共查询到20条相似文献，搜索用时 546 毫秒
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Rene Forsbergbi Arne Vestergaard Olesen Adel Alshamsi Arne Gidskehaug Sahrum Ses Majid Kadir 《Marine Geodesy》2013,36(3):221-232
The Military Survey Department (MSD) of the United Arab Emirates (UAE) undertook an airborne gravity survey project for the marine area of the country in 2009, especially to strengthen the marine and coastal geoid in the near-shore regions. For the airborne gravity survey, 5 km spacing coast-parallel flight lines were planned and surveyed. These lines were supplemented by cross-lines in order to assess the quality of the airborne gravity surveys. The flight lines were extended 10 km, spacing lines further offshore. A Beech King Air 350 aircraft was used for the surveys, collecting data at a typical flight speed of 170 knots and a typical flight elevation of 900–1500 m, depending on weather conditions and topography. Gravity was measured with a ZLS-modified LaCoste and Romberg gravimeter (S-99), augmented with a Honeywell strap-down inertial navigation system unit. The estimated accuracy for the airborne gravity data is better than 2.0 mGal r.m.s., as judged from the airborne track crossovers. The new airborne gravimetry data changed the UAE coastal geoid by up to 30 cm in some regions, highlighting the importance of airborne gravity coastal surveys. 相似文献
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使用BEDMAP2关于南极大陆及周围海域和JGP95E关于全球表面高程、冰厚和冰下及水深地形数据,采用球坐标系下的扇形球壳块重力效应公式,在极方位投影直角坐标网格节点上计算了南极大陆及周围海域的近区及远区的地形和艾黎均衡重力效应。南极大陆冰盖带来可观的正重力效应,南大洋负重力效应又影响到了南极内陆,全球地形/均衡重力效应与局部地形高低有关联性,而低负值区主要分布在环南极的陆坡。获得的约1n mile间距的地形和艾黎均衡重力效应网格数据可用于南极大陆及周边海域的重力改正,提供准确、一致的布格重力异常和艾黎均衡重力异常。 相似文献
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ABSTRACTDifferent types of gravity observations are available over coastal areas. The main challenge for coastal geoid determination is the proper fusion of heterogeneous gravity data including land, shipborne, airborne, and altimetry-derived gravity data. This paper describes the gravity data fusion and the computation of the gravimetric quasigeoid in the coastal area of mainland China. An iterative procedure of the weighted least-squares prediction based on rectangular harmonic functions is used for merging the land, altimetric, shipborne, and airborne gravity data. Applying the analytical continuation method in Molodensky's theoretic frame, the merged gravity data are then used to determine the gravimetric quasigeoid model by using the generalized Stokes' integral in a remove-compute-restore fashion. The gravimetric quasigeoid model is compared with the height anomalies determined at 662 GPS leveling points over the coastal region of mainland China, where both the geodetic height and the normal height are known. The standard deviations of the differences in the coastal provinces range from 1.8 to 4.4 cm. For the entire computation area, the mean and standard deviation of the differences are 27.9 and 3.9 cm, respectively. 相似文献
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Ulrich Fleischer 《Marine Geophysical Researches》1971,1(3):314-327
A regional survey of the southern Reykjanes Ridge (52°N to 57°N) shows an irregular topography: a rift valley which is only partly recognizable as such, with varying azimuth and some fracturezone-like interruptions. The survey also comprised gravity and magnetic measurements.The course of the axis as well as the perpendicular fractures show up well in the free air anomalies as relative troughs within an area of positive free air gravity (Figure 5). There is no indication of density variations within the topographic masses.The anomaly pattern of total magnetic intensity indicates the exact position of the rift axis and a bifurcation at about 55°N. From the parallel magnetic anomalies south of 55°N (Figure 2) a spreading rate can be deduced of 1.10 cm/yr perpendicular to the rift axis (Figure 3). This spreading rate is at the same time the plate movement involved.A survey of the Iceland-Faeroe Ridge with a 3–5 miles grid shows large gravity and magnetic anomalies over a smooth topography, indicating large pockets of light material, probably of volcanic origin. These areas have normal magnetization. Positive gravity anomalies forming a ring structure along the 200 m isobath are characterized by reversed magnetization.The dissimilarity in morphology, seismicity and inner structure between the two ridges that intersect in Iceland suggest that there is no relation between the two phenomena.Paper presented at the meeting of the International Gravity Commission, Paris, on September 8, 1970. 相似文献
