Accuracy of Normal Heights Determined Using Improved Geopotential Models

The accuracy of determining the Molodensky normal heights using geopotential models has been investigated. On the basis of geopotential model JGM-3/OSU91A the Molodensky normal heights can be computed with an accuracy of about ±35 cm at the GPS sites in the central part of Europe. On the basis of JGM-3/OSU91A improved the accuracy becomes higher, about ±14 cm.     

Determination of Geopotential Differences between Local Vertical Datums and Realization of a World Height System

The methodology developed for connecting Local Vertical Datums (LVD) was applied to the Australian Height Datum (AHD) and the North American Vertical Datum (NAVD88). The geopotential values at AHD and NAVD88 were computed and the corresponding vertical offset of 974 mm with rms 51 mm was obtained between the zero reference surfaces defined by AHD and NAVD88. The solution is based on the four primary geodetic parameters, the GPS/levelling sites and the geopotential model EGM96. The Global Height System (or the Major Vertical Datum) can be defined by a geoidal geopotential value used in the solution as the reference value, or by the geopotential value of the LVD, e.g. NAVD88.     

Improvement of Global Hydrological Models Using GRACE Data

After about 6 years of GRACE (Gravity Recovery and Climate Experiment) satellite mission operation, an unprecedented global data set on the spatio-temporal variations of the Earth’s water storage is available. The data allow for a better understanding of the water cycle at the global scale and for large river basins. This review summarizes the experiences that have been made when comparing GRACE data with simulation results of global hydrological models and it points out the prerequisites and perspectives for model improvements by combination with GRACE data. When evaluated qualitatively at the global scale, water storage variations on the continents from GRACE agreed reasonably well with model predictions in terms of their general seasonal dynamics and continental-scale spatial patterns. Differences in amplitudes and phases of water storage dynamics revealed in more detailed analyses were mainly attributed to deficiencies in the meteorological model forcing data, to missing water storage compartments in the model, but also to limitations and errors of the GRACE data. Studies that transformed previously identified model deficiencies into adequate modifications of the model structure or parameters are still rare. Prerequisites for a comprehensive improvement of large-scale hydrological models are in particular the consistency of GRACE observation and model variables in terms of filtering, reliable error estimates, and a full assessment of the water balance. Using improvements in GRACE processing techniques, complementary observation data, multi-model evaluations and advanced methods of multi-objective calibration and data assimilation, considerable progress in large-scale hydrological modelling by integration of GRACE data can be expected.     

Ionospheric Time-delay over Akure Using Global Positioning System Observations

Ionospheric time delay (VΔt) variability using Global Positioning System (GPS) data over Akure (7.15°N, 5.12°E), Nigeria, has been studied. The observed variability of VΔt in comparison to older results of vertical total electron content (TEC) across similar regions has shown equivalent signatures. Higher monthly mean values of VΔt (MVΔt) were observed during daytime as compared to nighttime (pre- and post-midnight) hours in all months. The highest MVΔt observed in September during daytime hours range between ~6 and ~21 ns (~1.80 and ~6.30 m) and at post-midnight, they are in the range of ~1 to ~6 ns (~0.3 to ~1.80 m). The possible mechanisms responsible for this variability were discussed. Seasonal VΔt were investigated as well.     

Global Event Location with Full and Sparse Data Sets Using Three-dimensional Models of Mantle P-wave Velocity

—?In order to improve on the accuracy of event locations at teleseismic distances it is necessary to adequately correct for lateral variations in structure along the ray paths, either through deterministic model-based corrections, empirical path/station corrections, or a combination of both approaches. In this paper we investigate the ability of current three-dimensional models of mantle P-wave velocity to accurately locate teleseismic events. We test four recently published models; two are parameterized in terms of relatively long-wavelength spherical harmonic functions up to degree 12, and two are parameterized in terms of blocks of constant velocity which have a dimension of a few hundreds of km. These models, together with detailed crustal corrections, are used to locate a set of 112 global test events, consisting of both earthquakes and explosions with P-wave travel-time data compiled by the Internation al Seismological Centre (ISC). The results indicate that the supposedly higher resolution block models do not improve the accuracy of teleseismic event locations over the longer wavelength spherical harmonic models. For some source locations the block models do not predict the range of observed travel-time residuals as well as the longer wavelength models. The accuracy of the locations largely varies randomly with geographic position although events in central Asia are particularly well located. We also tested the effect of reduced data sets on the locations. Multiple location iterations using 30 P-wave travel times indicate that teleseismic events may be located within an area of 1000?km² of the true location 66% of the time with only the model-based corrections, and increasing to 75% if calibration information is available. If as few as 8 phases are available then this is possible only 50% of the time. Further refinement in models and/or procedure, such as the addition of P _n phases, azimuth data, and consideration of P-wave anisotropy may provide further improvement in the teleseismic location of small events.     

