基于SRTM-DEM数据的三峡库区蓄水负荷模型及其地表重力与形变响应模拟

以三峡库区蓄水负荷变化为切入点,研究了库区因蓄水导致的地表重力与形变响应。通过高分辨率SRTM-DEM数据与三峡库区主干道及各支流边界的地形对应关系,构建得到不同蓄水水位下的蓄水负荷模型,并且给出了不同水位与库区整体库容量体积及受淹面积之间的数学拟合关系。在此基础上,结合弹性负荷响应理论及macson拟合方法,计算得到整个库区在蓄水第2阶段与第3阶段地表重力场及形变场的空间分布,以及库区蓄水库容量变化的60阶次球谐系数结果,并与GRACE监测结果进行了对比分析。GRACE去除CLM4.5模型后的陆地水储量可认为与三峡库区蓄水变化直接相关,两者之间的差异可能包含了在巨大水体负荷压力下出现的地下水渗透效应。本文理论模拟结果以期为实际观测资料的对比分析和相关校正提供支撑。有助于挖掘库区滑坡活动及水库地震等与库水负荷变化之间的关系。     

日长和地球引力场参数J_2的长期和长周期变化

用高精度的现代日长观测结果、近 2 0年的J2 变化的结果和古地球自转结果 ,讨论了日长和J2 变化的长期和长周期的主要特性 ,从理论和实测两方面分析了日长和J2 变化的关系及其异同 ,认为J2 变化的结果在地球动力学研究中的作用应予以重视 ,综合利用日长和J2 将使这两种资料的潜力得以进一步发挥。     

基于新参考系的极移改正

本文利用IAU2000决议中关于CIP的定义阐述了极移坐标系和极移坐标的定义,在总结微分旋转矩阵的性质的基础上给出了极移旋转矩阵的详细推导,结合极移产生的主要原因,详细介绍了目前国际上关于极移模型化工作的最新进展,最后给出了获取极移坐标和TIO位置的方法和途径。     

混凝土重力坝变形观测工作的布置

目前大部分混凝土重力坝的外部变形观测（特别是位移观测）均在坝体建成后才着手进行,因而对大坝建筑期间的形态变化无从了解。但是,从国内外的水工实践中看出,一般混凝土重力坝及其周围地基的最大变形是紧接着水库蓄水而发生的,水库蓄水则又往往在大坝尚未完全建成之前即已开始,特别对于高坝,这种情况更为普遍。因此,外部观测进行得太晚,必然会丧失了解坝体变化之最重要时机。近来虽然有些学者已纷纷提出变形观测应于蓄水前进行的意见,但到目前为止尚缺乏相应的实施措施。本文试图探讨一种大坝外部变形观测工作的布设方案并介绍与之相应的观测方法,俾能既顾及运转阶段长期细致的观测工作之进行,又考虑到施工期间与蓄水前后之变形量的测定。     

三峡水库蓄水对地壳形变及大地水准面的影响

利用资源三号(ZY-3)高分辨率遥感影像提取三峡库区水体数据,通过负荷格林函数积分模型法计算出三峡水库蓄水过程中水体对地壳形变及对大地水准面的影响。研究发现:1三峡库区近岸地壳垂直形变与水库水位呈负相关关系,大地水准面与水库水位呈正相关关系;水位上升,长江近岸地面水平向内形变,方向指向江心;2三峡水库蓄水造成的地壳垂直形变最大可达35mm左右,大地水准面形变最大值在8mm左右,而对库区地壳水平形变影响不超过0.5mm;3出现形变最大值的地点是忠县环湾一带,而并非是三峡大坝周边。     

