经验模态与小波分解在光学遥感内波参数提取中的应用

内波遥感参数提取是利用遥感影像研究海洋内波的重要手段,通过提取内波的基本参数可以对海洋内波的生成与传播机制进行进一步的研究。提出了利用经验模态分解、小波分解与高阶多项式拟合从光学影像中提取内波半波宽度的方法。经验模态分解与小波分解对内波剖面数据进行尺度分解,根据归一化方差最大来提取内波分量;多项式拟合基于内波剖面的亮暗条纹变化完全由内波调制的假设,对数据进行拟合,并根据一阶导数来提取半波宽度。用南海北部东沙岛附近2004年7月10日的中-巴资源卫星(China-Brazil Earth Resources Satellite,CBERS)影像对方法进行了验证。结果表明,3种方法能较好地提取所需参数,获取的内波半波宽度具有较好的一致性;上述方法在处理非平稳及非线性遥感数据上,具有非常明显的优势。基于一维非线性内波理论,通过提取的内波半波宽度,辅以水深和混合层深度数据,反演了内波的振幅。     

地理学研究范式的思考

地理学主要关注陆地表层自然和人文要素的空间分异规律研究,针对这一复杂系统的不同问题应该选择不同的研究方式。本文在思考以往地理学研究方式的基础上,将地理学研究范式概括为：地理经验科学研究范式、地理实证科学研究范式、地理系统科学研究范式和地理大数据研究范式。对不同地理科学问题应选取不同的范式加以研究,对有些复杂科学问题应采用多种研究范式加以解决。     

Water discharge variability of Changjiang （Yangtze） and Huanghe （Yellow） Rivers and its response to climatic changes

Influences of large-scale climatic phenomena, such as the E1Nifio/La Nifia-Southem Oscillation （ENSO） and the Pacific Decadal Oscillation （PDO）, on the temporal variations of the annual water discharge at the Lijin station in the Huanghe （Yellow） River and at the Datong station in the Changjiang （Yangtze） River were examined. Using the empirical mode decomposition-maximum entropy spectral analysis （EMD- MESA） method, the 2- to 3-year, 8- to 14-year, and 23-year cyclical variations of the annual water discharge at the two stations were discovered. Based on the analysis results, the hydrological time series on the inter- annual to interdecadal scales were constructed. The results indicate that from 1950 to 2011, a significant downward trend occurred in the natural annual water discharge in Huanghe River. However, the changes in water discharge in Changjiang River basin exhibited a slightly upward trend. It indicated that the changes in the river discharge in the Huanghe basin were driven primarily by precipitation. Other factors, such as the precipitation over the Changjiang River tributaries, ice melt and evaporation contributed much more to the increase in the Changjiang River basin. Especially, the impacts of the inter-annual and inter-decadal climate oscillations such as ENSO and PDO could change the long-term patterns of precipitation over the basins of the two major rivers. Generally, low amounts of basin-wide precipitation on interannual to interdecadal scales over the two rivers corresponded to most of the warm ENSO events and the warm phases of the PDO, and vice versa. The positive phases of the PDO and ENSO could lead to reduced precipitation and consequently affect the long-term scale water discharges at the two rivers.     

基于经验模态分解的地震瞬时属性提取

传统复地震道方法提取的地震瞬时属性存在物理意义不明确、对噪声敏感等不足,本文探讨基于经验模态分解的地震瞬时属性提取方法,得到不同尺度下的地震瞬时属性,由此得到的瞬时频率在数值上与地震主频对应较好.将该方法提取的属性应用到海上地震数据中,显示出较好的效果.     

An Empirical Tropical Instability Wave-induced Wind Stress Model in the Equatorial Pacific and its Incorporation into the Ocean Model

Abstract

Satellite observations revealed that there is a close relationship between perturbations of sea surface temperature (SST) and wind stress (τ) induced by tropical instability waves (TIWs; SST_TIW and τ _TIW). Using the empirical relationship observed between TIW-induced wind stress divergence (curl) and downwind (crosswind) SST gradients, this study establishes a TIW-induced wind stress field perturbation model τ _TIW?=?F(SST). This empirical model solves τ _TIW from the TIW-induced wind stress divergence and curl, which are estimated from the downwind and crosswind SST gradients. This empirical τ _TIW?=?F(SST) model can be incorporated into the ocean model to take into account the effect of τ _TIW. By comparing two experiments with and without the τ _TIW effect, this study demonstrates that τ _TIW has a substantial effect on the equatorial Pacific heat budget and induces the long-term mean SST to exhibit a 0.2°C difference, which is consistent with previous studies.     

