Ruey-Chang Wei

Acoustics and oceanographic observations collected during the QPE Experiment by Research Vessels OR1, OR2 and OR3 in the East China Sea in the Summer of 2009

Abstract : This document describes data, sensors, and other useful information pertaining to the ONR sponsored QPE field program to quantify, predict and exploit uncertainty in observations and prediction of sound propagation. This experiment was a joint operation between Taiwanese and U.S. researchers to measure and assess uncertainty of predictions of acoustic transmission loss and ambient noise, and to observe the physical oceanography and geology that are necessary to improve their predictability. This work was performed over the continental shelf and slope northeast of Taiwan at two sites: one that was a relatively flat, homogeneous shelf region and a more complex geological site just shoreward of the shelfbreak that was influenced by the proximity of the Kuroshio Current. Environmental moorings and ADCP moorings were deployed and a shipboard SeaSoar vehicle was used to measure environmental spatial structure. In addition, multiple bottom moored receivers and a horizontal hy drophone array were deployed to sample transmission loss from a mobile source and ambient noise. The acoustic sensors, environmental sensors, shipboard resources, and experiment design, and their data, are presented and described in this technical report.

THREE-DIMENSIONAL ACOUSTIC SIMULATION OF AN ACOUSTIC REFRACTION BY A NONLINEAR INTERNAL WAVE IN A WEDGE BATHYMETRY

Nonlinear internal wave (NIW) results in three dimensional acoustic effect such as ducting and whispering gallery effects in acoustic propagation. Acoustic energy restricted within internal wave crests (crest–crest) on the shelf constitutes the ducting effect, and energy confined along the crest when the source is located upslope from the NIW crest is known as the whispering gallery effect. Numerical experiments are presented in this paper for the study of 3D acoustic effects caused by both internal wave and wedge-bathymetry. 3D effects are predicted by Wide-Angle-FOR3D and the modal contents are calculated by MOS3DPEF. Following are the case studies detailing differences between 2D and 3D calculation, and the joint effect of propagating internal waves with upslope-bathymetry. Modeled time series of transmission Loss reveal that internal wave induces the oceanic waveguide and concentrate acoustic energy along the wave front. By modeling larger calculation ranges (20 km) and deeper deploying sources, the changing of the growth and decline of acoustic energy and lower acoustic mode amplitude by range, along the front of internal wave can be observed in this paper.

Observed acoustic arrival structure and intensity variability induced by transbasin nonlinear internal waves in the South China Sea basin

During the 2005‐2006 Windy Island Nonlinear Soliton Experiment (WISE), large‐amplitude internal waves were observed by in situ oceanographic sensors to propagate eastward from the Luzon Strait, through the deep basin, onto the shelf and Dongsha Plateau of the South China Sea year round except winter. In a parallel effort to measure the effects of these transbasin internal waves on long‐range, low‐frequency sound propagation, an acoustic source with a center frequency of 400‐Hz and bandwidth of 100‐Hz was moored on the west side of the deep basin transmitting a phase‐modulated m‐sequence signal every 15 min from February to October 2006. These periodic transmissions were recorded by a receiver moored 166 km to the east of the source. The recording was processed to give the arrival structure of a pulse and its temporal changes over the eight‐month period. The observed temporal variability in the arrival structure and in the acoustic intensity were analyzed using time‐series techniques and models with empha...

MEASUREMENT AND SIMULATION FOR WIND NOISES IN THE OCEAN ENVIRONMENTS WITH NONLINEAR INTERNAL WAVES

This study obtains wind noise variations by experimental data and simulated results to describe meteorological and oceanic effects. The ambient noise data were measured by a vertical line array in the 2001 ASIAEX South China Sea experiment. An acoustic propagation model is used in noise modeling for calculating the sound pressure of noises at receiving sites, including the effects of ocean environmental changes, bottom interactions, and noise fluctuations at different depths. Both range-independent and range-dependent sound speed profiles are generated with in-situ water temperature data. Results show fluctuating noise levels with variations in ocean environments. But the fluctuations are small such that only weak correlation exists in the acoustic noise data and ocean data. Results also indicate that using range-independent sound speed profiles can simulate noise field in range-dependent ocean environments with nonlinear internal waves for shallow regions with flat bottoms.

Initial study of ambient noise modeling for 2001 ASIAEX SCS Experiment

Although ambient noise has been an object of study for a long time, there is little modeling done for real ocean environment to reflect oceanographic changes. The numerical simulation in this study is based on PE code, with environmental and bathymetry data from the 2001 ASIAEX SCS experiment. Simple sources were distributed near sea surface in the model, and source levels in significant range were estimated by the wave height data of experiment. It is well known that strong internal waves often occur in the South China Sea, which can cause significant change in water temperature distribution, thus the sound propagation. Moreover, the roughness of sea surface and bottom are also important factors in noise energy distribution. In this initial study, the fluctuation of noise energy would be evaluated by the varying spatial ocean environment. The computational noise levels would be compared with measurements on vertical line array in ASIAEX SCS experiment for adjusting the parameters and source levels.

