A New Retracking Technique for Brown Peaky Altimetric Waveforms     

Fukai Peng 《Marine Geodesy》2018,41(2):99-125

A new Brown-Peaky (BP) retracker has been developed for peaky waveforms that usually appear within ～10 km to the coastline. The main feature of the BP is that it fits peaky waveforms using the Brown model without introducing a peak function. The retracking strategy first detects the peak location and width of a waveform using an adaptive peak detection method, and then estimates retracking parameters using a weighted least squares (WLS) estimator. The WLS assigns a downsized weight to corrupted waveform gates, but an equal weight to other normal waveform gates. The BP retracker has been applied to 4-year Jason-1 waveform (2002–2006) in two Australian coastal zones. The results retracked by BP, MLE4 and ALES retrackers have been validated against tide-gauge observations located at Burnie, Lorne and Broome. The comparison results show that three retrackers have similar performance over open oceans with the correlation coefficient (～0.7) and RMSE (～13 cm) between altimetric and tide-gauge sea levels for distance >7 km offshore. The main improvement of BP retracker occurs for distance ≤7 km to the coastline, where validation results indicate that data retracked by BP are more accurate (15–21 cm) than those by ALES (16–24 cm) and MLE4 (19–37 cm).  相似文献   

基于圆柱多段拟合的隧道中轴线提取方法研究     

荆海峰  李广云  王力  杨文锋 《大地测量与地球动力学》2018,38(2):211-215

提出基于圆柱多段拟合的隧道中轴线提取方法。首先对隧道点云数据进行预处理，并将点云按隧道走向分成不同区段；然后对各区段依据轴线与表面点云法线垂直关系，提取精度较低的中轴线；最后对各区段利用圆柱多段拟合，提取精度较高的中轴线。实验表明，隧道中轴线的提取在一定的采样区间具有较高的稳定性，对直线和弯曲的圆形隧道有良好的适用性，算法可靠，精度较高。  相似文献   

On the equivalence of two methods for computing partial derivatives of seismic waveforms—II. Laterally homogeneous initial model     

Robert J. Geller  Tatsuhiko Hara  Seiji Tsuboi 《Geophysical Journal International》1990,102(2):499-502

  相似文献   

AN EVALUATION OF SAS/GRAPH SOFTWARE FOR COMPUTER CARTOGRAPHY1     

Alan M. Baker  Rowan Faludi  David R. Green 《The Professional geographer》1985,37(2):204-214

The SAS® computer software system, widely used and respected for its capabilities in statistical analysis and data base management, now includes a new set of graphic and cartographic procedures called SAS GRAPH?. We have used these cartographic procedures in research on mapping ethno-cultural census data from metropolitan areas in Ontario and in undergraduate and graduate courses in computer cartography. On the basis of that experience, we describe and evaluate SAS/GRAPH'S cartographic capabilities and illustrate with maps drawn by various devices.  相似文献   

台湾海峡西岸重力场变化梯度场图像分析     

梁全强  刘序俨  黄声明  吴维日  陈新泽 《大地测量与地球动力学》2006,26(4):82-85

讨论了应用曲面拟合技术和利用离散的重力观测点的重力变化对特定研究区的重力场变化进行数值模拟以获取该区重力变化空间梯度场图像的具体方法;并应用该方法获得了2004年3月福建安溪3.6级地震前的重力变化空间梯度场图像,发现空间梯度场图像能清晰地反映出地震前重力场群体性变化的差异性;利用此方法对2005年6月~2006年3月间台湾海峡西岸重力场变化进行数值模拟,获得其空间梯度场图像。  相似文献   

西洋东大港水道流速垂线分布研究   总被引：2，自引：0，他引：2  

吴德安  张忍顺 《海洋工程》2005,23(1):88-92,96

对辐射沙洲海域东大港4#站位连续2个潮周期的流速测量资料进行了分析、研究,拟合给出了流速垂线分布关系,并根据实际测量资料确定了该站位6个水层的浑水水流尾流函数项表达式。这些表达式表明浑水水流尾流函数是相对深度和摩阻速度的函数。探讨分析了尾流函数的空间分布和潮周期过程。非恒定流的水流尾流函数项的准确表达,对于揭示含沙水流流速结构及水、沙相影响作用规律将起到启发和推动作用。  相似文献   

Waveform Shaping of Sonar Transducers for Improving the Vertical Resolution in Sub-bottom Sediments Profiling     

