Study on tidal gravity observations obtained at stations Zhongshan and Changcheng, Antarctic

IntroductionThe purpose of the studies on the tidal gravity observations on the Earth(s surface is to investigate the properties of the deformation and the tidal gravity variations of the Earth under the action of the luni-solar tidal force. These variations relate to the internal structure, shape and the medium(s rheology properties of the Earth (Wahr, 1981; Dehant, 1987). The theoretical studies and observations indicated that the amplitudes and the tidal parameters, including the amplitud…     

武汉超导重力仪观测最新结果和海潮模型研究

利用武汉台站GWR_C032超导重力仪观测资料,在对原始数据进行有效预处理的基础上作调和分析,获得反映地球内部介质特征的重力潮汐参数.基于卫星测高技术和有限元方法同时考虑验潮站数据作约束条件获得的多个全球海潮模型,利用负荷理论和数值褶积积分技术计算了重力负荷,对周日和半日频段内的重力潮汐参数实施负荷改正,提出了“负荷改正有效性”概念,研究了全球海潮模型适应性.数值结果说明,海潮改正的有效性高达91%（O1,NAO99）和92%（M2,ORI96）.基于11个海潮模型对主波（O1,K1,M2和S2）的负荷改正说明平均有效性为（86%,70%,73%和84%）,振幅因子与理论模型间的差异分别从（212%,155%,116%和080%）降到（031%,039%,034%和008%）,同时还说明利用NAO99和ORI96全球海潮模型能获得比其他模型更佳的负荷改正效果.文章还利用国际地球动力学计划网络其他7个台站的超导重力仪观测研究了全球海潮模型的适定性问题,结果说明不同模型中不同潮波具有明显的区域特点,早期构制的SCW80全球海潮模型仍可作为大地测量研究中的重要参考模型.     

中国大陆精密重力潮汐改正模型

利用理论和实验重力固体潮模型,充分考虑全球海潮和中国近海潮汐的负荷效应,建立了中国大陆的精密重力潮汐改正模型.结果表明,采用不同的固体潮模型会对重力潮汐结果产生相对变化幅度小于0.06％的差异;在沿海地区海潮负荷的影响约为整个潮汐的4％,而中部地区约为1％,其中中国近海潮汐模型的影响约占整个海潮负荷的10%,内插或外推潮波的负荷约占海潮负荷的3％.通过比较实测的重力数据表明,本文给出的重力潮汐改正模型的精度远远优于0.5×10^-8 m·s^-2,说明了本文构建的模型的实用性,可为中国大陆高精度重力测量提供有效参考和精密的改正模型.     

GPS Height and Gravity Variations Due to Ocean Tidal Loading Around Taiwan

This study presents predicts ocean tidal loading (OTL) effects using a Green’s function approach and validates a novel tidal model for Taiwan. Numerical integration of OTL is performed using the Gauss quadrature method and a local tidal model for the inner zone and a global model for the outer zone. Observed time series of GPS-derived vertical displacements and gravity variations (3–7 days) at five co-located GPS-gravimeter stations along the South East China and Taiwan coasts were utilized to assess the accuracy of the proposed models and two other models. The OTL-induced gravity variations are 3–16 μgal and the vertical site displacements are 13–27 mm. Generally, an OTL model using a mixed global and local tidal model generates better agreement with the observations than an OTL model using a global tidal model only. However, containing a local model inside a global model does not always produce a good agreement with the observations. The relatively large discrepancies between modeled and observed OTL values at some stations indicate that there is a need for an improved local tidal model in the study area. An erratum to this article can be found at     

地表潮汐应变的理论模型

本文的目的是建立一潮汐应变的理论模型,以供使用.模型由两方面组成,即日月引力导致的体潮应变及海洋负荷作用产生的负荷潮汐应变.前者,我们从wahr的潮汐模型出发,进行适当简化,从引潮位直接算出各应变分量,以提高计算速度;后者,我们使用了M2,S2,O1及K1四个主要海洋潮波的迭加,海图采用了Schwiderski的大洋图并顾及我国的局部潮图.      

