Abstract
We observed a distinct drop-off region in the bearing-time record of acoustic reverberation data acquired from the south-western continental margin of the Ulleung Basin, East Sea, in the summer of 2015. 3 kHz continuous waves with pulse lengths of 0.1, 0.3, and 1.0 s were used as source pulses, with an R/V Cheonghae vessel towing a variable depth source and a triplet towed array toward the deep sea from shallow water. The observed pattern changed as the R/V Cheonghae moved across the continental slope further into the sea. This pattern arises as a result of the downward-refracted beams in the 1/2 convergence zone interacting with the soft bottom. In addition, the boundary of the drop-off region was modeled with the two-way maximum travel time of the first bottom-reflected rays using the bathymetry model of the General Bathymetric Chart of the Oceans, 2020. Some discrepancies were observed when comparing the modeled curve to the measured results, and the inaccuracy of the bathymetry model on the continental slope could be the main cause of these discrepancies. This pattern could be useful for bathymetry mapping, as well as estimations of source and receiver configurations.
Highlights
IntroductionA mid-frequency deep-water target and reverberation experiment was performed using an active triplet towed array sonar system (ATASS) in the southwestern area of the Ulleung Basin in the Korean East Sea in August 2015 [1,2]
The active triplet towed array sonar system (ATASS) 15 experiment was conducted near the southwestern continental margin of the Ulleung Basin, East Sea, Korea, on 20–21 August 2015 (Figure 1), where the bathymetry was generated from the General Bathymetric Chart of the Oceans (GEBCO) 2020 with a 15 arc-second resolution grid
We presented the analysis of 3-kHz continuous wave (CW) reverberation measured in the southwest4
Summary
A mid-frequency deep-water target and reverberation experiment was performed using an active triplet towed array sonar system (ATASS) in the southwestern area of the Ulleung Basin in the Korean East Sea in August 2015 [1,2]. The goal of this experiment was to test the capability of the active array system and to process the beam time series at a water depth exceeding 1000 m using several pulse types. In the bearing-time record (BTR) of those measurements, we observed a distinct pattern that was not visible in deeper water with a flat bottom. We investigated the reasons contributing to this pattern and confirmed them using acoustic propagation modeling
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