Decimation and Spectrum Correlation Analysis of Gravity Solid Tide Signal Based on Surface-Simplex Swarm Evolution Optimization Algorithm

In order to reveal the correlation between the harmonic components in the earth's solid tidal wave and the non-correlation superposition relationship, and based on these relations, the tidal harmonic implicit in the gravitational solid tidal signal was analyzed. According to the position relationship among the Earth, the moon and the sun's rotating orbit, an orthogonal decomposition model of tidal force was established. Furthermore, on the orthogonal decomposition model of gravity solid tidal wave based on the independent component analysis of the improved SSSE intelligent optimization algorithm, the spectral correlation method was used to analyze the independent components of gravity solid tidal wave. Thus, the multiplicative demodulation after the orthogonal decomposition of the conformal wave was completely realized. Finally, the above model and algorithm were used to compare and analyze the actual observation data and the theoretical signal as reference background. The results show that the proposed model and method can effectively achieve the orthogonal decomposition of tidal harmonics, highlight the weak energy of the long period harmonics component, and reflect the change of tidal harmonic modulation relationship from the spectral correlation map.     

基于单形进化优化算法的重力固体潮信号解混及谱相关分析

为了揭示地球固体潮中谐波成分间的相关乘性调制关系与非相关叠加关系,并根据这些关系来分析重力固体潮信号中隐含的潮汐谐波。根据地球、月球与太阳旋转轨道的位置关系,建立了一个引潮力的正交分解模型。进一步,基于改进单形进化智能优化算法的独立分量分析的重力固体潮正交分解模型上,利用谱相关方法,对重力固体潮的独立成分进行谱相关分析,从而完整实现了潮汐谐波加性正交分解之后的乘性解调。最后,结合实际观测数据,并引入理论信号作为参考背景,利用以上模型与算法进行对比处理和分析。研究表明,所提出的模型与方法可以有效地实现潮汐谐波的正交分解,凸显能量较弱的长周期谐波分量,并从谱相关图谱中反映潮汐谐波调制关系的变化。     

确定卫星重力场中的海潮负荷影响问题

概要综述了确定卫星重力场恢复中的海洋负荷潮汐改正理论和精度估算问题。利用TPXO6海潮模型计算了海潮对卫星重力恢复的影响,与GRACE观测误差实施了对比。结果说明海潮M2波对卫星重力场恢复的影响最大,并主要体现在40阶以下的位系数上。海潮模型误差对低阶卫星重力场恢复的影响也是比较明显的。相关结果可有效降低GRACE恢复的低价重力场位系数的潮汐成分,为我国相应的学科研究提供有效参考。     

Using time series analysis to assess tidal effect on coastal groundwater level in Southern Laizhou Bay,China

Sea water intrusion is an environmental problem cause by the irrational exploitation of coastal groundwater resources and has attracted the attention of many coastal countries. In this study, we used time series monitoring data of groundwater levels and tidal waves to analyze the influence of tide flow on groundwater dynamics in the southern Laizhou Bay. The auto-correlation and cross-correlation coefficients between groundwater level and tidal wave level were calculated specifically to measure the boundary conditions along the coastline. In addition, spectrum analysis was employed to assess the periodicity and hysteresis of various tide and groundwater level fluctuations. The results of time series analysis show that groundwater level fluctuation is noticeably influenced by tides, but the influence is limited to a certain distance and cannot reach the saltwater-freshwater interface in the southern Laizhou Bay. There are three main periodic components of groundwater level in tidal effect range (i.e. 23.804 h, 12.500 h and 12.046 h), the pattern of which is the same as the tides. The affected groundwater level fluctuations lag behind the tides. The dynamic analysis of groundwater indicates that the coastal aquifer has a hydraulic connection with seawater but not in a direct way. Owing to the existence of the groundwater mound between the salty groundwater (brine) and fresh groundwater, the maximum influencing distance of the tide on the groundwater is 8.85 km. Considering that the fresh-saline groundwater interface is about 30 km away from the coastline, modern seawater has a limited contribution to sea-salt water intrusion in Laizhou Bay. The results of this study are expected to provide a reference for the study on sea water intrusion.     