中国地壳运动观测网络基准站倾斜固体潮观测中的海潮负荷信号改正问题

利用最新的全球海潮模型（Csr3.0,Fes95.2,Tpxo2,Csr4.0和Scw80)和中国近海海潮资料，基于标准地球模型负荷格林函数，采用Agnew的积分格林函数方法研究了倾斜固体潮观测中的海潮负荷效应。文章计算了中国地壳运动观测网络25个基准站8个主要潮流的倾斜负荷，数值结果说明对某一潮波而言，倾斜负荷振幅达10^-9弧度，沿海地区达10^-8弧度或更多。文章构制了北京和上海等8个主要台站的倾斜负荷随时间变化。     

Adaptability of the ocean and earth tidal models based on global observations of the superconducting gravimeters

As the gravity field is the most primary and direct physical quantity reflecting the density variation of the Earth’s interior and its geodynamic properties under various environmental changes and as the knowledge of the fine structure of the Earth’s interior and its geo-dynamics has a strong impact on space research, grav-ity observations become more and more important in Earth sciences. Therefore based on a global network of superconducting gravimeters (SGs), the Global Geo-dynamic Proje…     

Transcontinental tidal transect: European Atlantic coast-Southern Siberia-Russian Pacific coast

The paper presents results of measurements with digital tidal LaCoste-Romberg gravimeters on the European Atlantic coast-Southern Siberia-Russian Pacific coast transect in 1995–2005. The transect includes four West European (Chizé, Ménesplet, Mordelles, and Wikle), two South Siberian (Klyuchi and Talaya), and two Far Eastern (Zabakalskoe and Yuzhno-Sakhalinsk) stations. Gravimetric measurements at the Talaya station (SW Baikal rift zone) are supplemented by long-term laser extensometer observations. The position of the stations within the rectangle (45°–55°N, 0.4°–142°E) allows one to assess existing tidal strain models (WD93 and DDW99) and various ocean tide models (SCW80, CSR3, FES95, ORI96, CSR4, FES02, GOT00, NAO99, and TPX06). Data of intracontinental stations (with a small ocean effect at distances of 2000–3000 km) agree well with the DDW99 tidal strain model (with regard to the mantle viscosity). The uncertainty of digital tidal gravity measurements is 0.25%. Results of laser extensometer measurements are at the same accuracy level. Then, the Love and Shida numbers calculated at midlatitudes of the intracontinental zone of Eurasia from combined data are h = 0.6077 ± 0.0008, k = 0.3014 ± 0.0001, and l = 0.0839 ± 0.0001. The analysis of results of Pacific and Atlantic stations located at distances of 30–300 km from the ocean showed that the FES02, CSR4, GOT00, NAO99, and TPX06 ocean tide models are preferable.     

Determination of the long period tidal waves in the GGP superconducting gravity data

Several results about the long period (LP) tidal waves are obtained by the analysis of series of superconducting gravity data, provided by the Global Geodynamics Project (GGP). The most important result is the determination of a single group called LPMF, composed by all LP tides but representing accurately the parameters of the M_f wave. As the LP tidal generating potential is vanishing at latitudes ±35°15′52″ we cannot determine accurate tidal amplitude factors for the stations located between ±40° and ±30°. However, it is still possible to obtain tidal residual vectors and compare them with oceanic tidal loading computations. For 15 stations the NAO99 oceanic model is giving a coherent picture. For nine stations with M_f amplitude larger than 3 μgal (1 μgal = 10 nm s⁻²) a global analysis is obtained by introducing the loading effect of the ocean directly in the observation equations. The mean amplitude factor obtained for LPMF is larger than expected from the models and there is a significant phase lag, showing the imperfection of the tidal oceanic models for M_f. Other new result is the first separate estimation of the parameters of the LP tides, generated by the tidal potential of third degree, dominated by a Lunar declinational monthly wave, called here 3M_md. Due to their small amplitudes (under 1 μgal) these waves are practically hidden by the noise. Nevertheless, the quality of the data and the flexibility of the VAV analysis method [Venedikov, A.P., Arnoso, J., Vieira, R., 2001. Program VAV/2000 for tidal analysis of unequally spaced data with irregular drift and colored noise. J. Geodetic Soc. Jpn. 47 (1), 281–286; Venedikov, A.P., Arnoso, J., Vieira, R., 2003. VAV: a program for tidal data processing. Comput. Geosci. 29, 487–502.] allow getting significant results, in agreement with the theory of the Earth deformation by the tidal potential of third degree.     

