Venta），Francesco Sauro（Bologna大学和La Venta），Stefano Fabbri（Bologna / La Venta大学）。

Lechuza洞穴探险were organised by the Association La Venta Esplorazioni Geografiche with the scientific support of the BIGEA Department of the University of Bologna and with the collaboration of the Commissione Grotte E. Boegan in 2015. The scientific expedition in 2018 received funding from the National Geographic Society and was realised with the support of CONAF Chile. The Cenote monitoring is a multidisciplinary project organised as part of the Inside the Glaciers project with the collaboration of La Venta, BIGEA and the Regional Park of Fanes Sennes and Braies with the collaboration of Studio GST and Eli Friulia, the Speleo Club Proteo of Vicenza, the Gruppo Grotte Treviso and the Gruppo Speleologico Padovano.