scholarly journals Shallow-water acoustic tomography from angle measurements instead of travel-time measurements

2013 ◽  
Vol 134 (4) ◽  
pp. EL373-EL379 ◽  
Author(s):  
Florian Aulanier ◽  
Barbara Nicolas ◽  
Jérôme I. Mars ◽  
Philippe Roux ◽  
Romain Brossier
Keyword(s):  
Shallow Water ◽  
Travel Time ◽  
Acoustic Tomography ◽  
Angle Measurements

MAPPING TIDAL CURRENTS AND RESIDUAL CURRENTS BY USE OF COASTAL ACOUSTIC TOMOGRAPHY

2017 ◽  
Author(s):  
Xiao-Hua Zhu ◽  
Xiao-Hua Zhu ◽  
Ze-Nan Zhu ◽  
Ze-Nan Zhu ◽  
Xinyu Guo ◽  
...  
Keyword(s):  
Shallow Water ◽  
Shallow Water Equations ◽  
Mean Amplitude ◽  
Momentum Equation ◽  
Tidal Currents ◽  
Acoustic Tomography ◽  
Mean Values ◽  
Residual Currents ◽  
Water Depths ◽  
Deep Area

A coastal acoustic tomography (CAT) experiment for mapping the tidal currents in the Zhitouyang Bay was successfully carried out with seven acoustic stations during July 12 to 13, 2009. The horizontal distributions of tidal current in the tomography domain are calculated by the inverse analysis in which the travel time differences for sound traveling reciprocally are used as data. Spatial mean amplitude ratios M2 : M4 : M6 are 1.00 : 0.15 : 0.11. The shallow-water equations are used to analyze the generation mechanisms of M4 and M6. In the deep area, velocity amplitudes of M4 measured by CAT agree well with those of M4 predicted by the advection terms in the shallow water equations, indicating that M4 in the deep area where water depths are larger than 60 m is predominantly generated by the advection terms. M6 measured by CAT and M6 predicted by the nonlinear quadratic bottom friction terms agree well in the area where water depths are less than 20 m, indicating that friction mechanisms are predominant for generating M6 in the shallow area. Dynamic analysis of the residual currents using the tidally averaged momentum equation shows that spatial mean values of the horizontal pressure gradient due to residual sea level and of the advection of residual currents together contribute about 75% of the spatial mean values of the advection by the tidal currents, indicating that residual currents in this bay are induced mainly by the nonlinear effects of tidal currents.

scholarly journals Travel-time correction and preliminary results for ocean acoustic tomography in South China Sea

2019 ◽  
Vol 283 ◽  
pp. 04003
Author(s):  
Xingyu Ji ◽  
Hangfang Zhao
Keyword(s):  
Kalman Filter ◽  
South China Sea ◽  
Travel Time ◽  
South China ◽  
Sound Speed ◽  
Acoustic Tomography ◽  
Speed Profile ◽  
Travel Times ◽  
Sound Speed Profile ◽  
Hydrophone Array

An acoustic tomography trial experiment was conducted in South China Sea during May to August in 2016. Two moorings are installed apart from about 56.94 km, while each consists of one low frequency source, 20 hydrophones deployed from the depth of about 400 m to 1600 m, total 32 depth sensors and 3 compass and tilt sensors. Due to internal waves and currents in this area, as a typical value, horizontal drift of a mooring can reach 300 m, thus moorings drift need to be considered to correct ray travel-time. In this paper, the shape of a mooring is estimated firstly and locations of all hydrophone array elements are then calculated and finally used to determine travel-time perturbation of acoustic arrivals. The mooring is modelled as 2 curves, while the end of the mooring is fixed at the cement anchor on the sea floor. Optimization is used to acquire hydrophone location inferential solution. The inferred shape of hydrophone array and element locations are used to correct the travel-times measured in the experiment. We find that corrected travel-times match the trend of the change of sound speed profile better in the sea. Finally, the corrected travel-times are used to tomography of sound speed profile. AR (Autoregressive) process is used to describe the dynamic evolution of sound speed profile and Kalman filter is applied in the sequential estimation. The performances of the time-independent method and the method using AR process and Kalman filter are compared, reasonably the latter is better than the former in particular with abundant measured data.

Application of shallow-water acoustic tomography to measure flow direction and river discharge

2016 ◽  
Vol 51 ◽  
pp. 30-39 ◽  
Author(s):  
Masoud Bahreinimotlagh ◽  
Kiyosi Kawanisi ◽  
Mochammad Meddy Danial ◽  
Mohamad Basel Al Sawaf ◽  
Junya Kagami
Keyword(s):  
Shallow Water ◽  
River Discharge ◽  
Flow Direction ◽  
Acoustic Tomography

Acoustic tomography on the basis of travel-time measurement

2004 ◽  
Vol 15 (7) ◽  
pp. 1420-1428 ◽  
Author(s):  
Peter Holstein ◽  
Armin Raabe ◽  
Roland Müller ◽  
Manuela Barth ◽  
David Mackenzie ◽  
...  
Keyword(s):  
Travel Time ◽  
Time Measurement ◽  
Acoustic Tomography

ACOUSTIC TRAVEL-TIME PERTURBATIONS DUE TO SHALLOW-WATER INTERNAL WAVES IN THE YELLOW SEA

2014 ◽  
Vol 22 (01) ◽  
pp. 1440003
Author(s):  
FAN LI ◽  
XINYI GUO ◽  
TAO HU ◽  
LI MA
Keyword(s):  
Internal Wave ◽  
Shallow Water ◽  
Travel Time ◽  
Internal Waves ◽  
Yellow Sea ◽  
High Frequency ◽  
Simple Relation ◽  
Ocean Dynamics ◽  
The Yellow Sea ◽  
Acoustic Travel Time

Internal waves in shallow-water cause variations in sound speed profiles and lead to acoustic travel-time perturbations. In summer 2007, a combined acoustics/physical oceanography experiment was performed to study both the acoustical properties and the ocean dynamics of the Yellow Sea. The internal waves were recorded by the thermistor arrays. The receiving hydrophone array is enabled to monitor the acoustic travel-time fluctuations over the internal wave activities. It is shown that the activity of high frequency internal waves (having 3–6 min period) dominated the travel time perturbation. In this paper, we compare the data of high frequency internal wave with acoustic travel-time perturbation data and analyze the correlation between them. A simple relation between the modal travel-time perturbation and the displacement of the thermocline is developed which might be useful for monitoring purposes.

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