中国东西重力潮汐剖面

为了检验体潮与海潮的理论模型,分析了中国东西重力潮汐剖面（1981年9月-1985年1月）。同时,为研究LaCoste ET-20和ET-21重力仪的格值系统,建立了一条由17台LaCoste G型和2台LaCoste D型重力仪观测的重力垂直基线。在基线上标定的结果表明,ET-21重力仪的格值大了1％。由标定得到的格值计算剖面上各测站的潮汐因子,经海潮改正后,接近Wahr模型值,振幅因子的残差:O₁波小于0.3μGal,M₂波小于0.4μGal。但是上海和拉萨的观测经海潮改正后,相位迟后有很大的改善,振幅因子却更偏离于模型值,其潮汐异常主要是近海的海潮模型不完善,以及在海潮计算中,所采用的地球模型未考虑地壳与上地幔的横向不均匀性所引起。     

海潮负荷对地球内部潮汐应力和应变的影响

详细介绍了海潮负荷影响的计算理论,基于PREM地球模型计算了地球内部的负荷勒夫数及负荷格林函数;并以上海台和武汉台为例,计算了海潮负荷对不同深度处的应力和应变潮汐的影响. 结果表明:深度是影响海潮负荷应力的一个重要因素,在靠近计算点的区域,应力负荷的影响随深度增大而减小;而对于远离计算点的区域,应力负荷的影响却随深度增大而增大;另外,深度会影响某些应力和应变潮汐分量时间变化的相位. 在沿海地区,海潮负荷对应力和应变的影响超过了应力和应变固体潮的影响,因此该影响在应力和应变测量中必须要加以考虑.      

Modelling atmospheric and induced non-tidal oceanic loading contributions to surface gravity and tilt measurements

We investigate the contribution of atmospheric and its induced non-tidal oceanic loading effects on surface time-varying gravity and tilt measurements for several stations in Western Europe. The ocean response to pressure forcing can be modelled accordingly to the inverted barometer, i.e. assuming that air pressure variations are fully compensated by static sea height changes, or using ocean general circulation models. We validate two runs of the HUGO-m barotropic ocean model by comparing predicted sea surface height variations with hundred tide-gauge measurements along the European coasts. We then show that global surface pressure field, as well as a barotropic high-resolution ocean model forced by air pressure and winds allow in most cases a significant reduction of the variance of gravity residuals and, to a smaller extends tilt residuals.We finally show that precise gravity measurements with superconducting gravimeters allow the observation of large storm surges, occurring in the North Sea, even for inland stations. However, we also confirm that the continental hydrology contribution cannot be neglected. Thanks to their specific sensitivity feature, only tiltmeters closest to the coast can clearly detect the loading due to these storm surges.     

Temporal variations in free core nutation period

Based on the nearly diurnal resonance in the tidal gravity observations,the temporal variations in period of the Earth's free core nutation (FCN) are investigated by using the tidal gravity observations of 18-year duration recorded continu-ously with a superconducting gravimeter (SG) at Brussels. The effects of the global oceanic tide loading and local barometric pressure on the SG observations have been removed by using eleven high-precision global digital models of oceanic tides and barometric pressure me...     