A Comparison of Global and Regional GRACE Models for Land Hydrology

When using GRACE as a tool for hydrology, many different gravity field model products are now available to the end user. The traditional spherical harmonics solutions produced from GRACE are typically obtained through an optimization of the gravity field data at the global scale, and are generated by a number of processing centers around the world. Alternatives to this global approach include so-called regional techniques, for which many variants exist, but whose common trait is that they only use the gravity data collected over the area of interest to generate the solution. To determine whether these regional solutions hold any advantage over the global techniques in terms of overall accuracy, a range of comparisons were made using some of the more widely used regional and global methods currently available. The regional techniques tested made use of either spherical radial basis functions or single layer densities (i.e., mascons), with the global solutions having been obtained from the various major processing centers. The solutions were evaluated using a range of computed statistics over a selection of major river basins, which were globally distributed and ranged in size from 1 to 6 million km². For one of the basins tested, the Zambezi, additional validation tests were conducted through comparisons against a custom designed regional hydrology model of the region. We could not prove that current regional models perform better than global ones. Monthly mean water storage variations agree at the level of 0.02 m equivalent water height. The differences in terms of monthly mean water storage variations between regional and global solutions are comparable with the differences among only global or regional solutions. Typically they reach values of 0.02 m equivalent water heights, which seems to be the level of accuracy of current GRACE solutions for river basins above 1 million km². The amplitudes of the seasonal mass variations agree at the sub-centimetre level. Evident from all of the comparisons shown is the importance that the choice of regularization, or spatial filtering, can have on the solution quality. This was found to be true for global as well as regional techniques.     

GRACE/GOCE扩展重力场模型确定我国1985高程基准重力位的精度分析

高精度高程基准重力位的确定往往依赖于高精度全球重力场模型,其对全球和区域高程基准的高精度统一非常关键,GRACE、GOCE卫星重力计划极大地提高了全球重力场模型中长波的精度.本文首先对GRACE/GOCE卫星重力场模型的内符合和外符合精度进行讨论分析,结果说明卫星重力模型的截断误差影响可达到分米级水平,在确定高程基准重力位时该影响不可忽略.利用EGM2008模型扩展GRACE/GOCE卫星重力场模型至2190阶,可有效减弱卫星重力模型的截断误差影响,但不同模型扩展时的最优拼接阶次不同,其中DIR-1、DIR-5模型对应的最优拼接阶次分别为180阶和220阶,以GPS水准数据检验,扩展模型在中国区域的精度均优于18 cm.最后,基于最优拼接阶次获得的扩展重力场模型对我国1985高程基准重力位进行了估计,DIR-5和TIM-5模型对应数值分别为62636853.47 m²·s^-2和62636853.49 m²·s^-2,精度均为1.51 m²·s^-2;发现在中国区域模型大地水准面与GPS/水准数据的差值存在微弱的系统性倾斜,东西向倾斜约为9 cm,南北向倾斜约为1.4 cm,考虑倾斜改正后基于DIR-5和TIM-5模型估计我国1985高程基准重力位的精度提高了0.16 m²·s^-2.

