Profiling measurement of internal tides in Bali Strait by reciprocal sound transmission

Abstract

A reciprocal sound transmission experiment was carried out during June 10-13, 2015 along a cross-strait line in the Bali Strait with strong tidal currents to measure the vertical section structures of the range-averaged current and temperature at a 3 min interval. The five-layer structures of the range-averaged current and temperature in the vertical section were reconstructed by regularized inversion of the travel time data for two rays. The hourly-mean current showed the generation of nonlinear internal tides with amplitudes of 1.0-1.5 ms À1 and periods of 6 h superimposed on semidiurnal internal tides with amplitudes decreasing from the upper to lower layer. The hourly-mean temperature was characterized by variations with amplitudes of 1.0-1.5 C and periods of 6 and 8 h. The current variations showed an out-of-phase relation between the upper and lower layers while the temperature data varied in-phase for all five layers. The two-day-mean current and temperature showed a stratified structure, varying from À0:6 to À0:1 ms À1 and from 23.8 to 28.0 C, respectively. The five-layer current and temperature were significantly above the inversion errors.

Observing the Oceans Acoustically

“…Most recently, the focus has been on measuring in the straits associated with the Indonesian Through Flow (ITF). Measurements in the Bali Strait resolved a five-layer vertical structure of flow as well as strong non-linear tides (Syamsudin et al, 2017). Future plans are to sustain these measurements and extend them to the Lombok and other straits.…”

Observing Internal Solitary Waves in the Lombok Strait by Coastal Acoustic Tomography

“…The regularized inversion scheme proposed by Rajan et al (1987) and applied to ocean tomography by Syamsudin et al (2017) is adopted for three rays and four layers with depth ranges of 450-603, 300-450, 150-300, and 0-150 m for the first, second, third, and fourth layers, respectively. The travel time along the transmission path is calculated as follows:…”

“…The regularized inversion scheme proposed by Rajan et al () and applied to ocean tomography by Syamsudin et al () is adopted for three rays and four layers with depth ranges of 450–603, 300–450, 150–300, and 0–150 m for the first, second, third, and fourth layers, respectively. The travel time along the transmission path is calculated as follows: where y = {δ t i } is the one‐way travel time vector, x = {δC j } is the solution vector for the sound speed deviation, E = {−2l ij /C 0j 2 } is the transform matrix, and n = {n i } is the travel time error vector.…”

“…Coastal acoustic tomography (CAT), which was developed as a coastal‐sea application of ocean acoustic tomography (Munk et al, ), has been applied to various inland seas, estuaries, bays, and straits around Japan (Chen et al, ; Kaneko et al, ; Lin et al, ; Park & Kaneko, ; Yamaguchi et al, ; Yamaoka et al, ; Zhang et al, ; Zheng et al, ), China (Zhang et al, ; Zhu et al, ; Zhu et al, ; Zhu et al, ; Zhu et al, ), Indonesia (Syamsudin et al, ), and Taiwan (Huang et al, ). Subsurface‐moored CAT systems were deployed successfully around the underwater sound channel in the Luzon Strait in 2008 (Taniguchi et al, ).…”

Mapping Small-Scale Horizontal Velocity Field in Panzhinan Waterway by Coastal Acoustic Tomography

“…Initially, more comprehensive, multi-station measurements with CAT systems (more than five stations) were conducted by the Hiroshima University Group initially [ 6 , 7 , 8 , 9 ]. Of note, CAT has been highly applied in measuring various coastal–sea phenomena, including the tidal current [ 10 , 11 ], residual current [ 12 , 13 , 14 ], internal solitary waves [ 15 ], internal tides [ 16 ], tidal bores [ 17 ] and the coastal upwelling [ 18 , 19 ] et al This was attributed to its advantages, including low cost, compact system, simple instrument operation and easy execution on board. Additionally, it is worth noting that CAT reconstructs velocity structures with few sensors covering a wide range of survey zone [ 11 ], the traditional observation range (station-to-station distance), which might be less than 50 km in the coastal seas shallower than 100 m [ 2 ].…”