Comparison of Large-Scale Flows on the Sun Measured by Time-Distance Helioseismology and Local Correlation Tracking     

Michal Švanda  Junwei Zhao  Alexander G. Kosovichev 《Solar physics》2007,241(1):27-37

We present a direct comparison between two different techniques: time-distance helioseismology and a local correlation tracking method for measuring mass flows in the solar photosphere and in a near-surface layer. We applied both methods to the same dataset (MDI high-cadence Dopplergrams covering almost the entire Carrington rotation 1974) and compared the results. We found that, after necessary corrections, the vector flow fields obtained by these techniques are very similar. The median difference between directions of corresponding vectors is 24°, and the correlation coefficients of the results for mean zonal and meridional flows are 0.98 and 0.88, respectively. The largest discrepancies are found in areas of small velocities where the inaccuracies of the computed vectors play a significant role. The good agreement of these two methods increases confidence in the reliability of large-scale synoptic maps obtained by them.  相似文献   

Statistical analysis of soil variability in a humid forest landscape of Central Cameroon     

《International Journal of Applied Earth Observation and Geoinformation》2004,5(1):69-79

The quantitative evaluation of key factors of soil variability together with the spatial pattern of underlying variables are important steps in understanding the functioning of soilscapes. Fifteen physical and chemical variables describing 24 pedons were used to elucidate processes of soil differentiation in a humid forest environment in Southern Cameroon. Landscape positions delineated on the basis of remote-sensed imageries included flat convex summits (FCS), linear valley slopes (LVS), colluvial inland valleys (CIV), and alluvial floodplain. Ordination by principal component analysis (PCA) resulted in a three-factor model, which efficiently summarized the dataset explaining 81.4% of total soil variance (TSV). The pedogenetic factor of ferralitization emerged as the main factor accounting for 43.7% of TSV. Identified underlying processes included basic cation leaching, solum acidification, and in situ clay build up. Cation exchange properties as influenced by organic constituents and soil available P were the second and third most important factors associated with 26.7 and 11.4% of TSV respectively. Organic constituents and related biological processes had strong control on nutrient availability and cation-exchange properties, while soil available phosphorus (AP) showed a strong dependence on potential acidity and organic matter mineralization status. The analysis of variance highlighted significant differences for most soil properties across landscape position and soil depth except for organic carbon (OC), total nitrogen (TN), and total phosphorus. All the soils, however, have low pH, low basic cation saturation, and correlatively high exchangeable Al irrespective of their position in the landscape.  相似文献   

常加速度模型的简化自协方差最小二乘法     

林旭  罗志才  姚朝龙 《测绘学报》2014,43(11):1144-1150

“当前”统计模型自适应算法并非真正意义上的自适应目标跟踪算法,其性能与其中关键参数的选择有着直接的关系。本文以常加速度模型对机动载体进行建模,顾及其状态噪声协方差矩阵满足特定结构,提出了简化的自协方差最小二乘噪声协方差估计方法,该方法通过建立新息的相关函数序列与未知噪声协方差矩阵间的函数模型,并结合最小二乘法进行噪声协方差估计。数值仿真结果表明,当载体进行阶跃加速度运动或变加速度运动时,本文所提方法的目标跟踪精度均优于“当前”统计模型自适应算法。  相似文献   

Effect of the lower boundary position of the Fourier equation on the soil energy balance     

SUN Shufen  ZHANG Xia 《大气科学进展》2004,21(6):868-878

In this study, the effect of the lower boundary position selection for the Fourier equation on heat transfer and energy balance in soil is evaluated. A detailed numerical study shows that the proper position of the lower boundary is critical when solving the Fourier equation by using zero heat flux as the lower boundary condition. Since the position defines the capacity of soil as a heat sink or source, which absorbs and stores radiation energy from the sky in summer and then releases the energy to the atmosphere in winter, and regulates the deep soil temperature distribution, the depth of the position greatly influences the heat balance within the soil as well as the interaction between the soil and the atmosphere. Based on physical reasoning and the results of numerical simulation, the proper depth of the position should be equal to approximately 3 times of the annual heat wave damping depth. For most soils, the proper lower boundary depth for the Fourier equation should be around 8 m to 15 m, depending on soil texture.  相似文献   

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��ΰ  ������  ��ǿ 《大地测量与地球动力学》2014,34(5):134-138

?о???????EGM??DTM???????????????????????????????????????EGM2008??SRTM3???????????????????????????????????????????????????T^_zz???????????????????μ??????????????????????????????????????????????????????????????????????????????????????λ???????????????仯??????λ???????ж??????????????????????????????????????????  相似文献   

