Non-stationary covariance function modelling in 2D least-squares collocation

Standard least-squares collocation (LSC) assumes 2D stationarity and 3D isotropy, and relies on a covariance function to account for spatial dependence in the observed data. However, the assumption that the spatial dependence is constant throughout the region of interest may sometimes be violated. Assuming a stationary covariance structure can result in over-smoothing of, e.g., the gravity field in mountains and under-smoothing in great plains. We introduce the kernel convolution method from spatial statistics for non-stationary covariance structures, and demonstrate its advantage for dealing with non-stationarity in geodetic data. We then compared stationary and non- stationary covariance functions in 2D LSC to the empirical example of gravity anomaly interpolation near the Darling Fault, Western Australia, where the field is anisotropic and non-stationary. The results with non-stationary covariance functions are better than standard LSC in terms of formal errors and cross-validation against data not used in the interpolation, demonstrating that the use of non-stationary covariance functions can improve upon standard (stationary) LSC.     

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经典选权迭代法研究与两步抗差估计的提出

随着权函数的不同出现了不同的抗差估计方法,相应不同的抗差估计方法在一定程度上存在着不足或者缺陷。详细地论述了几种经典的选权迭代抗差估计方法的不足,并从理论出发,提出了两步抗差方案。     

Local and landscape effects on spatial patterns of mangrove forest during wetter and drier periods: Moreton Bay,Southeast Queensland,Australia

Land use/cover and mangrove spatial changes were assessed for ten sites and their sub-catchments in Southeast Queensland, Australia. Two time periods were involved: 1972–1990, a period of relatively high rainfall, and 1990–2004, which was significantly drier. Aerial photographs and Landsat satellite imagery were used to map the inter-tidal wetlands and classify the land use/cover in the sub-catchments. A Maximum Likelihood Classification was used to map three types of land cover: agriculture, built-up and plantation forest. Mangroves (mainly Avicennia marina) were the focus as they have been recorded over recent decades encroaching into salt marsh. The Mangrove-Salt marsh Interface (MSI) Index was developed to quantify the relative opportunity for mangroves to expand into salt marshes, based on the shared boundary between them. The index showed a consistent relationship with mangrove expansion and change. To address problems of high dimensionality and multi-collinearity of predictor variables, a Partial Least Squares Regression (PLSR) model was used. A key finding of this research was that the contribution of environmental variables to spatial changes in the mangroves was altered following a reduction in rainfall. For example, agriculture had more influence on mangrove expansion and change during the wet period than during the dry period.     

潮汐调和分析的一种算法

本文在常规潮汐调和分析方法的基础上，提出了一种由高低潮资料进行潮汐分析的算法。具体计算表明，该算法与现今通用的常规算法（即等间隔最小二乘法）相比，既可大大减少所需原始样本量，在相同记录长度内，是常规算法的三分之一还少，同时减少样本处理的前期工作量；又能保证潮位拟合的精度和预报的可信度，两者精度相当，结果一致。该算法原理简单、实用有效，对于局部样本缺损较易处理，具有实际应用价值。     

Stokes波的谱特性分析

应用理论推导及数值计算方法，对Stokes随机波的谱特性进行了分析。首先将波面方程，海水质点水平速度用一阶波面分量的非线性组合表示，应用平稳随机高阶短的降阶计算法则，得到了波面方程及海水质点水平速度与一阶波面分量的自相关函数之间的关系，从而确定了Stokes随机波浪的波浪谱密度及海水质点水平速度和加速度谱密度，进而求得有关波浪要素的均方根值。文章还应有数值计算方法，分析了波浪基本参数对均方根值的影响。     

杭州湾中部实测波浪特性分析

利用杭州湾中部一年实测波浪资料,分析该地区的波参数统计变化特性,采用最小二乘法拟合得出相关参数之间的关系式,并统计分析了频谱特性。结果表明:杭州湾中部以小浪和轻浪为主,在各月分布较为均匀,年平均周期为2.97 s;最大一次波浪过程为冷空气影响所致,影响强度大于台风莫拉克;常浪向分布在东北至东南向,其中又以小浪出现较多,对应的波周期以2~4 s为主;强浪向主要分布在西北和东北方向,对应的波周期主要分布在3~5 s;多数特征波参数之间相关关系较好;由谱分析得知风浪占多数,且以单峰为主。研究结果可为相关工程和理论研究提供基础资料。     

黄河口及其邻近水域强壮箭虫密度的时空分布及其与环境因子的关系

为探究强壮箭虫（Sagitta crassa）在黄河口及其邻近水域的时空分布特征及其与生物和非生物环境等因子的关系,本文依据2013—2014年在黄河口及其邻近水域6个航次的调查数据,采用丛生指标（I）、聚块性指标（A）和负二项分布参数的倒数（C_A）等聚集指标,分析了强壮箭虫的空间分布特征;应用广义可加模型（GAM）研究了强壮箭虫密度的时空分布和环境因子的关系。结果表明,黄河口及其邻近水域强壮箭虫平均密度为21.85 ind/m3,春、秋季高,冬、夏季低;其密度的空间分布以黄河入海口附近水域为密集中心,向远岸水域逐渐降低;强壮箭虫在黄河口及其邻近水域的聚集特征随密度的变化存在两次聚集和两次扩散;水深、表层水温和浮游桡足类密度是影响其密度时空分布的主要因子,总偏差解释率为55.11%,强壮箭虫密度随水深的增加而减小,随表层水温的升高先增加后减小,随桡足类密度的增加而增加。强壮箭虫密度受黄河口及其邻近水域环境因子变动的影响,具有明显的季节变化和空间分布规律。     

板内与板间地震活动时空分布的多重分形特征研究

利用多重分形分析方法,考察了中国大陆和台湾地区以及新西兰的地震活动广义应变释放时间和空间分布的多重分形特征. 结果表明,地震活动时空分布的多重分形特征与不同地球动力学环境关系密切. 强震活动时间分布在板间地区具有比板内地区更明显的丛集性, 对中小地震这种丛集性差异较小;强震活动空间分布在板内地区具有比板间地区更强的丛集性,但对中小地震则相反.      

A New Retracking Technique for Brown Peaky Altimetric Waveforms

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).