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1.
Comparison of Daily GRACE Gravity Field and Numerical Water Storage Models for De-aliasing of Satellite Gravimetry Observations 总被引：1，自引：0，他引：1
L. Zenner I. Bergmann-Wolf H. Dobslaw T. Gruber A. Güntner M. Wattenbach S. Esselborn R. Dill 《Surveys in Geophysics》2014,35(6):1251-1266
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. 相似文献
2.
Mapping the mesoscale surface velocity stream function by combining estimates of surface height from satellite altimetry
and surface currents from sequential infrared (sea-surface temperature) imagery using optimal interpolation is described.
Surface currents are computed from infrared images by the method of maximum cross-correlations (MCC) and are combined with
altimeter sea-level anomaly data from the TOPEX/Poseidon and ERS satellites. The analysis method was applied to 6 years of
data from the East Australian Current region. The covariance of velocity and sea-level data is consistent with the statistical
assumptions of homogeneous, isotropic turbulence, with typical length scales of order 220 km and time scales of 10 days in
this region. Augmenting the analysis of altimeter data with MCC velocity observations improves the resolution of the surface
currents, especially near the Australian coast, and demonstrates that the two data sources provide consistent and complementary
observations of the surface mesoscale circulation. The volume of MCC data is comparable to that from a satellite altimeter,
but with a more variable distribution of spatial and temporal resolution. In concert with altimetry, satellite radiometer
velocimetry represents a technique useful for retrospective analysis of currents from high-resolution satellite radiometer
data-sets.
Received: 3 July 2001 / Accepted: 16 November 2001 相似文献
3.
Seafloor pressure records, collected at 11 stations aligned along a single ground track of the Topex/Poseidon and Jason satellites,
are analyzed for their tidal content. With very low background noise levels and approximately 27 months of high-quality records,
tidal constituents can be estimated with unusually high precision. This includes many high-frequency lines up through the
seventh-diurnal band. The station deployment provides a unique opportunity to compare with tides estimated from satellite
altimetry, point by point along the satellite track, in a region of moderately high mesoscale variability. That variability
can significantly corrupt altimeter-based tide estimates, even with 17 years of data. A method to improve the along-track
altimeter estimates by correcting the data for non-tidal variability is found to yield much better agreement with the bottom-pressure
data. The technique should prove useful in certain demanding applications, such as altimetric studies of internal tides. 相似文献
4.
Surface elevation and current records contain non-tidal variance, often dismissed as noise. The processes responsible for the non-tidal component may also modulate the tidal signal, altering its strength and frequency structure. Because of their manner of generation and propagation, internal tides are inherently irregular. The non-stationary character of these and other tidal processes provides an integral and useful property of tidal records, because it provides an opportunity to obtain insights into tidal dynamics and the interaction of tidal and non-tidal processes. It is, moreover, productive to use multiple approaches in analyzing coastal and estuarine tidal processes so that both the time-varying and average frequency content are determined. Only by confronting the causes of non-stationary behaviour in this way can some of the remaining challenges in tidal analysis and prediction be overcome, e.g. shelf and estuarine currents, river tides, internal tides, tide-surge interactions and tidally influenced ecological processes. Several examples illustrate the utility of non-stationary tidal analysis methods.Responsible Editor: Jens Kappenberg 相似文献
5.
In this work, we address the Black Sea setup of Nucleus for European Modelling of the Ocean (NEMO), and in particular some
model enhancements associated with the most important characteristic of ocean dynamics in this semi-enclosed basin, that is
the sea-level variability and its relationship with water cycles and wind. Forcing data are presented in detail and compared
with previously used coarser-resolution data. One emphasis in this paper is on the statistical analyses of forcing data and
outputs from simulations with a focus on the sea level and its change. Numerical simulations are carried out as free run,
and alternatively, altimeter data assimilation based on displacement of water properties in the pycnocline is used. Comparisons
between the two runs identify the robustness of circulation driven by water balance and winter intensification. Problems in
the model to replicate the redistribution of water properties between the two sub-basins in free-run mode are also discussed,
which are observed during years with extreme climatic conditions. 相似文献
6.
