During the filming of the "Sakurajima - Capturing Rare Moments" I got to work closely with the scientists from Kyoto University's Disaster Prevention Research Insitute (DPRI), National Research Institute for Earth Science and Disaster Resilience (NIED) and the Sakurajima Volcanic Observatory (SVO). Already our high-resolution imagery captured from a close proximity to the volcano using our custom 8K drone was very useful to the scientists. But it was our expertise in 3D terrain mapping that really interested them. Basic 3D terrain models of the volcano exist, but they are either outdated, or have very low resolution. Sakurajima is so active - that the actual shape of the volcano changes on regular basis.

The large eruptions of Sakurajima are defined by the fact that it almost always erupts from more than just a single crater. The above paintings from the 1779 An-ei eruption are a great example, showing Sakurajima erupting from 4 separate locations. This has been confirmed by geological studies of the respective lava flows from the diferent eruptions - as can be seen in the below 3D model:

So the scientists had an idea: If we could terrain-map Sakurajima into precise and up-to-date 3D model, they can run various eruption simulations from many locations on the volcano. These simulations can then be used during an actual eruption (or even shortly prior - if the volcano deformations could help predict the eruption points) to guide disaster response and prioritise evacuation. These simulations take a very long time and a lot of computing power - it will be too late to try to run them once the eruption has began. Being able to simulate various scenarios - the scientist could then just refer to the correct one and act immediately. The question then became - how do you map such a large and active volcano?

One of my favorite proverbs is "If you fail to plan - you plan to fail !". But planing such a large-scale project was no easy task. To begin with, Sakurajima covers area of 77 km² (30 sq mi) - not your typical 3D terrain mapping project! Then you have to deal with the steep terrain. Most terrain mapping solutions are based on drone flights leveled in the horizontal plane. Some of the locations on the volcano are impossible to access - a 2 km radius (1.25 mi) around the currently active Minamidake crater is strictly off-limits - and even the wider area requires specialised permits. Most commercially-available drones are limited to maximum flight height of 500 m (1640 ft) from the take-off point - and that only if you can keep it under 120 m (400 ft) AGL (above ground level). Given that Sakurajima rises to 1117 m (3665 ft) directly from the surrounding ocean, this alone made the flight planing extremely complicated. And don't forget that Sakurajima is the most active volcano in Japan (and in the top 10 worldwide) - with eruptions occuring on average 2~3 times each day - and even between the eruptions the volcano is almost constantly off-gassing and releasing huge amounts of fine & highly-abrasive ash.

After a lot of initial research and testing - we have chosen to use terrain mapping mission planing SW from Drone Harmony AG (Switzerland). It was, at that time, one of only two solutions that implemented 3D terrain awareness when planing the drone flights. What set their solution apart was personalised attention and wilingness to work closely with us on adopting their existing solution to adress the unique challenges of our project. Their SW allowed us to semi-automate the complex flight operations, while giving us the freedom to manually adjust specific parameters for each flight. Frequently we would need to depart from a point on the volcano almost 3 km (1.9 mi) from the main crater, fly around the volcano beyond the visual sight (BVLOS) from our base and execute the mapping mission with enough battery power remaining to safely return. To simplify the operations, we have organised the volcano into 1 x 1 km (0.6 x 0.6 mi) grid, with each square requiring dozens of flights. In the first stage of the project we have focused on the southern and eastern portions of the volcano and the area surrounding the active crater:

It took us several months just to complete the first stage of mapping. Then it was time to process the phtogrammetry data into a 3D model that the scientist could use. We had to severely upgrade our computing render farm just to process the individual 1 km² sections. The weapon of choice here was the METASHAPE photogrammetry SW from Agisoft LLC. The initial results were incredible and the level of detail unprecendented for a project of this scale. We could identify details just few cm (1~2 in) across:

Each section's 3D model was then converted to a format compatible with the scientist's supercomputer used for the eruption simulations and exported in various resolutions. It turned out that at the full resolution our data was too mcuh even for the supercomputer and needed to be slightly reduced. NHK followed us through out each step and has released the first documentary focused the initial stage of the project - the 3D terrain mapping. It is 30 min long and I hope you enjoy watching it:

In 2022, David Adjiashvili - the CTO and Founder of Drone Harmony AG (Switzerland) was interviewed on the Drone Radio Show (episode 365) and discussed this project in great detail, the challenges it presented and the assistance provided directly by Drone Harmony. The project itself is also prominently featured in the Customer Stories section of the Drone Harmony website. You can listen to the full podcast episode, or select a specific chapter below:

Due to the restrictions related to the Covid pandemic (extending in Japan well into 2023) and the related severe restrictions on the NHK Enterprise's budgets, the completion of the full 3D model has been delayed. Currently more than a half of the volcano has been 3D terrain mapped with focus on the southern and eastern sections - where the majpority of the local residents live and where any future volcanic activity is expected...