Precise Positioning of Underwater Static Objects without Sound Speed Profile

A new method of positioning underwater static objects is presented based on Global Positioning System (GPS) acoustics. It adopts a model in which the ranging errors follow a quadratic relation with the travel time of acoustic signals. A least squares technique is used to estimate the effective sound speed. The precise location of an object can then be made. The simulation shows that the method is capable of determining the three-dimensional position with an accuracy of 5 cm in a water depth of 500 m. The operating time is respectively 5–10 minutes in 50–100 m depth and 20–30 minutes in 500 m depth.     

Use of P coda for determination of yield on nuclear explosions

Summary. Spectral analysis of P and P coda from NTS explosions recorded at NORSAR shows that magnitudes based on spectral integration of P coda provide a significantly more precise measure of yield than those based on the initial P . Coda amplitudes and spectra are considerably less sensitive to near-source variations than the direct P . A plot of P -coda magnitude, after correcting for the effects of attenuation in the upper mantle and the source spectrum based on knowledge of approximate yield or m_b , versus log yield appears to have a slope of unity. This implies that P coda from several stations (with different but known t * values) can be combined to improve the yield determinations further. Single station P coda from Soviet explosions can also be used to determine relative yields that appear to be at least as precise as those from Lg based on a network of stations.     

宁夏及周边地区爆破的基本概况

研究收集了宁夏全区及周边地区的爆破258次,对这些爆破丛集发生的地点进行现场落实,收集爆破类型、爆破时间、炸药量等资料。从爆破分布、不同类型爆破波形特征、场地及传播路径对爆破衰减影响等三方面进行研究。结果表明:爆破的波形记录特征不仅和爆破的类型有关,不同爆破场地及波传播路径在初动、周期、衰减速度均有不同表现,并解析了存在差别的原因与台站场地响应有关。     

Development and deployment of a precision underwater positioning system for in situ laser Raman spectroscopy in the deep ocean

The field of ocean geochemistry has recently been expanded to include in situ laser Raman spectroscopic measurements in the deep ocean. While this technique has proved to be successful for transparent targets, such as fluids and gases, difficulty exists in using deep submergence vehicle manipulators to position and control the very small laser spot with respect to opaque samples of interest, such as many rocks, minerals, bacterial mats, and seafloor gas hydrates. We have developed, tested, and successfully deployed by remotely operated vehicle (ROV) a precision underwater positioner (PUP) which provides the stability and precision movement required to perform spectroscopic measurements using the Deep Ocean Raman In situ Spectrometer (DORISS) instrument on opaque targets in the deep ocean for geochemical research. The positioner is also adaptable to other sensors, such as electrodes, which require precise control and positioning on the seafloor. PUP is capable of translating the DORISS optical head with a precision of 0.1 mm in three dimensions over a range of at least 15 cm, at depths up to 4000 m, and under the normal range of oceanic conditions (T, P, current velocity). The positioner is controlled, and spectra are obtained, in real time via Ethernet by scientists aboard the surface vessel. This capability has allowed us to acquire high quality Raman spectra of targets such as rocks, shells, and gas hydrates on the seafloor, including the ability to scan the laser spot across a rock surface in sub-millimeter increments to identify the constituent mineral grains. These developments have greatly enhanced the ability to obtain in situ Raman spectra on the seafloor from an enormous range of specimens.     

Tracking the North Korean nuclear explosion of 2006, using seismic data from Japan and satellite data from Taiwan

The location of the 2006 nuclear explosion in North Korea has been accurately imaged by back-projected regional Pn waves recorded by the Japanese Hi-net array. Based on the determined location, the nuclear explosion site can be identified from geo-referenced FORMOSAT-2 satellite images. The seismically determined epicenter is about 2.5 km northeast of the original estimate of its absolute location. Results indicate that a remote suspect event had been unambiguously detected and accurately located by a dense array within a regional distance. Employing ground truth correction, the satellite images can be referenced for shifting the array-determined epicenter to its absolute position. After correction, this event can be treated as a reference event for accurately locating future nuclear explosions. Our study utilizes public information from a dense seismic network and further demonstrates that commercial observation satellites can accurately monitor compliance with the Comprehensive Nuclear-Test-Ban Treaty, as well as earthquake and tsunami hazards almost in real time.     

A long‐range and high‐resolution underwater acoustic positioning system

Abstract

It is desired to track the location of an underwater data collecting platform using acoustic range data. A long‐range and high‐resolution acoustic system for underwater locating has been investigated. The system provides continuous and highly accurate tracking of a platform referenced to bottom‐mounted buoys. Each reference buoy contains an acoustic transponder, which is used to obtain ranging data from the transponder to the platform. The transponder has a signal source that is phase‐modulated by a maximal‐length binary sequence and a correlation processing unit to be capable of detecting received acoustic signals with high SNR in a noisy environment or in attenuation due to long‐range propagation, and to identify multipath acoustic signals. The acoustic system has been designed and sea tests tried. The results of that experiment have yielded capability of a submeter underwater acoustic positioning system.     

土-结爆炸冲击相互作用模爆试验相似设计方法

模爆试验是研究爆炸冲击荷载作用下地基动力性能、土-结爆炸冲击相互作用及埋地防护结构抗爆能力与破坏机理等的重要手段之一。模型相似设计是确保模爆试验能够尽可能真实地反映原型爆炸冲击动力性状的关键之一。以上覆饱和砂土层对浅埋地下圆拱直墙式防护隧道免遭炸弹触地爆炸触发地冲击波破坏的保护效应为研究目的,基于目前广泛应用的Bockinghamπ定理,采用量纲分析方法,并且结合考虑土-结体系非线性爆炸冲击动力响应、土-结接触面爆炸冲击动力响应以及爆炸地冲击波-结构动力相互作用等的相似性,求解土-结爆炸冲击相互作用模爆试验的模型设计相似关系。     

澄江动物群的核心价值:动物界成型和人类基础器官诞生

澄江动物群以富含多门类精美软躯体构造化石享誉学界,是寒武纪大爆发主幕的见证者;它亲眼目睹了地球动物树上几乎所有主要门类祖先的首次大聚会.对该动物群30多年的大规模调查研究大体上可以划分为3个阶段.始自1984年的第一个10年(1984 1994年),早期动物树上的基础动物亚界和原口动物亚界的大量门类被发现,然而对后口动...