P. Cobo  C. Ranz  A. Fernández  M. Cuesta  D.K. Anthony  M. Siguero 《Marine Geophysical Researches》2005,26(2-4):87-95

Vertical resolution is of fundamental importance in sonar exploration and is directly related to the duration of the acoustic pulse generated by the transducer. The shorter the radiated pulse, the higher the vertical resolution. Many sub-bottom profiling sonar systems use piezoelectric transducers because they are reversible and well understood. Piezoelectric projectors are normally resonant transducers, which are intrinsically narrowband. A piezoelectric transducer is usually driven by a tone-burst. However, it is possible to use Fourier techniques to find a pre-compensated electrical driving function so that the transducer radiates a prescribed wider band acoustic waveform. This technique can be applied to synthesize zero-phase cosine-magnitude, Gaussian, and bionic pulses, with a conventional sandwich transducer. Zero-phase cosine-magnitude waveforms provide minimum length pulses (and therefore maximum resolution) within a prescribed frequency band.The aim of this paper is to illustrate the synthesis of wideband acoustic pulses using an underwater piezoelectric projector. The conventional acoustic waveform radiated when a Tonpiltz transducer is transiently excited using a “click” and allows its frequency response function to be measured. This function is used to design the electrical signal which then drives the transducer so that it radiates the shortest pulse compatible with its mechanical response. The significant resolution enhancement of the waveform shaping process is illustrated by its application to a sediment wedge model.  相似文献   

潮汐性质相似性判断的两个指标及其应用   总被引：1，自引：0，他引：1  

黄辰虎  马福诚  吕良  许家琨  孙雪杰 《海洋测绘》2007,27(6):12-15

提出采用时差法的相关系数和最小二乘潮位拟合法的推算中误差,作为潮汐性质相似性强弱判断的两个量化指标。根据实测潮汐数据进行了有关计算,结果表明这两个指标可以用于潮汐性质相似性强弱的快速判断,另外推算中误差还可以用于验潮站潮位数据缺测时推算精度的检验,建议在沿岸海道测量水位改正作业中综合使用。  相似文献   

Estimation of Sea Ice Thickness from SARAL/AltiKa in Drifting Orbit Phase     

Purvee Joshi  Sandip R. Oza  Ujjwal K. Gupta  Shailendra Saini  D. Ram Rajak  I. M. Bahuguna 《Marine Geodesy》2020,43(3):302-323

Abstract

Intra and inter-annual variations in the sea ice thickness are highly sensitive indicators of climatic variations undergoing in the earth’s atmosphere and oceans. This paper describes the method of estimating sea ice thickness using radar waveforms data acquired by SARAL/Altika mission during its drifting orbit phase from July 2016 onwards yielding spatially dense data coverage. Based on statistical analysis of return echoes, classification of the surface has been carried out in three different types, viz. floe, lead and mixed. Time delay correction methods were suitably selected and implemented to make corrections in altimetric range measurements and thereby freeboard. By assuming hydrostatic equilibrium, freeboard data were converted into sea ice thickness. Results show that sea ice thickness varies from 4 to 5?m near ice shelves and 1 to 2.5?m in the marginal sea ice regions. Freeboard and sea ice thickness estimates were also validated using NASA’s Operation Ice Bridge (OIB) datasets. Freeboard measurements show very high correlation (0.97) having RMSE of 0.13. Overestimation of approximately 1–2?m observed in the sea ice thickness, which could be attributed to distance between AltiKa footprint and OIB locations. Moreover, sensitivity analysis shows that snow depth and snow density over sea ice play crucial role in the estimation of sea ice thickness.  相似文献   

晚中生代─新生代南海周缘地块运动与南海演化   总被引：1，自引：0，他引：1  

袁友仁  杨树康  汤贤赞  王保贵  侯红明  柳枞阳 《热带海洋学报》1994,(2)

报道了由华南几个盆地的古地磁数据综合而得的反映该区白垩纪以来古纬度变化曲线，结合Ｓｃｈｍｉｄｔｋｅ等（１９９０）发表的加里曼丹１５０Ｍａ以来的古地磁数据，表明华南与加里曼丹在４０Ｍａ前具有大致相同的古纬度变化史，差异仅出现在距今３０Ｍａ前后和１０Ｍａ以来。若此趋势可靠，则可作出下列推断：（１）南海的扩张只能发生在距今３０Ｍａ附近或１０Ｍａ以后华南与加里曼丹反向运动时期；距今３０Ｍａ的扩张已被广为接受；（２）华南与加里曼丹之向可能存在的古南海只能在９１Ｍａ之前存在；（３）南海演化可能存在两期扩张。南海的拟合可通过沿３５００ｍ等深线的先道时针旋转、后北向平移两个步骤完成。这与Ｈａｙａｓｈｉｄａ等（１９９１）提出的日本海张开与扩张模式很相似，提示东亚边缘海的形成和演化可能具有同样的机制。华南距今５０Ｍａ以来的古纬度变化与Ｔａｐｐｏｎｎｉｅｒ（１９８２）的传播挤出构造模式所预期的基本吻合，表明距今５０Ｍａ以来华南古纬度变化的运动学机制可用Ｔａｐｐｏｎｎｉｅｒ模式作解释。  相似文献