For the first time, researchers at Institute of Industrial Science, The University of Tokyo, quickly and efficiently measure the seafloor down to the centimeter-level using an unmanned aerial vehicle. Credit: Institute of Industrial Science, The University of Tokyo
Researchers from the University of Tokyo have developed an unmanned aerial vehicle (UAV) that can make high-precision, real-time seafloor measurements and communicate them to satellites to provide early warnings for earthquakes and tsunamis.
The Nankai Trough, off the coast of Japan’s Honshu island, lies in a megathrust earthquake zone. Megathrust earthquakes occur along the faults found between the boundaries of tectonic plates. They are the most powerful earthquakes on Earth.
There is a 70% chance a potentially devastating magnitude 8 or 9 earthquake will occur in this zone within the next 30 years.
In March, the Japanese Government’s Central Disaster Management Council released estimates that a worst-case scenario earthquake in the Nankai Trough could lead to 2.35 million buildings destroyed and a death toll of 298,000.
An earthquake that big would likely also trigger a tsunami, which would cause further devastation. So, there is a need for accurate, frequent and real-time seafloor measurements.
Seafloor measurements, which can detect earthquakes, are currently observed through the Global Navigation Satellite System-Acoustic (GNSS-A). Transponder stations on the seafloor collect the measurements and communicate them to satellites, usually via ships.
Seafloor crustal deformation monitoring using GNSS-A. Sea surface platforms, such as vessels, determine their antenna positions using GNSS. A seafloor station is pre-installed on the seafloor at depths deeper than 1,000 m, and acoustic ranging between the sea surface platform and the seafloor station is repeatedly performed. Credit: Yoshizumi et al 2025, Earth and Space Science, https://doi.org/10.1029/2025EA004237
However, there are several economic and physical factors that limit how frequently observations can be made using ships. The authors of the study were inspired to construct a more effective measuring technique.
Published in Earth and Space Science, the team designed an unmanned, seaplane-type drone which takes the place of a ship to feed the satellites information.
“We conducted initial experiments in a water tank,” says lead author of the study, Yuto Yoshizumi, “and found that the proposed system can detect distances to an accuracy within 2.1 cm.”
The research team also performed a series of at-sea tests off the coast of Japan under optimal sea conditions. Throughout these tests, the UAV was able to conduct frequent observations that were verified as accurate.
“The results were hugely encouraging,” says senior author Yusuke Yokota.
During the at-sea trials, the seaplane moved across the surface of the ocean at a speed of 6km/hr to prevent bubbles from disrupting the acoustic signal.
UAV-based GNSS-A was conducted at an actual Seafloor Geodetic Observation-Array site (red dot). The observation site used is located off Izu, Shizuoka Prefecture, Japan. Credit: Yoshizumi et al 2025, Earth and Space Science, https://doi.org/10.1029/2025EA004237
“These seafloor positioning measurements are the first ever achieved using a UAV,” says Yokota.
“We attained a horizontal root mean square error of approximately 1–2 cm, which is easily comparable to that of existing vessel-based systems.”
Accurate, real-time seafloor measurements are crucial for saving lives as they provide early warnings for earthquakes and tsunamis. The UAV-based GNSS-A system can provide this in a short period of time under optimal conditions.
“[The results] indicate that it has the potential to achieve an immediate response capability that has been difficult to achieve with conventional sea surface platforms,” write the authors.
“For achieving stable observation accuracy, the development of algorithms that evaluate the quality of observation data in real time and formulate optimal observation routes depending on the environment could be an important future research topic.”
With further development, the authors hope the seaplane-UAV can be used alongside the current detection systems.