First results of undersea muography with the Tokyo-Bay Seafloor Hyper-Kilometric Submarine Deep Detector

Tidal measurements are of great signifcance since they may provide us with essential data to apply towards protection of coastal communities and sea trafc. Currently, tide gauge stations and laser altimetry are commonly used for these measurements. On the other hand, muography sensors can be located underneath the seafoor inside an undersea tunnel where electric and telecommunication infrastructures are more readily available. In this work, the world’s frst underseafoor particle detector array called the Tokyo-bay Seafoor Hyper-Kilometric Submarine Deep Detector (TS-HKMSDD) was deployed underneath the Tokyo-Bay seafoor for conducting submarine muography. The resultant 80-day consecutive time-sequential muographic data were converted to the tidal levels based on the parameters determined from the frst-day astronomical tide height (ATH) data. The standard deviation between ATH and muographic results for the rest of a 79-day measurement period was 12.85 cm. 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, this muography application will become an established standard, demonstrating its efectiveness as practical tide monitor for this heavy trafc waterway in Tokyo and in other important sea trafc areas worldwide.