雷州马尾藻Sargassum leizhouense(Fucales,Phaeophyta)形态结构及分类研究   总被引：1，自引：0，他引：1  

赵素芬  孙会强  刘东超 《海洋与湖沼》2014,45(2):291-298

本研究通过对产于雷州半岛的雷州马尾藻(Sargassum leizhouense)形态结构进行研究,结合形态解剖、分类学特征等观察,比较了与同类组中其他3种马尾藻的特征差异,澄清了其分类地位,并修改了雷州马尾藻的检索表。结果表明,雷州马尾藻属于马尾藻属、真马尾藻亚属、叶托混生组、拟叶托混生亚组;尽管雷州马尾藻与该组的瓦氏马尾藻(S.vachellianum)、鳞茎马尾藻(S.bulbiferum)及滑托组的亨氏马尾藻(S.henslowianum)形态有许多相似之处,但其与上述3种马尾藻的主要差异在于球芽及分裂叶的有无。本研究不仅修改了雷州马尾藻分类地位,也为将来开展该马尾藻的人工繁育及养殖、加工提供帮助。  相似文献   

中国南海区1992-2012年的中尺度涡旋演化过程表达与统计分析     

杜云艳  易嘉伟  吴笛  贺志刚  王东晓  梁福源 《海洋学报(英文版)》2014,33(11):36-47

Automated identification and tracking of mesoscale ocean eddies has recently become one research hotspot in physical oceanography. Several methods have been developed and applied to survey the general kinetic and geometric characteristics of the ocean eddies in the South China Sea（SCS）. However, very few studies attempt to examine eddies＇ internal evolution processes. In this study, we reported a hybrid method to trace eddies＇ propagation in the SCS based on their internal structures, which are characterized by eddy centers, footprint borders, and composite borders. Eddy identification and tracking results were represented by a GIS-based spatiotemporal model. Information on instant states, dynamic evolution processes, and events of disappearance, reappearance, split, and mergence is stored in a GIS database. Results were validated by comparing against the ten Dongsha Cyclonic Eddies（DCEs） and the three long-lived anticyclonic eddies（ACEs） in the northern SCS, which were reported in previous literature. Our study confirmed the development of these eddies. Furthermore, we found more DCE-like and ACE-like eddies in these areas from 2005 to 2012 in our database. Spatial distribution analysis of disappearing, reappearing, splitting, and merging activities shows that eddies in the SCS tend to cluster to the northwest of Luzon Island, southwest of Luzon Strait, and around the marginal sea of Vietnam. Kuroshio intrusions and the complex sea floor topography in these areas are the possible factors that lead to these spatial clusters.  相似文献   

不确定度在多波束测深数据质量评估中的应用     

张志伟  暴景阳  肖付民  孙新轩  王少帅 《海洋测绘》2014,34(5):59-61

在海道测量中,由于无法对测量数据进行多余和重复观测,因而不能精确测定各种误差,同时也几乎没有测量成果质量的控制指标,这正是多波束测深数据质量评估所面临的现实且急需解决的难题。基于国际海道测量规范S-44(5th)的要求,研究了不确定度在多波束数测深数据质量评估中的应用。通过实例分析可知,测量结果的可用性在很大程度上取决于其不确定度的大小,不确定度越小,说明测量结果质量越高,越具有可靠性。因此,将不确定度充分合理地应用于多波束测深数据处理和评估是一种最为理想的途径。  相似文献   

高动态宽带信号码跟踪方法仿真分析     

田晓敏  王可东 《全球定位系统》2014,(6):29-32

针对高动态场景,单独的码环路很难实现跟踪,由于高动态载波跟踪的算法很成熟,通常应用载波跟踪结果对码环路进行辅助,针对窄体制信号,这种方法可以帮助消除码环的动态误差,但对宽体制信号来说,辅助力度减小。从高动态宽带信号码跟踪误差门限以及跟踪精度入手,分析了单独码跟踪算法的易失锁性,理论和仿真验证应用高动态载波跟踪结果辅助码跟踪算法的有效性,且具有高的跟踪精度。这为导航接收机的跟踪算法提供了理论依据。  相似文献   

高阶BOC调制信号无模糊跟踪技术性能比较     

刘中伟  黄仰博  唐小妹  欧钢 《全球定位系统》2014,(5):19-25

BOC调制方式提升了导航信号的性能和频谱资源利用率,但是自相关函数的多峰特性使信号接收面临新的问题。本文研究高阶BOC调制方式及其无模糊跟踪技术,主要分析了Bump-Jump算法、BPSK-like算法、SCPC算法和双环路算法,比较不同跟踪技术的硬件复杂度、计算复杂度、跟踪精度和跟踪稳定性,结果可为接收机设计提供参考。  相似文献