Observations of seabed bubbles of methane, an important greenhouse gas, at a natural marine hydrocarbon seep to evaluate the global methane budget per year is very important. The objective of this paper is to develop a new approach, in which the configuration and distribution of bubbles are adjusted before flow measurement, to measure cold seepage flow on seafloor by the wave form-amplitude parameters of acoustic transmission. After the spectrum analysis we lead to the height of the measurement window through which acoustic wave transmits to the opposite wave transducer is less than the distance which bubbles go up pass per second. And the bubble speed can be effectively measured by using the acoustic sensing system designed under the proposed height of the measurement window in the paper. The relationship between the bubble diameter and the measured acoustic wavelength is obtained under the Born approximation. Diameters of bubbles become smaller than 3 mm after they go through the honeycomb-core board and other structure parts, and the distribution of bubble populations is uniform. Spatial frequency spectrum analysis is applied to establish the relationship between geometry parameters of the piezoelectric transducer and the motion of bubbles, and the measurement accuracy of bubble velocity is expected to ± 2%. The nearly linear relationship between the amplitude of sound transmission and the gas bubble flow has been established through the experiment. It turns out to be an effective method of measuring the bubble flow.
LONG Jian-jun
,
HUANG Wei
,
ZOU Da-peng
,
DI Peng-fei
,
WU Jin-ping
. Method of measuring bubble flow from cool seeps on seafloor using acoustic transmission and preliminary experiments[J]. Journal of Tropical Oceanography, 2012
, 31(5)
: 100
-105
.
DOI: 10.11978/j.issn.1009-5470.2012.05.015
[1] CHEN DUOFU, SU ZHEN, CATHLES L M. Types of gas hydrates in marine environments and their thermodynamic -characteristics [J]. Terrestrial, Atmospheric and Oceanic Sciences, 2006, 17 (4): 723?737.
[2] JUDD A G, HOVLAND M, DIMITROV L I, et al. The geological methane budget at continental margins and its influence on climate change [J]. Geofliuds, 2002, 2 (2): 109?126.
[3] CABLE J E, BURNETT W C, CHANTON J P, et al. Field Evaluation of Seepage Meters in the Coastal Marine Environment [J]. Estuarine, Coastal and Shelf Science, 1997, 45 (3): 367?375.
[4] ROBERTS H. H. Fluid and gas expulsion on the northern Gulf of Mexico continental slope: Mud-prone to mineral-prone responses[M]// PAULL C K, DILLON W P. Natural Gas Hydrates: Occurrence, Distribution and Detection. New York: American Geophysical Union, 2001: 145?161.
[5] WASHBURN L, JOHNSON C, GOTSCHALK C C, et al. A Gas-Capture Buoy for Measuring Bubbling Gas Flux in Oceans and Lakes [J]. Journal of Atmospheric and Oceanic Technology, 2001, 18 (8): 1411?1420.
[6] GREINERT J, N?TZEL B. Hydroacoustic experiments to establish a method for the determination of bubble fluxes at cold seeps [J]. Geo-Marine Letters, 2004, 24 (2): 75?85.
[7] LEIFER I, BOLES J. Measurement of marine hydrocarbon seep flow through fractured rock and unconsolidated sediment [J]. Marine and Petroleum Geology, 2005, 22 (4): 551?568.
[8] NIKOLOVSKA A, WALDMANN C. Passive acoustic quantification of underwater gas seepage [C]//Proceedings of OCEANS 2006, Boston, MA, 2006. New York: IEEE, Dec. 2007: 1?6.
[9] ROBERTS D A, BRADLEY E S, CHEUNG R, et al. Mapping methane emissions from a marine geological seep source using imaging spectrometry [J]. Remote Sensing of Environment, 2010, 114 (3): 592?606.
[10] DEIMLING J S, GREINERT J, CHAPMAN N R, et al. Acoustic imaging of natural gas seepage in the North Sea: Sensing bubbles controlled by variable currents [J]. Limnology and Oceanography-Methods, 2010, 8: 155-171.
[11] SCHNEIDER VON, DEIMLING J. GasQuant—a hydroacoustic gas bubble monitoring system [R]. Victoria, Canada: University of Victoria, 2007：1?15.
[12] 陈忠, 颜文, 陈木宏, 等. 南海北部大陆坡冷泉碳酸盐结核的发现：天然气水合物新证据 [J]. 热带海洋学报，2006, 25 (1): 83?83.
[13] 徐华宁, 杨胜雄, 郑晓东, 等. 南中国海神狐海域天然气水合物地震识别及分布特征 [J]. 地球物理学报，2010, 53 (7): 1691?1698.
[14] 李灿苹, 刘学伟, 杨丽, 等. 气泡半径和含量对含气泡海水声波速度的影响 [J]. 现代地质，2010, 24 (3): 528 ?533.
[15] KAK A C. Principles of Computerized Tomographic Imaging [M]. New York: IEEE Press, 1999: 212?216.
[16] LEIFER I, DE LEEUW G, KUNZ G, COHEN L H. Calibrating optical bubble size by the displaced-mass method [J]. Chemical Engineering Science, 2003, 58 (23-24): 5211 ?5216.
[17] 钱祖文, 吴端. 气泡幕回声信号的起伏相关 [J]. 声学学报，1998, 23 (6): 505?508.
[18] 徐苓安. 相关流量测量技术 [M]. 天津: 天津大学出版社, 1988: 141?163.
[19] LONG JIANJUN, WU BAIHAI. Positioning Mobile Vehicle by Using Super-Short Baseline with AM Ultrasonic Beacon: ICMTMA 2009: Proceedings of International Conference on Measuring Technology and Mechatronics Automation, April 11-15, 2009 [C]. New Jersey: IEEE Computer Society, 2009, 3: 536?540.
[20] ORFANIDIS S J. Optimum Signal Processing. An Introduction [M]. 2nd ed. Englewood Cliffs, NJ: Prentice-Hall, 1996: 150?153.