Baptiste Mourre Pierre De Mey Yves Ménard Florent Lyard Christian Le Provost 《Ocean Dynamics》2006,56(5-6):473-486
We evaluate in this paper the ability of several altimeter systems, considered separately as well as together with tide gauges,
to control the time evolution of a barotropic model of the North Sea shelf. This evaluation is performed in the framework
of the particular model errors due to uncertainties in bathymetry. An Ensemble Kalman Filter (EnKF) data assimilation approach
is adopted, and observing-systems simulation experiments (OSSEs) are carried out using ensemble spread statistics. The skill
criterion for the comparison of observing networks is, therefore, not based on the misfit between two simulations, as done
in classic twin experiments, but on the reduction of ensemble variance occurring as a consequence of the assimilation. Future
altimeter systems, such as the Wide Swath Ocean Altimeter (WSOA) and satellite constellations, are considered in this work.
A single WSOA exhibits, for instance, similar performance as two-nadir satellites in terms of sea-level correction, and is
better than three satellites in terms of model velocity control. Generally speaking, the temporal resolution of observations
is shown to be of major importance for controlling the model error in these experiments. This result is clearly related to
the focus adopted in this study on the specific high-frequency response of the ocean to meteorological forcing. Altimeter
systems lack adequate temporal sampling for properly correcting the major part of model error in this context, whereas tide
gauges, which provide a much finer time resolution, lead to better global statistical performance. When looking into further
detail, tide gauges and altimetry are demonstrated to exhibit an interesting complementary character over the whole shelf,
as tide gauge networks make it possible to properly control model error in a ∼100-km coastal band, while high-resolution altimeter
systems are more efficient farther from the coast. 相似文献
7.
Besides providing an estimate of the changing ocean state, an important result of the dynamically consistent estimating the circulation and climate of the ocean (ECCO) state estimate approach is the provision of a posterior model–data residuals which contain important information about elements in the assimilated observations that are inconsistent with the model dynamics or with the information present in other ocean data sets that are being used as constraints in the assimilation procedure. Based on decreased GECCO2 model–data residuals, upon using the altimeter data through the ESA climate change initiative (cci) sea-level (SL) project, we show here that the recently reprocessed ESA SL_cci altimeter data set (SL1) has been improved relative to the earlier AVISO altimetry data set and is now more consistent with the GECCO2 estimate and with the information about the changing ocean state embedded in other ocean data sets. The improvement can be shown to exist separately for both TOPEX/POSEIDON and ERS data sets. The study reveals that especially in regions characterized by small sea surface height (SSH) variability and small signal-to-noise ratio in the SSH data, improvements can be on the order of 30% of previously existing model–data residuals. However, in some regions we can find degradations, particulary in those where GECCO2 has little skill in representing the altimeter data and where evaluation of the products with GECCO2 is thus not advisable. Upon the assimilation of the new SL1 data set, the GECCO2 synthesis was further improved. However, adding the sea surface temperature (SST) from the SST_cci project as additional constrain, no further impact can be identified. 相似文献
8.
热带气旋能在短期内造成海水和大气质量的重新分布,使得近海地表受力发生变化,进而产生非潮汐负荷形变,对现今高精度大地测量的影响已不容忽视.为了保证空间大地测量结果的精度和稳定性,热带气旋引起的地表形变必须进行有效的估计.因此本文联合NOS、GLOSS验潮站数据与海潮模型,通过获取非潮汐残余量分析了热带气旋“MATTHEW”引起的风暴潮.利用ECCO海洋环流模型、ERAin大气再分析模型、HUGO-m海洋动力学模型,分别估计了“MATTHEW”引起非潮汐海洋负荷、非潮汐大气负荷、动力学响应下非潮汐海洋负荷对地表位移的影响,结果表明热带气旋影响下的广大区域地表都不同程度受到非潮汐负荷的作用,最大位移分别达到-9.13 mm、3.31 mm、-6.11 mm,并且加入动力学响应的非潮汐海洋负荷要普遍大于IB(Inverted Barometer)响应下的结果.在对比不同位置站点所受负荷差异时,发现“大陆站”非潮汐海洋负荷形变普遍大于“岛屿站”,而“岛屿站”更易受非潮汐大气负荷的影响. 相似文献
9.