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利用卫星测高技术确定海洋重力场,垂线偏差数据作为导出观测量在实际工作中被普遍采用。利用物理大地测量边值问题的定义以及扰动位在球面边界条件下的解,给出了由垂线偏差计算大地水准面高、重力异常和扰动重力的公式。分析了不同积分计算公式在重力场阶谱表达形式下对垂线偏差误差的抑制作用,也分析了不同积分核函数的变化特性,得出基本结论:在利用卫星测高数据求解海洋重力场时,当以格网化海面垂线偏差数据计算重力场参数时,求解的大地水准面高的有效性和稳定性优于重力异常和扰动重力。 相似文献
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Ahmed Zaki Ahmed Hamdi Mansi Mohamed Selim Mostafa Rabah Gamal El-Fiky 《Marine Geodesy》2018,41(3):258-269
The determination of high-resolution geoid for marine regions requires the integration of gravity data provided by different sources, e.g. global geopotential models, satellite altimetry, and shipborne gravimetric observations. Shipborne gravity data, acquired over a long time, comprises the short-wavelengths gravitation signal. This paper aims to produce a consistent gravity field over the Red Sea region to be used for geoid modelling. Both, the leave-one-out cross-validation and Kriging prediction techniques were chosen to ensure that the observed shipborne gravity data are consistent as well as free of gross-errors. A confidence level equivalent to 95.4% was decided to filter the observed shipborne data, while the cross-validation algorithm was repeatedly applied until the standard deviation of the residuals between the observed and estimated values are less than 1.5 mGal, which led to the elimination of about 17.7% of the shipborne gravity dataset. A comparison between the shipborne gravity data with DTU13 and SSv23.1 satellite altimetry-derived gravity models is done and reported. The corresponding results revealed that altimetry models almost have identical data content when compared one another, where the DTU13 gave better results with a mean and standard deviation of ?2.40 and 8.71 mGal, respectively. A statistical comparison has been made between different global geopotential models (GGMs) and shipborne gravity data. The Spectral Enhancement Method was applied to overcome the existing spectral gap between the GGMs and shipborne gravity data. EGM2008 manifested the best results with differences characterised with a mean of 1.35 mGal and a standard deviation of 11.11 mGal. Finally, the least-squares collocation (LSC) was implemented to combine the shipborne gravity data with DTU13 in order to create a unique and consistent gravity field over the Red Sea with no data voids. The combined data were independently tested using a total number of 95 randomly chosen shipborne gravity stations. The comparison between the extracted shipborne gravity data and DTU13 altimetry anomalies before and after applying the LSC revealed that a significant improvement is procurable from the combined dataset, in which the mean and standard deviation of the differences dropped from ?3.60 and 9.31 mGal to ?0.39 and 2.04 mGal, respectively. 相似文献
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The geoid undulation on GRS80 in the Taiwan area at half‐degree grid points has been calculated using the reduced 30’ × 30’ block mean gravity anomalies and the OSU91A geopotential coefficient set up to degree and order 360. The OSU91A results have been used to compare with WGS84, CEM10C, and OSU86F geoid undulations determined in 18 first‐order triangulation stations of the Taiwan Geodetic Datum 1980 (TGD80). Comparisons have also been made between these free‐air anomalies determined from OSU91A, and terrestrial gravity anomalies. It has been found that the average difference between the OSU91A model‐derived, and 243 actual point free‐air anomalies is 16.8 ± 48.0 mgal. It has also been found that more reliable and dense terrestrial gravity data are needed, both for terrestrial observations and for the OSU91A model, to achieve the very high‐precision geoid on GRS80 in the area of study. 相似文献
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针对海洋区域离岸距离5～30km的范围内船载重力测量数据覆盖空白的现状,基于已有测线数据,对其进行不同空间距离采样形成对应的采样序列。利用动态时间规整算法计算其与初始测线数据的相关系数,依据相关系数与采样距离之间的关系,确定了最优重采样空间距离新方法。以最优重采样空间距离对测线数据进行重采样,利用拉格朗日插值算法,沿测线方向将测线数据向陆地推估。经过不同测线的内外部检核,结果表明船载重力测量向陆地方向扩展的保守距离约为5～10km,减少了船载重力测量数据在近岸海域覆盖空白的面积。本研究成果可为建立陆海一致垂直基准工作提供更全面的基础数据,技术方法可为航空重力、地磁等测线数据的精细处理及应用提供参考。 相似文献
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Sirsendu Chatterjee Rudradeb Bhattacharyya Laju Michael Kolluru Sree Krishna Tapan Jyoti Majumdar 《Marine Geodesy》2007,30(3):197-216
