A team of Czech divers and land surveyors are the first in Europe to have succeeded in scanning a flooded cave system. Using film footage from the water-filled Chýnov cave in south Bohemia, they created a detailed and accurate three-dimensional map. The main advantage of the so-called videogrammetry is its simplicity and speed.
The Chýnov cave, located near the town of Tábor some 100 kilometres south of Prague, was discovered in 1863 and opened to the public five years later. In the 1980s, speleologists found a lower, larger part of the cave system that was permanently filled with water. František Krejča from the management of the Chýnov cave explains:
“The first survey of the cave took place already in the 1980s, when the cave’s lower, water-filled part was discovered. The divers measured the flooded corridors using the traditional method of speleological mapping.
“But the map didn’t really correspond with the model of the upper-part of the cave. We could see that it didn’t fit. So we wanted to carry out a new mapping and we were looking for a method that would be simple and accurate.
“The Chýnov cave system is really a complex labyrinth with several different layers. We knew that if the scanning proved to be successful, it could be used for other flooded spaces as well.”
The team of explorers was led by geophysicist Jiří Šindelář from the Archaeological Institute of the Czech Academy of Sciences, who uses so-called non-destructive archaeology in mapping historical and archaeological sites. He decided to use the same 3D technology for scanning the cave:
“As you can imagine, exploring a flooded space is quite complicated and it can only be done by divers. The space is usually very tight and the divers often find their way back only by using their hands, since the water gets muddy and there is a zero visibility.
“Usually, the diver only has around 25 minutes to get back to safety so our task was to make a detailed map of the cave within a limited amount of time.
“We decided to adapt the technologies used for documenting archaeological sites for the use of the divers and within one 20-minute-dive we managed to scan 300 metres of the cave.”
“The cave serves as a water source for the village of Chýnov, but we still haven’t discovered how the water gets into the cave, because the source is in the permanently flooded part of the cave.
“To make progress in our research, we need a detailed map. This can help us for instance in marking a drinking water safeguard zone. But there are of course many other ways of using such 3D scans.”
The Cave Administration of the Czech Republic would like to use the new method of 3D scanning for mapping other cave systems in the country in the future.
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