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排序方式: 共有210条查询结果,搜索用时 15 毫秒
1.
Imaging of Buried Archaeological Materials: The Reflection Properties of Archaeological Wood 总被引:1,自引:0,他引:1
Stephanie H.L. Arnott Justin K. Dix Angus I. Best David J. Gregory 《Marine Geophysical Researches》2005,26(2-4):135-144
Effective marine archaeological site management demands detailed information on not only the spatial distribution of artefacts
but also the degradation state of the materials present. Although sonar methods have frequently been used in an attempt to
detect buried wooden shipwrecks they are currently unable to indicate their degradation state. To assess the sensitivity of
acoustic measurements to changes in the degradation state of such material, and hence the potential for sonars to quantify
degradation, laboratory measurements of compressional wave velocity, as well as bulk density for oak and pine samples, in
varying states of decay, were undertaken. These data enabled the calculation of theoretical reflection coefficients for such
materials buried in various marine sediments. As wood degrades, the reflection coefficients become more negative, resulting
in the hypothesis that the more degraded wood becomes, the easier it should be to detect. Typical reflection coefficients
of the order of −0.43 and −0.52 for the most degraded oak and pine samples in sand are predicted. Conversely, for wood exposed
to seawater the predicted reflection coefficients are large and positive for undegraded material (0.35 for oak, 0.18 for pine)
and decrease to zero or slightly below for the most degraded samples. This indicates that exposed timbers, when heavily degraded,
can be acoustically transparent and so undetectable by acoustic methods. Corroboration of these experimental results was provided
through comparison with high resolution seismic reflection data that has been acquired over two shipwrecks. 相似文献
2.
David Harris Robert K. Cessaro Fred K. Duennebier David A. Byrne 《Marine Geophysical Researches》1987,9(1):67-94
The Hawaii Institute of Geophysics began development of the Ocean Subbottom Seisometer (OSS) system in 1978, and OSS systems were installed in four locations between 1979 and 1982. The OSS system is a permanent, deep ocean borehole seismic recording system composed of a borehole sensor package (tool), an electromechanical cable, recorder package, and recovery system. Installed near the bottom of a borehole (drilled by the D/V Glomar Challenger), the tool contains three orthogonal, 4.5-Hz geophones, two orthogonal tilt meters; and a temperature sensor. Signals from these sensors are multiplexed, digitized (with a floating point technique), and telemetered through approximately 10 km of electromechanical cable to a recorder package located near the ocean bottom. Electrical power for the tool is supplied from the recorder package. The digital seismic signals are demultiplexed, converted back to analog form, processed through an automatic gain control (AGC) circuit, and recorded along with a time code on magnetic tape cassettes in the recorder package. Data may be recorded continuously for up to two months in the self-contained recorder package. Data may also be recorded in real time (digital formal) during the installation and subsequent recorder package servicing. The recorder package is connected to a submerged recovery buoy by a length of bouyant polypropylene rope. The anchor on the recovery buoy is released by activating either of the acoustical command releases. The polypropylene rope may also be seized with a grappling hook to effect recovery. The recorder package may be repeatedly serviced as long as the tool remains functionalA wide range of data has been recovered from the OSS system. Recovered analog records include signals from natural seismic sources such as earthquakes (teleseismic and local), man-made seismic sources such as refraction seismic shooting (explosives and air cannons), and nuclear tests. Lengthy continuous recording has permitted analysis of wideband noise levels, and the slowly varying parameters, temperature and tilt.Hawaii Institute of Geophysics Contribution 1909. 相似文献
3.
对单芯电缆传输这种通讯技术的原理进行了阐述;分析提出了部分电路、部件的技术指标;作为一种数据传输的手段,对单芯电缆传输技术在海洋专用CTD中的应用进行了相关论述. 相似文献
4.
海底勘查技术的最新发展 总被引:4,自引:0,他引:4
本文将介绍用于探测海底三维地质特征的海底勘查的最新发展。它主要包括海底地形测绘技术,海底形貌观测技术、海底地层声学探测技术等。 相似文献
5.
具有国际先进水平的CTD定标检测设备 总被引:1,自引:0,他引:1
在国家863计划的支持下,海洋技术研究成功研制了一套CTD仪器的校准设备,本文介绍了设备的组成,性能,设计经过与SBE设备进行了比较,表明该设备达到了EOCECTD设备的校准要求,同时,该设备是海洋技术研究所开发自有的高度CTD剖面仪的有力工具。 相似文献
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9.
投弃式海流剖面测量仪测量原理研究 总被引:1,自引:0,他引:1
根据投弃式海流剖面测量仪的测量原理建立了二维海流运动感生电场离散和连续模型,通过模型推导得到了海流与感生电场间的关系公式。通过对海流感生电磁场的分析,对海流测量的基本方法进行了研究,通过感生电磁场的量级的计算,确定了投弃式海流剖面测量仪研究的主要方向和关键技术。 相似文献
10.
基于九龙站风廓线雷达实时水平风数据制定了水平风数据的质量控制方法,首先求取中位数水平风场,其次构建实际观测风场和中位数风场的差值序列,然后求取差值序列的均方差,再根据差值均方差得到质控判别式,最后试验求取质控判别式中的质控阈值。通过对九龙站2017年风廓线雷达水平风数据质量控制发现,实测风向数据有2044185个,25721个没有通过质控,未通过质控的风向数据占总观测的比例是1.258%,风向数据在近地层通过质控的数据最多,随高度增加通过质控的数据量有所下降。实测风速数据有2044185个,18296个没有通过质控,未通过质控的风速数据占总观测的比例是0.895%,风速数据在2000~4000 m出错的最少,近地层次之,4500~7000 m出错的数据最多。质控后风廓线雷达和探空观测风数据的均方根误差减小,相关系数增加,风向数据质量在500~7000 m提升明显,风速数据在1500~8000 m之间提升明显。 相似文献