Su-Uk Son

Measurements of Monostatic Bottom Backscattering Strengths in Shallow Water of the Yellow Sea

ABSTRACT: Measurements of bottom backscattering strengths in a frequency range of 6-14 kHz were made on the shallow water off the southern Gyeonggi Bay in Yellow Sea in May 2013, as part of the KIOST-HYU joint acoustics experiment. Geological surveys for the experimental area were performed using multi-beam echo sounder, sparker system, and grab sampling to investigate the bottom topography, sub-bottom profile and composition of surficial sediment, respectively. In this paper, the backscattering strengths as a function of grazing angle (in range of 28° ~ 69°) were estimated and compared to the predictions obtained by Lambert’s law and APL-UW scattering model. Finally, the effects of geoacoustic parameters corresponding to the experimental area on the backscattering strengths are discussed.Keywords: Bottom backscattering, Reverberation, Bottom roughness, Seafloor volume scattering PACS numbers: 43.30.Gv, 43.30.Hw†Corresponding author: Jee Woong Choi (choijw@hanyang.ac.kr) Department of Marine Sciences and Convergent Technology, Hanyang University, 55 Hanyangdaehak-ro, Sangnok-gu, Ansan15588, Republic of Korea(Tel: 82-31-400-5531, Fax: 82-31-406-6255)

Laboratory measurements of backscattering strengths from two-types of artificially roughened sandy bottoms

In the case of sandy bottom, the backscattering from the interface roughness is significantly dominant compared to that from the volume inhomogeneities, and the power spectrum of interface roughness thus becomes the most important factor to control the scattering mechanism. Backscattering strength measurements with a 50-kHz signal were made for two types of roughness (smooth and rough interfaces) which were artificially formed on a 0.5-m thick sandy bottom in a 5-m deep water tank. The roughness profiles were estimated by the arrival time analysis of 5-MHz backscattering signals emitted by the transducer moving parallel to the interface at a speed of 1 cm/s, which were then Fourier transformed to yield power spectra. In this talk, the measurements of backscattering strength as a function of grazing angle in a range of 35 to 90° are presented. Finally, the effect of different roughness types on the scattering strength will be discussed in comparison with the predictions obtained by theoretical scattering m...

Underwater vector sensor communication in KOREX-17

The underwater acoustic communication channel is subject to multiple interactions with the ocean boundaries and refraction due to sound speed structure of water column, which produces significant time spread. This phenomenon is referred to as inter-symbol interference (ISI), which results in degradation of error performance. Recently, a time reversal technique has been used for reducing the ISI. However, this requires a large-size array with spatially separated receivers to obtain higher spatial diversity gain, and it becomes a limitation to its application in space-constrained environment. An acoustic vector sensor (combined pressure and particle velocity) can potentially yield a better communication performance relative to a system using only hydrophones. In this talk, communication data collected using a vector sensor known as IVAR (Intensity Vector Autonomous Receiver) during Korea Reverberation Experiment (KOREX-17) conducted in shallow water located at 34° 43′ N, 128° 39′ E on May 23–31, 2017. The characteristics of the channel as probed by a pressure-only versus combined pressure plus particle velocity system are discussed along with some performance results of a vector sensor communication system. [Work supported by the ADD(UD170022DD) and the National Research Foundation of Korea(NRF-2016R1D1A1B03930983).]

Geoacoustic inversion of 3.5-kHz towed receiver data from the KOREX-17

The Korea Reverberation Experiment 2017 (KOREX-17) was conducted in a shallow water located in the south of the Geoje island, Korea. During the experiment, sound propagation measurements were made using a 3.5-kHz CW signal along different 2 tracks to a distance of ~10 km from a bottom-mounted source, ARMS (Autonomous Reverberation Measurement System). The signals were received by a SRH (Self Recording Hydrophone), which was towed at a depth of ~20 m during the measurements. The sound speed profile was almost iso-velocity, and the sediment at the site was mainly composed of silt having a mean grain size of 6 phi. Since the sound propagation in shallow water is greatly influenced by sound interaction with the sediment, geoacoustic inversion was tried using a genetic algorithm based matched field processing in which the measured acoustic pressure field was compared to the simulated field predicted by a parabolic-equation based propagation model (RAM). The results are compared to the geoacoustic parameters obtained by the empirical relationship to mean grain size and a sediment layering information obtained by a chirp sonar survey. [Work supported by Agency for Defense Development, Korea (UD170014DD).]The Korea Reverberation Experiment 2017 (KOREX-17) was conducted in a shallow water located in the south of the Geoje island, Korea. During the experiment, sound propagation measurements were made using a 3.5-kHz CW signal along different 2 tracks to a distance of ~10 km from a bottom-mounted source, ARMS (Autonomous Reverberation Measurement System). The signals were received by a SRH (Self Recording Hydrophone), which was towed at a depth of ~20 m during the measurements. The sound speed profile was almost iso-velocity, and the sediment at the site was mainly composed of silt having a mean grain size of 6 phi. Since the sound propagation in shallow water is greatly influenced by sound interaction with the sediment, geoacoustic inversion was tried using a genetic algorithm based matched field processing in which the measured acoustic pressure field was compared to the simulated field predicted by a parabolic-equation based propagation model (RAM). The results are compared to the geoacoustic parameters ob...