     

CDMA2000 1x系统传输地震监测信号的性能分析

CDMA2000 1x系统通信容量大,具有频谱利用率高、传输质量好、保密性强、掉线率低、覆盖广等特点,适于对译码时延要求不高的数据传输业务。采用CDMA2000 1x系统实时传输地震监测信号具有丢包率低、电台发射功率小、总干扰电平低、系统的稳定性与可靠性较高的特点,符合地震信号传输的要求。     

Adaptive Management of the Storage Function for a Large Reservoir Using Learned Fuzzy Models

Water Resources - A single study investigates the possibility of using adaptive control of the reservoir Vranov Reservoir situated on the Dyje River. The control algorithm uses a fuzzy model that...     

Injection System for Multiwell Injection Using a Single Pump

Many hydrological and geochemical studies rely on data resulting from injection of tracers and chemicals into groundwater wells. The even distribution of liquids to multiple injection points can be challenging or expensive, especially when using multiple pumps. An injection system was designed using one chemical metering pump to evenly distribute the desired influent simultaneously to 15 individual injection points through an injection manifold. The system was constructed with only one metal part contacting the fluid due to the low pH of the injection solutions. The injection manifold system was used during a 3‐month pilot scale injection experiment at the Vineland Chemical Company Superfund site. During the two injection phases of the experiment (Phase I = 0.27 L/min total flow, Phase II = 0.56 L/min total flow), flow measurements were made 20 times over 3 months; an even distribution of flow to each injection well was maintained (RSD < 4%). This durable system is expandable to at least 16 injection points and should be adaptable to other injection experiments that require distribution of air‐stable liquids to multiple injection points with a single pump.     

Comparison of Daily GRACE Gravity Field and Numerical Water Storage Models for De-aliasing of Satellite Gravimetry Observations

Reducing aliasing effects of insufficiently modelled high-frequent, non-tidal mass variations of the atmosphere, the oceans and the hydrosphere in gravity field models derived from the Gravity Recovery and Climate Experiment (GRACE) satellite mission is the topic of this study. The signal content of the daily GRACE gravity field model series (ITG-Kalman) is compared to high-frequency bottom pressure variability and terrestrially stored water variations obtained from recent numerical simulations from an ocean circulation model (OMCT) and two hydrological models (WaterGAP Global Hydrology Model, Land Surface Discharge Model). Our results show that daily estimates of ocean bottom pressure from the most recent OMCT simulations and the daily ITG-Kalman solutions are able to explain up to 40 % of extra-tropical sea-level variability in the Southern Ocean. In contrast to this, the daily ITG-Kalman series and simulated continental total water storage variability largely disagree at periods below 30 days. Therefore, as long as no adequate hydrological model will become available, the daily ITG-Kalman series can be regarded as a good initial proxy for high-frequency mass variations at a global scale. As a second result of this study, based on monthly solutions as well as daily observation residuals, it is shown that applying this GRACE-derived de-aliasing model supports the determination of the time-variable gravity field from GRACE data and the subsequent geophysical interpretation. This leads us to the recommendation that future satellite concepts for determining mass variations in the Earth system should be capable of observing higher frequeny signals with sufficient spatial resolution.     

An Estimate of Global Mean Sea-level Rise Inferred from Tide-gauge Measurements Using Glacial-isostatic Models Consistent with the Relative Sea-level Record

This study is concerned with the influence of the glacial-isostatic adjustment caused by the last Pleistocene deglaciation on the present-day sea level. The viscoelastic deformation caused by the time-variable ice and ocean loads is simulated by computing the resulting perturbations for a spherical, self-gravitating, incompressible, Maxwell-viscoelastic earth model. The associated variation of the earth rotation is described in terms of the Liouville equation, which is solved by means of the MacCullagh formulae. This allows the determination of the vertical displacement and geoid height and, thus, the solution of the sea-level equation. We test several viscosity and ice models and evaluate them by comparison of the computed response with the Holocene relative sea-level record. Using the optimum combination of viscosity and ice models, we then estimate the influence of the last Pleistocene deglaciation on the tide-gauge measurements. A comparison between the observational and residual linear trends for the tide-gauge measurements shows a significant reduction of the variance and geographical variability for the latter, in particular for the formerly ice-covered regions of North America and Scandinavia. The favoured value determined for the global mean sea-level rise is (1.46±0.2) mm a⁻¹.     