利用交叉小波技术分析三峡水库蓄排水过程对库区降雨量的影响

三峡大坝蓄水过程对邻近区域气候的影响一直是国内外学术界广泛关注的热点问题。三峡大坝从2003年投入使用至今,水位从66 m上升至175 m,经历了3个蓄水阶段,为观测水库水位与库区降雨量相关性提供了极佳的窗口期。为了精准分辨两者在多周期多尺度的相互影响,基于三峡库区的4个国家气象观测站的历史逐日降雨数据和三峡蓄排水过程水位变化数据,进行交叉小波分析,提取能量谱、凝聚谱和相位谱,展现两类数据时频域多尺度的相关细节。结果表明,三峡大坝蓄排水过程对库区降雨有影响,第一期蓄水期最明显,表现为库区降雨年周期性相对减弱,高频模式增强;历史数据表明库区降雨主要表现为1.0 a主周期和2.0 a、4.0 a等多个次长周期;三期蓄水之后,库区降雨量的1.0 a主周期没有改变,而多个次长周期特征变化明显。交叉小波相位谱揭示水库蓄排水过程对库区降雨的人工调节和自然调节影响,前者表现为水位变化与降雨1.0 a主周期的完全反相,明显不同于蓄水之前的同相特征;后者表现为高频分量（1/128~1/32 a）的反相特征,其规模效应随大坝建成而增强。值得关注的现象是巴东站与荆州站的降雨存在3.5 a次长周期的反相特征,可能是大坝蓄水后改变了水循环的范围。     

目的及意义

<正> 本计划旨在增进人们对于极移和地球自转速度变化及其与地震、板块运动和其他地球物理现象可能的相关性的认识和了解。作为必要的先行步骤,建议:(1)证实甚长基线干涉测量(VLBI)及卫星激光测距技术,能以亚分米级的精度测定极移和地球自转速度变化。(2)综合分析甚长基线干涉测量与卫星激光测距数据,在此基础     

三峡水库蓄放水对地面重力变化的影响分析

针对目前对地面重力的影响分析多采用模拟计算,从而导致对蓄放水的影响范围和程度分析还存在不足的问题,该文利用资源三号(ZY-3)高分辨率多光谱遥感影像提取了三峡库区江河湖库水体数据,结合水位数据,通过负荷格林函数积分模型,计算出三峡水库蓄放水导致水位升降的过程中水体对地面重力变化的影响。研究发现:(1)以1a为周期,三峡库区库岸及长江近岸地面重力的变化趋势与水库的蓄放水时期对应;(2)三峡水库放水期间水位下降,水库库岸及长江近岸地面重力减小;蓄水期间水位上升,地面重力增大;(3)三峡水库蓄放水对库岸及长江近岸的地面重力影响最大可达1 000μGal以上,且距离长江中心线越近,地面重力变化越大。     

利用超导重力数据探测内核超速旋转的研究

内核存在约(0.27°~0.53°)/a的超速旋转,由此导致的全球年平均重力变化强度约为0.08~0.16μGal(0.8~1.6 nms-2)。除地震数据外,时变重力数据有可能成为探测内核超速旋转速率的重要信息源。对武汉九峰台站超导重力仪观测数据进行了潮汐改正、大气负荷改正、极移改正和日长变化改正,得到了经过各项改正后的时变重力信号;采用小波分析方法对上述时变重力信号进行了处理分析,得到了可供参考的结果;针对目前利用超导重力仪数据探测内核超速旋转所存在的困难提出了几个解决方案和建议。     

基于差分序列分析极移不规则变化及对模型拟合的影响

通过对近52年的极移数据进行二阶差分,发现极移不规则变化的活跃程度存在明显的分段特征。其中活跃部分大约持续6 100d,与地震的近6 500d的长活动周期以及章动的18.6a周期较接近;然后以ARMA模型为例,选取状况不同的4个不规则变化时段的极移数据进行模型的拟合与预报,并进行对比。结果表明:1若拟合数据处于活跃期,建模及预报的精度相对于处于平静期时较差;2拟合数据同时包含活跃期与平静期,拟合的残差出现病态分布,模型建立不成功;3拟合精度相当的不同模型,预测数据处于平静期要比处于活跃期时精度要好。     

Combinations of Earth-orientation measurements: SPACE97, COMB97, and POLE97

Independent Earth-orientation measurements taken by the space-geodetic techniques of lunar and satellite laser ranging, very-long-baseline interferometry, and the global positioning system have been combined using a Kalman filter. The resulting combined Earth-orientation series, SPACE97, consists of values and uncertainties for universal time, polar motion, and their rates spanning the period 28 September 1976 to 3 January 1998 at daily intervals. The space-geodetic measurements used to generate SPACE97 have then been combined with optical astrometric measurements to form two additional combined Earth-orientation series: (1) COMB97, consisting of values and uncertainties for universal time, polar motion, and their rates spanning the period 20 January 1962 to 1 January 1998 at 5-day intervals, and (2) POLE97, consisting of values and uncertainties for polar motion and its rate spanning the period 20 January 1900 to 21 December 1997 at monthly intervals. Received: 10 August 1998 / Accepted: 31 May 1999     