武汉台重力潮汐长期观测结果

采用武汉台超导重力仪(SG C032)14年多的长期连续观测资料,研究了固体地球对二阶和三阶引潮力的响应特征,精密测定了重力潮汐参数,系统研究了最新的固体潮模型和海潮模型在中国大陆的有效性.采用最新的8个全球海潮模型计算了海潮负荷效应,从武汉台SG C032的观测中成功分离出63个2阶潮汐波群和15个3阶潮汐波群信号,3阶潮波涵盖了周日、半日和1/3日三个频段.重力潮汐观测的精度非常高,标准偏差达到1.116 nm·s^-2,系统反映了非流体静力平衡、非弹性地球对2阶和3阶引潮力的响应特征.结果表明,现有的武汉国际重力潮汐基准在半日频段非常精确,但在周日频段存在比较明显的偏差,需要进一步精化.对于中国大陆的大地测量观测,固体潮可以采用Dehant等考虑地球内部介质非弹性和非流体静力平衡建立的固体潮理论模型或Xu 等基于全球SG观测建立的重力潮汐全球实验模型作为参考和改正模型,海潮负荷效应应该采用Nao99作为改正模型.     

香港地区重力固体潮和海潮负荷特征研究

介绍了在香港地区重力固体潮合作观测成果, 获得了该地区完整的重力固体潮实测模型. 利用全球和近海海潮模型以及岛屿验潮站数据较系统地研究了海潮负荷特征, 反演了全球海潮模型的适定性. 数值结果说明周日频段内的海潮模型要比半日频段内的模型更加稳定, 实施验潮站潮位高变化改正对精密确定重力固体潮相位滞后起重要作用. 文章还研究了重力观测残差和台站背景噪声水平. 本项研究填补了中国地壳运动观测网络在该地区重力固体潮观测空白, 为地表和空间大地测量提供有效参考和服务.     

中国固体潮向量空间分布特征的研究

本文对中比合作和我们独立获得的共10个台站17个仪器架次2890天的固体潮观测资料采用卡特莱特(Cartwright)的完全展开和维尼迪可夫(Venedikov)方法统一地进行了调和分析,并用中井(Nakai)方法对观测资料进行了拟合预处理以提高分析结果的信噪比,同时用线性内插方法处理了仪器灵敏度以资对比.本文着重讨论了分析结果所提供的我国大陆固体潮矢量空间分布的区域性特征及其与海洋负荷的关系.结果表明:中国大陆固体潮空间分布受到海洋负荷的明显控制.O1波尤为显着.文中讨论了仪器流变模型对观测矢量的影响.根据流变模型改正后的结果,所得到的地球对引潮力的实际响应的相位滞后,大多数发站都接近于-1,它论证了理论原则的正确性.文中还讨论了残差矢量与海洋负荷矢量的关系,它们的一致性最概括地说明了海洋负荷对固体潮的影响.文中用误差矢量的方法研究了分析结果的精度,它说明目前海潮改正的精度仍然是不够的.在上述工作基础上,文中最后得到了经海潮改正后的 M2波和 O1波的观测矢量.      

Synthetic tidal parameters for gravity over China and its neighbor area

The synthetic tidal parameters with high spatial resolution for gravity over China and its neighbor area are con- structed with Earth’s tidal model and ocean tide loading calculated using TPXO7 global ocean tide model as well as tidal data over China seas. The comparison between synthetic parameters and ones observed by spring gravime- ters at some seismic network stations and Hong Kong station and one observed by super-conducting gravimeter at Wuhan station shows that the average differences in amplitude factors and phases are smaller than 0.005 and 0.5° respectively; and that the discrepancies between observational and synthetic parameters are dependent on gravim- etric technique in that the synthetic parameters are in well agreement with the superconducting gravimetric obser- vations. This also indicates that the synthetic result is a good estimation for tidal gravity, and the numerical results in the present paper not only can provide ground and space gravimetry such as absolute gravimetry with correction model of tidal gravity, but also provide effective tidal parameters over areas where no observation is carried out.     