基于一种新智能优化算法与谱相关方法对重力固体潮的分析

根据月球与太阳相对于地球位置的关系,建立一个三维正交分解模型来揭示重力固体潮中包含的谐波成分。在此基础上,提出一种基于单形邻域与多角色进化策略智能优化算法的独立分量分析方法,用以提高算法效率和全局寻优能力;并结合谱相关方法,对重力固体潮观测数据进行处理和分析,观察其频域和时域的变化。最后引入理论信号和理论计算值作为参考背景,以凸显其异常变化特征。研究表明,利用该方法可以有效地反映出重力固体潮潮汐的日波、半日波、长周期波等特征。同时,发现重力固体潮潮汐的异常变化中隐含有地震前兆信息,通过对云南地区观测数据的分析,在排除测量误差和环境影响外,发现在地震前2~5个月内,重力固体潮的长周期波均呈现出规律性的异常变化。这反映出地震的前兆异常信息,可能对地震时间和地点的预测提供依据。     

DORIS as a potential part of a Global Geodetic Observing System

We have processed all available DORIS data from all available satellites, except Jason-1 over the past 10 years (from January 1993 to April 2003). Weekly solutions have been produced for stations positions coordinates, geocenter motion and scale factor stability. We present here accuracy presently achievable for all types of potential geodetic products. Typically weekly stations positions can be derived with a repeatability of 1.0–1.5 cm using data from 5 satellites simultaneously, showing the significant improvement in precision that has been gained recently using the additional new DORIS satellites. As an example, we show how such new results can detect displacement from large magnitude earthquakes, such as the 2003 Denali fault earthquake in Alaska. Displacements of −5 cm in latitude and +2 cm in longitude were easily detected using the DORIS data and are confirmed by recent GPS determination. The terrestrial reference frame was also well be monitored with DORIS during this 10-year period. Other geodetic products, such as tropospheric corrections for atmospheric studies are also analyzed. Finally, we discuss here the possible advantages and weaknesses of the DORIS system as additional geodetic tool, in conjunction with the already existing GPS, VLBI and SLR services, to participate in an Global Geodetic Observing System (GGOS).     

Accurate Establishment of Error Models for the Satellite Gravity Gradiometry Recovery and Requirements Analysis for the Future GOCE Follow-On Mission

Firstly, the new single and combined error models applied to estimate the cumulative geoid height error are efficiently produced by the dominating error sources consisting of the gravity gradient of the satellite-equipped gradiometer and the orbital position of the space-borne GPS/GLONASS receiver using the power spectral principle. At degree 250, the cumulative geoid height error is 1.769 × 10^?1 m based on the new combined error model, which preferably accords with a recovery accuracy of 1.760 ×10^?1 m from the GOCE-only Earth gravity field model GO_CONS_GCF_2_TIM_R2 released in Germany. Therefore, the new combined error model of the cumulative geoid height is correct and reliable in this study. Secondly, the requirements analysis for the future GOCE Follow-On satellite system is carried out in respect of the preferred design of the matching measurement accuracy of key payloads comprising the gravity gradient and orbital position and the optimal selection of the orbital altitude of the satellite. We recommend the gravity gradient with an accuracy of 10^?13?10^?15 /s², the orbital position with a precision of 1-0.1 cm and the orbital altitude of 200-250 km in the future GOCE Follow-On mission.     

On Gravity Inversion for Point Mass Anomalies by Means of the Truncated Geoid

The physical meaning of the truncated geoid, which is defined by the convolution of gravity anomalies with the Stokes function on a spherical cap of specified radius, has been studied by the authors. They investigated its relation to the density distribution, generating the surface gravity, and its potential use in inversion. Some progress results for simulated studies on point mass anomalies are presented. The behavior of the truncated geoid is controlled by the radius of the integration domain, hereinafter referred to as the truncation parameter, which is treated as a free parameter. The change of the truncated geoid in response to the change of the truncation parameter was studied in the context of the simulated mass distributions. By means of such computer simulations we have managed to demonstrate the clear sensitivity of the truncated geoid to the depths, in addition to the horizontal positions, of point mass anomalies generating the synthetic surface gravity. The objective of this paper is to illustrate, with the help of computer simulation as the method of our study, the contribution of the truncated geoid to the solution of the gravimetric inverse problem. Further work towards employing the truncated geoid in gravity exploration is being conducted.     

