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测距仪标称精度一般是根据基线场上的检测结果确定的,由于仪器检测时的条件与工程现场条件不一致,因而标称精度不能反映观测实际精度,以标称精度定权处理观测数据,影响测量成果的质量;在工程实际中,若多余观测边较多,运用二次平差法进行测距仪精度估计,可正确反映仪器实际观测精度,为仪器性能判别及数据处理提供客观依据。 相似文献
143.
A study of SAR remote sensing of internal solitary waves in the north of the South China Sea:I.Simulation of internal tide transformation 总被引:2,自引:1,他引:1
For settlement of the well-known problem of contemporary radar imaging models,i.e.,the pmblem of a general underestimation of radar signatures of hydrodynamic features over oceanic internal waves and underwater bottom topography in tidal watels at at high radar frequency bands(X-band and C-band),the impact of the ocean surface mixed layer turbulence and the significance of strat-ified oceanic model on SAR remote sensing of internal solitary waves are proposed.In the north of the South China Sea by utilizing seme observed data of background field the nonlinearity coefficient,the dispersion coefficient,the horizontal variability coefficient and the phase speed in the generalized K-dV equation are determined approximately.Through simulations of internal tide transfor-mation the temporal evolution and spatial distribution of the vertical displacement and horizontal velocity of intereal wave field are obtained.The simulation results indicate that the maximum amplitudes of internal solitary waves occur at depth 35 m,but the maximum current speeds take place at depth 20 m in this area of the sea(about 20°30'N,114°E)in August.It was noticed that considering the effects of flood current and ebb current respectively is appropriate to investigate influence of the background shear flow on coefficients of the K-dV equation.The obtained results provide the possibility for the simulation of SAR signatures of inter-nal solitary waves under considering the impact of ocean surface mixed layer turbulence in the companion paper. 相似文献
144.
A. Vela V. Pasqualini V. Leoni A. Djelouli H. Langar G. Pergent C. Pergent-Martini L. Ferrat M. Ridha H. Djabou 《Estuarine, Coastal and Shelf Science》2008,79(4):591-598
Mapping marine biocenoses is an efficient method for providing useful data for the management and conservation of Mediterranean lagoons. Fused images from two satellites, SPOT 5 and IKONOS, were tested as management tools for identifying specific ecosystems in the El Bibane lagoon, situated in southern Tunisia near the Libyan border. The objectives of this study were to provide a precise map of the entire El Bibane lagoon using fused images from SPOT 5 and to compare fused images from SPOT 5 and IKONOS over a test-area. After applying a supervised classification, pixels are automatically classified in four classes: low seagrass cover, high seagrass cover, superficial mobile sediments and deep mobile sediments. The maps of the lagoon revealed and confirmed an extremely wide distribution of seagrass meadows within the lagoon (essentially Cymodocea nodosa; 19 546 ha) and a large area of mobile sediments more or less parallel to the shore (3 697 ha). A direct comparison of overall accuracy between SPOT 5 over the entire area, SPOT 5 over the test-area and IKONOS over the test-area revealed that these tools provided accurate mapping of the lagoon environment (83.25%, 85.91% and 73.41% accuracy, respectively). The SPOT 5 images provided greater overall accuracy than the IKONOS image, but did not take into account the heterogeneous spatial structure of the seagrasses and sediments present in the lagoon environment. Although IKONOS imagery provided lower overall accuracy than SPOT 5, it proved a very useful tool for the mapping of heterogeneous structures as it enabled the patchiness of formations to be better taken into account. The use of SPOT 5 and IKONOS fused images appears to be very promising for completing the mapping of lagoons in other regions and countries of the Mediterranean Sea. 相似文献
145.
