Twelve boys and their coach trapped in a cave deep underground with dwindling air and the danger of being flooded by rising water levels. How did a determined international team find and rescue the boys? How did sophisticated geographical information systems (GIS), IoT sensors and 3D simulations assist the rescuers?
Tham Luang Nang Non is six mile long underground cave complex in Thailand’s Chiangrai province. A boy’s soccer team was reported missing in July 2018. Thai Navy SEAL divers’ found them in a cave that could only be reached after a six hour underground journey in the dark, swimming through narrow tunnels and climbing boulders. An international rescue teams with experts from Thailand, China, Japan, Australia, the US and Britain were able to rescue them.
How the boys were located
Cave maps that depicted twists and turns and cave dimensions helped divers orient themselves within the cave’s difficult passages as well as mark their progress. Divers began laying guide ropes and deploying spare oxygen tanks along the path. The map helped divers navigate through the maze of passageways and chambers and to mark all the dead-ends they checked. They progressed through the cave network trying to find the team. On the surface, the Thai Royal Army used topographic maps of the terrain and cave location to search for entrances. The recent high resolution aerial photos by Royal Thai Survey Department provided surface-level details. Engineers began to explore the 3D cross-section maps to calculate the distance to the center of the cave from multiple angles, hoping they could find a place to drill. Nine days into the search, British cave diving experts located the team gathered on a muddy shelf more than two miles from the cave entrance and a mile underground.
Technical challenges
- Mapping the underground cave and passages to plan the rescue operation
- Monitoring oxygen levels to prevent the boys and rescuers dying from hypoxia
- Tracking changing water levels and currents in the underground tunnels
- Transmitting data from deep underground
Esri ArcGIS was one of the apps used by the rescue team. Some apps and sensors described below are suitable for such use cases and included only for reference purposes.
ESRI3D mapping of caves
Thailand Department of Mineral Resources (DMR) obtained cave data from the Expedition Thai-Maros, a French-led surveying effort that recorded the extent and cross section of the cave in Dr. Martin Ellis’ book, The Caves of Thailand added details that were translated and shared. It provided the dimension of the passage cross-section that guided the dive team in searching for the kids and coach.
Seeing and interacting with geospatial data in 3D provides insights that just aren’t possible in 2D such as understanding the sub-surface terrain. It was vital for the rescuers to know the size of narrow tunnels as they had to to squeeze through narrow passages with oxygen tanks for the boys. Collectively, the data gave the mapping team what they needed to model and visualize the cave in 3D. These 3D cave maps were distributed and widely used by the British cave surveying team, the Thai Navy SEAL team, and the Department of Disaster Prevention and Mitigation staff.
ESRILIDAR (light detection and ranging) is often used to map caves and other surfaces. An optical Lidar sensor transmits laser beams and the reflection of the laser from the target is detected and analyzed by receivers. The receivers record the precise time from when the laser pulse left the system to when it is returned to calculate the range distance between the sensor and the target. This is combined with positional information GPS (Global Positioning System), and INS (inertial navigation system), to produce a very accurate three-dimensional representation.
Monitoring water and oxygen levels
Heavy rains and surging water levels in the cave made conditions extremely dangerous. The currents ripped off diving masks and sent divers drifting away from the guide ropes so it was essential to keep continuously track water conditions. Water flow readings collected by volunteers were supplemented with sensor readings and relayed to a command center above ground. As the mission shifted from search to rescue, the mapping team collected sensor readings on water and oxygen levels at the cave entrance, at 300 meters, and at 1,500 meters. Hourly map updates showed current water depth and air quality, alerting rescuers to changing conditions. The mapping team also monitored weather radar feeds to forecast and understand the volume of rain falling at the surface. Xylem, Nivus and Omega provide water flow sensors for such use cases. Advanced Micro Instruments and CO2Meter provide sensors to monitor oxygen levels and protect against asphyxiation.
Transmitting data from deep underground
Sensors underground are low-powered but have to transmit through soil and other obstacles. Transmissions from such sensors typically rely on LoRaWAN, Sigfox and NarrowBand-Internet of Things (NB-IoT). NB-IoT improves the power consumption of user devices, system capacity and spectrum efficiency, especially in deep coverage with battery life up to ten years.
Coordinating the rescue operations
As the mission shifted from search to rescue, the mapping team coordinated the creation of a sensor network to take readings of the rainfall and the manual readings of the cave water depth. The Department of Disaster Prevention and Mitigation used the data generated by continuous monitoring to coordinate the cave search and rescue. The map alerted rescuers to changing water and oxygen conditions in the cave at different observation points. The mapping team also monitored weather radar feeds to understand the volume of rain falling at the surface. Divers continued to plan and stage the rescue attempt, hoping to reduce each one-way trip under the nine hours it was taking.
Mission accomplished
As the Guardian reported, “The boys of the Wild Boar football team spent nine days in the dark, dank cave before being located by two British divers. They were brought out in three daring rescue operations starting on Sunday morning. An elite team of 19 divers were involved in ferrying the boys and their 25-year-old coach the approximately two-mile path from the muddy slope where they had been sheltering to the outside world.”
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