杭州湾南岸庵东潮坪现代沉积特征

在进行庵东潮坪水文要素定点测量的基础上,对地貌特征,沉积粒度,沉积构造及重向剖面作了全面分析与研究。结果表明,滩地位于杭州湾进、退潮流的交会点,控制其发育的主动力为潮汐作用,具明显的不规则半日潮特性,涨潮流强度远大于落潮流,造就了宽达十余公里的潮滩地貌。滩地水动力深受湾内水流影响,高潮期服从其总体潮流流向,导致潮坪上发育众多与杭州湾深槽系统相连的潮沟,破坏了沉积物正常分布规律,高潮坪存在一定向平行岸线的大型潮沟,受强劲水流影响,沉积粒度粗化,并因快冲快淤而产生变形构造;中潮坪接受退潮期潮沟漫岸物质,粒度相对较小,分选性变差,沉积构造以直脊流水波痕及板状交错层理为主;低潮坪潮流作用大、沉积粒度粗,分选性最佳,发育小型流水波痕,内部构造以槽状交错层理,“青鱼刺”层理及再作用构造为特征。潮坪近岸处潮沟迁移层序及浪成波痕层理的发现反映水动力异常强大,威胁人工海塘的安全,建议停止进一步围垦滩涂,采取促淤方法,抑制潮沟的发育,以维持滩地稳定。     

潮汐应力对滑坡的触发机理研究

已有的滑坡统计数据和研究成果显示,滑坡发生的时间具有明显的周期分布规律特征,除了与降雨季节相关的因素外,受日月引力潮的影响也较明显.本文对一定数量的滑坡发生的历史数据进行统计分析,得到滑坡的发生时间在1d内呈明显的分布特征.然后从固体潮理论出发,推导简化弹性地球模型地表的潮汐应力表达式,阐述了固体潮汐作为滑坡日周期因子...     

逆时偏移双向照明波场分离成像条件

通过对波场分离互相关成像条件与炮-检点双向照明互相关成像条件进行研究,将两种方法在噪声消除和补偿成像振幅畸变方面的优势进行结合,提高成像分辨率,改进现有成像条件。其主要步骤是将震源和检波点波场分离成它们的单程波传播分量,采用双向照明补偿互相关成像条件对需要的波场进行成像。通过对模型试算,验证了笔者提出的成像条件能有效的压制噪音,补偿成像振幅。     

Estimation and removal of non-tectonic effects from gravity survey data

When gravity survey accuracies of a few microgals are sought, many correction factors must be accounted for, including meter calibration constants, water-table level fluctations, solid-earth tides, ocean tides and in some cases rapid atmospheric fluctuations. Calculation of most of these correction factors is relatively straightforward. However, the effects of ocean tide loading are not as easily estimated, partly due to the lack of knowledge of the ocean tides themselves. Amplitude and phase factors for the better-known ocean tide components O₁ and M₂ have been theoretically computed for a grid in southern California in order to correct gravity survey data at arbitrary locations for these ocean tidal-loading components. The gravity data from a three-month period were recorded on a tidal gravimeter at the station PAS and then hand-digitized in order to test the ocean tide estimation program. The O₁ and M₂ ocean tidal components were effectively reduced to less than 0.5 μGal. The remaining high-frequency tidal components appear to be K₁ and S₂. If the ocean tides are not taken into account, as much as 16–20 μGal of error can occur solely due to the effect of ocean loading on the gravitational tides when comparing two surveys near Pasadena. The effect increases towards the coastline and decreases inland. Examples of reduced data from the CIT gravity survey network, which has been observed on an approximately monthly basis since 1974, will be shown.     

The Cyclic Spectrum Analysis of IMFs of EMD and Its Application to Gravity Tide

IMFs sifted out by EMD are the FM-AM components. In the paper, by the cyclic spectrum analysis, IMFs are demodulated as the two periodic components which are identical to the intrinsic physical concepts. Using the method, the half-day-tide M₂, the day-tide O₁, and the half-month-tide M_f are extracted from the gravity tide signal, and a conclusion is drawn that the half-day-tide M₂ and the day-tide O₁ are primary components of gravity tide signal, and the half-month-tide M_f is modulated in the half-day-tide M₂ and the day-tide O₁.     

利用球冠谐分析方法提取不同波长重力场异常

介绍球冠谐分析方法在重力场研究中的基本理论和计算方法。探讨了球冠谐系数与波长的关系，以及利用球冠谐分析方法提取不同波长的重量场力场异常，进而研究深部地壳结构的问题，最后给出一个实例。     

海上地震资料处理中的潮汐静校正处理研究及应用

海水因为受月亮引力的作用会产生潮汐现象,在海上地震资料中表现为假断层现象,这种现象会影响地震资料的成像质量,导致错误层位解释及储层预测,因此在地震资料处理中,需要进行潮汐静校正处理。这里讨论了如何应用海上采集的高程值计算出地震波来回通过基准海平面与放炮时海平面之间的薄层水体所经历的时间,再将全部地震数据都校置在同一观察平面,从而实现潮汐静校正处理的方法,并应用于海上某工区中,得到较为理想的效果。     

Tidal dynamics and low-frequency exchanges in the Aransas Pass,Texas

Current, water level and wind data collected from a study site at the Aransas Pass, Texas, during a 45-day period in mid 1977 are used to describe tidal motions and low-frequency, meteorologically-forced exchanges between the inner shelf and a series of intracoastal bays. Analysis of individual tidal constituents indicates a mixed but principally diurnal tide. Tidal constituents move through the Pass as nearly progressive waves. Asymmetry in the co-oscillating tidal motions is explained as a result of unequal frictional forces acting on flood and ebb currents in the Pass. Tidal excursions computed from the tidal harmonic constants and from cumulative net displacements suggest that tidal-period exchanges are not effective in flushing the bays even under tropic tidal conditions. Nontidal water levels are related to the cross-shelf component of the coastal windstress at statistically significant levels. This suggests that low-frequency local meteorological forcing, as a set-up or set-down of coastal water levels, plays a valuable role in assisting tidally-driven exchanges.     