印尼地区地震断层面上的海潮负荷应力特征

对印尼地区3574次M≥5.0地震震源断层面上的海潮负荷应力进行计算,研究了地震断层上的负荷应力随深度变化以及随断层倾角和走向的变化特征.结果表明,地震断层上的负荷正应力大于负荷切应力.逆断层上的负荷应力最大,其它依次为斜滑断层、正断层和走滑断层.倾角范围在0°—50°的断层上的负荷正应力随倾角增大有减小趋势,负荷切应力在30°—50°倾角范围的断层上较大.负荷应力随断层走向的趋势性变化不明显.不同类型断层上的负荷正应力和切应力在震源深度15km处均达到最大,之后随深度增加而减小.当震源深度小于40km时,断层面上的海潮负荷应力的量级与固体潮应力相当.因此指出,在潮汐应力对地震影响的研究中,对震源深度小于40km的海洋和沿海地震,除固体潮汐应力外还需要考虑海潮负荷应力的影响.     

High-frequency loading effects by the Ligurian Sea — a statistical investigation

In the present work we analyzed the high-frequency band of crustal tilts at Genoa in order to investigate indirect loading effects by the quarter-diurnal oceanic tides, as well as by an observed oceanic oscillation of 3.66 h which was previously ascribed to the proper oscillation of the Ligurian Sea. With this aim two hourly series of tidal observation recorded by an horizontal pendulum along a NS direction have been submitted to spectral analyses (1 May 1965-28 February 1966; 1 June 1966-31 December 1966).Power spectra revealed two peaks near the periods of 6.15 and 3.66 h and highly resolved Fourier spectra allowed us to detect the loading effects by the oceanic tides M₄, MS₄ and MK₄. As regards to the oscillation of 3.66 h we have found a spreading of spectral lines and non-significant values for the phases. This result provides a decisive verification of the existence of a proper oscillation of the Ligurian Sea regarded as a wide oscillating system with an open boundary from Nice (Côte d'Azur) to Calvi (Corsica).Finally, a spectral analysis performed on sea-level observations at Genoa revealed a complete correspondence between ocean and earth oscillations in the quarter-diurnal band and at the frequency of the longitudinal free oscillation of the Ligurian basin, with a mean amplitude ratio of about 1 mseca/mm.     

Tidal loading along a profile Europe-East Africa-South Asia-Australia and the Pacific Ocean

A knowledge of the vertical component of the oceanic tidal load to a precision of at least one microgal is essential for the geophysical exploitation of the high-precision absolute and differential gravity measurements which are being made at ground level and in deep boreholes. On the other hand the ocean load and attraction signal contained in Earth tide gravity measurements can be extracted with a precision which is sufficient to characterize the behaviour of the oceanic tides in different basins and this provides a check of the validity of the presently proposed cotidal maps. The tidal gravity profiles made since 1971 from Europe to Polynesia, through East Africa, Asia and Australia, with correctly intercalibrated gravimeters, comprise information from 91 tidal gravity stations which is used in this paper with this goal in mind.A discussion of all possible sources of error is presented which shows that at the level of 0.5 μgal the observed effects cannot be ascribed to computational or instrumental errors. Cotidal maps which generate computed loads in agreement with the Earth tide gravity measurements over a sufficiently broad area can be used with confidence as a working standard to apply tidal corrections to high-precision measurements made by using new techniques in geodesy, geophysics and geodynamics, satellite altimetry, very long baseline interferometry, Moon and satellite laser ranging and absolute gravity. The recent cotidal maps calculated by Schwiderski for satellite altimetry reductions agree very well with land-based gravimeter observations of the diurnal components of the tides (O₁, K₁ and P₁ waves) but his semi-diurnal component maps (M₂, S₂ and N₂ waves) strangely appear less satisfactory in some large areas. The maps of Hendershott and Parke give good results in several large areas but not everywhere. More detailed investigations are needed not only for several coastal stations but mainly in the Himalayas.