Analysis of decade-long time series of GPS-based polar motion estimates at 15-min temporal resolution

We present results from the generation of 10-year-long continuous time series of the Earth’s polar motion at 15-min temporal resolution using Global Positioning System ground data. From our results, we infer an overall noise level in our high-rate polar motion time series of 60 \(\upmu \hbox {as}\) (RMS). However, a spectral decomposition of our estimates indicates a noise floor of 4 \(\upmu \hbox {as}\) at periods shorter than 2 days, which enables recovery of diurnal and semidiurnal tidally induced polar motion. We deliberately place no constraints on retrograde diurnal polar motion despite its inherent ambiguity with long-period nutation. With this approach, we are able to resolve damped manifestations of the effects of the diurnal ocean tides on retrograde polar motion. As such, our approach is at least capable of discriminating between a historical background nutation model that excludes the effects of the diurnal ocean tides and modern models that include those effects. To assess the quality of our polar motion solution outside of the retrograde diurnal frequency band, we focus on its capability to recover tidally driven and non-tidal variations manifesting at the ultra-rapid (intra-daily) and rapid (characterized by periods ranging from 2 to 20 days) periods. We find that our best estimates of diurnal and semidiurnal tidally induced polar motion result from an approach that adopts, at the observation level, a reasonable background model of these effects. We also demonstrate that our high-rate polar motion estimates yield similar results to daily-resolved polar motion estimates, and therefore do not compromise the ability to resolve polar motion at periods of 2–20 days.     

Prediction of polar motion

Based on an analysis of polar motion behavior, we found the possibility of predicting polar motion up to one year in advance. Comparing these predicted polar coordinates with the observed ones (smoothed), the rms of the differences is about 0".02. The differences of the relative polar motion are much smaller. For any time interval of 20–30 days throughout the whole year, the rms of the relative polar motion differences is about 0".01. It appears that 80–90% of the polar motion is composed of the stable, predictable Chandler and annual terms.     

An improved empirical model for the effect of long-period ocean tides on polar motion

Because the tide-raising potential is symmetric about the Earth’s polar axis it can excite polar motion only by acting upon non-axisymmetric features of the Earth like the oceans. In fact, after removing atmospheric and non-tidal oceanic effects, polar motion excitation observations show a strong fortnightly tidal signal that is not completely explained by existing dynamical and empirical ocean tide models. So a new empirical model for the effect of the termensual (Mtm and mtm), fortnightly (Mf and mf), and monthly (Mm) tides on polar motion is derived here by fitting periodic terms at these tidal frequencies to polar motion excitation observations that span 2 January 1980 to 8 September 2006 and from which atmospheric and non-tidal oceanic effects have been removed. While this new empirical tide model can fully explain the observed fortnightly polar motion excitation signal during this time interval it would still be desirable to have a model for the effect of long-period ocean tides on polar motion that is determined from a dynamical ocean tide model and that is therefore independent of polar motion observations.     

Modeling and forecast of the polar motion excitation functions for short-term polar motion prediction

Short-term forecast of the polar motion is considered by introducing a prediction model for the excitation function that drives the polar motion dynamics. The excitation function model consists of a slowly varying trend, periodic modes with annual and several sub-annual frequencies (down to the 13.6-day fortnightly tidal period), and a transient decay function with a time constant of 1.5 days. Each periodic mode is stochastically specified using a second-order auto-regression process, allowing its frequency, phase, and amplitude to vary in time within a statistical tolerance. The model is used to time-extrapolate the excitation function series, which is then used to generate a polar motion forecast dynamically. The skills of this forecast method are evaluated by comparison to the C-04 polar motion series. Over the lead-time horizon of four months, the proposed method has performed equally well to some of the state-of-art polar motion prediction methods, none of which specifically features forecasting of the excitation function. The annual mode in the ₂ component is energetically the most dominant periodicity. The modes with longer periods, annual and semi-annual in particular, are found to contribute more significantly to forecast accuracy than those with shorter periods.     