Data analysis and modeling of broadband acoustic propagation perpendicular to internal wave fronts and sand dune crests in the South China Sea

Very large subaqueous sand dunes were discovered on the upper continental slope of the northeastern South China Sea (SCS) in the spring of 2007 during an ONR 322OA-funded field experiment which was designed to study the large transbasin internal solitary waves (ISW) that are generated by tidal forcing in the Luzon Strait. These internal waves and sand dunes are important acoustical features, as it is expected that they will cause significant anomalies in the acoustical field. In the spring of 2014, a broadband source was deployed to transmit 850-1150 Hz LFM signals to receivers on a mooring in the center of the sand dune field. The acoustic transect was oriented perpendicular to the dune crests, ISW fronts and isobaths. Data analysis and extended modeling are presented to quantify the degree to which these features impact the propagation of broadband signals in the 100-2000 Hz band as a function of source depth and frequency.

Analysis of low frequency ocean ambient noise induced by internal wave in sand dune region of northern South China Sea

Most powerful internal waves in oceans were found in South China Sea, which were generated in Luzon Strait and mainly driven by tides. In past decades, researches of internal wave’s effects on ocean processes have been concentrated on the slope of continental shelf, where transformations of internal waves were significant, so were the induced phenomena. In recent years, large groups of underwater sand dunes were discovered along the upper continental slope, whose formation was speculated to be related to internal wave’s energy. In 2014, acoustical and oceanographic moorings were deployed in the sand dune region to study acoustical fluctuations due to the coupled effects of internal waves and sand dunes. Ocean ambient noise data were collected by four SHRUs (Several Hydrophone Recording Unit) and one VLA (Vertical Line Array) at different depths, analysis, and comparison of noise during internal wave events were presented in this study. Low frequency noises were generated by the passing of internal wave, i...

Estimation of rainfall contribution to ocean ambient noise in Northeastern Taiwan Sea

Ocean ambient noise data were collected by underwater MACHO (MArine Cable Hosted Observatory) system, deployed by Central Weather Bureau, at northeastern sea of Taiwan from October of 2011 to March of 2012. With most rainfall of Taiwan in the area of measurement, the rain-generated underwater noise was studied in an attempt to estimate rainfall contribution by the correlation analysis with the acoustic data. Due to the intermittent nature of rain fall occurrence, significant rainfall events with extended period were extracted from the weather data measured at nearest Su-ao weather station, and then patched together to form a rainfall intensity time series. Linear regression between corresponding ocean ambient noise level time series of several frequencies and rainfall intensity data were performed, so the characteristic frequency for prediction can be decided. Duration of this study was divided into Fall, Winter, and Spring, then the statistics and distributions of ambient noise level at different frequencies and rainfall intensities were calculated, so that seasonal variations were also discussed.

Analysis of ambient noise in the habitat of Indo-Pacific humpback dolphin (Sousa chinensis) in the West Coast of Taiwan

The west coast of Taiwan is one of the major habitats of Indo-Pacific humpback dolphin (Sousa chinensis). Ambient noise, changes with natural environment and human activities, is possible to affect the behaviors of marine mammals. Thus, it is necessary to conduct a long-term and systematic investigation of ambient noise in this area. This study deployed two underwater acoustic recorders (SM2M) in New Huwei River of the Yun-Lin coastal area (site YL) and Waisanding sandbar (site WS). 68- and 45-day acoustic data were collected in site YL and site WS. Results show that the low-frequency noise in site WS is lower than site YL due to the contributions of shipping or mechanical noises. In site YL, ambient noise of 1 to 2 kHz contains periodic changes because of the behaviors of croakers. Croakers usually appears before midnight in site YL, but no similar phenomenon is found in site WS. The frequency overlap between hearing range of marine mammal and high-level ambient noise is possible to cause the masking effect, even hearing loss. [Sponsored by the Forestry Bureau, Council of Agriculture, Taiwan under project “Population Ecology of Chinese White Dolphins and Ambient Noise Monitoring in its Habitat” No. 101-08-SB-14).]

Numerical study of the spatial and temporal variability of ambient noise in the coastal region east of Taiwan Strait

Noise soundscape represents the characteristics and spatial distributions of the ambient noise level under various noise source mechanisms. This is a significant index while describing an underwater acoustic environment, especially in the subjects related to marine mammal protection. Under the effects of topography, sediment, and oceanographic features, underwater soundscape varies with time and space. This paper focuses on estimating mean soundscape of wind driven noise and shipping noise and their spatial and temporal variability in the coastal region east of Taiwan Strait, which is the main habitat of the Sousa Chinensis. The ambient noise is studied numerically and local wind field and shipping density observed by Automatic identification Systems (AIS) are applied to generate noise source field. As for the ocean environment, the time varying/spatial dependent temperature profiles generated by the Taiwan Coastal Ocean Nowcast/Forecast System (TCONFS), which formulated on the basis of the Princeton Ocea...