DGPS在航道的水下地形与水深测量中的应用示例

ＧＰＳ动态实时差分定位模式具有精度高,性能可靠,使用方便等优点,它在许多领域都展示了广阔的应用前景,本文将以ＤＧＰＳ在航道的水下地形与不深测量方面的具体应用为例予以简单介绍,代与同行交流。     

DGPS在广西沿海海底地形测绘中的应用

DGPS（DifferentialGlobalPositioningSystem）测量技术即差分定位技术,包括实时差分和后处理差分定位技术,正在远海和近海测量中得到广泛应用。后处理差分定位与微波定位及GPS实时差分定位相比,具有作用距离远,不受基准台与船台之问的障碍物影响以及减少基准台等优点。对于近海大比例尺（大于1：1万）测量,可采用实时差分定位的方法,而小于1：1万中小比例尺海底地形图测绘及海上其他工程测量,采用后处理差分定位,既能满足精度要求,又能提高工作效率。本文主要介绍利用DGPS后处理定位方法,在测绘广西沿海1：5万海底地形图中的应用情况。     

废弃的黄河三角洲的地形特征及演化

根据2005年开展的海底地形调查资料并结合前人资料,对废弃的黄河口三角洲海区的海底地形特征及演化进行了分析。通过分析表明,近20年来,本区海岸处于侵蚀状态,蚀退速率约在50～80 m/a之间,海底地形处于冲涮状态,5m和10m等深线向岸方向移动600～900 m左右。     

Impact of Ocean Mean Dynamic Topography on Satellite Data Assimilation

The response of an eddy-permitting ocean model to changes imposed by the use of different mean dynamic topographies (MDT) is analyzed in a multivariate assimilation context, allowing the evaluation of this impact, not only on the surface circulation, but also on the interior ocean representation. The assimilation scheme is a reduced-order sequential Kalman filter (SEEK). In a first set of experiments, high resolution sea surface temperature, along-track sea surface height and sea surface salinity from climatology are assimilated into a 1/3° resolution North and Tropical Atlantic version of the HYCOM model. In a second experiment, in situ profile data are assimilated in addition to the surface measurements.

The first set of experiments illustrates that important differences in the representation of the horizontal model circulation pattern are related to differences in the MDT used. The objective of assimilation is to improve the representation of the 3D ocean state. However, the imperfect representation of the mean dynamic topography appears to be an important limiting factor with regard to the degree of realism obtained in the simulated flow.

Vertical temperature and salinity profiles are key observations to drive a general circulation ocean model toward a more realistic state. The second set of experiments shows that assimilating them in addition to sea surface measurements is a far from trivial exercise. A specific difficulty is due to inconsistencies between the dynamic topography diagnosed from in situ observations and that diagnosed from sea surface height. These two fields obtained from different data sources do not contain exactly the same information. In order to overcome this difficulty, a strategy is proposed and validated.     

Traveling wavefront ray tracing and its applications

The current discussion of whether marine geodesy is something entirely new or part of oceanography or geodesy can be clarified by re‐examining our notions about the basic business of geodesy. This paper contends that the same basic geodetic services, which were needed for millenia to chart and control new territory, are being adapted now to the marine environment to suit modern accuracy standards. In a brief historical review it is shown that conceptually, the oceanic regions were always an integral part of geodetic concern. The oceans were certainly part of the world for the ancient map makers and for Pythagoras’ spherical earth model. Notions connected with the marine geoid were implied in ancient speculations. Distances and directions at sea, even depths, were determined to meet the requirements of the times. With the modern sophistication in geodetic theory and measuring techniques, these ideas became more refined and demanding in turn, but they were there all the time. For obvious reasons, land geodesy developed faster; marine geodesy will catch up now, because only now there is the technical capability and also an urgent economic motivation.     

Major Features of Topography,Geology, and Crustal Stability in the Taiwan Strait: A Scientific Approach to the Problem of the Taiwan Strait Tunnel Project

This article discusses briefly the major features of topography, geology, and crustal stability of the possible Taiwan Strait Tunnel Project (TST Project) area. Any one route of the conceived TST Project is larger than either of the English Channel Tunnel or the Seikan submarine Tunnel (Japan) by at least three times in length, and the topographic and geologic conditions are rather more complex and complicated than those of the former two projects. Moreover, the Taiwan Strait is a seismic risk area. Hence, the selection of the route of the submarine tunnel should take advantage of the favorable conditions in the topographic, geologic, seismologic, and other fields to avoid the unfavorable circumstances. At the end of the article, two supposed by comparable routes, especially the south one of TST Project are discussed.     

2.5-D DC Resistivity Modeling Considering Flexibility and Accuracy

We highlighted the flexibility of using unstructured mesh together with the local refinement by a resistivity model with complicated topography. The effect of topography is emphasized. Based on this, we calculated a specific class of layered models and found that the accuracy is not always satisfactory by utilizing the standard approach. As an improvement, we employed the layered earth as the reference model to calculate the wavenumbers. The comparison demonstrates that the accuracy is considerably improved...     

基于Hv方法的三轴液压振动系统频响函数估计的研究

三轴液压振动系统是实验室内模拟振动环境的主要设备,其主要功能是精确地复现给定的功率谱和时间历程。振动控制技术是实现这一目标的关键技术,它以频响函数估计为基础。频响函数估计的精度影响控制过程的快速性和稳定性。本文对几种典型的频响函数估计方法进行了分析,针对传统方法精度低且受到矩阵病态条件约束等缺点,应用特征分析与摄动理论构造了一种多入多出的Hv方法,并且应用三轴液压振动系统的实测数据对其进行了检验。结果表明该方法是适用的。     

The linearisation of three dimensional drag force in random seas with current

A frame invariant linearisation method for three-dimensional drag force in random seas with current is presented. Numerical results are compared with those obtained from a commonly used linearisation method which is based on a non-frame invariant approximation to the drag force. Significant differences are discovered and the present method is found to show closer agreement with computed time histories of the true drag force.     

Spatial Distribution of Shelf- and Slope-Dwelling Fishes Collected by Bottom Longline off Lanzarote and Fuerteventura, Canary Islands

Abstract. A total of 1789 fish belonging to 38 families and 73 species were collected at depths between 18 and 1102 m during 216 bottom longline operations off Lanzarote and Fuerteventura, Canary Islands, between February 1994 and December 1995. For each species the depth distribution is provided. Length-weight and depth-size relationships are reported for three shelf-dwelling species. The bigger-deeper relationship found in two of them contrasts with the bigger-shallower pattern of the deeper living trichiurid Lepidopus caudatus . In November 1997, nine additional bottom longline operations were carried out off eastern Fuerteventura at depths between 805 and 1217 m. In this area, after earlier studies in October 1995, a spawning aggregation of the morid Mora moro was encountered for the second time. The catches of 1997 revealed a strongly male-biased sex ratio. Also, the males showed a significantly lower gonadosomal index than two years earlier. These findings indicate slight interannual variations in reproductive timing and an earlier arrival of male Mora moro at the spawning grounds. Clear variations in the number of fish collected at adjacent sites possibly reflect a preference for distinct microhabitats. Preliminary evidence of local upwelling of cold water above the spawning grounds is provided by satellite imagery.