The long-term variability of the non-tidal circulation in Southampton Water, a partially mixed estuary, was investigated using 71-day acoustic Doppler current profiler (ADCP) time series. The data show evidence that the spring–neap tidal variability of the turbulent mixing modulates the strength of the non-tidal residual circulation, with subtidal neap tide surface flows reaching 0.12 m s–1 compared to <0.05 m s–1 at spring tides. The amplitude of the neap-tide events in this non-tidal circulation is shown to be related to a critical value of the tidal currents, illustrating the strong dependence on tidal mixing. The results suggest that the dominant mechanism for generating these neap-tide circulation events is the baroclinic forcing of the horizontal density gradient, rather than barotropic forcing associated with ebb-induced periodic stratification. While tidal turbulence is thought to be the dominant control on this gravitational circulation, there is evidence of the additional effect of wind-driven mixing, including the effects of wind fetch and possibly wave development with along-estuary winds being more efficient at mixing the estuary than across-estuary winds. Rapid changes in atmospheric pressure also coincided with fluctuations in the gravitational circulation. The observed subtidal flows are shown to be capable of rapidly flushing buoyant material out of the estuary and into the coastal sea at neap tides.Responsible Editor: Iris Grabemann 相似文献
10.
Jin-Song von Storch 《Ocean Dynamics》2010,60(3):759-770
This paper analyzes variations of vertical velocity w simulated by the 1/10° Ocean General Circulation Model for the Earth Simulator (OFES). Strong w-variability is found in the deep oceans. When w is WKBJ-normalized, the standard deviation averaged over the Southern Ocean increases with depth and is larger than 8 × 10 − 3 cm/s throughout the water column below 1,500 m. Evidences are presented that link this w-variability to internal waves generated by quasi-steady currents over topography. The aliasing errors in lag-3-day correlations
suggest a bottom generation of near-inertial waves. A scale analysis indicates that vertically propagating waves that can
be resolved by the OFES model are waves with frequencies of the order of inertial frequency and wavelengths comparable to
the order of the grid size. The vertical energy flux associated with these waves is substantial. When integrated globally,
the vertical energy flux is upward in the upper 4 km and reaches maximum values of about 0.8 TW at about 1 to 2 km depth.
Thus, the w-variability in the 1/10° OFES integration points not only to a strong bottom generation of near-inertial internal waves in
the deep Southern Ocean but also to the possibility that the power provided by internal waves generated by non-tidal currents
over topography can be comparable to the power provided by internal waves generated by tidal flows over topography. 相似文献
11.
2008年3月21日和2014年2月12日,新疆和田地区于田县先后发生两次M_s7.3地震.为分析两次地震前是否存在重力短临异常信号,应用Tsoft软件对原始数据进行理论固体潮改正和气压改正,并基于小波分解去除其低频趋势,有效提取了两次地震前国家连续重力观测网多台g-Phone重力仪的高频扰动信息.结果表明两次地震前都记录到高频扰动信号.2008年地震前牡丹江、沈阳台和漳州台三个台站记录到的高频扰动信号,主频分布在0.2~0.4 Hz.2014年地震前8个台站记录到两组不同频段的扰动信号.第一组信号集中在震前6天的东北台站,第二组扰动信号出现在震前3天的东南台站.两组扰动信号振幅呈现从北到南、从东到西逐步衰减的时空分布规律·同时期的气象资料显示局部强降雨与第二组扰动异常存在良好的相关性.对高频重力信号的时频分析结果表明震前第一组扰动信号存在异常频段0·13~0.18 Hz.应用扰动源扫描算法对2014年两组扰动信号进行空间定.位,结果显示第一组信号扰动源位置与于田震中相距约1935 km,不在于田地震的孕震区内;第二组信号扰动源来自海上.2008年和2014年于田地震第二组震前扰动信号与强降雨以及海浪影响相关.2014年第一组信号与于田地震的关系仍待进一步研究. 相似文献
12.
Yanghua Wang 《Geophysical Prospecting》2002,50(6):665-672
The delay‐time Radon transform parametrizes coherent events in a seismic gather by the far‐offset trace delay time, instead of the conventional parabolic curvature or ray parameter. The reformulation may give a different physical insight into the aliasing effect in the Radon transformation and may also lead to a different algorithm. The delay‐time parametrization enables modelling of a seismic gather as the sum of coherent events with any form of moveout curve. For example, a parabolic curve can be used for traces within a moderate offset range and a linear moveout for far‐offset traces. When using this delay‐time Radon transform, it is the number of traces, rather than the spatial sampling, of the input gather that directly controls aliasing in the Radon transform image. A preconditioning operator that implicitly increases the number of input traces by spatial reconstruction (without physically performing the spatial resampling) may minimize aliasing noise in the Radon transform image. 相似文献
13.
