A Benthic Terrain Classification Scheme for American Samoa   总被引：2，自引：0，他引：2  

Emily R. Lundblad  Dawn J. Wright  Joyce Miller  Emily M. Larkin  Ronald Rinehart  David F. Naar  Brian T. Donahue  S. Miles Anderson  Tim Battista 《Marine Geodesy》2006,29(2):89-111

Coral reef ecosystems, the most varied on earth, continually face destruction from anthropogenic and natural threats. The U.S. Coral Reef Task Force seeks to characterize and map priority coral reef ecosystems in the U.S./Trust Territories by 2009. Building upon NOAA Biogeography shallow-water classifications based on Ikonos imagery, presented here are new methods, based on acoustic data, for classifying benthic terrain below 30 m, around Tutuila, American Samoa. The result is a new classification scheme for American Samoa that extends and improves the NOAA Biogeography scheme, which, although developed for Pacific island nations and territories, is only applicable to a maximum depth of 30 m, due to the limitations of satellite imagery. The scheme may be suitable for developing habitat maps pinpointing high biodiversity around coral reefs throughout the western Pacific.  相似文献   

Comparison of volcanic rifts on La Palma and El Hierro, Canary Islands and the Island of Hawaii     

J. Acosta  E. Uchupi  D. Smith  A. Muñoz  P. Herranz  C. Palomo  P. Llanes  M. Ballesteros 《Marine Geophysical Researches》2003,24(1-2):59-90

The meso-scale (km) morphology of the well-studied volcanic rift zones on the Island of Hawaii is compared to the morphology of the lesser known rift zones of La Palma and El Hierro, Canary Islands. We find that there are both differences and similarities in their morphologic characteristics. In general, the rift zones on La Palma and El Hierro are shorter (a few tens of km in length) than those on Hawaii (ranging up to >100 km in length), perhaps reflecting both magma supply and composition. Many of the rift zones on Hawaii have well defined axial zones, both on-and offshore. In contrast, the rift zones on La Palma and El Hierro display various geometries ranging from linear ridges having smooth to irregular crests to structures with a broad fan-like morphology in plan view. The pronounced fanning may be a reflection of: 1) the stress field within the rift being insufficient to trap dikes within a narrow region, 2) dike injection and volcanism shifting laterally through time, 3) volcanoes building nearly one atop of another in the Canary Islands, superimposing the stress field of one structure on the other and thus yielding a more complex distribution of gravitational stresses, and 4) low rate of magma supply producing low magma pressures and thus randomly oriented dike injections. Irregularities and curvature along the axes of the rifts on La Palma and El Hierro may be a reflection of differences in the rate of magma production. Unlike the volcanoes on the Island of Hawaii there may be insufficient volumes of lavas erupted on La Palma and El Hierro to smooth out irregularities. The superposition of rifts from different volcanoes may also add to topographic irregularities in the Canary Islands, especially if eruption rates are low.  相似文献   

Merged GLORIA sidescan and Hydrosweep pseudo-sidescan: Processing and creation of digital mosaics     

Robert T. Bird  Roger C. Searle  Valerie Paskevich  David C. Twichell 《Marine Geophysical Researches》1996,18(6):651-661

We have replaced the usual band of poor-quality data in the near-nadir region of our GLORIA long-range sidescan-sonar imagery with a shaded-relief image constructed from swath bathymetry data (collected simultaneously with GLORIA) which completely cover the nadir area. We have developed a technique to enhance these pseudo-sidescan images in order to mimic the neighbouring GLORIA backscatter intensities. As a result, the enhanced images greatly facilitate the geologic interpretation of the adjacent GLORIA data, and geologic features evident in the GLORIA data may be correlated with greater confidence across track. Features interpreted from the pseudo-sidescan may be extrapolated from the near-nadir region out into the GLORIA range where they may nt have been recognized otherwise, and therefore the pseudo-sidescan can be used to ground-truth GLORIA interpretations. Creation of digital sidescan mosaics utilized an approach not previously used for GLORIA data. Pixels were correctly placed in cartographic space and the time required to complete a final mosaic was significantly reduced. Computer software for digital mapping and mosaic creation is incorporated into the newly-developed Woods Hole Image Processing System (WHIPS) which can process both low- and high-frequency sidescan, and can interchange data with the Mini Image Processing System (MIPS) most commonly used for GLORIA processing. These techniques are tested by creating digital mosaics of merged GLORIA sidescan and Hydrosweep pseudo-sidescan data from the vicinity of the Juan Fernandez microplate along the East Pacific Rise (EPR).  相似文献   

