10:45 AM - 12:15 PM
[SSS12-P07] Seafloor Pressure Observation for Field Evaluation of New Silicon Resonant Sensor Using MEMS Technology
Keywords: MEMS silicon resonant pressure sensor, Seafloor precise pressure observation, Free-fall pop-up type Ocean Bottom Pressure gauge(OBP)
For observations of vertical crustal deformation and tsunamis, precise pressure measurement on seafloor is useful. At the present, pressure observations using precise quartz resonant sensors have been mainly conducted. A new silicon resonant sensor using Micro Electro Mechanical Systems (MEMS) technology are recently developed for Nankai Trough seafloor network for earthquakes and tsunamis-net (N-net) and has advantages of low-power consumption, compact-size, constant quality, and high sensitivity. The developed sensor has high stability due to small size of a sensing unit, and individual difference of the sensors is small because of using the MEMS technology. In addition, influence of movement of the sensor itself is small because pressure for measurement is directly transferred to the sensing unit. These advantages are suitable for precise pressure observation on seafloor. Before routine observations using this new sensor, we evaluate performance of the new silicon resonant sensor for seafloor pressure observation, particularly implementation to N-net.
Free-fall pop-up type Ocean Bottom Pressure gauge (OBP) using a quartz resonant sensor has already been developed and used for routine observations. The new silicon pressure gauge also outputs data as frequency change, and a supply voltage for the new sensor is similar to that of the existing sensor. Therefore, we can replace only the pressure gauge of the OBP system. The recorder inside the OBP measures frequency of signals from the pressure gauge using frequency counter and store frequency value with time stamp to SD cards. We assembled the OBP for the filed evaluation of the new silicon sensor. The new silicon pressure gauge has a pressure vessel made by stainless steel, and has two oscillators for separation of effects of pressure and temperature. For measurement, a frequency reference for counting is provided by Chip Scale Atomic Clock (CSAC) in the recorder. A time windows to estimate frequency of outputs from the gauges was set to 1 s.
Slow-slip events frequently occurred below off-Boso peninsula region, near Tokyo. Therefore, we have performed monitoring using OBPs for more than 10 years. Evaluation of the new pressure gauge was carried out with this observation. We deployed an OBP with a new sensor on August 23, 2021 in the region off Boso peninsula, Chiba Prefecture, Japan by the R/V Shinsei-maru KS21-19 cruise. Water depth was 3,436 m. The deployment position of the OBP with the new sensor is the same as position of ordinary OBP with the precise quartz resonant sensor, which monitors vertical movement and tsunamis. The data from the new sensor and the ordinary sensors can be compared for evaluation of the new sensor. The first OBP was successfully recovered on November 4, 2021 and the second OBP with another new silicon sensor was deployed at the same place on the same day during the R/V Shinsei-maru KS21-26 cruise. The second OBP was recovered on March 13, 2022 by the R/V Kaiyo-maru No.3. The ordinary OBP continued the observation during two observations of OBPs with the new sensor.
As a result of two observations, we obtained total 203-day records. We estimated ambient noise spectra using recovered data, and compare the new sensors to the ordinary sensor. Spectra using about 4.5 hour data were estimated every 1 hour and we calculated probability using all obtained spectra. All sensors have identical noise level at periods longer than about 50 s. However, the new silicon sensor seems to have higher noise levels at periods between 50 s and 10 s. During the second observation period, a volcano in Tonga erupted and sea level fluctuation was observed worldwide. The OBPs were recorded this sea-level fluctuation. The data were applied bandpass filter from 3600s to 10 s. The waveform from both sensors are identical, and both sensors indicate amplitude of sea-level changes were 7 hPa.
Free-fall pop-up type Ocean Bottom Pressure gauge (OBP) using a quartz resonant sensor has already been developed and used for routine observations. The new silicon pressure gauge also outputs data as frequency change, and a supply voltage for the new sensor is similar to that of the existing sensor. Therefore, we can replace only the pressure gauge of the OBP system. The recorder inside the OBP measures frequency of signals from the pressure gauge using frequency counter and store frequency value with time stamp to SD cards. We assembled the OBP for the filed evaluation of the new silicon sensor. The new silicon pressure gauge has a pressure vessel made by stainless steel, and has two oscillators for separation of effects of pressure and temperature. For measurement, a frequency reference for counting is provided by Chip Scale Atomic Clock (CSAC) in the recorder. A time windows to estimate frequency of outputs from the gauges was set to 1 s.
Slow-slip events frequently occurred below off-Boso peninsula region, near Tokyo. Therefore, we have performed monitoring using OBPs for more than 10 years. Evaluation of the new pressure gauge was carried out with this observation. We deployed an OBP with a new sensor on August 23, 2021 in the region off Boso peninsula, Chiba Prefecture, Japan by the R/V Shinsei-maru KS21-19 cruise. Water depth was 3,436 m. The deployment position of the OBP with the new sensor is the same as position of ordinary OBP with the precise quartz resonant sensor, which monitors vertical movement and tsunamis. The data from the new sensor and the ordinary sensors can be compared for evaluation of the new sensor. The first OBP was successfully recovered on November 4, 2021 and the second OBP with another new silicon sensor was deployed at the same place on the same day during the R/V Shinsei-maru KS21-26 cruise. The second OBP was recovered on March 13, 2022 by the R/V Kaiyo-maru No.3. The ordinary OBP continued the observation during two observations of OBPs with the new sensor.
As a result of two observations, we obtained total 203-day records. We estimated ambient noise spectra using recovered data, and compare the new sensors to the ordinary sensor. Spectra using about 4.5 hour data were estimated every 1 hour and we calculated probability using all obtained spectra. All sensors have identical noise level at periods longer than about 50 s. However, the new silicon sensor seems to have higher noise levels at periods between 50 s and 10 s. During the second observation period, a volcano in Tonga erupted and sea level fluctuation was observed worldwide. The OBPs were recorded this sea-level fluctuation. The data were applied bandpass filter from 3600s to 10 s. The waveform from both sensors are identical, and both sensors indicate amplitude of sea-level changes were 7 hPa.