Oceanographic effects on mid-frequency acoustics during KOREX-17

A 9-day mid-frequency, shallow water experiment was conducted off Geoje Island, Republic of Korea, in May 2017. The experiment consisted of transmission, reverberation, and backscatter measurements. The experiment site includes a shallow bay, with water depth less than 30 m, which opens to the Korea Strait where the depth reaches 60 m at a range of a few kilometers from the bay entrance. While the bathymetry of the site is well documented, the geo-acoustic properties of the area is complex, comprised of mud with rock outcrops and regions of sand. The oceanography during the experiment was dominated by tidal forcing and this is expected to be the main source of temporal variability in propagation and reverberation at the site. This paper focus on understanding the variability of the water column in space and time by analyzing data from CTD casts and from a CTD chain, supplemented by data from a nearby oceanographic buoy. A preliminary assessment of the impact of this variability on transmission loss is also examine. [Work supported by the Office of Naval Research and the Agency for Defense Development.]A 9-day mid-frequency, shallow water experiment was conducted off Geoje Island, Republic of Korea, in May 2017. The experiment consisted of transmission, reverberation, and backscatter measurements. The experiment site includes a shallow bay, with water depth less than 30 m, which opens to the Korea Strait where the depth reaches 60 m at a range of a few kilometers from the bay entrance. While the bathymetry of the site is well documented, the geo-acoustic properties of the area is complex, comprised of mud with rock outcrops and regions of sand. The oceanography during the experiment was dominated by tidal forcing and this is expected to be the main source of temporal variability in propagation and reverberation at the site. This paper focus on understanding the variability of the water column in space and time by analyzing data from CTD casts and from a CTD chain, supplemented by data from a nearby oceanographic buoy. A preliminary assessment of the impact of this variability on transmission loss is als...

Measurements of high frequency acoustic transmission loss during SAVEX15

Transmission loss measurements in high frequency range along with the ocean environmental measurements were made during the Shallow-water Acoustic Variability EXperiment 2015 (SAVEX15) in the south of Jeju Island, Korea, where the water depth is about 100 m. Two vertical line arrays (VLAs) were moored with a distance of 5.5 km, covering the water column between 24 and 80 m. Continuous waves in a frequency band of 10-25 kHz were transmitted from a vertical source array at depths of 30-45 m. Sound speed and temperature profiles were measured using a standard/stationary conductivity-temperature-depth (CTD), underway CTD, and temperature loggers attached to the two VLAs. The measured sound speed profiles consistently reveal a sound speed minimum layer (SSML) at depths between 30 to 50 m. During the SAVEX15 period, the perturbations in the SSML derived by various kinds of internal waves were observed. In this talk, the temporal fluctuations of the measured transmission loss are presented, and the results are d...

Measurements of mid-frequency bottom interacting signals in Jinhae bay located on the southern coast of Korea

Acoustic bottom interacting measurements were conducted in shallow water (nominal water depth of 60 m) in Jinhae bay, southern coast of Korea, using 4 to 12 kHz CW signals in May 2015 and 2016. The surficial sediment at a site is mainly composed of silty clay with a mean grain size of 8 phi. Since the seafloor is relatively soft, the bottom-bounced path was very weak compared to direct and sea-surface-bounced paths. On the other hand, a strong arrival reflected from the sub-sediment layer was received after the bottom-bounced arrival especially at lower frequencies. The arrival time difference between the arrival reflected from water-sediment interface and that reflected from the second interface is used to estimate the sound speed in the surficial sediment layer. In addition, the bottom loss as a function of grazing angle are estimated using the bottom-bounded path. Finally, the results are compared to the sedimentary structure imaged by chirp sonar survey. [Work supported by Agency for Defense Developme...

Influence of multipaths on coherent acoustic communication in shallow water channel

In shallow water communication channel, acoustic interactions with sea surface and bottom interfaces cause the inter-symbol interference that hinders the efficient and reliable communication. In this case, signal-to-multipath ratio (SMR) rather than signal-to-noise ratio can be used as an indicator to describe the quality of the communication channel. However, it is difficult to estimate precisely the SMR from the measured communication data. In this talk, we propose the energy fraction of the channel impulse response existing within one symbol duration as an alternative to SMR. Communication experiment was conducted on the southern coast of Korea in waters 45 m deep in source-receiver ranges of 100 m to 1 km. The Bit-error-rate performance is compared to the energy fraction in one symbol duration. In addition, the correlation between the energy fraction in a symbol and SMR is investigated through a Monte Carlo simulation.