Development of Local IDF-formula Using Controlled Random Search Method for Global Optimization

The aim of the study is to present the effective and relatively simple empirical approach to rainfall intensity-duration-frequency-formulas development, based on Controlled Random Search (CRS) for global optimization. The approach is mainly dedicated to the cases in which the commonly used IDF-relationships do not provide satisfactory fit between simulations and observations, and more complex formulas with higher number of parameters are advisable. Precipitation data from Gdańsk gauge station were analyzed as the example, with use of peak-overthreshold method and Chomicz scale for rainfall intensity. General forms of the IDF-function were chosen and the parameter calibration with use of CRS algorithm was developed. The compliance of the obtained IDFformulas with precipitation data and the efficiency of the algorithm were analyzed. The study confirmed the proposed empirical approach may be an interesting alternative for probabilistic ones, especially when IDFrelationship has more complex form and precipitation data do not match “typical” hydrological distributions.     

The 3-D Truncation Filtering Methodology Defined for Planar and Spherical Models: Interpreting Gravity Data Generated by Point Masses

This paper focuses on one particular way of linear filtering the gravity data to facilitate gravity inversion or interpretation. With the use of integral transforms the gravity anomalies are transformed into new quantities that allow an easier interpretation with the help of pattern recognition. As the integral transforms are in fact filters, and as the regions of integration are caps with a variable radius, which can be systematically changed as a free parameter, we refer to such methodology as the truncation filtering. Such filters may be understood as weighted spherical windows moving over the surface, on which the gravity anomaly is defined, the kernel of the transform being the weight function. The objective of this paper is to define and deploy the truncation filtering for a planar model, i.e. for a homogenous horizontally infinite layer with embedded anomalous masses, and for a spherical model, i.e., for a homogenous massive sphere with embedded anomalous masses. Instead of the original gravity anomaly, the quantities resulting from the truncation filtering are interpreted/inverted. As we shall see, this approach has certain benefits. The fundamental concept of the truncation filtering methodology is demonstrated here in terms of the model consisting of one point mass anomaly.The relationship between the depth of the point mass and the instant of the onset of the dimple pattern observed in sequences produced by truncation filtering the synthetic gravity data generated by point masses is, for both the planar and spherical models, compiled by computer simulations, as well as derived analytically. It is shown, that the dimple pattern is a consequence of truncating the domain of the filter and is free of the choice of the kernel of the filter. It is shown, that in terms of the mean earth and depths of point masses no greater than some 100 km the spherical model may be replaced by a planar model from the perspective of the truncation filtering methodology. It is also shown, that from the viewpoint of the truncation filtering methodology the rigorous gravity anomaly may be approximated by the vertical component of the gravity disturbance. The relationship between the instant of the dimple onset and the depth of the point mass thus becomes linear and independent of the magnitude (mass) of the point mass.     

Discussion of the Features of Synthetic Amplitude-Distance Curves of Teleseismic P Waves for Global Earth Models

The reason why the synthetic amplitude distance curves of P-waves for models IASP91 and PREM, observed for shallow sources up to epicentral distance of 28°, oscillate is illustrated by means of synthetic seismograms. Furthermore the position of the beginning of the diffraction of the P-wave at the CMB, depending on the prevailing signal period, is discussed in connection with the extension of Fresnel volumes.     

Using Grey System Theory for Earthquake Forecast

By combining conventional grey correlation analysis,grey clustering method and grey forecasting methods with our multi-goal forecast thoughts and the techniques of grey time series processing,we develop six different grey earthquake forecast models in this paper,Using the record of major earthquakes in Japan from 1872 to 1995,we forecast future earthquakes in Japan.We develop an earthquake forecast model.By using the major earthquakes in Japan from 1872 to 1984,we forecast earthquakes from 1985 to 1995 and check the precision of the grey earthquake models.We find that the grey system theory can be applied to earthquake forecast.We introduce the above analysis methods and give a real example to evaluate and forecast.We also further discuss the problems of how to improve the precision of earthquake forecast and how to strengthen the forecast models in future research.