采用全球地球动力学计划观测网中13台超导重力仪长期连续观测资料,探讨了长周期核模检测的可能性。采用相同的方法剔除了所有13个观测序列中的重力潮汐信号、仪器漂移和大气重力信号,估计了各个序列的功率谱密度及其积谱密度,估计并分析了非潮汐不同频段背景噪声。结果表明,在两个潮汐间频段（0.047~0.075cph和0.089~0.117cph)和亚潮汐频段(0.172~0.333cph),全球超导重力仪的平均噪声水平分别为0.0649,0.0350nm/s2和0.0138nm/s2,可以检测到的全球谐信号幅度极限分别为0.0416,0.0231nm/s2和0.0098nm/s2,表明全球超导重力仪观测资料基本可以识别长周期核模信号.在全球超导重力观测中,在潮汐间频段发现周期分别16.55,15.79,11.00h和10.09h的全球谐信号谱峰,可能来自于液核长周期振荡;在亚潮汐频段没有Smylie 1992年发现的Slichter模信号,但存在8个全球谐信号的谱峰,参考现有的理论模拟结果,Slichter模是这些信号可能的来源之一. 相似文献
14.
GPS数据处理通常采用Helmert七参数转换将瞬时站坐标转换到指定的框架下,但瞬时站坐标中尚未模型化的季节性地表负载会影响平移参数(地心运动)和尺度参数的估值,进而影响测站坐标;不均匀的测站分布会加剧这一影响.本文利用GRACE重力场系数仿真GPS地表负载的实验表明,基于网平移法采用实际的IGS站至少能够恢复90%的地心运动信号.地表负载及GPS实际测站的不均匀分布可以解释大约30%的GPS尺度的周年变化.相对于IGb08的所有框架站,目前采用91个全球均匀分布的核心站作为框架转换的基准是合理的.采用IGb08的所有框架站进行转换会导致U方向误差增加,特别是对框架站密集的欧洲区域(误差均值约为1mm).因此框架转换时,应尽量选取均匀分布的测站,同时不估计尺度参数. 相似文献
15.
《Continental Shelf Research》1995,15(8):981-1014
Low frequency sea-level variations and associated geostrophic currents in the central Great Barrier Reef (GBR) region near Townsville are studied using optimally-lagged multivariate regression. The analyses show that pressure-adjusted coastal sea levels and mid-shelf geostrophic currents are influenced predominantly by local along-shelf wind stress at the weather time-scale, and by climatic variables, such as atmospheric pressure and temperature, at seasonal and inter-annual time-scales. These forcing variables can specify sea levels over annual and inter-annual time-scales with a forecasting skill of 0.53 and 0.22, respectively (where 1.0 is perfect skill). Associated along-shelf geostrophic currents can be forecast with a skill of 0.57 over an annual time scale. If, instead, absolute coastal sea levels or offshore sea-level differences are used to specify the along-shelf geostrophic current, the forecasting skill is 0.75. A characteristic El Niño/Southern Oscillation (ENSO) response is detected for time periods up to 25 years in monthly sea-level both at Townsville and at western Pacific island sea-level stations. This spatially coherent response varies in intensity and phase within the Coral Sea. Sea-level differences show a pattern which characterizes known features of the large-scale circulation of the Coral Sea. These very low frequency sea-level variations in the Coral Sea must be taken into account to obtain accurate predictions of along-shelf geostrophic current variations on seasonal and inter-annual time scales. Regression analysis and a diagnostic river plume model show that the influence of the major rivers can produce sea-level changes due to buoyancy of order 5 cm. The corresponding errors in geostrophic velocities estimated using pressure-adjusted Townsville sea-level data alone are of order 5 cm s−1 rms. 相似文献
16.
