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Warren J.D. Stanton T.K. McGehee D.E. Dezhang Chu 《Oceanic Engineering, IEEE Journal of》2002,27(1):130-138
It is well known that the behavior of zooplankton and, in particular, their orientation distribution dramatically affects the level of backscattered acoustic energy. As a result, interpretation of acoustic survey data in the ocean is subject to error. In order to quantify these effects, laboratory data from two important classes of animals were collected. The data involved broad-band (350-650 kHz) acoustic signals insonifying individual animals whose orientation was varied over the range 0°-360° in 1° increments. The animals were from two major anatomical groups: fluid-like (decapod shrimp; Palaemonetes vulgaris) and elastic-shelled (periwinkles; Littorina littorea). The data were analyzed both in the time domain (with pulse compression processing) and the frequency domain. Averages of the laboratory data over different orientation distributions illustrate the variability in average target strength that can be expected in the ocean environment. The average target strength of the shrimp varied by 3 dB when averaged over orientation distributions centered around broadside and end-on incidence. In addition, size estimates from pulse compression processing of the broad-band echoes were made for various orientation distributions for both the shrimp and periwinkles. These results show the necessity of animal orientation information for the proper interpretation of acoustic backscatter data 相似文献
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东海陆架盆地岩石密度与磁性 总被引：9，自引：0，他引：9
本文在东海陆架盆地２０口钻井１６０块岩心标本物测定和１７口钻井密度测井的基础上，通过整理、分析、统计，给出了东海陆架盆地的岩石密度和磁性特征。 相似文献
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稻田CH4排放和土壤,大气条件的关系 总被引：12，自引：1，他引：12
在杭州地区利用静态箱法对稻田CH_4排放进行连续观测,结果证明CH_4排放率有较大的日变化和季节变化,CH_4排放率的日变化较复杂,除了和温度变化一致的峰型外,还有夜间峰、双峰型、多峰等。CH_4排放率的季节波动较大,在分蘖期和长穗前期分别有一较大峰值,早稻和晚稻的变化规律略有不同。稻田CH_4排放规律可用稻田中有机物含量的变化和空气、土壤温度的变化等作一定性解释。 早稻和晚稻的CH_4排放总量有较大的差别,平均来看,早稻的排放量为0.46g·m~(-2)·d~(-1),晚稻为0.80g·m~(-2)·d~(-1)。稻田CH_4排放也有较大的年际变化,1988年全年CH_4排放量为0.23g·m~(-2)·d~(-1),1989年为0.95g·m~(-2)·d~(-1),施肥对CH_4排放有一定的影响,施有机肥的稻田CH_4排放量最高,施化肥的稻田次之,不施肥的稻田CH_4排放量最低。 相似文献
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川西马井构造上部地层裂隙发育,地层承压能力低,布井密集,钻井时易与邻井气层窜通,发生漏失,甚至造成复杂型井漏。虽然常规桥塞堵漏亦能堵漏成功,但由于地层承压能力低而易发生复漏和反吐,堵漏一次成功率低。为提高堵漏效果和一次成功率,在原有堵漏技术的基础上,引入高效堵漏剂,通过室内配方优化及施工工艺完善,形成了高效桥塞堵漏技术。现场试验表明该技术堵漏一次成功率高,堵漏效果良好,为低承压力地层、易漏失层以及易与邻井气层窜通等造成的复杂型井漏提供了新的堵漏思路,对解决其它复杂井漏也具有一定的指导意义。 相似文献
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随着经济的发展,建筑装修损失占地震总损失的比重越来越大,对于大中城市装修损失的评估越来越引起人们的重视,而损失比是地震经济损失评估中非常关键的参数。本文在对损失比的概念及其国内外研究现状综合分析的基础上,采用现场抽样与专家咨询(Delphi法)相结合的方法,通过加权统计给出了不同结构类型、不同使用功能的建筑装修震害损失比取值范围。最后,将本文给出的取值范围与其它文献取值进行了对比分析,结果表明:在相同破坏等级下,装修破坏损失比要高于主体结构损失比,且在中等破坏及以上破坏等级下,前者要远大于后者。 相似文献
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Dezhang Chu Dajun Tang Austin T.C. Hinton A.A. Arthur R.I. Jr. 《Oceanic Engineering, IEEE Journal of》2001,26(1):70-83
In acoustic tomographic system capable of performing in situ two-dimensional (2D) acoustic imaging of shallow water sediments is described. This system is capable of resolving inhomogeneities greater than 10 cm and differentiating sound-speed variations greater than 2%, A tomographic inversion is performed in a 2D vertical slice of about 1 m 2 (1 m×1 m) using three identical probes, with each consisting of 70 evenly distributed transducers. In normal deployments, two of the probes are oriented vertically and are separated by about 1 meter, and the third is positioned horizontally right above the two vertical probes. The additional horizontal probe greatly improves the horizontal resolution of the system compared to conventional crosshole tomographic setups. Numerical simulations are performed to evaluate the influences of arrival time detection error and transducer position error on the performance of the tomography system. For an arrival time of 500 ns (standard deviation) and a position error of 4 mm (standard deviation), sound-speed anomalies of greater than 0.8% can be correctly predicted near the upper portion (close to the horizontal probe) and are resolvable near the lower portion. A controlled laboratory experiment was conducted to evaluate the performance of the system. The location of a polyurethane block (Conap EN22) used as a known target is correctly predicted while the inverted sound speed is about 9% lower than that from its actual value. Field data taken from a saturated muddy site are presented and analyzed. The inverted mean sound speed and attenuation are about 1480 ms-1 and 20 dBm-1, respectively 相似文献