Abstract
Tidal measurements are of great significance since they may provide us with essential data to apply towards protection of coastal communities and sea traffic. Currently, the tide gauge stations, satellite-based, pressure-based and ultrasonic-based techniques are commonly used. However, with these techniques, sensors have to be either floated on the sea surface or sunk onto the seafloor. The former option makes it difficult to conduct the tide measurements in high traffic maritime sea channels, and the latter option requires the construction of undersea electric and telecommunication infrastructures to support real time monitoring. On the other hand, with muography, sensors can be located underneath the seafloor inside, for example, an undersea tunnel where the electric and telecommunication infrastructures are more readily available. In this work, the world’s first under-seafloor particle detector array called the Tokyo-bay Seafloor Hyper-Kilometric Submarine Deep Detector (TS-HKMSDD) was deployed underneath the Tokyo-Bay seafloor for conducting submarine muography. Time-sequential muographic data were converted to the tidal levels above the detector and compared with the data acquired from the nearby tide gauge station. The results were consistent, indicating that submarine muography could be an alternative tool for tide measurements. We anticipate that if the length of the TS-HKMSDD is extended from 100 m to a full-scale as large as 9.6 km to provide continuous tidal information along the tunnel, muography will become an established standard, demonstrating its effectiveness as practical tide monitor for this heavy traffic waterway in Tokyo and in other important sea traffic areas worldwide.