近海岸区域平均海面高在大地测量学、物理海洋学以及地球物理学研究中具有非常重要的意义.受各种条件的制约和限制,目前卫星测高技术主要应用于深海区域,在近海区域尤其是海岸线附近区域的应用几乎为空白.本文根据ERS-1测高卫星回波波形特征,采用五参数线性模型,由最小二乘拟合方法,对近海区域尤其是靠近海岸线附近的ERS-1测高波形数据进行波形重构.比较波形重构前、后解算平均海面高,表明波形重构技术不仅明显改善了解算近海海面高的精度,而且增加了近海测高海平面的分辨率,并使卫星测高有效观测延伸至海岸线附近.随后,本文利用波形重构后海面高数据构造了近海多年平均海平面,并对我国近海海平面特征进行了初步分析. 相似文献
17.
PIERRE KEATING 《Geophysical Prospecting》1993,41(8):983-993
Gravity survey station locations are, in general, inhomogeneously distributed. This inevitably results in interpolation errors in the computation of a regular grid from the gravity data. The fractal dimension of the station distribution can be used to determine if an interpolated map is aliased at a specific wave-length and, moreover, it is often possible to determine an optimum gridding interval. Synthetic distributions of gravity station locations have been used for theoretical studies and it is found that for randomly distributed data there is a range of sizes for which the spatial data distribution has a fractal dimension of 2; that is, Euclidean. The minimum length scale at which the distribution ceases to be Euclidean is the optimum interpolation interval obeying Shannon's sampling theorem. For dimensions less than 2, the optimum interpolation interval is the shortest length at which the scaling regime is constant. In this case the gravity field cannot be interpolated without introducing some aliasing. As the fractal dimension characterizes the data distribution globally over the whole study area, the actual gridding interval, in some cases, will be smaller in order to represent short-wavelength features properly in the more densely sampled sub-areas, but this may generate spurious anomalies elsewhere. The proposed technique is applied to the station distribution of the Canadian national gravity data base and a series of sub-areas. A fractal dimension of 1.87 is maintained over a range of sizes from 15 km to over 1600 km. Although aliasing occurs, since the gravity field certainly contains much shorter wavelength anomalies, aliasing errors may be minimized by selecting the proper interpolation interval from the fractal analysis. 相似文献
18.
Petr Vaníček 《Physics of the Earth and Planetary Interiors》1978,17(3):265-280
The aim of this investigation is to develop a simple technique that would allow us to use the sea-level records for detecting contemporary vertical crustal movements of duration from several months to several years. The choice of auxiliary data needed for any such analysis is restricted to the regularly available meteorological data to make this approach possible in routine search for precursory movements in earthquake-prone areas. A linear mathematical model is designed to evaluate the effect of atmospheric temperature and pressure variations, river discharge, long periodic tides and Chandlerian motion. Spectra of the residual sea-level variations are also shown. It is concluded that local episodic crustal movements of a magnitude larger than some 10 cm may be detectable by this approach. If finer resolution is needed then it it necessary to also account for steric level, wind, and sea-current variations, for which data are largely non-existent. 相似文献
19.
选取溧阳重力连续观测台站gPhone连续重力仪2011年1月1日至2018年7月31日整点值观测数据进行预处理,对于连续性较好的2017年重力观测数据,分析其固体潮汐变化M_2波潮汐因子及非潮汐变化的残差曲线特征,并以Δ3 500 km、M_S 5.0地震事件为例,检验gPhone重力仪的地震记录能力。分析认为,溧阳台gPhone重力仪观测数据日趋稳定,潮汐信号可靠,非潮汐变化的残差曲线对地震有一定程度的反应,可记录到一定范围内MS≥5.0地震的同震信号,信号记录特征与震中距及震级相关。 相似文献
20.
This contribution investigates two different ways for mitigating the aliasing errors in ocean tides. This is done, on the one hand, by sampling the satellite observations in another direction using the pendulum satellite mission configuration. On the other hand, a mitigation of the temporal aliasing errors in the ocean tides can be achieved by using a suitable repeat period of the sub-satellite tracks.The findings show, firstly, that it is very beneficial for minimizing the aliasing errors in ocean tides to use pendulum configuration; secondly, optimizing the orbital parameter to get shorter repeat orbit mode can be effective in minimizing the aliasing errors. This paper recommends the pendulum as a candidate for future gravity mission to be launched in longer repeating orbit mode with shorter “sub-cycle” repeat periods to improve the temporal resolution of the satellite mission. 相似文献