Geoid and gravity anomalies derived from satellite altimetry are gradually gaining importance in marine geoscientific investigations. Keeping this in mind, we have validated ERS-1 (168 day repeat) altimeter data and very high-resolution free-air gravity data sets generated from Seasat, Geosat GM, ERS-1 and TOPEX/POSEIDON altimeters data with in-situ shipborne gravity data of both the Bay of Bengal and the Arabian Sea regions for the purpose of determining the consistencies and deviations. The RMS errors between high resolution satellite and ship gravity data vary from 2.7 to 6.0 mGal, while with ERS-1 data base the errors are as high as 16.5 mGal. We also have generated high resolution satellite gravity maps of different regions over the Indian offshore, which eventually have become much more accurate in extracting finer geological structures like 85° E Ridge, Swatch of no ground, Bombay High in comparison with ERS-1satellite-derived gravity maps. Results from the signal processing related studies over two specific profiles in the eastern and western offshore also clearly show the advantage of high resolution satellite gravity compared to the ERS-1 derived gravity with reference to ship gravity data. 相似文献
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The knowledge of the bedrock topography (instead of the ocean-floor relief) is required in various geoscience studies investigating the evolution and structure of the oceanic lithosphere. The gross density structure and thickness of marine sediments were obtained from ocean drilling data or seismic surveys. Alternatively, marine gravity data corrected for the ocean and sediment density contrasts can be used for a detailed mapping of the bedrock topography. In this study, we compute and apply the sediment stripping correction to marine gravity data. The sediment density distribution is approximated by a 3-D density model derived based on the analysis of density samples from the Deep Sea Drilling Project. Methods for a spherical harmonic analysis and synthesis are utilized in computing the sediment stripping correction. Results show that this correction varies between 0 and 32 mGal. We also demonstrate that the approximation of heterogeneous sediment structures by a uniform density model yields large errors. The spectral analysis reveals a high correlation (>0.75) between the sediment-stripped marine gravity data and the bedrock topography. The application of the sediment stripping correction to marine gravity data enhanced the gravitational signature of the sediment-bedrock interface. 相似文献
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《Marine Geodesy》2012,35(1):63-85
AbstractWe introduce an iterative inversion method to address the problems in high-order seafloor topography inversion using gravity data (gravity anomaly and vertical gravity gradient anomaly), such as the difficulty in computing the equation and the uniqueness of the calculation results. A part of the South China Sea is selected as the experimental area. Considering the coherence and admittance function of gravity topography and vertical gravity gradient topography, the inversion band of the gravity anomaly and vertical gravity gradient anomaly in the study area is 30?km–120?km. Seafloor topography models of different orders are constructed using an iterative method, and the performance of each seafloor topography model is analyzed against ETOPO1 and other seafloor topography models. The experimental results show that as the inversion order increases, the clarity and richness of seafloor topographic expression continuously improve. However, the accuracy of seafloor topography inversion does not improve significantly when the inversion order exceeds a certain value, which is related to the contribution of high-order seafloor topography to gravity information. The results show that the accuracy of BGT4 (inversion model constructed by the gravity anomaly) is slightly poorer than that of BVGGT4 (inversion model constructed by the vertical gravity gradient anomaly) in areas with complex topography, such as multi-seamounts and trenches, and the results are generally better in areas with flat seafloor topography. 相似文献
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从地球重力场测量要素出发,按照局部重力场模型、区域重力场模型、全球重力场模型求解的发展思路,分析了对地球重力场测量技术手段的要求。根据高-低卫星跟踪卫星的距离和距离变率开展定轨研究的概念,梳理了卫星跟踪卫星重力测量系统的发展。针对卫星跟踪卫星重力测量技术的内涵,分析了高-低卫星跟踪卫星测量模式（SST-hl）和高-低低卫星跟踪卫星测量模式（SST—hll）的地球重力场测量本质。 相似文献
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海洋环境调查数据的客观分析图像是调查结果的直观体现,也是进一步科学研究的基础。在环境要素空间分布复杂的近海海域及陆架坡区,我们发现利用现有插值方法得到的结果有时会出现之前没有被关注到的局部异常,如常用的Kriging方法或三角网线性插值方法插值得到的图像有时会出现或轻或重的"藕"状或"台阶"状的层化结构异常。本文提出一种针对原始数据采用坐标变换方法,并联合使用三角网线性插值法和Kriging法两种方法进行数据插值,从而有效地避免了类似"藕"状或"台阶"状的层化结构假象,解决了插值方法在海洋环境调查数据插值过程中遇到的一个实际问题,也是对现有插值方法的一种补充。 相似文献
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经过三维重力正演计算，我们从台湾的布格重力异常中求得了深部重力异常，其深度相当于地壳下层。分析对比之后发现，深部重力异常等植线的形态，较好地反映了台湾的现代构造地貌特征。如东部等值线的同步弯曲，犹如错断水系，反映现代板块运动的方向；中部大面积零值和负值线圈闭，反映中央山脉的整体上升；在一些等值线聚合成梯度的地带，又往往是某些深断裂的反映。是否可以这样认为，深部重力异常是地壳深处介质密度沿某一方向的 相似文献