Atmospheric and oceanic forcing of the rapid polar motion

The rapid polar motion for periods below 20 days is revisited in light of the most recent and accurate geodetic and geophysical data. Although its amplitude is smaller than 2 mas, it is excited mostly by powerful atmospheric processes, as large as the seasonal ones. The residual amplitude, representing about 20% of the total excitation, stems from the oceans. Rapid polar motion has an irregular nature that is well explained by the combined influence of the atmosphere and the oceans. An overall spectrum reveals cycles principally at 20, 13.6 (fortnightly tidal period) and 10 days (corresponding to the normal atmospheric mode Y₃¹{\Psi_3^1}), but this is only an averaged feature hiding its strong variability over seasonal time scales. This explains why it is so delicate to determine an empirical model of the tidal effect on polar motion. The variability in both amplitude and phase of the 13.6-day term is probably caused by a lunar barometric effect, modulated by some sub-seasonal thermal processes. The irregularities of the prominent cycles of the short-term polar motion are well explained by the atmospheric and oceanic excitations. The oceanic variability reinforces the atmospheric one, as they were triggered by the same agent, maybe seasonal and inter-annual thermal variations.     

Hydrological excitation of polar motion by different variables from the GLDAS models

Continental hydrological loading by land water, snow and ice is a process that is important for the full understanding of the excitation of polar motion. In this study, we compute different estimations of hydrological excitation functions of polar motion (as hydrological angular momentum, HAM) using various variables from the Global Land Data Assimilation System (GLDAS) models of the land-based hydrosphere. The main aim of this study is to show the influence of variables from different hydrological processes including evapotranspiration, runoff, snowmelt and soil moisture, on polar motion excitations at annual and short-term timescales. Hydrological excitation functions of polar motion are determined using selected variables of these GLDAS realizations. Furthermore, we use time-variable gravity field solutions from the Gravity Recovery and Climate Experiment (GRACE) to determine the hydrological mass effects on polar motion excitation. We first conduct an intercomparison of the maps of variations of regional hydrological excitation functions, timing and phase diagrams of different regional and global HAMs. Next, we estimate the hydrological signal in geodetically observed polar motion excitation as a residual by subtracting the contributions of atmospheric angular momentum and oceanic angular momentum. Finally, the hydrological excitations are compared with those hydrological signals determined from residuals of the observed polar motion excitation series. The results will help us understand the relative importance of polar motion excitation within the individual hydrological processes, based on hydrological modeling. This method will allow us to estimate how well the polar motion excitation budget in the seasonal and inter-annual spectral ranges can be closed.     

利用小波分解改进极移预报模型

为进一步提高极移预报精度,将小波分解引入极移预报中。首先利用小波分解对极移序列进行分解,分离低频分量与高频分量,然后对低频分量建立最小二乘外推模型,获得极移序列的趋势项外推值与残差序列,最后采用自回归（autoregressive,AR）模型对高频分量与残差序列之和进行预报,最终极移的预报值为最小二乘外推值与AR模型预报值之和。结果表明,小波分解可以明显改善最小二乘外推与AR组合模型的极移预报精度,尤其对于中长期预报改善更为明显。     

Predictability of the Earth’s polar motion

The numerical prediction of the Earth’s polar motion is of both theoretical and practical interest. The present paper is aimed at a comprehensive, experimental study of the predictability of polar motion using a homogeneous BIH (Bureau International de l’Heure) data set for the period 1967–1983. Based on our knowledge of the physics of the annual and the Chandler wobbles, we build the numerical model for the polar motion by allowing the wobble period to vary. Using an optimum base length of six years for prediction, this “floating-period” model, equipped with a nonlinear least-squares estimator, is found to yield polar motion predictions accurate to within 0″.012 to 0″.024 depending on the prediction length up to one year, corresponding to a predictability of 89–82%. This represents a considerable improvement over the conventional fixed-period predictor, which, by its nature, does not respond to variations in the apparent wobble periods (in particular, a dramatic decrease in the periods of both the annual and the Chandler wobbles after the year 1980). The superiority of the floating-period predictor to other predictors based on critically different numerical models is also demonstrated.