Reciprocal acoustic transmission experiment at Mihara-Seto in the Seto Inland Sea, Japan

Taniguchi, Nobuyuki; Takahashi, T.; Yoshiki, Kengo; Yamamoto, Hironori; Sugano, Tsukasa; Mutsuda, Hidemi; Sakuno, Yuji

doi:10.1250/ast.42.290

Cited by 2 publications

(9 citation statements)

References 9 publications

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“…In our previous report on this experiment, we showed that there were spike-like variations in the path-averaged currents between the S2 and S4 stations and the S3 and S4 stations with a slight time lag (Figure 4 in Taniguchi et al, 2021b). Such spike-like variation is found in almost every ebb tide.…”

Section: Resultssupporting

confidence: 50%

“…For the path between S2 and S3, the path-averaged current observation failed during low tides because of the shallow bank near station S3 (Taniguchi et al, 2021b). During no observation, using r i =1.02 caused relatively large ensemble spread (panel B3).…”

Section: Resultsmentioning

confidence: 99%

“…This indicates that the time interval between the Kalman updates may be extended although we conducted the acoustic transmission and the Kalman updates every two minutes. Note that however, there is flow patterns that cause spike-like or triangle-shape variation in the pathaveraged currents (Taniguchi et al, 2021a;Taniguchi et al, 2021b); thus, one still needs high-frequent transmissions to measure (record) the pathaveraged currents as references. Also, sufficiently frequent measurements and updates can recursively pull the ensembles toward the measured solution and do not allow the ensembles to diverge (to bimodal) even in strongly nonlinear dynamics (Evensen et al, 2022).…”

Section: Discussionmentioning

confidence: 99%

“…The other idea is about the transmission timing of the signal: the start time of each pulse was synchronized among all stations by using the one pulse-per-second signal of GPS, but time-shifted slightly so that the arrival signals do not overlap at all stations. Some of the results of the experiment are found in a report by Taniguchi et al (2021b).…”

Section: Field Observationmentioning

confidence: 91%

“…Table 1 summarizes the transmission signal parameters for this experiment. In the experiment, we introduced two ideas on signal transmission (Taniguchi et al, 2021b). The first idea was about the periodicity of m-sequences: the transmission signal in the experiment was one period of an m-sequence of 2,047 digits (i.e., 11th order m-sequence; Table 1), but the last 63 and first 64 digits of the m-sequence were respectively added to the head and tail of the m-sequence to achieve the original auto-correlation property of repeated m-sequences.…”

Section: Field Observationmentioning

confidence: 99%

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Reconstruction of horizontal tidal current fields in a shallow water with model-oriented coastal acoustic tomography

Taniguchi

Mutsuda²,

Arai³

et al. 2023

Front. Mar. Sci.

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Reciprocal acoustic transmission and coastal acoustic tomography (CAT) is a powerful tool for measuring tidal currents in shallow coastal water, especially if data assimilation is employed. In previous CAT data assimilation studies, the ensemble Kalman filter (EnKF) has been implemented to assimilate observed path-averaged velocity, but ad-hoc procedures called localization and inflation, which compensate for issues associated with using ensemble approximation, were not always implemented. In this study, EnKF is applied to assimilate the path-averaged currents obtained from a reciprocal acoustic transmission experiment conducted at Mihara-Seto in the Seto Inland Sea, Japan, with four acoustic stations in 2020 to reconstruct spatiotemporal variations of tidal currents at the observation site. We executed EnKF with several combinations of different values of the inflation, localization, and the number of ensemble members. The resulting data assimilated velocity reconstructions are compared with acoustic Doppler current profiling (ADCP) results. The results show that data assimilation with EnKF improved the velocity reproduction compared with the model prediction and that implementing covariance inflation contributed to additional improvements. The covariance localization did not improve the results in our case. The best result in terms of fractional error variance (FEV) between the ADCP velocity was obtained from the case with 980 ensemble members with a covariance inflation of 1.01; the FEV was 7.9%. The case of 98 ensemble members with a covariance inflation of 1.01 resulted in similar performance; the FEV value was 8.2%. Thus, with the covariance inflation, the number of ensemble member used in previous CAT studies are reasonable. In the study, we also clarified the reason for the high-frequency variation in the observed path-averaged currents in a preliminary experiment; the path-averaged currents had captured the spatiotemporal variation of vortex generation associated with island wakes. The reciprocal acoustic transmission with EnKF can capture short-period variation over a long period; thus, it can be used in studies of coastal physical processes with various time scales.

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Section: Resultssupporting

confidence: 50%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Field Observationmentioning

confidence: 91%

Section: Field Observationmentioning

confidence: 99%

See 3 more Smart Citations

Reconstruction of horizontal tidal current fields in a shallow water with model-oriented coastal acoustic tomography

Taniguchi

Mutsuda²,

Arai³

et al. 2023

Front. Mar. Sci.

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Application of coastal acoustic tomography: calibration of open boundary conditions on a numerical ocean model for tidal currents

Taniguchi,

Mutsuda,

Arai

et al. 2024

Front. Mar. Sci.

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Coastal acoustic tomography (CAT), which measures path-averaged currents from reciprocal acoustic transmission experiments and reconstructs velocity fields from the multiple path-averaged current data, is useful for monitoring tidal currents in coastal shallow water, especially if data assimilation is employed. Previous CAT data assimilation studies have focused on state estimation problems, i.e., the reconstruction of tidal currents and following dynamical discussion. In this study, we investigate the use of path-averaged currents in a boundary control problem. Specifically, we aim to use the observed path-averaged currents to determine the parameters of a numerical ocean model, which were tidal amplitudes and phases as the open boundary conditions in this study. We investigate two methods: using the ensemble Kalman filter (EnKF) results and a linearization approach called model Green’s function method. Both calibration methods decreased the amplitudes of tidal constituents at the open boundaries. We compare the model performance between the model predictions with and without the calibration of the open boundary conditions. The model predictions with the calibrated open boundary conditions improved the agreement with the observed path-averaged current. We also implemented the sequential updates of EnKF with the two calibrated open boundary conditions. The EnKF results with the independently calibrated two open boundary conditions improved the agreement with the comparison data obtained by acoustic Doppler current profiler measurement compared with the original EnKF result with the initial open boundary conditions.

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Reciprocal acoustic transmission experiment at Mihara-Seto in the Seto Inland Sea, Japan

Cited by 2 publications

References 9 publications

Reconstruction of horizontal tidal current fields in a shallow water with model-oriented coastal acoustic tomography

Reconstruction of horizontal tidal current fields in a shallow water with model-oriented coastal acoustic tomography

Application of coastal acoustic tomography: calibration of open boundary conditions on a numerical ocean model for tidal currents

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