Empirical relationships between diversity of invertebrate communities and altitude in rivers: Application to biomonitoring

The relationships between the diversity of invertebrate communities and the altitude of sampling sites were analysed in 438 benthic samples, collected between 1982 and 1991, in 56 rivers of western Switzerland. Diversity, estimated from total number of taxa (genus or family) and from number of taxa intolerant of pollution, was positively correlated with increasing altitude. In contrast, density of human population and the level of organic pollution were negatively correlated with increasing altitude. Therefore, the upstream increase of invertebrate diversity was attributed to the decrease of human population which is the main source of organic pollution. In this study, altitude was used, instead of organic pollution, to predict diversity. Empirical relationships between diversity and altitude were applied to surveys of water quality to describe the general altitudinal pattern characteristic for each region and to single out anomalous sites and rivers. In addition, changes in the altitudinal patterns of diversity can be used to monitor the recovery of rivers from pollution.     

近50年来黑龙江省冻土厚度的时空变化特征

基于MK检验、滑动t检验、EOF分析方法,使用近50年（1961-2012年）黑龙江省32个气象基准台站逐日冻土观测数据、气温观测数据,对黑龙江省冻土厚度时空变化特征进行了分析。结果表明：① 近50年黑龙江省冻土厚度减少了12.86 cm,下降速率为-0.53 cm/a,以2001年为界发生了突变。② 冻土厚度空间分布呈现由北厚南薄格局,中部地区冻土厚度较同纬度其他区域偏低;空间变化呈现南部冻土厚度降低快,北部降低慢,中部与西部、东南部呈相反变化的特征,伊春、铁力、漠河观测点为冻土变化敏感区。③ 气温是影响黑龙江省冻土厚度变化的主要因素,与冻土厚度相关系数为-0.611。本文的主要贡献为揭示了黑龙江省冻土厚度的空间变化特征,为相关研究及各级政府规划提供了依据。     

打桩挤土的现场试验研究及土体位移的计算公式

打桩挤土使周围土体发生位移,对周围其他桩及附近原有建筑物和基础设施产生破坏。本文通过典型工程打桩过程中的监测数据,运用小孔扩张理论结合回归分析方法导出了计算土体位移量的经验公式。运用该公式可定量预估挤土程度,防止意外事故的发生。     

基于EOF分析对南海西北海域水体光谱特性的研究

This study presents an analysis of the spectral characteristics of remote sensing reflectance(R_(rs)) in northwestern South China Sea based on the in situ optical and water quality data for August 2018.R_(rs)was initially divided into four classes,classes A to D,using the max-classification algorithm,and the spectral properties of whole R_(rs) were characterized using the empirical orthogonal function(EOF) analysis.Subsequently,the dominant factors in each EOF mode were determined.The results indicated that more than 95% of the variances of R_(rs) are partly driven by the back-scattering characteristics of the suspended matter.The initial two EOF modes were well correlated with the total suspended matter and back-scattering coefficient.Furthermore,the first EOF modes of the four classes of R_(rs)(A-D R_(rs)-EOF_1) significantly contributed to the total variances of each R_(rs) class.In addition,the correlation coefficients between the amplitude factors of class A-D R_(rs)-EOF_1 and the variances of the relevant water quality and optical parameters were better than those of the unclassified ones.The spectral shape of class AR_(rs)-EOF_1 was governed by the absorption characteristic of chlorophyll a and colored dissolved organic matter(CDOM).The spectral shape of class B R_(rs)-EOF_1 was governed by the absorption characteristic of CDOM since it exhibited a high correlation with the absorption coefficient of CDOM(a_g(λ)),whereas the spectral shape of class C R_(rs)-EOF_1 was governed by the back-scattering characteristics but not affected by the suspended matter.The spectral shape of class D R_(rs)-EOF_1 exhibited a relatively good correlation with all the water quality parameters,which played a significant role in deciding its spectral shape.     

Recent Advances in Prediction and Processing of Strong Ground Motions

We present an overview of our recent results on utilizing small earthquakes in the earthquake engineering practice. Site-specific ground motion time-histories of large earthquakes can be successfully simulated using recordings of small earthquakes which are often referred to as 'empirical Green's functions' in seismology. Another important practical problem is whether and how these observations can be used in seismic risk studies which are based on empirical attenuation relations for ground motion parameters. We study a possibility of extrapolating attenuation relations for small earthquakes, to larger magnitudes using the data from the Garner Valley downhole array in Southern California. Finally we introduce efficient ground motion processing techniques in frequency- and time-domains and apply them to site response estimation.