Seismicity modulation by external stress perturbations in plate boundary vs. stable plate interior

Characterization of critically stressed seismogenic fault systems in diverse tectonic settings can be used to explore the stress/frictional condition of faults, along with its sensitivity for seismicity modulation by periodic stress perturbation. However, the process of seismicity modulation in response to external stress perturbation remains debated. In this paper, the characteristic difference in the seismicity modulation due to resonance destabilization phenomenon governed by rate-and-state friction is presented and validated with the globally reported cases of seismicity modulation in diverse tectonic settings. The relatively faster-moving plate boundary regions are equally susceptible for both shorter-period (e.g., semi-diurnal, diurnal, and other small tidal constituents) and long-period (e.g., semi-annual, annual, pole tide and pole wobble) seismicity modulation processes in response to stress perturbations from natural harmonic forcing, including tidal, semi-annual, annual, or multi-annual time scales. In contrast, slowly deforming stable plate interior regions and diffuse deformation zones appear to be more sensitive for long-period seismicity modulation of semi-annual, annual, or even multi-annual time scales but less sensitive for short-period seismicity modulation. This finding is also supported by the theoretical model predictions from the resonance destabilization process and worldwide documented natural observations of seismicity modulation in diverse types of tectonic settings.     

Shoreline Energy and Sea Level Dynamics in Lower Chesapeake Bay: History and Patterns

A long-term (1948–2010) shoreward energy history of upper tidal shorelines in lower Chesapeake Bay was developed using a simple calculation of kinetic energy from corresponding wind and tide data. These data were primarily used to determine the likelihood of shoreline energy increases coincident with local sea level rise. Total annual shoreward energy ranged from 620 kJ/m of shoreline in 1950 to 17,785 kJ/m of shoreline in 2009. No clear linear trends are apparent, but mean annual energy shows an increase from 2,732 kJ/m before 1982 to 6,414 kJ/m since then. This increase in mean energy was accompanied by more numerous spikes of comparatively higher annual energy. Shoreward energy delivered to lower Chesapeake Bay’s upper tidal shorelines was enabled by an increasing amount of time per year that tidal height exceeds mean high water, accompanied by increasing heights of tidal anomalies. An index termed the Hydrologic Burden was developed that incorporates the combination of time and tidal height that demonstrates this increasing trend. Although opportunities for greater shoreward energy increased as the Hydrologic Burden increased, and even though there is evidence that greater energy was delivered to the shorelines during the latter time series, energy per hour delivery was shown not to have increased, and may have decreased, due to a steady reduction in average wind speed in lower Chesapeake Bay since the mid-1980s. Energy delivery in lower Chesapeake Bay was primarily from the northeast, and energy delivery over the time series is shown to organize symmetrically around a point between the northeast and north–northeast directions. This is evidence of a self-organizational phenomenon that transcends changes in local wind and tide dynamics.     

潮汐应力对滑坡的触发机制及与时间相关性探讨

已有的滑坡统计数据和研究成果显示,滑坡发生的时间具有明显的周期分布规律特征,除了与降雨季节相关的因素外,受日月引力潮的影响也较明显。从固体潮理论出发,推导简化弹性地球模型地表的潮汐应力表达式,阐述固体潮汐作为滑坡日周期因子对滑坡的影响。在安全系数表达式中考虑潮汐应力的作用,并从表达式中阐述潮汐应力触滑的机制,剖析潮汐应力触发滑坡机制。以1985年的湖北省秭归县新滩特大型滑坡作为算例,采用折线滑动为破坏模式,论述潮汐应力与时间的相关性,以及边坡稳定性安全系数与时间的相关关系。计算结果表明,潮汐应力与边坡安全系数随时间均呈明显日周期及半日周期变动,该边坡稳定性系数的极差与不考虑潮汐应力下的稳定性系数的比值达到3.4%;滑坡发生的时间与潮汐应力处于峰值的时间较为吻合,说明潮汐应力很可能是除降雨等主因之外的触发临界状态滑坡发生的另一因素。     