At-sea distribution of female southern elephant seals relative to variation in ocean surface properties   总被引：3，自引：0，他引：3  

Bradshaw  Corey J.A.; Higgins  Jane; Michael  Kelvin J.; Wotherspoon  Simon J.; Hindell  Mark A. 《ICES Journal of Marine Science》2004,61(6):1014-1027

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Segmentation and morphotectonic variations along a slow-spreading center: The Mid-Atlantic Ridge (24°00′ N– 30°40′ N)     

Jean-Christophe Sempéré  Jian Lin  Holly S. Brown  Hans Schouten  G. M. Purdy 《Marine Geophysical Researches》1993,15(3):153-200

Analysis of Sea Beam bathymetry along the Mid-Atlantic Ridge between 24°00 N and 30°40 N reveals the nature and scale of the segmentation of this slow-spreading center. Except for the Atlantis Transform, there are no transform offsets along this 800-km-long portion of the plate boundary. Instead, the Mid-Atlantic Ridge is offset at intervals of 10–100 km by nontransform discontinuities, usually located at local depth maxima along the rift valley. At these discontinuities, the horizontal shear between offset ridge segments is not accommodated by a narrow, sustained transform-zone. Non-transform discontinuities along the MAR can be classified according to their morphology, which is partly controlled by the distance between the offset neovolcanic zones, and their spatial and temporal stability. Some of the non-transform discontinuities are associated with off-axis basins which integrate spatially to form discordant zones on the flanks of the spreading center. These basins may be the fossil equivalents of the terminal lows which flank the neovolcanic zone at the ends of each segment. The off-axis traces, which do not lie along small circles about the pole of opening of the two plates, reflect the migration of the discontinuities along the spreading center.The spectrum of rift valley morphologies ranges from a narrow, deep, hourglass-shaped valley to a wide valley bounded by low-relief rift mountains. A simple classification of segment morphology involves two types of segments. Long and narrow segments are found preferentially on top of the long-wavelength, along-axis bathymetric high between the Kane and Atlantis Transforms. These segments are associated with circular mantle Bouguer anomalies which are consistent with focused mantle upwelling beneath the segment mid-points. Wide, U-shaped segments in cross-section are preferentially found in the deep part of the long-wavelength, along-axis depth profile. These segments do not appear to be associated with circular mantle Bouguer anomalies, indicating perhaps a more complex pattern of mantle upwelling and/or crustal structure. Thus, the long-recognized bimodal distribution of segment morphology may be associated with different patterns of mantle upwelling and/or crustal structure. We propose that the range of observed, first-order variations in segment morphology reflects differences in the flow pattern, volume and temporal continuity of magmatic upwelling at the segment scale. However, despite large first-order differences, all segments display similar intra-segment, morphotectonic variations. We postulate that the intra-segment variability represents differences in the relative importance of volcanism and tectonism along strike away from a zone of enhanced magma upwelling within each segment. The contribution of volcanism to the morphology will be more important near the shallowest portion of the rift valley within each segment, beneath which we postulate that upwelling of magma is enhanced, than beneath the ends of the segment. Conversely, the contribution of tectonic extension to the morphology will become more important toward the spreading center discontinuities. Variations in magmatic budget along the strike of a segment will result in along-axis variations in crustal structure. Segment mid-points may coincide with regions of highest melt production and thick crust, and non-transform discontinuities with regions of lowest melt production and thin crust. This hypothesis is consistent with available seismic and gravity data.The rift valley of the Mid-Atlantic Ridge is in general an asymmetric feature. Near segment mid-points, the rift valley is usually symmetric but, away from the segment mid-points, one side of the rift valley often consists of a steep, faulted slope while the other side forms a more gradual ramp. These observations suggest that half-grabens, rather than full-grabens, are the fundamental building blocks of the rift valley. They also indicate that the pattern of faulting varies along strike at the segment scale, and may be a consequence of the three-dimensional, thermo-mechanical structure of segments associated with enhanced mantle upwelling beneath their mid-points.  相似文献   

