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

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, tide gauge stations and laser altimetry are commonly used for these measurements. On the other hand, muography sensors can be located underneath the seafloor inside an undersea tunnel where 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. The resultant 80-day consecutive time-sequential muographic data were converted to the tidal levels based on the parameters determined from the first-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 effectiveness as practical tide monitor for this heavy traffic waterway in Tokyo and in other important sea traffic areas worldwide.

Periodic sea-level oscillation in Tokyo Bay detected with the Tokyo-Bay seafloor hyper-kilometric submarine deep detector (TS-HKMSDD)

“…In this work, 20 muographic sensor modules (MSMs) were deployed inside the Aqua-Tunnel to construct a linear array of MSMs called the Tokyo-Bay Seafloor Hyper-Kilometric Submarine Deep Detector (TS-HKMSDD). Since a detailed description of HKMSDD can be found elsewhere 49 , it is only briefly introduced here. Each MSM consisted of two scintillation detectors, a high-voltage power supply unit (HVU) (Technoland Z-SYS 070HV), and a discriminator-coincidence unit (DCU) (Technoland Z-SYS 070DC), and only the events producing signals at both detectors in coincidence were considered muon events.…”

“…For validation of the current FFT computation, Fig. 5 compares the results of the FFT of MCR and ATH 49 as they were recorded during the previous 2 months (August 1–September 30). Four fundamental tidal constants are well reproduced, and the spectrum shapes are almost identical between MCR and ATH.…”

“…Figure 6 shows the time series of the abnormal tides measured muographically between 15:50 on October 1 and 07:20 on October 2, 2021. These time series were derived by subtracting ATH from the tide levels converted from MCR 49 . The decay curves (Eq.…”

Periodic Sea-Level Oscillation in Tokyo Bay Detected with the Tokyo-Bay Seafloor Hyper-Kilometric Submarine Deep Detector (TS-HKMSDD)

“…In this work, 20 muographic sensor modules (MSMs) were deployed inside the Aqua-Tunnel to construct a linear array of MSMs called the Tokyo-Bay Sea oor Hyper-Kilometric Submarine Deep Detector (TS-HKMSDD). Since a detailed description of HKMSDD can be found elsewhere 49 , it is only brie y introduced here. Each MSM consisted of two scintillation detectors, and only the events producing signals at both detectors in coincidence were considered muon events.…”

“…For validation of the current FFT computation, Figure 5 compares the results of the FFT of MCR and ATH 49 as they were recorded during the previous 2 months (August 1 -September 30). Four fundamental tidal constants are well reproduced, and the spectrum shapes are almost identical between MCR and ATH.…”