Cheng-Wu CHEN Hsien-Chueh Peter YANG Chen-Yuan CHEN Alex Kung-Hsiung CHANG Tsung-Hao CHEN 《中国海洋工程》2008,22(1):43-56
Internal solitary wave propagation over a submarine ridge results in energy dissipation, in which the hydrodynamic interaction between a wave and ridge affects marine environment. This study analyzes the effects of ridge height and potential energy during wave-ridge interaction with a binary and cumulative logistic regression model. In testing the Global Null Hypothesis, all values are p 〈0.001, with three statistical methods, such as Likelihood Ratio, Score, and Wald. While comparing with two kinds of models, tests values obtained by cumulative logistic regression models are better than those by binary logistic regression models. Although this study employed cumulative logistic regression model, three probability functions p^1, p^2 and p^3, are utilized for investigating the weighted influence of factors on wave reflection. Deviance and Pearson tests are applied to cheek the goodness-of-fit of the proposed model. The analytical results demonstrated that both ridge height (X1 ) and potential energy (X2 ) significantly impact (p 〈 0. 0001 ) the amplitude-based refleeted rate; the P-values for the deviance and Pearson are all 〉 0.05 (0.2839, 0.3438, respectively). That is, the goodness-of-fit between ridge height ( X1 ) and potential energy (X2) can further predict parameters under the scenario of the best parsimonious model. Investigation of 6 predictive powers ( R2, Max-rescaled R^2, Sorners' D, Gamma, Tau-a, and c, respectively) indicate that these predictive estimates of the proposed model have better predictive ability than ridge height alone, and are very similar to the interaction of ridge height and potential energy. It can be concluded that the goodness-of-fit and prediction ability of the cumulative logistic regression model are better than that of the binary logistic regression model. 相似文献
146.
Evaluation of Inference Adequacy in Cumulative Logistic Regression Models: An Empirical Validation of ISW-Ridge Relationships 总被引:3,自引:0,他引:3
Internal solitary wave propagation over a submarine ridge results in energy dissipation, in which the hydrodynamic interaction between a wave and ridge affects marine environment. This study analyzes the effects of ridge height and potential energy during wave-ridge interaction with a binary and cumulative logistic regression model. In testing the Global Null Hypothesis, all values are p<0.001, with three statistical methods, such as Likelihood Ratio, Score, and Wald. While comparing with two kinds of models, tests values obtained by cumulative logistic regression models are better than those by binary logistic regression models. Although this study employed cumulative logistic regression model, three probability functions p^1, p^2 and p^3, are utilized for investigating the weighted influence of factors on wave reflection. Deviance and Pearson tests are applied to check the goodness-of-fit of the proposed model. The analytical results demonstrated that both ridge height (X1) and potential energy (X2) significantly impact (p<0.0001) the amplitude-based reflected rate; the P-values for the deviance and Pearson are all >0.05 (0.2839, 0.3438, respectively). That is, the goodness-of-fit between ridge height (X1) and potential energy (X2) can further predict parameters under the scenario of the best parsimonious model.Investigation of 6 predictive powers (R2, Max-rescaled R2, Somers'D, Gamma, Tau-a, and c, respectively) indicate that these predictive estimates of the proposed model have better predictive ability than ridge height alone, and are very similar to the interaction of ridge height and potential energy. It can be concluded that the goodness-of-fit and prediction ability of the cumulative logistic regression model are better than that of the binary logistic regression model. 相似文献
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149.
Realistic numerical simulations of nonlinear internal waves (NLIWs) have been hampered by the need to use computationally expensive nonhydrostatic models. In this paper, we show that the solution to the elliptic problem arising from the incompressibility condition can be successfully approximated by a few terms (three at most) of an expansion in powers of the ratio (horizontal grid spacing)/(total depth). For an n dimensional problem, each term in the expansion is the sum of a function that satisfies a one-dimensional second-order ODE in the vertical direction plus, depending on the surface boundary condition, the solution to an n-1 dimension elliptic problem, an evident saving over having to solve the original n-dimensional elliptic problem. This approximation provides the physically correct amount of dispersion necessary to counteract the nonlinear steepening tendency of NLIWs. Experiments with different types of NLIWs validate the approach. Unlike other methods, no ad hoc artificial dispersion needs to be introduced. 相似文献
150.
VRS RTK在地籍测量中的应用与研究 总被引:1,自引:0,他引:1
为了解决地籍测量外业要求时间短、精度较高等技术问题,在理论研究的基础上,在某市城区采用了VRS RTK技术建立测量控制网.通过成果分析得知.由于基于载波相位的GPS相对定位具有较高精度,只要控制网变形可以忽略或者进行建模,则不需要进行相邻控制点的联测,因此布设VRS RTK是非常适合的,减少了传统控制网埋石造标工作量.在RTK多测站解算中,建立了由电离层、对流层和卫星轨道引起的GPS观测误差在空间和时间的相关模型,得出在人口密集或重要经济地区布设局域GPS网的设计与测量模式. 相似文献