A study on reflection pattern of swells from the shoreline of peninsular India

Information on reflected surface gravity waves from the shoreline is required for understanding the coastal hydrodynamics. We have quantified the reflected swells (frequency band 0.045–0.12 Hz) from the west and east coast of India based on the spectral wave data derived from the directional waverider buoys. Reflection coefficient, ratio of the reflected and incident spectral energy, was used to quantify the reflected waves. Influence of the seasons, cyclone, relative depth, land/sea breeze, tides and tidal current on the reflected waves were examined. For the locations off the west coast of India, seasons have large impact on the reflection coefficient and were relatively less during the monsoon season due to the increase in incident wave energy. Locations off the east coast of India show almost the same reflection coefficient throughout the year and have no significant seasonal variations. The reflection coefficient off Puducherry was higher than that for other locations due to the low incident wave energy. The reflection coefficient was low during the cyclone period, but the reflected energy during cyclone was higher than that during the normal condition due to the high incident wave energy. High-energy reflected waves show large variation with tide due to the trapping and dissipation of reflected wave by bottom friction and this effect cause low reflection in deep water location than shallow water location. The reflection coefficient decreases with increase in relative depth off west coast of India.     

Analytical models for the groundwater tidal prism and associated benthic water flux

The groundwater tidal prism is defined as the volume of water that inundates a porous medium, forced by one tidal oscillation in surface water. The pressure gradient that generates the prism acts on the subterranean estuary. Analytical models for the groundwater tidal prism and associated benthic flux are presented. The prism and flux are shown to be directly proportional to porosity, tidal amplitude, and the length of the groundwater wave; flux is inversely proportional to tidal period. The duration of discharge flux exceeds the duration of recharge flux over one tidal period; and discharge flux continues for some time following low tide. Models compare favorably with laboratory observations and are applied to a South Atlantic Bight study area, where tide generates an 11-m³ groundwater tidal prism per m of shoreline, and drives 81 m³ s?^?1 to the study area, which describes 23% of an observational estimate. In a marine water body, the discharge component of any oscillatory benthic water flux is submarine groundwater discharge. Benthic flux transports constituents between groundwater and surface water, and is a process by which pollutant loading and saltwater intrusion may occur in coastal areas.     

利用GPS提取南极Amery冰架海潮信号

潮汐运动是冰架短期垂直运动的来源, 对冰架影响十分显著. 选取2003/2004年度南极夏季期间中国在Amery冰架上连续5 d的GPS数据, 利用GAMIT/GLOBK进行数据处理, 获取了由海潮引起的冰架垂向运动时间序列;垂直方向精度优于0.18 m, 并且和中国南极中山验潮站的潮汐变化曲线进行了对比, 获得了一致的结论. 利用GPS测量海潮可为精化南极地区的海潮模型提供可靠的现场数据, 对南极冰盖物质平衡研究及冰海交互动力学模型研究有着重要的作用.     

Application of genetic algorithm technique to inverse modeling of tide–aquifer interaction

Modeling of tide–aquifer interaction plays a vital role in the management of coastal aquifer systems. A novel and robust methodology is presented in this paper for estimating aquifer parameters of coastal aquifers from tide–aquifer interaction data using tide–aquifer interaction model and genetic algorithm (GA). Two stand-alone computer programs were developed to optimize hydraulic diffusivities of unconfined and confined coastal aquifers at multiple sites using GA technique and tide–aquifer interaction model and considering two approaches (‘lumped tidal component approach’ and ‘multi-tidal component approach’). Five sets of real-world tide–aquifer interaction data at two sites of an unconfined aquifer and one set of tide–aquifer interaction data at three sites of a confined aquifer were used to demonstrate the efficacy of the methodology. The analysis of the GA-based inverse modeling results indicated that the ‘multi-tidal component approach’ yields more accurate and reliable hydraulic diffusivities for the unconfined aquifer (RMSE = 0.0129–0.0521 m, NSE = 0.70–0.97, and d1 = 0.91–0.99) as well as for the confined aquifer (RMSE = 0.0204–0.0545 m, NSE = 0.95–0.97, and d1 = 0.99) compared with the ‘lumped tidal component approach’. A comparative evaluation of data-size revealed that the short-duration datasets of the unconfined aquifer provide more reliable estimate of hydraulic diffusivity than the long-duration datasets. Further, it was found that the spring and neap tidal data yield unreasonable values of hydraulic diffusivity with considerably high values of RMSE and very low values of r ², NSE, and d1, thereby suggesting that spring and neap tidal data are not suitable for aquifer parameter estimation. Overall, it is concluded that the GA-based tide–aquifer interaction model following ‘multi-tidal component approach’ is the most efficient tool for estimating aquifer parameters of unconfined and confined aquifers from tide–aquifer interaction data. The developed methodology is also applicable to other coastal basins of the world irrespective of hydrogeological settings.