Multibeam Bathymetry of the Håkon Mosby Mud Volcano     

Andreas?BeyerEmail author  Rike?Rathlau  Hans?Werner?Schenke 《Marine Geophysical Researches》2005,26(1):61-75

The Håkon Mosby Mud Volcano is a natural laboratory to study geological, geochemical, and ecological processes related to deep-water mud volcanism. High resolution bathymetry of the Håkon Mosby Mud Volcano was recorded during RV Polarstern expedition ARK XIX/3 utilizing the multibeam system Hydrosweep DS-2. Dense spacing of the survey lines and slow ship speed (5 knots) provided necessary point density to generate a regular 10 m grid. Generalization was applied to preserve and represent morphological structures appropriately. Contour lines were derived showing detailed topography at the centre of the Håkon Mosby Mud Volcano and generalized contours in the vicinity. We provide a brief introduction to the Håkon Mosby Mud Volcano area and describe in detail data recording and processing methods, as well as the morphology of the area. Accuracy assessment was made to evaluate the reliability of a 10 m resolution terrain model. Multibeam sidescan data were recorded along with depth measurements and show reflectivity variations from light grey values at the centre of the Håkon Mosby Mud Volcano to dark grey values (less reflective) at the surrounding moat.  相似文献   

A Review About SAR Technique for Shallow Water Bathymetry Surveys     

范开国  黄韦艮  贺明霞  傅斌 《中国海洋工程》2007,21(4):723-731

Synthetic Aperture Radar(SAR)has become one of the important tools for shallow water bathymetry surveys.This has significant economic efficiency compared with the traditional bathymetry surveys.Numerical models have been developed to simulate shallow water bathymetry SAR images.Inversion of these models makes it possible to assess the water depths from SAR images.In this paper,these numerical models of SAR technique are reviewed,and examples are illustrated including in the coastal areas of China.Some issues about SAR technique available and the research orientation in future are also discussed.  相似文献   

舰载浅水激光测深系统研究   总被引：1，自引：0，他引：1  

刘建国  刘文清  王亚萍  魏庆农 《海洋技术学报》2001,20(2):30-32

本文提出了近海浅水区域水深测量的激光双频相位法测量方案，采用声光调制1064nm和532nm光波分别测量水面和水底距离。在实验室进行了该系统的模拟实验，证实了该方案的可行性。  相似文献   

采用重力异常的导纳理论推估海底地形   总被引：3，自引：2，他引：1  

欧阳明达  孙中苗  翟振和  刘晓刚 《测绘学报》2015,44(10):1092-1099

系统探讨了采用重力异常的导纳理论推估海底地形的方法。在频率域内对海底地形和重力异常的相关性进行了分析,确定在20~300 km波段内两者相关系数最高,适合通过重力异常反演。以皇帝海山链为例,分别采用未补偿导纳模型和顾及挠曲补偿的导纳模型开展研究,其中涉及的地壳厚度和有效弹性厚度等参数通过均衡响应函数法得到。引入余弦低通滤波器,有效地解决了向下延拓过程中产生的高频震荡问题。算例结果表明,采用重力异常的导纳理论能够有效地反演海底地形,结果真实可靠,反演模型的相对精度在6%左右,与ETOPO1模型相当,且能够刻画出ETOPO1模型中未显现的地形细节。由于地形变化剧烈,反演模型在海山链沿线附近精度不甚理想。  相似文献   

Thermal Modelling Fo the Suboceanic Lithospheric Flow     

Véronique Dechoux 《Geophysical Journal International》1993,114(1):156-164

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